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FluxHandbook_Ver1.0a

1. esteeseetisttitititttttitititititertnereretenerererenereret 96 2 6 Data logger svieaxsiudsnnsovvsnnsiiadinnsuiidsaveviaksnndasbils a aa ia aie aiaa iaia 103 2 7 Detection and reduction of nojise lt tcececeeeeeeee ee ee eee ee ee ee ee ee ee ee ee ee nese ea eaeseeesneneeeneaeaeaeseneeees 106 Related information for chapter 2 s ssesseeessesensseseeseserseennnnasteesessesestenansnas tosses snseenenens 109 3 Micro meteorological Observation 31 Radiation seiiet sis wi tin eee ae A ei es ee ee ee i ee ee 116 3 1 1 Solar radiation esis ihetsetesgectechiopahesdesands E EEE EEEE A AE T 116 3 1 2 Longwave radiation seeeeeeeeetetetettetttetttetttetetttttttttttetnnttntttetntntnnntnnnnnnnnnnnnnnnn nnmn 119 SUL 3 Netitadiation eere nro Ee ean EEE EEA EER ERRE na ace EE E E E EEANN 122 3 1 4 Photosynthetically active radiation photosynthetic photon flux density eseeeereee 124 Appendix 3 1 1 Necessary factors to obtain the solar position eeret eres eee eee teeter eee 128 Appendix 3 1 2 Conversion of measurement units 6 60s eee eines 129 3 2 Wind direction wind velocity iiesliccnnaiiversvommiinciias vapstiwetennsiuas macnueliasiwaneGuniueresssaines 130 3 3 Air temperature 6666 eee 135 Appendix 3 3 1 Unit conversion 06600 60 141 3 4 Humidity 6000 ienie nities 142 Appendix 3 4 1 Definitions of humidity 0 000000000 ies 145 Appendix 3 4 2 Equilibrium relative humidity of
2. http www ratocsystems com english http www ratocsystems com products rs232c html in Japanese http www nfcorp co jp english IWATSU TEST INSTRUMENTS CORPORATION Japan http www iti iwatsu co jp index_e html http www nfcorp co jp english http www adcmt com index htm 111 Prac tical Handbook of Tower Flux Observation Ver 1 0 Low pass filter NF CORPORATION Japan Noi se cut transformer DENKENSEIKI Research Institute Co Ltd Japan UPS DENKENSEIKI Research Institute Co Ltd Japan OMRON Corporation Japan SANWA SUPPLY INC Japan SANYO DENKI CO LTD Japan Parts and supplies Some examples Paper towel Kimwipes S Ply 4 4 x8 4 Bx 280 Kimberly Clark Corporation US 1 10 11 12 13 14 15 16 17 18 Tube connectors NIHON PISCO CO LTD Japan Tube connectors Swagelok Company US http www nfcorp co jp english http www denkenseiki co jp english http www denkenseiki co jp english http www omron com http www omron co jp ped j dengen product ups in Japanese http www sanwa co jp in Japanese http www sanyodenki co jp en http www kimberly clark com 2 2 http www pisco co jp english pisco htm 2 3 http www swagelok com 2 3 Tubes and PTFE products CHUKOH CHEMICAL INDUSTRIES LTD Japan http www chukoh co jp eng 2 3 Tubes and polyethylene products HAGITEC CO
3. 2001 Particularly for several hours after sunrise the value of CO storage change sometimes becomes as large as or larger than that of the flux According to Baldocchi et al 2000 the value of the daily CO storage change total over 24 hours becomes close to zero thus can be neglected for evaluating NEE However evaluations of CO storage change are required for evaluations of NEE on the time scale of 30 to 60 minutes 4 Tips In Equation 2 4 1 the horizontal vertical advection and horizontal turbulence flux terms are neglected As a result NEE is expressed only in terms of the vertical turbulence fluxes and storage change Due to technical constraints flux observations at the present time usually neglect the horizontal transport terms by assuming horizontal homogeneity Furthermore because the vertical advection term is difficult to estimate it is not included in the evaluation of NEE in most cases Accordingly it is important to select a site that matches the assumptions in Equation 2 4 1 as closely as possible A study on the vertical advection term has been conducted by Lee 1998 In recent years attempts have been made to evaluate the horizontal vertical advection terms on the basis of observations Aubinet et al 2003 Aubinet et al 2005 Leuning et al 2008 Tips 2 4 1 Measuring procedures CO storage change is evaluated from the temporal change of the atmospheric CO concentration in the air below th
4. intercompare radiometers within a region and calibrate the standard radiometers against the World Radiometric Reference at the International Pyrheliometer Comparison a meeting that takes place every five years The Regional Radiation Centers in the Asia district are located in Japan and India Tips 3 1 1 118 3 1 Radiation Measuring method For measuring global solar radiation a measuring instrument should be deployed horizontally in a location at which the instrument does not get shielded from radiation in any direction In order to measure the terrestrial energy balance or albedo two pyranometers with identical characteristics are set up one facing upward and the other facing downward Albedometers equipped with a combination of upward and downward facing pyranometers are also commercially available As measurement errors may occur when the glass dome is not clean the dome should be cleaned regularly with Kimwipes Kimberly Clark Corporation US or cotton soaked in alcohol In general the output of a pyranometer is approximately 7 mV kWm and small When data are transmitted over a long distance the use of thick shielded signal wires is recommended to avoid externally generated noise For long term observations it is desirable to install an arrester on the terminal board to prevent instrument damage due to lightning y Tips A digital multimeter tester with a resolution of 0 01 mV if one is available is useful for c
5. s rays should preferably hit the panels at a right angle but since the sun s angle changes daily and seasonally solar panels are usually set at an angle of 10 40 degrees facing south north in south hemisphere The influence of surrounding obstacles on the panels is taken into account as well as the influence of the panels themselves on flux observations Tips 1 2 6 1 2 4 Lightning surge countermeasures Lightning damage on tower observations Since lightning tends to strike tall pointed objects observation towers are prone to lightning strikes Electric current lightning surge generated by lightning momentarily produces a large current and a high voltage and these can damage observation facilities There are two kinds of surges a direct lightning surge caused by direct strikes on a tower and a lightning induced surge caused by strikes on the surrounding area Both cause damage that can include destruction and breakdown of electronic observation equipment Surges caused by direct lightning strikes generate a particularly large amount of energy and they can cause severe damage including fires For flux observation facilities installation of lightning protection equipment is required by law when the facility is first established and additional measures can also be taken to ensure the protection and safety of observation equipments The former includes installing a lightning rod on an observation tower and the latter includes pr
6. 134 158 130 131 World Radiation Center 116 118 World Radiometric Reference WRR wind direction wind tunnel wind vane windmill anemometer 118 124 53 49 50 52 53 71 80 81 zero calibration Zero gas 193 Practical Handbook of Tower Flux Observation Ver 1 0 List of authors 1 1The Observation site 1 2 Building infrastructure NAKAI Yuichiro FFPRI MIYATA Akira NIAES 1 2 1 Obtaining Land use Permission eee eeeeeeceseceeeseeeeeeee KOMINAMI Yuji FFPRI MIYATA Akira NIAES 1 2 2 Tower construction and maintenance cceeeeeeseeeeseeeeeeereeees SHIMIZU Takanori FFPRI MIYATA Akira NIAES 1 2 3 Electric power supply ee eee cee ceeeceeeeeeeeeeeeseceseenaeeaeeneeees KOMINAMI Yuji FFPRI NAKAI Yuichiro FFPRI 1 2 4 Lightning Surge Countermeasures eee eee eee eeeeeeeeeeeees YAMANOI Katsumi FFPRI 1 2 5 Observation Hut sesso rre essere orree penera rretra rE EEFE RASER PFS NAKAI Yuichiro FFPRI 1 26 Other eiaeiiio ease ee ee NAKAI Yuichiro FFPRI MIYATA Akira NIAES 1 3 Measurement variables c0c0csesessssseessssssesssesssssssssssessssererenees NAKAI Yuichiro FFPRI MIYATA Akira NIAES 2 1 Ultrasonic anemo thermometers SATS ccccceccseseseseseseseseseseeeee SHIMIZU Takanori FFPRI 2 2 Open path COVH20 analyzerS sssesssrssrssiirssrisieronesesersntoessrsseriserissseni MANO Masayoshi NIAES 2 3 Closed path CO analyZers cececsssessescseeseeeceeceseceeeeeeneeeceeea
7. 136 137 138 147 149 166 167 168 DEC technique see disjunct eddy covariance technique 88 78 90 162 dehumidification dehumidifier detection area 51 53 81 dew point hygrometer 142 72 73 74 161 162 72 73 74 116 digital 30 34 46 77 79 81 82 102 103 104 105 108 119 124 132 166 107 119 dew point generator diaphragm pump diffuse radiation digital multimeter tester direct radiation 116 disjunct eddy covariance technique DEC technique 101 dome coefficient 120 dryer air 69 77 78 dry bulb thermocouple 58 59 dry bulb thermometer 138 143 eddy accumulation method 96 eddy covariance method 2 28 35 67 77 78 83 96 97 101 102 103 106 106 107 116 152 electromagnetic noise electromagnetic wave equation of time 128 fine wire thermocouple fine wire thermometer 58 61 flow distortion 30 32 37 50 51 68 69 74 76 77 88 89 164 94 95 flow meter flux averaging period footprint 3 7 forest management map 2 189 Index four component radiometer 122 123 fragmentation 101 gas chromatograph electron capture detector GC ECD 100 flame ionization detector GC FID 99 101 mass spectrometer GC MS 100 101 global solar radiation 116 119 124 groundwater level 23 harmonic current 106 heat sink type of radiometer 116 119 hemispherical image 24 high frequency fluctuation correction 83 high frequency flux loss 44 45 46 61 64 h
8. 3 5 Soil temperature and soil heat flux 3 5 Soil temperature and soil heat flux 3 5 1 Soil temperature The soil temperature near the earth s surface is high in the day and low at night as a result of solar radiation Its daily variation is sinusoidal As the measuring depth increases the sinusoidal daily variation decreases in amplitude and the phase shifts backwards Because the litter layer on the ground surface of a forest tends to become thicker and its border with a soil is less clear as one goes deeper into a cold climate region caution should be exercised in the measuring depth Types of instruments There are three types of thermo sensors for measuring soil temperature thermocouple thermistor Photo 3 5 1 and platinum resistance Photo 3 5 2 For more details refer to Section 3 3 Air temperature Because soil has a larger time constant than air there is no need for a sensing unit to be small It can be made larger to make it more waterproof This is necessary due to the high water content of soil Photo 3 5 1 Thermistor thermometer Photo 3 5 2 Platinum resistance thermo sensor 107 L Campbell Photograph courtesy C HPT 5 JM Climatec Photograph courtesy of of Climatec Inc Climatec Inc A thermocouple can be handmade For soil temperature observation T type copper constantan thermocouples are generally used To create a thermocouple compensation lead wire consisting of a copper wire and a constantan w
9. 7 and moisture flux w q 39 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 Appendix 2 1 1 Sample program The following is a sample program for acquiring ATI K Style Probe data using a Campbell CR1000 data logger and the compact flash module CFM100 Campbell CR1000 Program for ATI SAT Declare Variables and Units PUBLIC ATI K as STRING 100 PUBLIC SAT 4 Units SAT ms 1 Deg C Define Data Tables DataTable Tablel 1 1 Datalnterval 0 100 mSec 10 CardQut 1 1 Sample 4 SAT FP2 Sample 1 ATI_K string If activate raw strings will be recorded EndTable Main Program Begi nProg Serial Open Coml 9600 0 0 500 The 3rd number corresponds to Parity Bits length Flow ctrl Scan 100 mSec 10 0 Serialln ATI_K Coml 100 13 500 ASCII 13 is Carriage Return SplitStr SAT ATI_K 4 0 The last 0 corresponds to split by number Call Tabl e Tabl el Next Scan EndProg 40 2 2 Open path CO H O gas analyzers 2 2 Open path CO H 0 gas analyzers 2 2 1 Measurement of fluctuating CO concentration by an open path gas analyzer An open path CO gas analyzer measures the number of CO molecules within the open path of the instrument Because the CO measurement by the instrument is based on the absorption of infrared energy by COs the attenuation of infrared radiation is the basic output value from the analyzer The output value is converted to the nu
10. LTD Japan Filters Advantec Toyo Kaisha Ltd Japan Filters Millipore Corporation US http www hagitec co jp homeeng htm 2 3 http www advantec co jp english 2 3 http www millipore com 2 3 Seal tape and PTFE products NITTO DENKO CORPORATION Japan Mass flow controllers Yamatake Corporation Japan http www nitto com 2 3 http www azbil com 2 3 Mass flow controllers and flowmeters KOFLOC KOJIMA INSTRUMENTS INC Japan Solenoid valves CKD Corporation Japan Solenoid valves TAKASAGO ELECTRIC INC Japan Solenoid valves KOGANEI CORPORATION Japan Dehumidifiers Perma Pure LLC US Pumps Enomoto Micro Pump Mfg Co Ltd Japan Pumps KNF Neuberger GmbH Germany Pumps Gast Manufacturing Inc US Programmable relay ZEN OMRON Corporation Japan http www kofloc co jp kofloc_e index html 2 3 http www ckd co jp english 2 3 http www takasago elec com 2 3 2 4 http ww1 koganei co jp en 2 3 http www permapure com 2 3 http www emp co jp in Japanese 2 3 2 4 http www knf com 2 3 http www gastmfg com 2 3 http www ia omron com 2 3 19 Programmable relay SDM CD16AC Campbell Scientific Inc US http www campbellsci com 2 3 112 Related information for chapter 2 20 Swagelok Gaugeable tube fittings and adapter fitting Swagelok Company US http www swagelok com 2 4 21 Three way solenoid valves FSS 0306YN Flon Industry
11. Then PortSet 1 1 If IfTime 720 1440 Min Then PortSet 1 0 If IfTime 1430 1440 Min Then PortSet 1 1 If IfTime 1440 1440 Min Then PortSet 1 0 L e 4 EndProg Photo 2 3 2 CR1000 control board and an example of a circuit which controls a solenoid valve with the use of a mechanical relay Fig 2 3 2 An example of a program written with the CRBasic software 8 Calibration A CO analyzer is calibrated by drawing CO gas standard gas of different known concentrations into the sample cell In the calibration procedure gases of two different concentrations are usually used a gas with no CO zero gas and a gas with a CO concentration slightly higher than that of the air to be measured span gas These two gases are used to calibrate the zero point offset and span The value of the zero offset can be detected from the data obtained from the time of the zero gas supply As for the span drift it can be calculated from the difference between the output value from the time of the zero gas supply and that from the time of the span gas supply The zero point offset and span drift can be checked at the time of flux calculations after the data collection For a more refined calibration of the analyzer span gases of two different concentrations can be used In this case use 1 a standard gas with a CO concentration that is slightly lower than that at the observational site of interest and 2 a standard gas with a CO concentrati
12. Tips 3 7 1 Tips For snowfall measurement a windshield should be placed around the tipping bucket to prevent a wind induced reduction in the catching rate The size of the windshield is not standardized but depends heavily on the wind velocity and snow quality of the measuring site In one windy area for example the placement of more than one windbreak plate with a height exceeding 2 m was suggested for one tipping bucket Usually the reliability of data is significantly improved by enclosing the snow gauge within a cylinder that is two or three times the size of the bucket cylinder and raising its top about 20 cm higher than the bucket Tips 3 7 2 Calibration A tipping bucket is calibrated with water that is gauged using a graduated measuring cylinder The tipping bucket seldom deviates from the norm enough to need re calibration 3 7 2 Snow survey snow depth snow weight Types of instruments During a snow season continuous observation of snow accumulation is practiced extensively to gain information on snowfall Snow depth To visually determine snow depth a snow gauge is used Automatic measuring instruments include a laser type and an optical type in addition to the ultrasonic type that is employed by AMeDAS Automated Meteorological Data Acquisition System Ultrasonic sensors and laser sensors are installed above the snow surface to measure the distance from the sensor to the snow surface Photo 3 7 2 Optical senso
13. and magnesium perchlorate or Drierite The air within the reference cell can be circulated by the pump housed inside the LI 7000 LI 7000 manual LI COR 4 Tips While both the use of chemicals and a reference gas CO and H O free gas come with advantages and disadvantages these methods require replacement of either gas cylinders or chemicals Gas cylinders need replacement when they run out and chemicals need replacement when their effect wears out Make sure to replace the gas or chemicals before the gas runs out or the chemicals wear out The interval for the gas replacement can be extended with the use of a large gas cylinder Although the appropriate interval for chemical replacement depends on the conditions under which the analyzer is used manufacturers recommend a week for the interval Our past experiences suggest that the chemicals actually last for 2 weeks to a month depending on the ambient conditions of the analyzer Tips 2 3 3 2 Solenoid valves One of the advantages of a closed path analyzer is that the analyzer can be automatically calibrated For the automatic calibration the flow path of the sampled air needs to be branched to create flow paths for the calibration gas Refer to Fig 2 3 1 These flow paths are often created with the use of solenoid valves which can be opened and closed by providing electric voltage electric current Furthermore the use of three way valves as in Fig 2 3 1 is recommended T
14. flux measurements due to errors in the estimate of the sensible heat flux Specifically the effect of instrument surface heating causes the sensible heat flux measured within the measurement path of the open path analyzer H Wm to deviate from that measured by a SAT H Wm The presence of this deviation AH H Hol is 59 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 becoming commonly recognized in the field of flux observation refer to Appendix 2 2 7 as a result of past research findings including 1 downward CO flux observed by open path analyzers even during periods with no photosynthetic activity Harazono et al 2000 2 results based on comparisons of CO fluxes observed by open path analyzers to those observed by closed path analyzers H does not have to be taken into consideration e g Hirata et al 2005 and 3 findings from measurements of air temperature fluctuations within the measurement paths of open path analyzers e g Grelle and Burba 2007 Ono et al 2008 An equation based on an instrument surface heat balance analysis has been proposed to evaluate AH that is as a correction method although it is limited to a specific open path analyzer LI 7500 Burba et al 2008 Heusinkveld et al 2008 The correction method proposed by Burba et al 2008 is intended to be versatile so that it can be easily applied to previously acquired data as well as newly acquired data However the
15. in Japanese 173 Practical Handbook of Tower Flux Observation Ver 1 0 GRAPHTEC Corporation Japan GL220 GL800 GL820 http www graphteccorp com HIOKI E E CORPORATION Japan MEMORY HiLOGGER 8420 MEMORY HiLOGGER 8430 20 http www hioki com OMRON Corporation Japan ZR RX40A http www ia omron com Single function data logger HIOKI E E CORPORATION Japan TEMPERATURE LOGGER 3632 TEMPERATURE LOGGER LR5011 HUMIDITY LOGGER LR5001 PULSE LOGGER LR5061 VOLTAGE LOGGER 3635 3645 VOLTAGE LOGGER LR5041 5042 5043 http www hioki com O T amp D Corporation Japan Thermo recorder Ondotori TR 51S 52S TR 51i 52i TR 71Ui 72Ui Precipitation recorder Amembo RF 3 Voltage logger VR 71 http www tandd co jp in Japanese O Onset Computer Corporation US Temperature Relative Humidity Data Logger HOBO U23 Pro v2 http www onsetcomp com RS 232 to RS 422 485 converter Moxa Inc US Transio A52 53 http www moxa com RS 232 to USB conversion cable I O DATA DEVICE INC Japan USB RSAQS series http www iodata com http www iodata jp product mobile serial in Japanese O RATOC Systems international Inc Japan REX USB60F http www ratocsystems com english http www ratocsystems com products rs232c html in Japanese It can be used for connecting an Ondotori data logger T amp D Corporation with a PC with a multiple core CPU Parts and supplies Some examples
16. it is best to avoid addition of unnecessary electrical lines Tips 1 2 7 4 Tips There is often little space for connecting protective elements such as ceramic arresters to a terminal block To prevent these elements from touching they should be protected with heat shrink tubing or insulating tubing Photo 1 2 10 Tips 1 2 8 17 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 1 1 2 5 Observation hut Flux observations often require an observation hut where computers and data loggers can be stored The hut should be as small as possible so as not to disturb the observation environment Building the hut close to the tower will shorten the length of plumbs and wires and will be conducive for operation but the hut must be placed at a distance that ensures it does not impact the observation environment A simple heating ventilating or air conditioning facility may be needed depending on the climatic conditions It is better for the floor of the hut to be above the ground level This makes it more difficult for soil and sand to be brought into the hut and it also makes it easier for you to keep the inside of the hut clean For a hut used for storing gas cylinders for calibration of CO concentration it is more convenient to bring the cylinders into the hut when the hut is built near a road It is also a good idea to set up two huts one for storing gas cylinders and the other for storing data loggers and other mea
17. of w according to the moving average value of w Photo 2 5 2 In order to exclude the influence of the low frequency wind velocity variation the averaging time for w is selected based on the actual observation conditions and the averaging time is frequently set to 15 minutes or less When the averaging time is 15 minutes and the data are recorded at 10 Hz the sign of w is determined using the moving average of the 9 000 data values up to and including the data value obtained 0 1 seconds before the determination of the sign In the REA method a threshold value is sometimes defined for the purpose of eliminating from the analysis the effects of extremely low wind velocities that is wind velocities which are lower than the minimum resolution of the data logger or the anemometer In this case when the wind velocity is smaller than the threshold value the trace gas is not stored but vented out instead A deadband is set The characteristics of each trace gas are different including its absorptivity boiling point and atmospheric lifetime Therefore the REA system needs to be configured exclusively for the trace gas to be measured by taking into account its properties and the requirements of the analysis method For example large Tedlar bags made of PTFE are often used for storing methane For storing a VOC such as isoprene or terpene a reservoir system consisting of multiple air sampling tubes or consisting of canisters is frequently used Photo 2
18. should be grounded to protect the observation equipment with protective elements such as ceramic surge arresters or varisters The connecting location and the surge path are the same as those for SPD in a power circuit Fig 1 2 2 Ceramic arresters are small and well suited for connection to the terminal block The terminal block should be connected to a ground that has little earth resistance Photo 1 2 10 Ceramic arrester left and arresters connecting the terminal block right Installation of the ground bar A ground bar should be installed as a countermeasure against noise and lightning surges that may damage signal lines and electric power supply These grounds should be separate from the lightning rod ground Photo 1 2 9 The ground for electric power supply is installed when the source facility is constructed As shown in Photo 1 2 10 a ground is needed when countermeasures are taken against surges in signal lines A ground that is installed for such a purpose should have a ground resistance of 100 Q or less In an area of ordinary geology simply inserting a 50 100 cm ground bar into the earth Photo 1 2 11 is enough to keep the resistance within 100 Q The ground bar should be inserted into a soil that is as moist as possible and the tip of the bar should be at a depth of 40cm or more Argilliferous soil is 16 1 2 Building infrastructure preferable Sometimes it is difficult for a ground to work effectively in gravelly s
19. technical development With regard to the use of forests owned by prefectural governments and other municipalities the process of obtaining permission varies from community to community Some local governments have systems that allow for land lease and prefectural forest use Contact the division in charge of forests and follow the necessary procedures If the target forest is designated as a protected forest or an erosion control area then you need to acquire a protected forest work permit or an erosion control work permit just as you would have done for the use of private land Protected forests When large scale construction and other work are to be performed in a protected forest area you can file a petition for the designation of the protected forest to be cancelled To apply for such cancellation either of the following two conditions is required when no reason can be found for the forest to be designated as a protected area or when the outcome of research will be significant in terms of public benefit and will be more important than the protection of the forest In reality however there is only a slight chance that any such application will be accepted even if it meets the requirements outlined above So when you undertake a small scale observational study in a protected forest you need to apply for a permit register the observation tower and cabin as temporary buildings and obtain a permit to cut down a few trees a protected fore
20. 2008 Transition to the World Infrared Irradiance Standard at Tateno BSRN Station Journal of the Aerological Observatory 68 37 41 in Japanese with an English abstract Ohkubo S Adachi M Ono K Motohka T and Nishimura W 2009 Report of AsiaFlux Workshop 2009 Integrating Cross scale Ecosystem Knowledge Bridge and Barriers Climate in Biosphere 9 D 2 in Japanese Ohtani Y 1999a Air temperature Jn Handbook of forest environmental survey environmental measurement in forest Forest environmental survey editorial committee ed 284pp Hakuyusha 132 136 in Japanese Ohtani Y 1999b Solar radiation Shortwave radiation Jn Handbook of forest environmental survey 181 Practical Handbook of Tower Flux Observation Ver 1 0 environmental measurement in forest Forest environmental survey editorial committee ed 284pp Hakuyusha 124 127 in Japanese Ohtani Y Mizoguchi Y Watanabe T Yasuda Y Okano M 2001 Seasonal change of CO flux above an evergreen needle leaf forest in temperate region Fujiyoshida Japan GER Report CGER M 011 2001 129 132 Ohtani Y Mizoguchi Y Yasuda Y and Watanabe T 2005 Micrometeorological estimation of nocturnal net production of forest ecosystem By a continuous observation of CO concentration change in canopy Proceedings of joint conference on environmental engineering in agriculture 2005 88 in Japanese Okada K 2002 Foot print analysis In Recent advance
21. 38 Amiro B 2010 Estimating annual carbon dioxide eddy fluxes using open path analysers for cold forest sites Agricultural and Forest Meteorology 150 1366 1372 AsiaFlux Steering Committee ed 2007 Practice of flux observations in terrestrial ecosystems http www asiaflux net members material html available exclusively for AsiaFlux members It is the English translated edition of AsiaFlux Steering Committee ed 2003 TO 000000000000 OOOUOUOUUUUUUUO Aubinet M Berbigier P Bernhofer Ch Cescatti A Feigenwinter C Granier A Gr nwald Th Havrankova K Heinesch B Longdoz B Marcolla B Montagnani L and Sedlak P 2005 Comparing CO storage and advection conditions at night at different CARBOEUROFLUX sites Boundary Layer Meteorology 116 63 94 Aubinet M Grelle A Ibrom A Rannik U Moncrieff J Foken T Kowalski A S Martin P H Berbigier P Bernhofer C Clement R Elbers J A Granier A Gr nwald T Morgenstern K Pilegaard K Rebmann C Snijders W Valentini R and Vesala T 2000 Estimates of the annual net carbon and water exchange of forests the EUROFLUX methodology Advances in Ecological Research 30 113 175 Aubinet M Heinesch B and Yernaux M 2003 Horizontal and vertical advection in a sloping forest Boundary Layer Meteorology 108 397 417 Baldocchi D Falge E Gu L Olson R Hollinger D Running S Anthoni P Bernhofer Ch Davis K Evans R Fuentes J Goldstein A
22. 4 2 The test chamber used for the calibration of the HMP4S5 series is commercially available With it instrumental outputs can be adjusted A humidity measuring chip and a module can be replaceable 144 Appendix 3 4 1 Definitions of humidity 1 3 4 Humidity Appendix Name unit Conversion Definition Water vapor pressure e Pa Saturation vapor pressure e Pa e g Sprung Equation 1 The partial pressure of water vapor in the humid atmosphere The maximum water vapor pressure the air can hold at a given temperature Saturation deficit eg Pa Relative humidity Specific humidity q kgkg Mixing ratio x kgkg Absolute humidity in some engineering fields kgkg Absolute humidity kgm Vapor density in some engineering fields kgm Percentage humidity saturation Dew point temperature Cap C 0 00794e 1 0 00366 T 273 15 Approximation 3 Hayashi 1988 The difference between the saturation vapor pressure and the water vapor pressure Vapor pressure as a percent of the saturation vapor pressure The mass of water vapor per unit mass of moist air ratio of molecular weight of vapor to that of dry air 0 622 The mass of water vapor per unit mass of dry air ratio of molecular weight of vapor to that of dry air 0 622 The mass of water vapor per unit volume of moist air
23. 74 75 76 89 98 99 membrane filter 70 tubing 74 75 PTR MS see proton transfer reaction mass spectrometer pump 62 67 68 69 70 71 72 73 74 75 76 77 78 79 82 83 87 88 89 90 93 94 97 98 101 102 106 pyranometer 116 117 118 119 123 124 167 pyrheliometer 117 118 pytradiometer 122 123 124 quantum sensor 124 125 129 167 radiation thermometer 135 139 148 rain gauge 156 157 159 rainfall interception 23 range of data logging 103 REA method see relaxed eddy accumulation method 164 69 70 71 88 137 rectangular weir reference cell reference junction regulator 88 91 relaxed eddy accumulation method REA method 96 97 98 99 100 101 102 relay 79 80 102 166 resolution 57 98 104 106 119 131 162 167 RS 232C 34 81 82 104 105 166 RS 422 104 runoff 23 sample air 62 67 69 71 73 76 77 88 93 94 49 68 69 70 80 82 88 89 90 91 28 96 97 103 106 23 sample cell sampling rate sap flow velocity 191 Index SAT see ultrasonic anemometer thermometer satellite image 2 scaffolding tower 8 9 SDI see serial data interface SDM _ see synchronous device for measurement Seebeck effect 137 sensitivity constant 149 sensor separation 44 45 47 61 64 serial data interface SDI 104 shadow band shadow ball shadow plate 118 sheath 135 shelter 62 135 138 139 140 142 143 shield shielding 14 106 107 shortwave radiation 2
24. Analytik Gesellschaft m b H Germany V amp F Analyse und Messtechnik GmbH Germany Tunable diode laser spectrometers Los Gatos Research Inc US DLT 100 Picarro Inc US G2311 f Campbell Scientific Inc US Chemiluminescent analyzers Hills Scientific US Yanaco New Science Inc Japan 2 6 Data loggers Campbell Scientific Inc US KEYENCE CORPORATION Japan NR 1000 TEAC CORPORATION Japan es8 OMRON Corporation Japan ZR RX20 40A RS 232 to RS 422 485 Converters Moxa Inc US TCC 80 Cables for RS 232 to USB conversion Related information for chapter 2 http www ptrms com http www vandf com http www lgrinc com http www picarro com http www campbellsci com http hills scientific com http english yanaco co jp http www campbellsci com TATYO KEIKI Co Ltd Japan the sole agent of Campbell http www taiyokeiki co jp in Japanese HIOKI E E CORPORATION Japan MEMORY HiLOGGER LR8430 20 http www hioki com http www keyence com http www teac co jp indexe html http www omron com http www moxa com I O DATA DEVICE INC Japan USB RSAQS series http www iodata com http w ww iodata jp product mobile serial in Japanese O RATOC Systems international Inc Japan REX USB60F 2 7 Oscilloscope NF CORPORATION Japan Digital multimeter O NF CORPORATION Japan O0 ADC CORPORATION Japan
25. CO exchange NEE of the plant community The radiation solar radiation and PAR profile can be measured for a detailed investigation of the photoenvironment of the complicated forest crown layer Table 1 3 1 Variables required for flux measurement radiation Over the canopy Under the canopy Downward Upward Downward Upward Shortwave radiation essential essential A A Longwave radiation A A B B Photosynthetically active radiation essential essential A A Spectroradiation B B C C radiation of different wavelengths Net radiation B B C C Table 1 3 2 Profile vertical distribution measurement variables Measurement variables Rank Air temperature profile B Humidity profile B Wind velocity profile B Soil temperature profile A PAR profile B CO density profile A Other Measurement variables can be adopted or rejected according to the characteristics of the observation site and the purpose of the study Table 1 3 3 22 1 3 Measurement variables recommendations and order of precedence Table 1 3 3 Other measurement variables Measurement variables Rank Atmospheric pressure A Soil heat flux Temperature of canopy surface leaf surface temperature C Snow depth A Snow water equivalent C Water quality of precipitation C Soil moisture profile A Groundwater level and quality C Amount of fog drip precipitation resulting from thick fog condensing on leaves Water level water temperatu
26. D W T 1982 Calculation of carrier gas effects in non dispersive infrared analyzer I Theory Tellus 34 376 384 Griffith D W T Keeling C D Adams J A Guenther P R and Bacastow R B 1982 Calculation of carrier gas effects in non dispersive infrared analyzer II Comparisons with experiments Tellus 34 385 397 Gunji T Matsuoka N Kimura R and Kon H 2008 Estimation of latent heat flux using a fine wire thermocouple and a sonic anemometer thermometer Proceedings of annual conference of the Society of Agricultural Meteorology of Japan 2008 56 in Japanese Hanafusa T Aoshima T and Watarai Y 2005 A Simple Method to Estimate the Latent Heat Flux by a Sonic Anemometer thermometer with a Fine Thermometer Bulletin of the Terrestrial Environment Research Center The University of Tsukuba 6 11 15 In Japanese with an English abstract Hanafusa T Fujitani T Kobori Y and Mitsuta Y 1982 A new type sonic anemometer thermometer for field operation Papers in Meteorology and Geophysics 33 1 19 Harazono Y Miyata A Ota N and Oechel W C 2000 Greenhouse gas flux at Arctic tundra ecosystem in winter and thawing period Proceedings of 24th Conference on Agricultural and Forest Meteorology 193 194 Haslwanter A Hammerle A Wohlfahrt G 2009 Open path vs closed path eddy covariance measurements of the net ecosystem carbon dioxide and water vapour exchange A long term perspective Agricultural and Forest Mete
27. Here Osa represents the saturated volumetric water content mm and c and c are constants that can be obtained by the pressure plate method using a pressure plate dehydrator In the pressure plate method the lower section of a collected soil sample is exposed to the atmosphere while the upper section is subjected to high pressure and soil water content is reduced by the pressure difference Calibration The relationships between the volumetric water content and other parameters that are measured directly in soil by a sensor such as neutron transmittance electric resistance thermal conductivity and permittivity differ a great deal depending on soil components and constituents Values put out by a soil moisture meter should not be fully trusted but should be corrected with the results obtained by the oven method Soil samples must be collected under various wet and dry soil conditions so that a wide range of soil water contents can be obtained Sampling tubes of 100 cc and 400 cc should be used After a sample is weighed it is put in an oven at a temperature of 105 C so that the water can evaporate The volumetric water content can be calculated by dividing the weight reduction g by the volume of the sampling tube cm Comparisons are made between the volumetric water content obtained by the oven method and the measurements made by the sensor to find an approximation By putting a sensor observation value into the approximation the volu
28. Japan CPR AS 1 vertical type http www weather co jp in Japanese PREDE CO LTD Japan PFH 01 http www prede com file 32html htm EKO INSTRUMENTS CO LTD Japan MH 120 _ http www eko usa com http www eko co jp eko a a08 fr html in Japanese Unit water bath Low temperature water bath unit O TAITEC Co Ltd Japan Thermominder SX 10R Cool bath CB 40 http e taitec com 171 Practical Handbook of Tower Flux Observation Ver 1 0 3 4 Ventilated psychrometer 0 0 0 PREDE CO LTD Japan PFH 01 CLIMATEC Inc Japan CPR AS 1 2 EKO INSTRUMENTS CO LTD Japan MH 120 http www prede com file 32html htm http www weather co jp in Japanese http www eko usa com http www eko co jp eko a a08 fr html in Japanese Dew point hygrometer 0 Yokogawa Denshikiki Co Ltd Japan E 771 http www yokogawa com jp ydk Polymeric humidity sensor O Vaisala Oyj Finland HMP45A HMP45D http www vaisala com HMP45 has been replaced by HMP155 Humidity and Temperature Probe since March 2009 This new sensor is protected with a sintered PTFE filter therefore having a longer response time 90 60sec and the probe is larger 40mm in diameter and 279mm in length thus compatibility should be carefully considered when replacing the old model Infrared hygrometer O LI COR Inc US LI 840 LI 7000 LI 7500 http www licor com 3 5 Thermistor Onset Computer Corporation US S TMA ht
29. Japan http www flon ind com in Japanese 2 5 113 114 Miucro meteor Observ Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 3 1 Radiation All objects that are at a temperature higher than 0 K emit energy in the form of electromagnetic waves The amount of emitted energy is proportional to the fourth power of the absolute temperature of the object Stefan Boltzmann Law The amount of solar radiation emitted by the sun is close to the theoretical value of the radiation from a black body at a temperature of approximately 5 800 K The spectral peak of the solar radiation is observed around the wavelength of 0 5 um Ninety nine percent of the total solar energy occurs at wavelengths from 0 15 to 3 um In contrast the temperature of the Earth s atmosphere is approximately 300 K The spectral peak of radiation emitted by the Earth s atmosphere is observed around the wavelength of 10 um Most of the radiated energy from the atmosphere occurs at wavelengths from 3 to 100 um At the Earth s surface radiation that originated from both the sun and the Earth s atmosphere is observed In this section methods for measuring the radiation originating from these two sources will be discussed 3 1 1 Solar radiation Solar radiation is the energy released by the sun After this radiation enters the atmosphere it is partially absorbed and scattered by air molecules water vapor and dust Solar radiation that reaches
30. LI 7500A or LI 7200 A comparison Tcehnical Note 130 1 7 Liu H Peters G and Foken T 2001 New equations for sonic temperature variance and buoyancy heat flux with an omnidirectional sonic anemometer Boundary Layer Meteorology 100 459 468 Massman W J 2000 A simple method for estimating frequency response corrections for eddy covariance systems Agricultural Forest Meteorology 104 185 198 Matsumoto S 2005 Notes on Calculation Methods of the Solar Declination and Equation of Time 180 Literature cited Architectural Institute of Japan Tohoku Chapter Research Report 68 85 96 in Japanese Matsuoka M and Hayashi Y 2008 Characteristics of latent heat flux estimated from sonic anemometer thermometer and thermocouple Agricultural Meteorology in Kanto E Journal 5 11 in Japanese Mauder M Oncley S P Vogt R Weidinger T Ribeiro L Bernhofer Ch Foken T Kohsiek W De Bruin H A R and Liu H 2007 The energy balance experiment EBEX 2000 Part II Intercomparison of eddy covariance sensors and post field data processing methods Boundary Layer Meteorology 123 29 54 McCree K J 1972 Test of current definitions of photosynthetically active radiation against leaf photosynthesis data Agricultural Meteorology 10 443 453 Miyata A and Mano M 2002 Influence of subzero temperature on sensitivities of three open path infrared gas analyzers Proceedings of the 2nd International Workshop on Advanced Flux Netwo
31. M Asai T Kawamura T Shitara H Nitta T and Maejima I 1986 Dictionary of climatology and meteorology 742pp Ninomiya Shoten in Japanse Devices and instruments Model number in italic indicates previous or discontinued model 3 1 Pyranometer O EKO INSTRUMENTS CO LTD Japan MS 802 MS 402 MS 601 ML020VM http www eko usa com 168 Related information for chapter 3 Hukseflux Thermal Sensors B V The Netherlands SR11 LP02 http www hukseflux com Kipp amp Zonen B V The Netherlands CMP 21 CMP 6 CMP 3 SP Lite2 http www kippzonen com PREDE CO LTD Japan PCM 01 http www prede com file 32html htm THE EPPLEY LABORATORY INC US PSP http www eppleylab com Pyrheliometer Su EKO INSTRUMENTS CO LTD Japan MS 56 MS 101D http www eko usa com THE EPPLEY LABORATORY INC US NIP http www eppleylab com Kipp amp Zonen B V The Netherlands CH 1 CHP 1 http www kippzonen com n tracker EKO INSTRUMENTS CO LTD Japan STR 21 STR 22 http www eko usa com THE EPPLEY LABORATORY INC US SMT 3 ST 1 ST 3 http www eppleylab com Kipp amp Zonen B V The Netherlands SOLYS 2 2AP http www kippzonen com PREDE CO LTD Japan ASTX 2 http www prede com file 32html htm Shadow band Kipp amp Zonen B V The Netherlands CM 121B CM 121C SOLYS 2 2AP http www kippzonen com PREDE CO LTD Japan PSB 100 PR
32. SAT measurements at observation sites with a large variation in wind direction However when the wind direction is parallel to the measurement path of the horizontally mounted open path gas analyzer the sensor head of the analyzer interferes with the analyzer s measurement This measurement interference reduces the valid range of wind directions for the open path gas analyzer which is considered a disadvantage of the horizontal mounting of an open path gas analyzer Furthermore the frequency response characteristics of the co spectra i e fluxes from the horizontal mounting method and the methods for correcting flux losses at high frequencies are both currently limited Refer to Appendix 2 2 2 for flux losses at high frequencies Sensor separation distance The ideal separation distance between the open path gas analyzer and the SAT is 15 to 20 cm and no larger than 30 cm The sensor separation distance needs to be at least 15 cm Otherwise the influence of the sensor head on the wind velocity measurement becomes large When the sensor separation distance is larger than 30 cm the flux losses at high frequencies become large particularly for an ecosystem with a small canopy height such as a grass field and the uncertainty increases for the flux loss correction The sensor separation distance is defined as the distance between the center of the open path gas analyzer measurement path and that of the SAT measurement path When the sensor sep
33. The damping of a fluctuating concentration by continuous sampling through a tube Australian Journal of Physics 16 454 463 Suyker A E and Verma S B 1993 Eddy correlation measurement of CO flux using a closed path sensor Theory and field tests against an open path sensor Boundary Layer Meteorology 64 391 407 Yasuda Y and Watanabe T 2001 Comparative measurements of CO flux over a forest using closed path and open path CO analysers Boundary Layer Meteorology 100 191 208 85 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 2 4 CO storage change Net Ecosystem CO Exchange NEE is generally expressed as the sum of the CO flux observed over the vegetation surface and the observed CO storage change that takes place over time in the space between the ground surface and the flux measurement height Pe d 2 4 1 a 2 4 1 NEE F F w Where F CO flux at the measurement height mgm s F CO2 storage change mg m s w vertical wind velocity ms pe CO2 concentration mgm t time s z height m z flux measurement height m fluctuating component and mean value The value of the CO storage change is small over short plant canopies such as crops However over tall plant canopies such as forests the value of the CO storage change becomes sufficiently large with respect to the value of CO flux that the CO storage change cannot be neglected Baldocchi et al
34. a tank style weir triangular weir rate of an open channel flow Photograph Mase paddy flux site Courtesy of Senecom Inc Water meter If the maximum flow rate within a pipeline is on the order of the flow rate of tap water a propeller type water meter can be used A paddlewheel water meter which is frequently used for household applications is simple in its construction low in price a few thousand yen each and rarely breaks down However agricultural water is not free of objects and impurities such as algae which can cause the water meter to breakdown Therefore water meters are often not well suited for use in agricultural water As for 164 3 8 Water level water temperature irrigation and drainage electromagnetic water meters they are expensive however they contain no moving parts giving them a broader range of application than propeller type water meters Finally warranty conditions need to be reviewed for both types of water meters as the use of drinking water is presumed by the manufacturers Measuring method Initially 1 the types of irrigation and drainage at the field and 2 the locations of the intake or drainage outlet and the elevation drop need to be assessed If the head drop between the intake or drainage outlet and the water surface is large install a tank style weir in that space If there is sufficient water pressure inside the pipeline install the tank near the water outlet and introduce water into
35. and specially preserved areas in national parks and quasi national parks When you set up an observation station in special areas and in specially preserved areas of national parks or quasi national parks you need to obtain permission from the proper authorities For a national park obtain permission from the Environment Minister for a quasi national park obtain permission from the Prefectural Governor Articles 13 and 14 of The National Parks Act The installation of facilities is Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 1 strictly regulated in these areas and it is therefore difficult to build a tower larger than the simple one such as shown in Photo 1 1 1 National and public forests When the observation tower or roads used to access the research site are part of a national forest you need to obtain a Permit for Using National Forest for entering the forest First visit the local forest management office and forest administrative bureau for applying to obtain permission to use the forest and start negotiating with them sincerely For land use activities that entail observations to be made as part of a public research project you can collaborate with public research organizations by following the procedures outlined in the Implementation Guideline for Technical Development of Forest Office and in this case no land use fee will be charged Instead you will be obliged to submit annual reports on the implementation of
36. angle ts solar altitude 4 saturation ratio m m gt 0 volumetric water content mm gat saturated volumetric water content m m O water content kgkg A wavelength m p air density kgm De CO mass density kgm mgm Pee CO concentration molmol Pa dry air mass density kgm Pe concentrations of the atmospheric trace gas mgm o Stefan Boltzmann constant 5 67051x10 8 Wm K Ow standard deviation of w ms Q latitude D absolute humidity kgm D percentage humidity D relative humidity X temperature in Fahrenheit F y matric potential Pa w 27 365 or 27 366 Q equation of time h a Cy C2 j constants ky ko ka a 186 187 Practical Handbook of Tower Flux Observation Ver 1 0 Index APAR see absorbed PAR absolute radiometer 116 absorbed PAR APAR 125 AC power see alternating current power aerial photography 2 AGC albedo see automatic gain control 119 meter 119 alternating current power AC power 13 105 106 107 analog 132 30 34 46 77 81 82 103 104 105 108 104 98 104 130 131 132 133 134 104 166 167 15 16 17 119 21 23 65 139 142 145 analog digital resolution anemometer applied voltage arrester atmospheric pressure 161 162 attenuation of CO concentration fluctuation 67 79 83 41 67 72 46 51 52 automated calibration automatic gain control AGC 117 134 130 129 automa
37. are not clean the domes and covers should be cleaned regularly with alcohol and Kimwipes Because polyethylene domes deteriorate quickly they need to be replaced frequently 123 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 Data processing A net pyrradiometer evaluates the net radiation from the output voltage and the sensitivity coefficient of the sensor When a four component radiometer is used or when the individual components of downward upward shortwave radiation and downward upward longwave radiation are measured the following equation is used for calculating the net radiation Ra SV ST L LT 3 1 4 Where Rnet net radiation Wm S downward shortwave radiation global solar radiation Wm S1 upward shortwave radiation reflected solar radiation Wm L downward longwave radiation Wm and Lt upward longwave radiation Wm 3 1 4 Photosynthetically active radiation photosynthetic photon flux density Photosynthetically active radiation PAR refers to radiation with a wavelength between 400 and 700 nm which are the wavelengths that chlorophyll can absorb It is synonymous with photosynthetic photon flux 27 which can be converted into Wm Appendix 3 1 2 density PPFD Its basic unit is umolm Types of instruments Instruments for measuring PAR include spectroradiometers that are capable of measuring irradiance according to wavelength and quantum sensors that selectively s
38. calibration Step 1 The objective of Step 1 is to check the sensitivity and offset of the LI 7500 as it was operated at the observational site The calibration gases required for Step 1 are zero gas and one or more concentrations of span gas for both CO and H20 Supply calibration gas to the open path gas analyzer and check the sensor output This procedure is performed on the analyzer while its condition is left the same as it was at the observational site that is 52 2 2 Open path CO H O gas analyzers before any cleaning is performed on the lenses located at the ends of the measurement path To avoid removing the accumulated dirt and dust from the lenses supply the CO gas first and then the H O gas This procedure determines the sensitivity and offset of the LI 7500 in its condition from the observational site as well as the degree of dirt and dust accumulation on the lenses While the sensitivity drift of the analyzer is usually less than 1 3 thus small the offset of the instrument can be as large as approximately 10 ppm Subsequently clean the lenses with water and Kimwipes When the lenses are completely dry supply the calibration gas again and check the sensor output At this time either CO or H2O gas can be supplied first This procedure determines changes in the sensitivity and offset of the LI 7500 itself These changes are small under usual circumstances sensitivity drift less than 1 3 offset change a few ppm St
39. can be calculated from the following relationships For the span length of d m the travel times t and t are expressed as d d t t 2 1 1a 2 1 1b C tva C Vy respectively By subtracting the inverse of Equation 2 1 1b from that of Equation 2 1 la the following relationship can be obtained to calculate va pes 2 129 2i 6 By taking the sum of the inverse of Equation 2 l la and that of Equation 2 l 1b and using the relationship between the speed of sound c and the sonic virtual temperature Ty K e 403T the following equation can be obtained for calculating Ty 28 2 1 Ultrasonic anemometer thermometers SATs 2 2 T ae ee 2 ee m 1 2 1 3 403 403 2 t 6 The air temperature can be calculated from the sonic virtual temperature measured by a SAT The calculation procedure requires corrections for the effects of the horizontal wind cross wind contamination and the water vapor content as described in a later section pp 38 39 Refer to Kaimal and Gaynor 1991 and Hignett 1992 for the details of the corrections Types of SATs The SATs that are generally used for field observations are three dimensional SATs 3D SATs They are equipped with three pairs of sensors and the three orthogonal components of the wind velocity parallel to the x y and z axes or the u v and w axes are output The z axis or w axis indicates the axis aligned in the direction of gravity Unlike one dimension
40. changes in electrical properties of polymer membranes in response to changes in atmospheric water content The 142 3 4 Humidity leading instruments are those in the HMP4S series discontinued model replaced by HMP155 marketed by Vaisala Oyj Finland Photo 3 4 1 Although requiring an external energizer they are small enough to be equipped in a radiosonde Because of their easy maintenance in comparison with that for wet and dry bulb thermometers they are used for continuous observation There are a few things that need to be kept in mind the sensor response time of about 15 seconds is slightly longer than that of other sensors the sensor reads 100 continuously and takes time to recover once condensation forms on the sensing unit Photo3 4 1 A thin film polymeric humidity sensor and a platinum resistance thermo sensor in HMP45D Pt100 Infrared hygrometers The hygrometer operates by sensing the infrared absorptivity of water vapor which gives it a fast response time The instrument needs to be maintained and calibrated frequently as its cell is prone to smudging during the observation of high humidity air See Section 2 2 Open path CO H O gas analyzers and 2 3 Closed path CO gas analyzers for details Measuring method As dirt on the web bulb of a wet and dry bulb thermometer prevents water from evaporating evenly which causes large errors the gauze needs to be changed periodically In preparing ga
41. compensation circuit is usually built in to deal with this problem In some cases in which the difference in temperature between a sensor and a water body like in a well is significant the compensation accuracy may be less than in conventional cases Laser water level meter A laser is aimed at the water surface and the distance to the water surface is calculated based on the arrival time of the reflected light A laser displacement gage is used to obtain measurements in millimeters If the target water is clear the laser may penetrate the water instead of reflecting off the water This can cause error To prevent this a plain float is used with the laser directed to reflect off the float Capacitive water level meter The water level is measured on the principle that the electrostatic capacity between electrodes is proportional to the volume of some fluid Those that are commercially available have electrodes ranging from 0 5 to 2 m in length Because the measurement range covered by one sensor is narrower than that of other instruments fluctuations in water level should be investigated in advance so that the right instrument with an optimal length of electrode can be selected Hydrostatic water level meter This instrument calculates the hydraulic pressure from diaphragm displacement and then converts it into the water level The atmospheric pressure needs to be measured simultaneously However certain 161 Practical Handbook of Towe
42. downward upward infrared radiometers Net pyrradiometers A net pyrradiometer includes upward and downward facing light receiving surfaces and the temperature difference between the two light receiving surfaces is measured with a thermopile Table 3 1 3 Photo 3 1 5 For protection from the wind the light receiving surfaces are covered by domes made of polyethylene that allows radiation of all wavelengths to pass through Because conventional polyethylene is soft domes made of this material e g MF 11 EKO are pressurized with dry air On the other hand the Q 7 Radiation and Energy Balance Systems Inc REBS US is equipped with rigid polyethylene domes which require no internal pressurization Finally the light receiving surfaces of the NR Lite2 Kipp amp Zonen are Teflon coated instead of being covered by polyethylene domes This design reduces maintenance work Table 3 1 3 Commonly used net pyrradiometers Model Manufacturer Spectral range um MF 11 EKO 0 3 30 NR Lite2 Kipp amp Zonen 0 2 100 Q 7 REBS 0 25 60 Photo 3 1 5 Net pyrradiometers Left NR Lite2 Kipp amp Zonen Photograph courtesy of Kipp amp Zonen B V Right MF 11 EKO Photograph courtesy of EKO INSTRUMENTS CO LTD 122 3 1 Radiation Tips Radiometers can be damaged by crows and other birds Particularly when net pyrradiometers with polyethylene domes are used protective measures need to be implemented For example
43. for the analysis of trace gases the analysis requires a few minutes to a few tens of minutes and the eddy covariance method cannot be used In this case the relaxed eddy accumulation REA as outlined by Businger and Oncley 1990 can be used instead In the REA method air samples are collected in two isolated reservoirs An air sample is collected into one of the two reservoirs according to whether it was sampled with an upward or downward vertical wind velocity positive w or negative w respectively After air samples have been collected over a specified time period the concentration of the atmospheric trace gas in the air sample in each reservoir is analyzed Subsequently the difference in the concentrations of the atmospheric trace gas between the two air samples Apg mgm is calculated The value of the flux F mgms can be evaluated by multiplying the value of Apg the standard deviation of w ow ms and an empirical coefficient b Thus the REA method replaces the eddy covariance method when the concentration of a trace gas to be measured is small and the observation calls for the use of a gas analyzer e g GC that requires some time for concentration analysis Measurement principle The REA method is a variant of the true eddy accumulation method In flux measurements with the true eddy accumulation method the flow rate for the atmospheric air sampling is adjusted in proportion to the magnitude of the vertical wind velo
44. forest canopy umolm s specific humidity kgkg soil heat flux Wm soil heat flux at the bottom of the lowest soil layer Wm resistances at 0 C Q resistances at 100 C Q infrared radiation that passes through a dome Wm net radiation Wm upward shortwave radiation reflected solar radiation Wm downward shortwave radiation global solar radiation Wm time s time required for an acoustic signal to travel between the transceivers s culmination time h flux averaging period s standard time h absolute temperature K triple point temperature of water 273 16 K air temperature K sensor body temperature K dome temperature K soil temperature K sonic virtual temperature K actual sonic virtual temperature K wind velocity ms wind velocity component parallel to the path ms wind velocity component normal to the path ms volume of gaseous phase m volume of liquid phase m volume of solid phase m 185 Practical Handbook of Tower Flux Observation Ver 1 0 vertical wind velocity ms w W weight of liquid phase g W weight of solid phase g x mixing ratio kgkg Xs mixing ratio in saturated air kgkg g height m Za thickness of a soil layer m Ze flux measurement height m B solar zenith angle longitude Yo meridian declination of the sun ratio of molecular weight of vapor to that of dry air a hour
45. hand a super fine thermocouple for which the end of the thermocouple wire is welded and processed to 13 um is supplied by manufacturers such as OMEGA Engineering INC US Although finer thermocouples have higher responsiveness they are more susceptible to vibration and therefore need to be carefully handled Thermocouple Copper connector wire ompensation lead wire wire Data logger Fig 3 3 1 Thermocouple circuit Photo 3 3 4 Sheathed thermocouple 138 3 3 Air temperature v Tips For silver brazing soldering a copper crucible or a copper plate is heated with a burner at a high temperature and borax and silver solder are put into the crucible to melt After trimming the junction sections of the thermocouple are put in the crucible and soldered The wire diameter is reduced if necessary and the junction is coated with insulation For electric welding a spot welder and optional welding tweezers for thermocouples are appropriate Although welding kits can be handmade easily Ohtani 1999a due caution has to be taken as the resistor generates very high heat The production of a thin thermocouple requires a welder whose voltage and pulse width can be adjusted Tips 3 3 3 Measuring method In measuring temperature the thermometer should be placed in a shelter to prevent influences of radiation rainfall and snowfall In Japan shelters equipped with a fan that blows at a speed of 3 ms or
46. is based on the initial and final values of sensitivity over the period under consideration See below In the former method if an incidence such as a power outage occurred that would change the sensitivity of the analyzer the investigator should consider adjusting only the data collected after the incidence If no such incidence occurred adjust the data collected after the most recent calibration or after the mid date between the previous and present calibrations In the latter method two further options can be considered In the first option the average of the two values of sensitivity is used to adjust the collected data In the second option the value of sensitivity can be calculated by distributing the difference between the two values of sensitivity in proportion to the time elapsed number of days between the latest calibration and the one before However there is no obvious solution for adjusting the collected data if no information on the change of sensitivity with time is available Determine the sensitivity to be applied for data adjustment by taking the magnitude of sensitivity change and the length of the observational period into consideration Changes in the offset value have no impact on the calculation of co variance therefore as long as CO number density mixing ratio has been measured additionally by a closed path analyzer the flux calculation will not be influenced by the change in the offset values If no closed path CO ana
47. left over tubing should not be discarded but instead should be kept for other uses PFA tubing a type of fluorine resin fluoroplastic tubing is characterized by low permeability to the surrounding gases and is transparent in color which allows the investigator to check for accumulations of dirt and dust inside the tubing Tips 2 3 8 4 Tips In relation to Tips 2 3 7 the standards of screws that are widely used for screw in tube connectors include 1 PT screws that conform to International Organization for Standardization ISO standards and also to Japan Industrial Standards JIS and 2 NPT screws that conform to American National Standards Institute ANSI standards While both of these kinds of screws are taper screws the helix and pitch angles differ between the two kinds of screws and mixed usage of these screws causes leakage Therefore make sure to check the standard of the screws to be used and also to match up the standards of the male and female parts Furthermore because tubing is sized in inches and millimeters the investigator needs to be cautious when selecting tubing for use Tips 2 3 9 5 Mass flow controller A mass flow controller is a device to control the flow of sampled air for attaining a constant flow rate It is highly recommended to install this device as a part of the measurement system The detailed principles of the operation of a mass flow controller will not be discussed here Temporary flow r
48. mixing ratio is expressed as the ratio of CO mass density p kgm to dry air density p kgm that is Po __ Pe Pa Mm p e where m molecular weight of CO kgmol J ma molecular weight of dry air kgmol p A2 2 1 atmospheric pressure Pa e water vapor pressure Pa p partial pressure of CO Pa The partial pressure of CO p is related to CO concentration as p p pX10f where p is the CO concentration umolmol 65 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 Appendix 2 2 7 Literature which reports a negligible effect of instrument surface heating on open path analyzer measurements Some literature such as Giasson et al 2006 and Haslwanter et al 2009 reported that the effect of instrument surface heating on the flux measurements by an open path analyzer is negligibly small At the observation site of Giasson et al 2006 winter CO flux indicating absorption of CO by the ecosystem which is caused by the effect of instrument surface heating was not observed Amiro 2010 suggested that high wind speeds might have reduced the effect of instrument surface heating leading to the results observed by Giasson et al 2006 Specifically concurrent with the cooling of the instrument directly by the wind Ho Aboay the ratio of Ho see Appendix 2 2 3 to the sensible heat flux generated at the instrument surface Hpody Wm might have decreased with increasing wind
49. mounted on the instrument The cylinder has a small opening and has been treated to control internal reflection For continuous measurements an automatic solar tracker e g STR 21 EKO SOLYS 2 Kipp amp Zonen and SMT 3 EPPLEY can be employed Photo 3 1 2 117 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 Vin IRA f h Ww f P Photo 3 1 2 Pyrheliometer MS 56 EKO equipped with Solar tracker STR 21 EKO Photograph courtesy of EKO INSTRUMENTS CO LTD Diffuse radiometers In order to measure diffuse solar radiation by eliminating direct sunlight a shadow band plate or ball e g PSB 100 PREDE CO LTD Japan CM 121B Kipp amp Zonen and SBS EPPLEY is mounted on a pyranometer For continuous measurements a sun tracker e g SOLYS 2 Kipp amp Zonen and STR 22 EKO can be used so that the position of the shadow plate changes automatically according to the position of the sun Photo 3 1 3 Photo 3 1 3 Measurement of diffuse solar radiation Left SOLYS 2 Kipp amp Zonen Photograph courtesy of Kipp amp Zonen B V Right STR 22 EKO Photograph courtesy of EKO INSTRUMENTS CO LTD v Tips The World Radiation Center in Davos Switzerland maintains the absolute reference radiometers In individual districts of the World Meteorological Organization WMO a WMO Regional Radiation Center has also been designated Regional Radiation Centers maintain standard radiometers
50. needs to be turned off by setting the relevant value to 0 seconds 81 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 Similarly the LI 7000 is also capable of outputting digital signals using an RS 232C connection the latest versions of the LI 7000 also allow a USB connection and outputting analog voltage signals only in DAC output Analog DAC output can be allocated to DAC1 to DAC4 equivalent of Channel 1 to Channel 4 by assigning appropriate measurement values to appropriate channels The investigator can set the range of the measurement values of DAC1 and DAC2 to either 0 5 V or 5 5 V as the full scale e g set the range of 0 5 V for the CO concentration range of 300 500 ppm Furthermore a smaller voltage range such as 0 2 5 V or 0 625 0 625 V can be selected as the full scale for DAC3 and DAC4 As with the LI 6262 both the digital and DAC outputs from the LI 7000 can be smoothed using the smoothing filtering function however this function in principle is not needed for eddy covariance measurements 10 Location of pump deployment In the system illustrated in Fig 2 3 1 the pump is placed upstream of the analyzer and the interior of the sample cell is pressurized The entire portion of the system after the pump is pressurized With this pump arrangement sampled air must pass through the pump before reaching the analyzer Therefore with this arrangement it is impossible to avoid
51. noise which are rarely found in similar publications All of the authors of this handbook have been engaged in long term flux monitoring in forest or cropland sites and have expertise in eddy covariance flux observation I sincerely appreciate the efforts of the authors to spend their valuable time to share their experiences and knowhow with the readers and expect this handbook to be utilized as a practical reference by eddy covariance users and in training courses on eddy covariance flux observation It is also my hope that another practical handbook which focuses on the processing of eddy covariance data and is complementary to the present handbook will be published in the near future August 2011 MIYATA Akira Director Agro Meteorology Division National Institute for Agro Environmental Sciences iv Practical Handbook of Tower Flux Observation Ver 1 0 Contents Editorial board meee meee mre e weer emer eee e eres eres esse esse sees sees esse Ee Ee EEE EEE EEE EEE TEED EE EEE EEE EE EEE DEDEDE EEE ODED EE EEE EEE EEE E EES 1 Preface Penn rr rr rr rrr rr rr rr eer rer re ii Preface to English edition ee i i i ir iy iv 1 Observation Planning and the Selection of Flux Observation Sites 11 The obs rvation site ierit ees eas iwwlde edit anes ae es eee eee ed ead eee ela 2 1 2 Building infrastructure 1 ssssseseseseeeseeeeeeeeeeeeeeeeeeeeeveeeeeeeeneesneesnensneesneesneesnensnensneesneesnenanae 5 1 2 1 Obtaining land use permi
52. not pleasant for a landowner or manager to have his land damaged even if compensation is provided Long term observational studies on a private land require such careful consideration Photo 1 2 14 Boardwalk installed around tower Tura Russia Fences and security A high tower should be fenced off from the surrounding area so that people cannot freely access the tower as there is a possibility that a person under the tower could be injured by a falling object The fence 19 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 1 also prevents casual passers by from trying to climb the tower out of curiosity A No Trespassing sign should be posted on the fence However in case of an observation site located on an agricultural land the tower is generally not as high and a fence may affect the observation results The fence can also obstruct agricultural work where machinery is used so it is often not set up at such sites But in case of an observation site located far from town measures against theft or deliberate destruction of measuring instruments are needed For example the deployment of a security guard or the installation of a security camera is effective at forest sites The former is an especially practical measure to take at observation sites located in countries where labor costs tend to be low Communications It is better to provide a telephone line to the site to ensure emergency contact although this i
53. observation and analysis and examinations of factors affecting observation error was published Lee et al ed 2004 With the manual and the handbook a guideline has been created for handling factors which cause uncertainties in observation data On the other hand of the issues associated with uncertainties in observation data errors induced by phenomena that depend heavily on the terrain conditions of the observation site e g complex terrain are fundamental causes of uncertainties in observation data and are rooted in the principle of measurements and analysis This issue remains as a research topic which needs to be continuously addressed Accordingly the number of literature references on observations by the eddy covariance method has increased compared to the time when such observations were initiated However when observations and analyses by the eddy covariance method are attempted in practice detailed technical information that is not described in the existing publications becomes necessary for many of the tasks associated with the project such as starting a new observation site deployment of the observation system and analyses and quality control of the data Given this circumstance it has been proposed that data quality and distribution among researchers be increased by making the necessary technical information available on the internet and allowing researchers who are aware of the necessity of standardizing the data to share techn
54. of Leuning and King 1992 and Leuning and Judd 1996 on the cross sensitivity of the E 009 showed that the characteristics of the cross sensitivity of individual instruments vary according to the serial numbers even within the same model Therefore when the E 009 or the OP 2 is used for observations the degree of cross sensitivity needs to be assessed with indoor experiments such as those of Kohsiek 2000 or from the shape of the co spectrum Monji 2003 Table 2 2 1 Open path CO gas analyzers Outside dimensions Model Manufacturer Path length Weight Output signal diameter and length LI 7500 LI COR 12 5 cm 6 5x30 cm 0 75 kg 0 5 V RS 232C SDM E 009 Advanet 20 cm 11x45 5 cm 5 5 V Multiple OP 2 ADC folded path 7 6x37 cm 1 1 kg 5 5V 20 cmx4 Outside dimension and weight are those of the sensor head Synchronous Device for Measurement communication protocol of Campbell This product has been discontinued A commercially available open path gas analyzer usually consists of a sensor head a control box a power supply unit and a mountable calibration tube Furthermore accessories such as instrument specific software are available for some of the commercially available open path gas analyzers When selecting an open path gas analyzer the user needs to take into consideration the cable lengths because the length of the cable between the sensor head and the control box as well as the length of the cable for the
55. of the sensible heat flux the following relationship holds between the sensible heat flux and the coefficient b wT bo T T 2 5 3 where the left and right sides of the equation represent the sensible heat flux determined from the eddy covariance method and that determined from the REA method respectively The variables T and T represent the average air temperatures K from the times when the values of w are positive and negative respectively The above equation can be solved for b as w T b 2 5 4 o T T The structure of the system used for the REA method The system for collecting atmospheric trace gases consists mainly of a SAT solenoid valves pumps a mass flow controller air sampling reservoirs a programmable recording device such as a CR1000 Campbell Scientific Inc US and a PC According to the sign positive or negative of the vertical wind velocity w the air sample which has been drawn in near the SAT Air inlet is sorted into the appropriate reservoir The air sample is sorted with the use of a solenoid valve Photo 2 5 1 that is operated at high speed Refer to Figs 2 5 1 and 2 5 2 the red and blue lines indicate the flow paths for the positive and negative values of w respectively The flow rate of the sampled air is controlled by a mass flow controller so that the flow rate can be maintained at a constant value However it is critical to set the flow rate low 0 2 Lmin or less to
56. output signals of the measured values are limited in some models of open path gas analyzers Regarding the LI 7500 the value of the time lag of the output signal and the deployment method of the analyzer vary among its product model which can be identified by the serial number When the LI 7500 is selected for use the user needs to be aware of its serial number in order to address these issues See Appendix 2 2 1 for details Advanet Inc of Japan was one of the first companies to commercialize open path gas analyzers in 1985 with the E 009 series For many years the E 009 series was very popular and used in multiple field observations After LI COR introduced the LI 7500 in 2000 the number of LI 7500 users gradually increased Currently as of 2008 the LI 7500 is becoming the world wide de facto standard instrument 42 2 2 Open path CO H O gas analyzers vy Tips Manufacturers do not always notify users of the latest information related to open path gas analyzers such as version upgrades of the firmware Users are advised to visit the manufacturers websites every 3 to 6 months to check for the latest information on the instruments Tips 2 2 1 Measurement method 1 Method of deploying an open path gas analyzer Two factors are considered important when an open path gas analyzer is deployed 1 the open path gas analyzer needs to be deployed in such a way that it does not interfere with the measurements made by the ultraso
57. position of the calibration tube is inappropriate the value of AGC will increase The value of AGC also needs to be checked immediately after the initiation and before the cessation of calibration gas supply to ensure that the calibration tube is not misaligned While H O gas 51 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 is supplied despite an appropriate mounting of the calibration tube the value of AGC can increase by approximately 10 compared to the value of AGC without the calibration tube 4 The flow rate of the calibration gas should be set to 0 5 1 0 Lmin Adjust the flow rate after the initiation of the calibration gas supply Also make sure to check the flow rate before shutting off the calibration gas supply 5 The CO reading should stabilize in less than 5 to 10minutes after the initiation of the calibration gas supply In the case of H2O 10 to 30 minutes or sometimes longer are required for the reading to stabilize after the calibration gas supply has been initiated The stabilization of the H2O reading frequently requires some time especially when zero H O gas is supplied subsequent to supplying calibration gas that contains H20 6 For analysis use the data that are acquired in the last 1 to 3 minutes of the calibration gas supply and during which the output value is stable 7 In the course of H2O calibration make sure that the dew point temperature is always at least 3 to 5 C lower than t
58. speed an effect reported by Ono et al 2009 66 2 3 Closed path CO gas analyzers 2 3 Closed path CO gas analyzers The eddy covariance method that uses a closed path CO2 gas analyzer closed path gas analyzer hereafter was developed when no open path CO gas analyzers were yet available for long term stable CO measurements e g Leuning and Moncrieff 1990 Leuning and King 1992 Suyker and Verma 1993 The eddy covariance method that is based on the measurements from a closed path gas analyzer evaluates CO fluxes from the wind velocity fluctuations observed by an ultrasonic anemometer thermometer and fluctuations of the atmospheric CO concentration observed by a closed path gas analyzer In the meantime the LI 7500 LI COR Inc US which was discussed in Section 2 2 Open path CO H O gas analyzers has become commercially available and has been used widely As a result the number of observational sites which newly adopt a closed path gas analyzer for the eddy covariance method is probably decreasing On the other hand the use of a closed path gas analyzer provides the following advantages AsiaFlux Steering Committee 2007 1 long term stable measurements can be made 2 calibration can be automated and 3 the magnitude of the density fluctuation correction is small Advantage 1 can be achieved because the sensing element of a closed path gas analyzer is protected from direct exposure to the atmosphere and rainfall Aut
59. the E 009 and the OP 2 However the following cautions are also important Although calibration tubes are available as accessories for both open path gas analyzers the calibration tubes are not equipped to measure temperature or pressure for converting the units of the calibration gas concentration unlike the LI 7500 Therefore a thermocouple or a thermistor needs to be used to measure the temperature inside the calibration tube or the temperature of the wall of the calibration tube As for the pressure measured values near the calibration tube are desirable however the use of a constant such as 101 3 kPa is acceptable as an approximation Both open path gas analyzers undergo changes in their sensitivities in environments with extremely low air temperatures Miyata and Mano 2002 When the open path gas analyzers are used outside the temperature range stated in the product manual the sensitivity and the temperature dependency of the offset needs to be investigated prior to usage This caution is also applicable to the LI 7500 The product manual of the E 009 Advanet 1996 calls for a flow rate of about 5Lmin for the calibration gas The OP 2 is equipped with a temperature sensor inside the sensor head Temperature data can be output from the sensor however these data are intended to calibrate the drift of the CO and H20 outputs Thus it is advisable to avoid using these data as approximations of the temperature inside the calibration
60. to be addressed especially for those sites 3 Maintenance The maintenance of an open path gas analyzer is relatively easy During regular visits to the observation site it is advisable to follow the instructions below 1 Using the display panel of the sensor and or the data recorder make sure that the signal output is within the normal range When the signal output is abnormal one of the following may be the cause of the abnormal values O Dirt and or dust accumulated on the lenses located at the end of the measurement path see instruction 2 below Loose connections of cables or signal wires Trouble with the power and voltage supplies Blown fuse HM OI Co Co Abnormality in the environment surrounding the control box e g high temperature or water intrusion 47 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 O Broken cables or signal wires O Deterioration of desiccant or other chemicals if they are in use In addition to the possible causes above if an LI 7500 is used for the measurement the sensor diagnosis information should also be checked When SDM is used check Diagnostic value The diagnosis information can also be checked by connecting the sensor to a PC with the designated software 2 Clean the lenses remove dirt and or dust accumulated on the lenses on the measurement paths with water and Kimwipes Kimberly Clark Corporation US or other cleaning tissues Even when the lense
61. to the signal cables as in Photo 2 7 1 2 Electromagnetic waves Cell phones wireless LANs and CPUs can be sources of noise Measuring instruments should be kept away from such equipment and should be shielded with metal or other conductive materials 3 Power supply It is effective to apply a noise cut transformer or a lightning shielding transformer to the power supply circuit in order to suppress extrinsic high frequency noise and surges Photo 2 7 2 Problems due to instantaneous power failure or voltage fluctuations can be avoided by including an uninterruptible power supply UPS in the power supply circuit Photo 2 7 3 The investigator needs to be also aware that noise may be generated by the switching power supply that is used for supplying DC power to various measuring sensors 107 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 Photo 2 7 2 Noise cut transformer for power supply Photo 2 7 3 Uninterruptible power supply unit UPS It is sometimes quite difficult to identify appropriate measures for noise reduction In designing an observation system which is robust against noise the following points should be kept in mind 1 The power supply for the measuring instruments should be separated from that for other electric devices The use of a noise cut power transformer is effective to separate the measuring system from other components 2 When a transformer or a filter is used the primary and se
62. uV Tips 2 6 2 The CR1000 and CR3000 data loggers Campbell Scientific Inc US are highly flexible and are compatible with various measuring instruments The CR1000 and CR3000 data loggers allow the user to program the voltage measurement range the logging interval and the applied voltage These data loggers are also capable of numerical computations thus can also record turbulence statistical data While many of the sensors which allow digital output use the RS 232C format some use RS 422 or SDI 12 Serial Data Interface at 1200 baud rate Because of the RS 232C standard the cable length is limited to 10 m or less If the separation distance between the sensor and the data logger is more than 10m an optical cable can be used together with a transducer for extending the connection length between the sensor and the data logger RS 422 signals can be transferred at a maximum speed of 10 Mbps up to a distance of 1 2 km An RS 422 signal can be converted to an RS 232C signal with a commercially available signal converter The CR1000 and CR3000 data loggers are equipped with both SDI and RS 232C communication ports and thus are useful when the sensor and the data logger need to be deployed far apart A PC can also be used as a data logger When a sensor capable of analog output is used with a PC an 104 2 6 Data logger analog to digital AD conversion board is required Many of the sensors which output digital signals are equipped with
63. ultraviolet gas analyzers are also called Lyman alpha hygrometers or Krypton hygrometers H O molecules absorb ultraviolet radiation more readily than infrared radiation Therefore the path length of an open path ultraviolet gas analyzer can be shortened to a few cm and the spatially smoothed values of HO measured by an open path ultraviolet gas analyzer are higher in resolution than those measured by an open path IRGA The path length of the KH20 manufactured by Campbell see next paragraph is about 1 cm which is one tenth to one twentieth of the path length of an open path IRGA Some research requires the use of a short measurement path length for example for evaluating the turbulence transport and dissipation rate within a plant canopy In this case an open path ultraviolet gas analyzer is frequently chosen for use The disadvantages of open path ultraviolet gas analyzers include the short lifetime of the radiation source and 57 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 the large temporal variation of the calibration coefficients that are required for converting the ultraviolet attenuation into H O number density Accordingly open path ultraviolet gas analyzers cannot be operated over a long time period on the order of years without investing a significant amount of labor Finally when H2O measurements are made by open path ultraviolet gas analyzers corrections are required for the cross sensitivity of H2O and
64. variable that occur at finer scales than the path length are sometimes sought for example in the case of measurements conducted near the ground surface In such cases a SAT which is equipped with short paths and a non orthogonal probe i e a configuration in which multiple paths intersect at the same point in space should be utilized 36 2 1 Ultrasonic anemometer thermometers SATs The amount of missing high frequency signals to be corrected due to path length averaging varies according to the atmospheric stability e g Kristensen and Fitzjarrald 1984 On the other hand some studies such as Aubinet et al 2000 report that sufficient corrections of the signals for path length averaging can be made with the comprehensive method proposed by Moore 1986 which does not depend on the atmospheric stability When a slanted path 3D SAT is used the wind velocity and sonic virtual temperature are calculated from the measurements made over the three paths of the SAT For this reason caution is necessary for correcting missing high frequency signals due to path length averaging Horst and Oncley 2006 Errors associated with SAT induced flow distortion When a SAT is used for observations its probe is fixed in the wind velocity field It is thus believed that flow distortion is induced by the sensor and the frame of the SAT itself Blockage of the wind by the sensors is called transducer shadow This effect becomes the main source o
65. years of the Webb Pearman and Leuning density corrections Boundary Layer Meteorolgu 139 37 59 Lee X Massman W J and Law B E ed 2004 Handbook of Micrometeorology A Guide for Surface Flux Measurements and Analysis Kluwer Academic Publishers Boston Leuning R and King K M 1992 Comparison of eddy covariance measurements of CO fluxes by open and closed path CO analysers Boundary Layer Meteorology 59 297 311 Leuning R and Moncrieff J 1990 Eddy covariance CO flux measurements using Open and Closed path CO analysers Corrections for analyser water vapour sensitivity and damping of fluctuation in air sampling tubes Boundary Layer Meteorology 53 63 76 Leuning R and Judd M J 1996 The relative merits of open and closed path analyzers for measurement of eddy fluxes Global Change Biology 2 241 253 Leuning R Zegelin S J Jones K Keith H and Hughes D 2008 Measurement of horizontal and vertical advection of CO within a forest canopy Agricultural Forest Meteorology 148 11 1777 1797 LI COR 2002 LI 7500 and direct solar radiation LI 7500 Field Note 1 Publication Number 75H102 LI COR Inc LI COR 2003 Using CO and H20 Scrubbers with LI COR Gas Analyzers Publication Number IRG4 101 LI COR Inc LI COR 2004 LI 7500 CO H20 Analyzer Instruction Manual LI COR Inc LI COR 2011a LI 7500A Open Path CO2 H20 Analyzer Instruction Manual LI COR Inc LI COR 2011b Transitioning from an LI 7500 to an
66. 01 http www prede com file 32html htm Skye Instruments Ltd UK SKP 215 http www skyeinstruments com 3 2 Vane anemometer O R M Young Company US Model 12005 Microvane amp 3 Cup Anemometer Model 05103 Wind Monitor http www youngusa com Wind vane Makino Applied Instruments Inc Japan VR536 http business 1 plala or jp manox in Japanese Yokogawa Denshikiki Co Ltd Japan A 802 http www yokogawa com jp ydk in Japanese Windspeed Limited trading as Vector Instruments UK W200P http www windspeed co uk Anemometer Makino Applied Instruments Inc Japan AF750 http business plala or jp manox in Japanese Yokogawa Denshikiki Co Ltd Japan A 702 http www yokogawa com jp ydk in Japanese Windspeed Limited trading as Vector Instruments UK W100 Series http www windspeed co uk Ultrasonic anemometer R M Young Company US Model 85000 Ultrasonic Anemometer http www youngusa com Vaisala Oyj Finland WMT700 WINDCAP http www vaisala com Gill Instruments Ltd UK WindSonic http www gill co uk Pitot tube Okano Works Ltd Japan http www okanoworks com en main_en html Differential pressure gauge Setra Systems Inc US Model 239 http www setra com tra 170 3 3 Related information for chapter 3 Platinum resistance thermometer 0 Vaisala Oyj Finland HMP45A HMP45D http www vaisala com HMP45A
67. 03 41 n When the sonic virtual temperature is evaluated from the vertical path of a vertical path 3D SAT vn is equivalent to the horizontal wind velocity measured by the SAT In this case the cross wind effect can be corrected relatively easily However a somewhat complex method is necessary for the correction of the cross wind effect when slanted path 3D SATs are used particularly for the models in which the sonic virtual temperature is evaluated from the measurements averaged over the three paths Liu et al 2001 4 Tips Among the slanted path 3D SATs in which the sonic virtual temperature is evaluated from the measurements averaged over the three paths of an instrument the CSAT3 manufactured by Campbell outputs a sonic virtual temperature which has been corrected for the cross wind effect Furthermore concise procedures for correcting the cross wind effect for the WindMaster R3 and HS manufactured by Gill can be found in their product manuals Attention User Manual Issue 04 April 2009 for the WindMaster amp WindMaster Pro states that the virtual temperature output by the SAT has been corrected for the cross wind effect Whether the output value of the virtual temperature has been corrected for the cross wind may depend on whether the data are collected by an old or a new model Thus the investigator needs to inspect the manual for the details on cross wind correction Tips 2 1 8 38 2 1 Ultrasonic anemometer
68. 1 Arrestor SG GV series OTOWA Electric Co Ltd Japan http www otowadenki co jp eng 3 1 2 Signal circuit arrestor CN226 series Fuji Electric Technica Co Ltd Japan http www fe technica co jp in Japanese 3 1 3 BNC connecter UG 89 U 40 HIROSE ELECTRIC CO LTD Japan http www hirose com 3 1 4 Coaxial cable RG58A U Fujikura Ltd Japan http www fujikura co jp eng 3 1 5 DC reference voltage generator 3K02 NEC Avio Infrared Technologies Co Ltd Japan http www nec avio co jp en 3 1 6 Digital multi meter PC510a Sanwa Electric Instrument Co Ltd Japan http overseas sanwa meter co jp 3 1 174 10 11 12 13 14 15 16 17 18 19 20 21 22 Related information for chapter 3 Ethanol 99 5 500 ml Wako Pure Chemical Industries Ltd Japan http www wako chem co jp english 3 1 Hand auger Daiki Rika Kogyo Co Ltd Japan http www daiki co jp en 3 5 3 6 Paper towel Kimwipes S Ply 4 4 x8 4 Bx 280 Kimberly Clark Corporation US http www kimberly clark com 3 1 Plastic adhesive tape 0 2 mmx19 mmx10 m NITTO DENKO CORPORATION Japan http www nitto com 3 1 3 3 3 4 3 5 3 6 Precision resistance RNS1 8YCT52A 1001 Bmetal film resistor 0 1 accuracy and 1kQ resistance KOA Corporation Japan http www koaproducts com english 3 1 Double layer slit conduits PMA AG Switzerland http www pma ch pma_com 3 5 Flexibl
69. 1 summarizes the major open path gas analyzers that are available as commercialized products The measurement principle of all the products is the same that is their measurements are based on the infrared absorption characteristics of CO molecules All the sensors listed in Table 2 2 1 are also equipped with interference filters for the infrared absorption waveband of H O molecules Thus all the sensors are able to measure the number of HO molecules per unit volume mol H Om simultaneously with that of CO The details of the measurement principle and the structure of typical open path gas analyzers are summarized in Kohsiek 2000 Kohsiek 2000 also gives the details of the cross sensitivity see next paragraph and a method for evaluating the cross sensitivity When CO is measured by an open path gas analyzer the presence of H O changes the infrared absorption characteristics of CO molecules The effect of H2O molecules on the measurement of the CO 41 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 number density cross sensitivity needs to be taken into consideration to evaluate the CO number density accurately Kohsiek 2000 The control box of the LI 7500 LI COR Inc US takes into account the cross sensitivity LI COR 2004 however the E 009 Advanet Inc Japan and the OP 2 ADC BioScientific Ltd UK do not adjust their measurement outputs for the cross sensitivity Furthermore the indoor experiments
70. 2 61 116 124 signal cable 33 34 106 107 108 signal wire 47 48 119 silencer 88 89 92 silver brazing silver soldering 138 139 147 23 156 158 159 158 snow depth snow survey snow water equivalent SWE 23 159 156 158 159 50 52 70 71 snow weight soda lime soft ionization mass spectrometer 101 11 23 149 150 151 128 13 22 46 56 63 64 116 117 118 119 120 121 122 124 139 147 149 150 162 soil heat flux solar altitude solar radiation 128 69 71 72 78 79 80 82 87 88 89 90 91 93 94 97 98 99 102 21 28 29 30 35 37 solar zenith angle solenoid valve sonic virtual temperature 38 39 59 span calibration 53 span gas 52 53 71 80 88 spectroradiation 22 spectroradiometer 21 124 Practical Handbook of Tower Flux Observation Ver 1 0 spectrum analyzer 106 standard gas 50 67 71 80 81 static capacitors 152 Stefan Boltzmann Law 116 120 stemflow 23 subsampling 68 78 79 suction flow rate 68 89 super fine thermocouple 138 SWE see snow water equivalent switching power supply 105 107 synchronous device for measurement SDM 34 35 42 46 47 48 TDLS see tunable diode laser spectroscopy tedler bag 98 temperature dependence 161 tester see digital multimeter thermal desorption unit 100 thermistor 49 54 59 136 137 147 148 162 thermometer 136 147 thermocouple 54 56 57 58 59 61 135 137 138 139 142 14
71. 5 3 Air sampling tubes are made of stainless steel or glass are as small as 6 mm in diameter and are filled with adsorbent Canisters used for the reservoir system are vacuum vessels made of glass or stainless steel The reservoir system collects the atmospheric air by automatically switching the flow path at regular time intervals with the use of programmable relays The measurement system needs to be designed in 98 2 5 Relaxed eddy accumulation REA method such a way that analysis results of high accuracy can be achieved Specifically it is necessary to 1 maintain a constant flow rate at a point as close to the air inlet as possible 2 sort the air samples with a high speed response time and 3 store the air samples by minimizing the effects of degradation by ozone as well as adsorption in the flow path To meet these requirements it is useful to block ultraviolet radiation add an ozone scrubber and use PTFE materials or heating tubes Photo 2 5 2 Control section of a system which is Photo 2 5 3 An example of multiple VOC designed for the REA method and uses a CR1000 reservoirs sampling tubes Fujiyoshida forest Fujiyoshida forest meteorology research site meteorology research site Measurement procedure A typical procedure for trace gas flux measurement is as follows 1 Observation of w with a SAT and calculation of the time averaged value of w 2 Determination of the sign of w switchover of the solenoid valves and
72. 7 162 135 137 138 142 148 116 119 120 121 122 132 thermometer thermopile three cup anemometer throughfall 23 33 35 135 147 tilt check time constant 42 46 47 63 68 156 157 time lag of the signal output tipping bucket rain gauge topographic map 2 transducer 28 30 104 131 shadow 37 triangular weir 164 true solar time 128 tube 12 42 49 50 51 52 53 54 57 62 68 70 74 77 91 97 98 99 100 132 133 144 149 155 162 192 connector tubing connector 75 76 82 tunable diode laser spectrometer TDLS 101 ultrasonic anemometer thermometer SAT 28 29 31 32 33 34 35 36 37 38 39 43 44 45 46 47 58 59 60 61 64 67 96 97 98 99 102 135 29 30 32 33 36 37 29 30 31 36 37 38 29 30 31 37 38 56 57 58 probe slanted path vertical path ultraviolet gas analyzer underdrain 160 uninterruptible power supply UPS 107 108 vegetation map 2 velocity of light 129 volatile organic compound VOC 96 98 99 100 101 13 106 107 voltage drop voltage fluctuation 140 163 164 165 water bath water meter water level discharge curve 165 wavelength 22 56 57 116 119 122 124 127 129 wet bulb thermocouple 58 59 wet bulb thermometer 138 22 43 44 45 47 130 132 134 37 131 132 133 130 132 wind velocity 21 22 28 29 30 31 32 33 35 36 37 38 44 58 61 64 67 86 96 97 98 102 130 131 132 133
73. 92 2005 from the Chronological Scientific Tables Culmination time h the time when the sun passes the meridian over the observation point t 12 0 _Q A3 1 4 15 Solar zenith angle the angle between the zenith and the sun cosp singsind cosp cos cose A3 1 5 where latitude Solar altitude the angle between the sun and the horizon viewed from the observation point sinc singsind cosp cos cose A3 1 6 128 3 1 Radiation Appendix Appendix 3 1 2 Conversion of measurement units The relationship between molar photon flux density Fy molm s and radiant flux density F Wm of single wavelength can be expressed with Equation A3 1 7 A Fa aT Ah Cj where 4 wavelength m 4 Avogadro s number 6 023 x 10 mol A Planck s constant 6 626 X 10 Js and c velocity of light 2 9979 10 ms A3 1 7 Thus the relationship between photon flux density Fo molm s and radiant flux density Fy Wm integrated in the PAR wavelength range is expressed with Equation A3 1 8 700 Fy 8 36x107 AF d4 A3 1 8 400 PAR measured by a quantum sensor is limited to the integrated values and other values for each wavelength are unknown Accordingly the conversion into radiant flux density is mostly done with Equation A3 1 9 where a constant a 4 24 4 57 in the case of natural light is given on the basis of experimental results of McCree 1972 for the sake of
74. 996 Additional staff members are required for the measurement of other items such as micrometeorological variables Advances in measurement equipment have reduced the need of maintenance and thus number of staff Even then it is better to avoid working alone in high places on a tower Tips 1 1 1 Selecting a flux measurement point When candidate sites have been identified you should reconnoiter them and if possible view them from above Select an appropriate observation point to set up a tower or pole and ensure that there is a vast expanse of flat terrain and homogeneous vegetation on its windward side It is desirable to set the flux measurement height at least twice as the vegetation height However due to technical limitations and micrometeological footprint restrictions see section that contributes to the observed flux 1 2 2 Tower construction and maintenance the height of the flux measurement might be lowered in some instances Avoid areas that have artificial facilities such as buildings and power transmission lines or areas that have cars and other traffic facilities nearby This is because gas emissions from traffic and electrical noise can invalidate your observational data It is ideal to have an areal allowance of the same ecosystem for conducting ecological and pedological surveys which would disturb vegetation and soil but without affecting flux observation In most of the Asian countries it is not rare that
75. B 100 http www prede com file 32html htm THE EPPLEY LABORATORY INC US SBS SDK http www eppleylab com Infrared radiometer EKO INSTRUMENTS CO LTD Japan MS 202 __ http www eko usa com THE EPPLEY LABORATORY INC US PIR http www eppleylab com Kipp amp Zonen B V The Netherlands CGR 3 CGR 4 Net 0 0 http www kippzonen com pyrradiometers and four component net radiation sensor EKO INSTRUMENTS CO LTD Japan MF 11 MR 60 http www eko usa com Hukseflux Thermal Sensors B V The Netherlands NRO1 http www hukseflux com Kipp amp Zonen B V The Netherlands NR Lite2 CNR 1 CNR 2 CNR 4 http www kippzonen com Radiation and Energy Balance Systems Inc US Q 7 or Campbell Scientific Inc US Q7 1 http www campbellsci com 169 Practical Handbook of Tower Flux Observation Ver 1 0 Spectroradiometer O EKO INSTRUMENTS CO LTD Japan MS 700 _ http Avww eko usa com O ASD Inc US FieldSpec Handheld2 http www asdi com THE EPPLEY LABORATORY INC US PSP http www eppleylab com PAR sensors LI COR Inc US LI 190 http www licor com EKO INSTRUMENTS CO LTD Japan ML 020P _http www eko usa com Kipp amp Zonen B V The Netherlands PAR Lite PQS 1 http www kippzonen com KOITO ELECTRIC INDUSTRIES LTD Japan IKS 27 http www koito ind co jp eco koito environ PREDE CO LTD Japan PAR
76. BioScientific Ltd UK OP 2 Campbell Scientific Inc US KH20 2 3 Closed path CO gas analyzers O LI COR Inc US LI 6262 LI 7000 2 4 Closed path CO gas analyzer LI COR Inc US LI 820 LI 840 Ai is r sampling devices Dylec Inc Japan MEIWAFOSIS CO LTD Japan System building CLIMATEC Inc Japan Control modules 2 5 Programmable data loggers Campbell Scientific Inc US Gas chromatographs SHIMADZU CORPORATION Japan Agilent Technologies Inc US Applied Technologies Inc US K Style Probe Gill Instruments Ltd UK WindMaster R3 HS Campbell Scientific Inc US SDM CD16AC SONIC CORPORATION Japan TR 61A B C TR 90AH SAT 540 550 http www u sonic co jp english http www apptech com http www gill co uk http www youngusa com http www youngusa com products http www youngusa com PRICELIST pdf METEK Meteorologische Messtechnik GmbH Germany USA 1 http www metek de http www campbellsci com http www licor com http www adc co uk http www campbellsci com http www licor com http www licor com http www dylec co jp in Japanese http www meiwafosis com in Japanese http www weather co jp in Japanese http www campbellsci com http www campbellsci com index cfm http www shimadzu com http www home agilent com 110 Soft ionization mass spectrometers Ionicon
77. Deploy the SAT probe pointing into the direction of the prevailing wind and the direction in which the flow distortion by the tower and the probe itself is minimized Flow distortion will be discussed on p 37 Regarding 1 it is desirable to use a boom that is more than 1 5 times the width of the tower through which wind passes Hirano and Saigusa 2007 When the use of such a boom is not feasible deploy the SAT as far as possible from the tower taking into account the tasks required for deployment and maintenance Caution 2 is especially important for the deployment of a SAT with a structure which disturbs the wind flowing through the backside of the probe e g the TR 61A and TR 61C manufactured by SONIC the HS manufactured by Gill and the CSAT3 manufactured by Campbell The backside of a probe usually corresponds to the side to which cables are connected Probes and parts In the process of deploying a SAT probe fittings are required to attach the probe to the tower In most cases the SAT probe or the boom provided by the SAT manufacturer is secured to a base by screws or U bolts The base in turn is secured to the tower by half clamps and or U bolts The simplest base can be 32 2 1 Ultrasonic anemometer thermometers SATs made by drilling holes in a flat plate Because the size of the base and the positions of the holes depend on the SAT and the tower specification the investigator usually needs to build a base on his her ow
78. Katul G Law B Lee X Malhi Y Meyers T Munger W Oechel W Paw K T Pilegaard K Schmid H P Valentini R Verma S Vesala T Wilson K and Wofsy S 2001 FLUXNET a new tool to study the temporal and spatial variability of ecosystem scale carbon dioxide water vapor and energy flux densities Bulletin of the American Meteorological Society 82 2415 2434 Baldocchi D Finnigan J Wilson K Paw U K T and Falge E 2000 On measuring net ecosystem carbon exchange over tall vegetation on complex terrain Boundary Layer Meteorology 96 257 291 Baldocchi D Valentini R Running S Oechel W and Dahlman R 1996 Strategies for measuring and modelling carbon dioxide and water vapour fluxes over terrestrial ecosystems Global Change Biology 2 3 15 168 Burba G G Anderson D J Xu L and McDermitt D K 2005 Solving the off season uptake problem correcting fluxes measured with the LI 7500 for the effects of instrument surface heating Progress report of an ongoing study PART 1 THEORY Poster presentation AmeriFlux 2005 Annual Meeting Boulder Colorado Burba G G McDermitt D K Grelle A Anderson D J and Xu L 2008 Addressing the influence of instrument surface heat exchange on the measurements of CO flux from open path gas analyzers Global 177 Practical Handbook of Tower Flux Observation Ver 1 0 Change Biology 14 1 23 Businger J A and Oncley S P 1990 Flux measurement with conditional sam
79. LNO i nc LNO i f Flow Meter Filter SV 1 i Sv 2 i SV n EE z IK Manual Valve H La r H m i Dehumidifier COM i a Programmable i z Di COM D Sequence Controller o gi y Solenoid Valve i i com LF ne Synchronize ea maan SV a F Pe Pump hy RY near a Data GOMES na I Si vindncsinuinushcuicniawadainuulitus SV b IRGA Q M LI 6262 LI 7000 O StdGas Zero Sample cell MFC 1 m in M lt LE MFC Mass Flow Controller 0 StdGas Span MFC 2 RV Ne na Fig 2 4 1 A sample system for measuring CO concentration profiles lt Reference cell Le To De COz desiccant assembly The piping in the system can be classified into the following three flow paths 1 Flow path for supplying sampled air and calibration gas to the sample cell of the CO analyzer blue path in Fig 2 4 1 O Main flow path sampled air O Merging flow path calibration gas zero and span gases 2 Flow path for supplying reference gas to the reference cell of the CO analyzer red path in Fig 2 4 1 3 Flow path for supplying dry air for dehumidification purple path in Fig 2 4 1 The system itself and cautions regarding its use will be explained by following the flow path for the sampled air and calibration gases in Fig 2 4 1 blue path Inlets for sampled air Fix the end of the tubing so that it points downward to prevent rain droplets from entering refer to Tips 2 4 2 and photos 2 4 1 2 4 3
80. Moderately priced air filters should be selected for use as the filters need to be replaced frequently Air filters should be replaced once every two to four weeks depending on the amount of pollution in the air Caution is necessary in selecting both the number of filters to be used and the pore diameters of the filters since these factors can increase the load on the pump Dehumidifiers 0 When only CO concentration is measured it is recommended that moisture in the sampled air be removed in order to prevent problems caused by dew formation in the measurement system Purge gas dry air that is supplied into the dehumidifiers should be prepared with the use of silica gel or heatless dehumidifiers Refer to Section 2 3 Closed path CO gas analyzers The investigator needs to ensure that the dehumidifier is firmly connected to the system tubing Some dehumidifiers are prone to becoming disconnected from the system tubing 90 2 4 CO storage change Solenoid valves merging of calibration gas SV a SV b O The reference gases for the CO analyzer flow through the solenoid valves O Attach a pressure regulator to each reference gas cylinder O Follow the operation manual for proper use of the regulator Because the maximum allowable working pressure varies according to the pressure gauge attached to the regulator select a pressure gauge with a full scale pressure range of 1 5 to 2 times the pressure to be applied For ex
81. O on the measurements Details of the required corrections are discussed in van Dijk et al 2003 As of now the KH20 manufactured by Campbell is one of the open path ultraviolet gas analyzers that are available for purchase The price of the instrument is about 1 1 to 1 2 million yen available through TAIYO KEIKI Co Ltd Japan as of November 2008 less expensive than the open path IRGAs that are discussed in Section 2 2 1 Measurement of fluctuating CO concentration by an open path gas analyzer Therefore the KH20 is an appropriate choice when a system needs to be constructed only for H2O flux observations with a relatively low budget The use of a KH20 is also appropriate for research which requires a short measurement path length as mentioned earlier However the reader is reminded that a KH20 is not well suited for long term continuous measurements Refer to Section 2 2 1 for the deployment method of an ultraviolet open path gas analyzer as it is the same as that for an open path IRGA For the calibration method and maintenance of ultraviolet open path gas analyzers refer to the product manuals 3 Thermocouples Unlike open path gas analyzers thermocouples can be used to directly measure H20 in the atmosphere by the sensing element of the instrument itself There are two methods for measuring H O with thermocouples One method uses a thermocouple psychrometer and the other method uses the combination of a SAT and a thermoco
82. OR Inc US for example has a voltage output range between 0 and 10 mV which corresponds to between 0 and 3 000 umolm s of photons If a given data logger has a resolution of ImV its physical value is equivalent to a resolution of only 300 umolm s Thus a data logger with a resolution of 0 01 mV or so must be chosen In order to take advantage of measurement precision of a sensor its measurement accuracy as well as its resolution should be taken into consideration Some instruments such as resistance thermometers need applied voltage and preheating to turn on the electricity for a few seconds before measurement For these instruments loggers capable of controlling applied voltage and preheating should be selected to facilitate measurement and reduce power consumption 167 Practical Handbook of Tower Flux Observation Ver 1 0 Related information for chapter 3 Further reading AsiaFlux Steering Committee ed 2007 Practice of flux observations in terrestrial ecosystems http www asiaflux net members material html available exclusively for AsiaFlux members It is the English translated edition of AsiaFlux Steering Committee ed 2003 TO OOO0U0U000000U00 OOOUOUUUUUUUD Forest environmental survey editorial committee ed 1999 Handbook of forest environmental survey environmental measurement in forest 284pp Hakuyusha in Japanese Hokkaido branch of Japanese Society of Snow and Ice ed 1991 Procedures f
83. Obtaining the cooperation of local residents is also essential for conducting a successful study Prior preparation is ideal as it ensures that many obstacles are removed before the study begins Continuous year round observation is ideal in principle in many cases however that is not always possible due to limited budgets human resources and electric power supply In such case we should reduce the number of Chapter 1 Photo 1 1 1 A supportive year round weather station Tura Russia observation items and the duration of observation to secure the indispensable data Moreover it is desirable to set up an additional weather station in a readily accessible location where security and electric power for collecting supportive meteorological data throughout the year Photo 1 1 1 1 2 Building infrastructure 1 2 Building infrastructure This section describes some public procedures of the government with cases of Japan as examples When setting up an observation station in other countries it is necessary to proceed corresponding each local or national government 1 2 1 Obtaining permission for land use example of case in Japan Private land It is difficult to provide a general explanation of the procedures involved in acquiring permissions for land use for studies that include the construction of towers or roads on private land It is necessary to discuss the procedures with the land owners and also be sincere and patie
84. Practical Handbook of Tower Flux Observation im A o 4 Y l 4 2 j rf Editorial Board of Practical Handbook of Tower Flux Observation Editorial Board Editorial Board Chairman YAMANOI Katsumi Hokkaido Research Center FFPRI Members in alphabetical order HIRATA Ryuichi Faculty of Agriculture Hokkaido University KITAMURA Kenzo Department of Meteorological Environment FFPRI MAEDA Takahisa Institute for Environmental Management Technology AIST MATSUURA Shoji NILGS MIYAMA Takafumi Kansai Research Center FFPRI MIZOGUCHI Yasuko Hokkaido Research Center FFPRI MURAYAMA Shohei Institute for Environmental Management Technology AIST NAKAI Yuichiro Department of Meteorological Environment FFPRI OHTANI Yoshikazu Department of Meteorological Environment FFPRI ONO Keisuke Agro Meteorology Division NIAES TAKAHASHI Yoshiyuki Center for Global Environmental Research NIES TAMAI Koji Department of Soil and Water Conservation FFPRI YASUDA Yukio Tohoku Research Center FFPRI Secretary MIZOGUCHI Yasuko Hokkaido Research Center FFPRI YUTA Satoko Department of Meteorological Environment FFPRI Matsunosato 1 Tsukuba Ibaraki 305 8687 JAPAN Department of Meteorological Environment Forestry and Forest Products Research Institute FFPRI Phone 81 29 873 3211 main E mail ffnet man ffpri affrce go jp Practical Handbook of Tower Flux Observation Ver 1 0 Preface Ef
85. Take appropriate measures to avoid taking in rain droplets dust and insects 88 2 4 CO storage change Suction tubing piping For outdoor piping weather proof tubing such as that made of PTFE often marketed as Teflon should be used Flexible tubing e g tubing made of polyurethane is easy to handle in small spaces within the system Negative pressure occurs in the flow path upstream of the pump while positive pressure occurs in the flow path downstream of the pump Caution is necessary to prevent leakage along the flow path under negative pressure Caution is necessary to ensure that joints and other parts along the pressurized positive pressure flow can withstand the expected maximum pressure Manual valves O A high suction flow rate of air is desirable to shorten the travel time of the air between the air inlet and the sample cell Excess air should be vented before solenoid valves in order to reduce the pressure to a value less than the maximum allowable pressure of the solenoid valves and the sample cell reduce the load on the pumps and prevent dew formation in the mass flow controller The flow rate can be controlled with manual valves When setting up the system use a flow meter to decide how far to open each valve During this step the flow rate of the air after the manual valves should be adjusted to a value close to that set by the mass flow controller Caution is necessary to avoid openi
86. The ratio of the absolute humidity in moist air to the mixing ratio in saturated air xs expressed as a percentage The temperature at which cooled moist air becomes saturated i e condensation starts EIE IG Cw p i 755 Where Ca dry bulb temperature C Cw wet bulb temperature C p total atmospheric pressure Pa es Saturation vapor pressure Pa at a wet bulb temperature Cw and j constant 0 5 when the wet bulb is not frozen and 0 44 when the wet bulb is frozen 145 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 2 above water surface 8 2969 2 1 qT 1 sonsooiog 2 1 047x107 110 a 1 logio 10795741 a 4 76955 0 42873x10 410 ty 0 78614 above ice loge 9 09685 7 1 3 566541og 7 0 87682 1 2 0 78614 a a 1 Where 7 absolute air temperature K and T triple point temperature of water 273 16 K e inf 3 Cap C e In c Ga Where c and c2 constants c 17 2693882 and cz 237 3 above water surface and c 21 8745584 and c2 265 5 above ice Appendix 3 4 2 Equilibrium relative humidity of air with chloride saturated solution 0 C 5 C 10 C 15 C 20 C 25 C 30 C KNO 97 96 95 95 94 93 92 KCI 88 87 86 86 85 84 NaCl 76 76 75 75 75 75 75 MgCl 6H O 34 33 33 33 33 33 32 unit Japanese Industrial Standards Committee JIS Z 8806 2001 Humidity measurement methods 146
87. Tips 2 3 15 7 Tips When H O concentration is measured simultaneously with CO concentration the analyzer needs to be calibrated for its H O concentration output There is little water vapor in the standard gas or pure air that is used for CO calibration thus either gas can be used as the zero gas for H O calibration As for the span adjustment a dew point generator e g LI 610 LI COR can be used A dew point generator produces air with a desired dew point The use of an LI 610 allows on site calibration However make sure to set the dew point temperature lower than the air temperature of the site Tips 2 3 16 9 Data output from the analyzer The value of the concentration measured by the analyzer is output as a digital or analog signal The LI 6262 is capable of RS 232C output digital or voltage output analog There are two options for the analog output raw voltage output and DAC output The raw voltage output is the output in which no corrections or calculations have been applied thus calibration coefficients are required to convert the raw voltage output to concentration values On the other hand DAC output is the output in which the value of the concentration has been converted to voltage signals ranging from 0 to 5 V The LI 6262 is equipped with a data smoothing function which enables smoothing of the output signal However because this function is not necessary for eddy covariance measurements the smoothing function
88. a e aee EEE Saos e Enae SHIMIZU Akira FFPRI Photo 2 2a catherine srren enie e oee o TE E KOMINAMI Yuji FFPRI Fig 2 3 locen enano nieee a a Hee kate da NR OHTANI Yoshikazu FFPRI Photo 2 4 1 2 4 2 right 3 5 7 ee eeceescssesessecceeceeeeceeeeesaeaeeeeeaeeneeees MIZOGUCHI Yasuko FFPRI Photo 25 A 2 Cb sess 253 tea ce sotent a A E YUTA Satoko FFPRI PHO 24 3 ENEE A TAKAHASHI Yoshiyuki NIES Photo 3 1 1 left 3 1 2 3 1 3 right 3 1 5 right 3 1 6 right 3 5 6 EKO INSTRUMENTS CO LTD Photo 3 1 1 right 3 1 3 left 3 1 5 left 3 1 6 left 0 eee eeeeeeeeeeee Kipp amp Zonen B V PHOOL I Ae sea redeti tee ate geet eset CLIMATEC Inc Photo 3 523 ce tchsetteesteiee Soe teeieer Gita d nese oui eee CHINO CORPORATION Photo 3 525 sas steis sities Haste ateiess Assad adil ase keds PREDE CO LTD Pig 3 641 Aesth asia eit E al einen wee CAMPBELL SCIENTIFIC INC Photo 3205 Is ocecsscaivevehdastdiuberevcvebigsvsiabsceucegndsaudinncivestsaudinedentacebiackdisvenuestes Decagon Devices Inc PHOU6 3 1622 EEE E EE actrees bie Gata eames aie Daiki Rika Kogyo Co Ltd Photo 31623 sostiene ie a teese aene adeis IIDA Shinichi FFPRI Phot 3 8 3 resnost esre ees eE SDE eade EEKE ESEE e Senecom Inc All trademarks are the property of their respective owners 195
89. a flow meter that can measure a flow rate of approximately 1 Lmin and allows flow rate adjustment at an increment of approximately 0 1 Lmin A float type flow meter is frequently used for 50 2 2 Open path CO H O gas analyzers calibration Dew point generator A dew point generator is usually used for H O calibration In the field of research flux observations the LI 610 portable dew point generator manufactured by LI COR is used as the de facto standard dew point generator The LI 610 is already equipped with a floating ball flow meter therefore connect the LI 610 directly to the calibration tube with a length of tubing It is better to avoid including a flow meter between the LI 610 and the calibration tube as the inclusion of a flow meter increases the likelihood of condensation or leakage within the system Other equipment Other equipment required for calibration includes the following the calibration tube for the LI 7500 a PC running the software for the LI 7500 analyzer LI7500 exe hereafter referred to as LI 7500 software and a serial cable to connect the control box to the PC When the pressure inside the calibration tube is measured a barometer will also be required For this measurement a regular barometer used for meteorological observations such as the PTB210 manufactured by Vaisala is sufficient 2 Calibration procedure The procedure for calibrating an LI 7500 that has been in operation at an observati
90. aE ea Naar iaaii easa ia 184 idet ecco el ii eles isk ate wee ats ep EAE RAEAN vd hatha EOE td ae ba ide haw EAEE EREE E 188 List Of GUO gsi omnsoean sa craian tecteagonsaiinn cape ERa yaaa REEERE ERRE aaO a Eiaa atatia RREN tines 194 vii viii Observation and the Selecti Flux Observation Sites Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 1 1 1 The observation site This section describes how to select appropriate sites for performing long term continuous observations of energy and CO fluxes Basic concept When selecting a site you must clarify the purpose of your proposed observation by answering the question In what type of ecosystems will these flux measurements be taken Specifically you must determine the following required conditions beforehand vegetation type dominant species density height and age climatic conditions soil characteristics potential disruptions in the ecosystem due to natural causes and potential disruptions in the ecosystem because of man made changes such as tree trimming or land development Then search for an appropriate observation site based on these variables Careful site selection is important as it can profoundly affect the validity of your observational data preliminary studies on possible observation sites are worthwhile Flux measurements performed using the eddy covariance method postulate fewer atmospheric or land surface condition as compared to those perfo
91. added to the air mixture from each measurement height depends on the thickness of the air layer that is represented by the measurement height The CO storage change within the forest canopy is calculated from the temporal change in the evaluated value of the average CO concentration of the forest canopy In summary as these examples show various types of measuring systems can be designed Calculation method Theoretically the CO storage change is evaluated from the difference between the instantaneous CO concentration at the beginning of the flux averaging period and that at the end of the flux averaging period However this method yields calculation results that differ significantly from the true concentration change of interest Finnigan 2006 Although the CO storage change is sometimes evaluated from the difference in the 30 minute average values of CO concentration this approach underestimates the values that are sought Finnigan 2006 Baldocchi et al 2000 calculated the CO storage change from the temporal change of the CO concentration profile four measurement heights that was obtained from data collected every 120 seconds Because measurements of CO concentration profiles do not provide accurate CO concentration profiles 94 2 4 CO storage change at the beginning and the end of the flux averaging period Yang et al 2007 calculated the CO3 storage change by applying a spline interpolation to the measurement values
92. age drop voltage drop due to a capacity shortage of the power source or a large distance from the switchboard and flicker low frequency oscillation of the power supply voltage Particularly when observations are conducted in remote sites or in the areas at which the power supply is unstable the investigator needs to pay attention to the condition of the supplied power Noise detection The use of commercially available instruments for turbulence observations does not usually pose any serious noise related problems because those instruments are equipped with sufficient noise reduction measures However at the beginning of an observation or with the replacement of an instrument the data need to be checked to make sure that they are free of abnormalities The most basic data checking procedure is to plot and check the raw measurement values while all the measuring instruments are connected If the measurement values include spikes biased values or ripples related to the power supply frequency abnormal values will be noticeable even in the data collected at the measuring frequencies that are usually adopted for turbulence observation approximately 10 Hz Data can be checked in more detail for noise if the data signals are monitored by an oscilloscope or a spectrum analyzer When noise is found the source needs be identified However there is no set way to identify the source of noise and the source can be detected only through trying out variou
93. agricultural areas other than permanent grasslands are managed in sections of one hectare or less Each section may use a different management method and this can have an adverse effect on the observation results It is important to take this factor into consideration when conducting a preliminary survey on an observation site Access It is desirable that there is a road leading to the observation tower so that heavy equipment can be carried into the tower for maintenance Where there is no road one should be built or if it is difficult to build a road because of strict restrictions on the use of roads or due to steep slopes installing a monorail is a good option However since emissions from vehicles can adversely affect observation results it is necessary to have some restrictions on traffic Remote site There are some areas that are difficult for people to access but they must be observed as they are considered important ecosystems We call an observation site installed in such an area as a remote site What steps must be taken to conduct a long term survey at such remote sites It is impossible to install commercial power lines in such locations Access is also extremely inconvenient To enable observational Practical Handbook of Tower Flux Observation Ver 1 0 studies in such an area we should first plan how to address problems with the living environment such as problems relating to transportation and accommodation
94. air sampling depends on the tubing length tubing diameter and the pump capacity The air flow rate through the system after the pump is determined primarily by the maximum flow rate allowed by the CO analyzer For example the maximum flow rate of the LI 6262 is 10 Lmin LI 6262 manual LI COR while no such value is set for the LI 7000 The LI 7000 manual states that its maximum flow rate is unlimited In Fig 2 3 1 the rate of the sampled air flow through the system after the pump is set to 2 0 Lmin in order to enhance the efficiency of the moisture removal by the membrane dehumidifier Depending on the system configuration the air discharge rate out of the pump can sometimes be increased to a value much larger than the maximum flow rate allowed by the CO analyzer One of the methods to achieve such air discharge rates out of the pump is called sub sampling Refer to Suyker and Verma 1993 and Tips 2 3 13 In this method excess flow is vented out of the air sampling system between the pump and the CO analyzer When this method is utilized a large suction flow rate can be achieved in the flow path between the air inlet and the pump As a result the time lag between the air sampling and the output of the changing CO concentration can be reduced The use of a mass flow controller is recommended for controlling the flow rate of the sampled air although a flow meter that is equipped with a flow rate control function can also be used for this p
95. air with chloride saturated solution 146 3 5 Soil temperature and soil heat flux 00666 60 eee 147 3 5 1 Soil temperature e1seeeeeeeseeeenerenetenensnetenetsesnesseesenesesentenssnesenessesesaeeennees 147 3 59 Soil Heat tix son Peseinethrsvenocers beset ies cacdguenhan E nao tewenase tens senetovennie saws 149 3 6 Soil moistufe eie aa tees E ea E EEE a EEE EEA eke en eee este Doeesew bee eee ee 152 3 7 Precipitation snow water equivalent SWE snow survey snow depth snow weight 156 3 7 1 Precipitation rainfall snowfall seseseseeeeeeeneseeesenesensteseensenssensasaeesesssasasanees 156 3 7 2 Snow survey snow depth snow weight seeeeeeeeetesesteettesessettstetttetttstnsttnntnnnntntnnntnt t 158 3 8 Water level water temperature irrigation and drainage eeee eset teeter teeter teen tree ereeereeeree 160 3 80 Water level se sstteancwtat mesa an iinet oavesbuinn tative betes ninnee te th eaves 161 3 8 2 Water temperature seeecereseresenererereetttsentnenennesenasenessenssaseennseneueasasaenenenes 162 3 8 3 Irrigation and drainage sseseseeeeteteeeeeeeteeetteetteneeaseeasasasesaeasasasasaeaeasaeees 163 3 9 Data logger setetest ieee 166 Related information for chapter 3 ssssseseeeeseeeseeeeeeeeeeeeeeeeeeeneneneeeeeeeeeseneeeseeeeeeeeeeeeeesenas 168 Literature cited S886 2A AA AE AA A E E RE a aa 177 List of symbols sotasnscusinasea iannis ene e aii
96. ake the tension in the stays of a tower will change slightly because of vibrations caused by wind and the observer s movements on the tower It is thus preferable to measure the tension of the stays once a year using a tension meter and to adjust the tension based on these measurements It is also necessary to constantly check for corrosion of the metal joints on the tower and to replace them when necessary by ordering the parts from a supplier or by contacting the tower builders Especially for a tower built in a forest even if the tower itself is designed to sustain vibrations induced by strong winds it is conceivable that a tree could fall on the tower or on the stays and cause severe damage To prevent this any tree that could potentially interfere with the tower or the stays should be cut down In a forest with a fully closed canopy cutting down a single tree creates a gap in the forest but the influence on the observational results appear to be small e g Kelliher et al 1995 If many trees need to be felled there are concerns that labor for cutting and transporting them will be considerable and that the habitat will change Instead of cutting trees it is recommended that the target trees be tied to other trees with a steel wire Photo 1 2 5 Trees that are tied together do not fall as easily as single trees and the risk of their causing damage to the tower or to the stays is also much lower The Kahoku Experimental Watershed of the Fo
97. al SATs which measure the scalar flux in only the vertical direction the use of 3D SATs allows calculations of momentum fluxes coordinate transformations in the post data acquisition stage and correction for the cross wind effect on the sonic virtual temperature acquired by the SATs There are various types of 3D SATs Commercially available 3D SATs are durable enough for field observations and are characterized by a fair level of reliability Specifications of well trusted SATs that have often been deployed for observations both in Japan and abroad are summarized in Table 2 1 1 The 3D SATs that are frequently used in observations are classified below according to the configuration of the frame that supports the sensors probe Vertical path 3D SATs Some 3D SATs measure the vertical component of the wind velocity with a pair of sensors that constitute a path parallel to the vertical axis and measure the horizontal components of the wind velocity with two pairs of sensors that lie in a horizontal plane These 3D SATs will be referred to as vertical path 3D SATs in this section When the paths are orthogonal to one another the 3D SATs are called orthogonal type orthogonal probe Vertical path 3D SATs include the TR 61A Table 2 1 1 the TR 61C Table 2 1 1 Photo 2 1 1 a and the TR 90AH all manufactured by SONIC CORPORATION Japan former Kaijo Sonic Corp and the K Style Probe Table 2 1 1 Photo 2 1 1 b manufactured by Applied Technolog
98. alues of the gas analyzer The following measures can be taken to mitigate the effect of the flow rate pulsation First when the pump is placed upstream of the analyzer resistance such as a mass flow controller or a membrane dehumidifier made of resin can be placed between the pump and the analyzer This measure can sometimes reduce the effect of the flow rate pulsation significantly Second when sample air is drawn by a pump located downstream of the analyzer a buffer tank or similar device can be placed between the pump and the analyzer to mitigate flow rate pulsation When a diaphragm pump is placed upstream of the analyzer dust which originates from the diaphragm inside the pump frequently contaminates the interior of the cell of the analyzer To avoid such contamination make sure to install a filter on the exhaust side of the pump Maintenance method As diaphragms wear out they need to be replaced regularly When a diaphragm is damaged due to cracks or other causes the flow rate may decline and air leakage may occur Diaphragms and valves are sold separately as replacement parts so it is advisable to purchase a few in advance as spares When the flow rate declines it is suggested to replace the diaphragm of the pump as a first measure It is also recommended to replace the valves at the air inlet and outlet at the same time If the flow rate does not recover despite the replacement of the diaphragm the pump itself might have come to the en
99. ample consider a pressure regulator with an inlet primary pressure gauge and an outlet secondary pressure gauge If the values of the maximum pressure at the inlet and the supply pressure at the outlet are assumed to be 15 Mpa and 0 1 MPa respectively select a regulator that has pressure gauges with full scale ranges of approximately 25 MPa and 0 2 MPa Use a secondary pressure adjustment valve to reduce the pressure sufficiently to avoid applying an excessive load to the system The pressure range of the secondary pressure adjustment valve should be appropriate for the pressure tightness of the piping downstream so that improper opening closing of this pressure adjustment valve will not impose an excessive load on the piping Do not select a secondary pressure adjustment valve with high pressure tightness for versatility Mass flow controllers O The flow rate should be set by taking into account the maximum allowable flow rate for the cells of the CO analyzer Filters O Gelman filters have directionality and must be installed accordingly Sample cells of the gas analyzer O0 The investigator needs to confirm the maximum allowable inflow rate into and the maximum allowable pressure inside the sample cells by referring to the manual Ventilation from the gas analyzer O When the flow rate is low installation of an exhaust tube suggested length approximately 30 cm on an empirical basis is required in order to avoid the influen
100. an RS 232C interface However because RS 232C ports are now obsolete interfaces on PCs as of 2008 most PCs as of 2008 are not equipped with these ports Thus a USB RS232C conversion cable or an RS 232C extension board is needed to use a PC as a data logger Because many types of data loggers support data input to PCs data can be automatically uploaded to a PC on a regular schedule in order to make up for the insufficient memory size of a data logger Most data loggers record data in a binary format in order to maximize memory usage Furthermore most of the software which comes with data loggers transfers data to PCs and converts the data on the PCs to the CSV format or other versatile formats HTTP server and FTP server functions are also available on some data loggers Measuring procedures When an AC power supply is used to operate a data logger an earth connection is necessary to avoid noise in the data The internal switching power supply in a data logger generates noise It is also effective to filter out the noise according to the frequency of the power supply Noise is caused mainly by electromagnetic induction Effective countermeasures against noise include the following 1 the signal and power cables should be separated as much as possible 2 shielded cables should be used 3 twisted pair cables should be used 4 the cables should be shortened as much as possible 5 the cables should not be looped and 6 the cables should be fi
101. and HMP45D output value in voltage and temperature respectively HMP45 has been replaced by HMP155 Humidity and Temperature Probe since March 2009 Kawaso Electric Industrial Co Ltd Japan Sheath thermo resistance http www kawaso co jp en Hayashi Denko co ltd Japan Platinum resistance thermometer element http www hayashidenko co jp en Thermocouple thermometers Grant Instruments Cambridge Ltd UK CS U VL50 0 http www grant co uk CLIMATEC Inc Japan Ct 0 32 http www weather co jp in Japanese Hayashi Denko co ltd Japan Sheathed thermocouple http www hayashidenko co jp en Thermistor Campbell Scientific Inc US 107 L http www campbellsci com Onset Computer Corporation US HOBO http www onsetcomp com Thermocouple type of HOBO HOBO U12 thermocouple logger is also available T amp D Corporation Japan Thermo recorder Ondotori http www tandd co jp in Japanese Platinum thermometer type of Ondotori Ondotori Pt is also available HIOKI E E CORPORATION Japan TEMPERATURE LOGGER 3632 http www hioki com TATEYAMA KAGAKU INDUSTRY Co Ltd Japan D717 http www tateyama jp eng Radiation thermometer O0 CLIMATEC Inc Japan C IRR P http www weather co jp in Japanese O NEC Avio Infrared Technologies Co Ltd Japan Infrared thermograph http www nec avio co jp jp products ir thermo en Shelter CLIMATEC Inc
102. aration distance is measured in addition to the value of the sensor separation distance the following information needs to be 44 2 2 Open path CO H O gas analyzers recorded the north south as well as the east west distance cm between the center of the open path gas analyzer measurement path and that of the SAT measurement path Alternatively the bearing of the position of the open path gas analyzer can be recorded with respect to the center of the SAT measurement path The set of information described here will be required for correcting the flux loss at high frequencies and or quality controlling the data If the centers of the measurement paths are situated at different heights this information should also be recorded Because of limited research on the topic our understanding is currently limited on flux loss due to the vertical separation distance between the centers of the measurement paths e g the frequency response characteristics of co spectra and the method for correcting for flux loss However future research may require flux loss correction and lead to appropriate methods for correcting the flux losses due to sensors installed at different heights When an open path gas analyzer is calibrated the sensor head needs to be temporarily removed from and placed back into its deployment location Therefore it is recommended that the sensor head is mounted in such a manner that the position of the analyzer with respect to the SAT r
103. are the collective term for gas analyzers for which the measurement sections for the sample gas are exposed open to the atmosphere Ordinarily as the measurement principle open path gas analyzers utilize the absorption characteristics of particular wavelengths of radiation by gaseous molecules e g H O and CO2 Specifically the infrared source situated at the end of the measurement path emits a well defined amount of infrared radiation to a detector that is situated at the 56 2 2 Open path CO H O gas analyzers other end of the measurement path The infrared radiation measured by the detector provides a measurement of the attenuation of the infrared radiation over the measurement path between the infrared source and the detector This measurement is then used to calculate the number density of gaseous molecules in the measurement path In general the response time of open path gas analyzers is shorter than that of closed path gas analyzers Open path gas analyzers are able to sample data at rates as high as 10 to 20 Hz allowing accurate measurements of the fluctuating number density of gaseous molecules However because the measurement path is exposed to the atmosphere the infrared source and detector of an open path gas analyzer are subject to influences from the ambient environment Therefore open path gas analyzers are not well suited for stable and accurate measurements of the absolute magnitude of the number density of gaseous molec
104. asuring turbulence produce output data at 0 5 V it is desirable to use a data logger capable of data logging in the range between 0 and 5 V 103 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 Table 2 6 1 Data loggers used for turbulence measurements Model manufacturer A D resolution Maximum Logging rate Memory medium CF optional CR3000 Campbell 83 33 uV 45 V 40 Hz USB flash drive optional CF optional CR1000 Campbell 667 uV 5 V 10 Hz USB flash drive optional es8 TEAC discontinued model 16 bit 5 V 5 kHz CF USB flash drive NR 1000 KEYENCE 16 bit 5 V 10 Hz CF USB flash drive MEMORY HiLOGGER LR8430 20 500 uV 10 V 10 Hz CF USB flash drive HIOKI ZR RX20 40A OMRON 16 bit 5 V 10 Hz USB flash drive y Tips The resolutions of the sensor and the data logger also need to be taken into account in data logging Resolution is the minimum signal variation that can be recognized by the sensor or the minimum signal variation that is allowed in the digital data after an AD conversion by the data logger As an example consider a sonic anemometer with a resolution of 0 005 ms If the measurement range is set to 30 ms and the analogue output range of the anemometer is 1 V the size of the minimum output signal is approximately 166 7 uV The minimum output from this case can be recorded only with a data logger with a resolution of at least 166 7
105. ate control can be performed manually with a flow meter with a needle valve float type However a change in the flow rate with time cannot be avoided In contrast a mass flow controller is able to adjust the flow rate exactly to the pre set flow rate A mass flow controller also suppresses pump pulsation pressure variation thus serving a dual purpose 76 2 3 Closed path CO gas analyzers Tips When a mass flow controller is used the work required by the investigator to control the flow rate is substantially reduced Some of the commercially available mass flow controllers are equipped with the capability of outputting the flow rate in analogue or digital format which allows the investigator to monitor the flow rate The author has used mass flow controllers manufactured by Horiba Ltd Japan and Yamatake Corporation Japan The author recalls that it was a thrilling experience to use a mass flow controller for the first time the flow rate variation due to pump pulsation disappeared and the float of the flow meter stopped moving Tips 2 3 10 3 Tips A minimum pressure difference is required between the inlet and the outlet of a mass flow controller The value of the required minimum pressure difference depends on the model In order to fulfill the requirement of the minimum pressure difference appropriate decisions need to be made about the pump settings and the opening and closing of a relief valve Note If the pressure dif
106. ater in large pores is the first to go out The matric potential represents the amount of energy required for soil pores to hold water in capillary action and adsorption or the amount of energy required by plant roots to draw water in The value is positive when the soil water is at saturation and negative otherwise The matric potential per unit volume is expressed in Jm Nm Pa Hydraulic head Jkg m s m which is a specific measurement of the amount of water energy per unit weight converted into the height of water column is often referred to as a simple presentation of matric potential One meter of hydraulic head corresponds to 9 86 hPa Other indexes of soil moisture include water content kgkg and saturation ratio 7 m m They are obtained from Equations 3 6 2 and 3 6 3 respectively Soil consists of water air and soil particles or a liquid phase a gaseous phase and a solid phase The combined volume of the liquid and gaseous phases is the total pore volume a id 3 6 1 V Vi4V VFN 49 PE ga 3 6 2 y 3 6 2 7 3 6 3 1 ANA Here V volume m W weight g r liquid phase s solid phase and a gaseous phase Types of instruments Instruments for measuring the volumetric water content in soil include time domain reflectrometry TDR moisture meters such as the CS616 L produced by Campbell Scientific Inc US Fig 3 6 1 On the principle that the permittivity of soil fluctuates acc
107. be 45 7 9 Digital Analog lt 30W Wieser et al 2001 SONIC zru Wyngaard et al 1985 1 X2 DA 600 TR 61C 0 2 Vertical path orthogonal probe 90 5 Digital Analog lt 30W Shimizu et al 1999 91 9 amp 2 Wieser et al 2001 SAT 540 550 0 1 Slanted path omni directional probe 45 2 7 Digital Analog 4w None ATI K Style Prob 0 15 Vertical path orthogonal probe 90 lt 1 0 Digital Low _ Kaimaleral 1990 see also ATI yle Pro ertical path orthogonal probe igita homepage X1 X2 MA 1 2 W operating _ Campbell CSAT3 0 115 Slanted path boom probe 60 LI Digital Analog at 20 Hz Cristen et al 2001 WindMaster UE NEAN Digital van der Molen et al 2004 2 0 144 Slanted path directional probe 45 0 9 1 7 0 66W n WindMaster pro lanted path omni directional probe 45 CPO nalog optional Nakai et al 2006 gt X2 5 zi der Molen et al 2004 2X2 Gil R3 50 100 0 144 Slanted path omni directional probe 45 0 9 Digital Analog 3 6W e ON HS 50 100 0 144 Slanted path boom probe 48 75 2 5 Digital Analog 3 6W Cristen et al 2001 K Even within the same model the path length may differ by a few mm X1 Evaluation of transducer shadowing only 2 correction formula available 30 2 1 Ultrasonic anemometer thermometers SATs Photo 2 1 1 Configuration of SAT probes a SONIC TR 61C vertical path orthogonal probe Yamashiro forest hydrology research site b ATI K Style Prob
108. be vs wind velocity given by the tested anemometer y Tips Equation to obtain the wind velocity u ms using a Pitot tube Bernoulli s law dP 1 2 pu where dP the difference between total pressure of wind vertical to a Pitot tube hole and static pressure of wind parallel to a Pitot tube hole Pa and p air density kgm Tips 3 2 2 4 Tips With the aim of establishing national standards of low wind velocity the National Metrology Institute of Japan has constructed an underground tunnel that is unaffected by surrounding conditions where the accuracy of anemometers at low wind velocities can be tested by mounting them on a car and running the car at low speeds Tips 3 2 3 133 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 Data processing 1 Wind direction Wind direction is the direction from which wind blows The direction is indicated by cardinal points e g N NNE in azimuth degrees from 0 to 360 clockwise from north or in 16 or 36 points of the compass for which the circumference is divided into 16 or 36 sections Fig 3 2 2 Fig 3 2 2 Notation of wind direction It is desirable to use the average vector as the representative wind direction index In this case data of wind direction and wind velocity need to be collected simultaneously In some cases the scalar average and the prevailing wind direction within a given time period can be used as the average wind
109. bs are in the SAT measurement paths remove the objects O If the surfaces of the sensors are extremely dirty wipe them with a soft cloth wetted with alcohol or distilled water In addition in the case of a long term SAT deployment it is desirable to follow the procedures below every few months to a year O Check the wind velocity offset O Correct the sonic virtual temperature by referring to the data collected by a thermo hygrometer near the SAT height O Check if the tilt angle has changed from the time of deployment and adjust it if necessary Although it is recommended that the wind velocity offset be checked indoors the offset can also be checked on a SAT while it is still deployed In this case cover the SAT with a large plastic bag and check if 35 Practical Handbook of Tower Flux Observation Ver 1 00 Chapter 2 the values of the three wind velocity components fluctuate near zero If the offset values are large the SAT is likely defective the data acquired after the offset check need to be examined quickly and carefully to make a decision about repairing the SAT 4 Tips The probe head of the TR 61 A B C manufactured by SONIC can be easily changed by the user When an abnormality arises on the TR 61 it can sometimes be resolved by replacing the probe head which includes the sensors Because a backup probe head is not as expensive as a SAT itself it is desirable to have a backup probe head ready when a TR 61 probe i
110. c resistor whose resistance decreases as the temperature rises Because the rate of change in resistance in response to temperature variation is pronounced this thermometer is well suited to measuring very subtle temperature changes A thermistor element can be made smaller than a platinum thermo resistor which is advantageous for the production of size reduced temperature sensing units Error and noise caused by resistance of the lead wires can be mitigated by increasing the signal output and electric resistance of the element Accordingly remote measurement away from a data logger through extended lead wire becomes possible The instrument requires regular inspections as it may be susceptible to self heating and the age related changes in the element are relatively great Because the instrument has strong nonlinearity and its elements are not standardized it is usually used with a linearizer integrated special converter Various handy low priced thermometers with a power source and a data logger in such as the HOBO series produced by Onset Computer Corporation US Photo 3 3 1 and the Ondotori series by T amp D Corporation Japan Photo 3 3 2 are commercially available Most are used for low cost automatic continuous measurement and multi point observation of the thermal environment Photo 3 3 1 HOBO by Onset thermistor thermometer Photo 3 3 2 Ondotori by T amp D thermistor thermometer 4 Tips When no linearizer is available tempe
111. calculating the heat flux on the basis of temperature change and heat capacity in each soil layer Equation 3 5 1 is called thermal integration Fig 3 5 1 i l O O 0 gt C Az AT 0 65 1 Here Q soil heat flux Wm C volume heat capacity of soil Jm K za thickness of each soil layer m T soil temperature Q soil heat flux at the bottom of the lowest soil layer Wm and i subscript indicating soil layer i The volume heat capacity is strongly affected not only by soil components but also by 150 3 5 Soil temperature and soil heat flux soil moisture Therefore soil moisture measurement is also required Temperature and Soil moisture sensor mit Soil heat flux plate in the combination method Fig 3 5 1 Conceptual image of the temperature integration method and the combination method 151 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 3 6 Soil moisture The two main indexes of soil moisture are volumetric water content 0 mm and matric potential Y Pa The former is the volume of water as a fraction of the total volume of soil which is used to obtain an unsaturated diffusion coefficient of soil water The latter is often referred to in discussions of water absorption by plant roots and soil water movement There are various sizes of pores in soil Water caught in smaller pores requires more energy to be extracted Thus when soil water is released the w
112. ce accretion In installing a wind vane it should be noted that true north and magnetic north differ 4 Tips The difference between geographic true north and magnetic north is called magnetic declination D The declination differs from place to place and changes over time The value as of 0 00 on Jan 1 2000 is approximated by the following equation National Astronomical Observatory of Japan 2005 7 37 142 21 622 Ag 7 672 Ay 0 442 Ag 0 320AQAY 0 675Ay D 2000 0 Ag 9 37 N Ay y 138 E where latitude and y longitude Record of wind velocity wind direction data Wind velocity sensors come in two types in terms of the readout one with pulse counts and the other with voltage For wind direction measurement potentiometers that operate on the basis of resistance are commonly used Most ultrasonic anemometers are capable of producing voltage output of wind velocity measurements for the x and y axes as well as digital output of wind direction measurements Calibration Anemometers must be checked frequently To three cup anemometers which contain moving parts pre and post observation tests should be given Ultrasonic anemometers which have no moving parts require little maintenance However the voltage signal released from ultrasonic anemometers with analog output is likely to include some residual deviation about 20 30 mV at a wind velocity of 0 ms As the amount of residual
113. ce of heating remains under investigation as of today 2008 and journal articles associated with the topic continue to be published e g Heusinkveld et al 2008 Thus investigators are advised to keep up with the latest research trends and future announcements by the manufacturer 64 2 2 Open path CO H O gas analyzers Appendix Appendix 2 2 4 Issues associated with horizontally deployed open path gas analyzers The value of the CO number density measured by an open path gas analyzer is that within the measurement path Accordingly when the measurement path length is 20 cm CO number density variations occurring at a length scale smaller than 20 cm are averaged When an open path gas analyzer is deployed vertically CO number density variations occurring at a length scale smaller than 20 cm in the vertical direction are averaged Numerous studies have been conducted on the smoothing of CO number density fluctuations measured by open path gas analyzers mounted vertically thus the smoothing effect can be evaluated and or corrected When an open path gas analyzer is deployed horizontally CO2 number density variations occurring at a length scale smaller than 20 cm in the horizontal direction are averaged In the vertical direction CO number density variations occurring only at very small length scales are averaged For this case there exists little research in the literature on the smoothing of CO number density fluctuations and no app
114. ce of the outside air 91 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 A funnel and a tea strainer Photo 2 4 1 a film canister Photo 2 4 2 or a silencer Photo 2 4 3 can be added to the air inlet When a film canister is used it is recommended that a small wad of synthetic cotton be placed inside the canister to prevent insects from entering Tips 2 4 2 Photo 2 4 3 Air inlet silencer It is suggested that the investigator refer to the above mentioned cautions for the path marked in red as well as the path marked in blue 92 2 4 CO storage change 1 Control system method The system controls the following two components 1 Sample air intake at individual measurement heights control of the pumps and solenoid valves turning on off of P 1 P n and SV 1 SV n in Fig 2 4 1 2 Calibration gas control of solenoid valves turning on off of SV a and SV b An example of the control for the sample air intake is shown in Fig 2 4 2 In this example the pump at the height of the next measurement is turned on in advance so that the relevant sample air is drawn to the location immediately ahead of the analyzer This technique minimizes the delay in the arrival time of the sample air of interest at the time of switching measurement points hh mi P1 SV1 P2 5V2 P3 S5V3 P4 SV4 P5 5V5 SVa SVb hh mi 0 0 0 0 0 O O 0 0 0 0 0 0 1 off on Pn n 105 pump SVn n 105 a b sol
115. city Over a given length of time air samples are accumulated in two reservoirs one for positive w and one for negative w wind velocities ms This procedure allows evaluation of the time averaged value of the concentration of the trace gas of interest pg mgm As a true eddy accumulation method Komori et al 2004 proposed a method that uses syringes connected to a high speed pulse motor which is synchronized with a pulse generator In the true eddy accumulation method the vertical flux of a trace gas F mgm s is expressed as follows F w p w p 2 5 1 Because the true eddy accumulation method requires control of the sampling flow rate at a high rate of response the measuring system becomes complex On the other hand the measurement procedure is simplified in the REA method by keeping the sampling flow rate constant In the REA method the vertical 96 2 5 Relaxed eddy accumulation REA method flux of a trace gas F is expressed as follows F b 0 Ap 2 5 2 where Ap is the difference in the average concentration of an atmospheric trace gas between the two sampling reservoirs and o is the standard deviation of w within a specified time period The variable b is an empirical coefficient and can be determined from other variables such as the sensible heat flux which can be measured with the eddy covariance method If the value of b for an atmospheric trace gas flux is assumed to be equal to that
116. condary lines should be wired separately and in such a way that they do not get close to each other 3 The power and signal lines should be kept as far apart as possible When it is unavoidable to cross the two they should meet at right angles When the power and signal lines are installed in an observation hut or on an observation tower each line should be inserted through separate cable outlets and or separate vertical pipes so that each line is clearly separated from the other 4 The signal cable should be made as short as possible to avoid looping 5 The measuring instruments data loggers and signal cables should be kept from devices which produce noise 6 The earth connection should be carefully arranged The grounding wires of all measurement instruments should be connected together and to a solid earth terminal y Tips In recent years an increasing number of turbulence observation instruments provide digital output Digital output is often less susceptible to noise than analog data output thus the use of digital output is recommended if it is compatible with the data logger Tips 2 7 1 108 Related information for chapter 2 Related information for chapter 2 Further reading SDI 12 http www sdi 12 org Aubinet M Grelle A Ibrom A Rannik U Moncrieff J Foken T Kowalski A S Martin P H Berbigier P Bernhofer C Clement R Elbers J Granier A Gr nwald T Morgenstern K Pilegaard K Rebma
117. convenience Fo axF A3 1 9 It should be noted that the constant is not always the same as the radiant energy at each wavelength changes according to atmospheric and other conditions 129 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 3 2 Wind direction wind velocity The direction from which air moves to is called the wind direction and the distance air moves per unit time is the wind velocity Wind has to be measured not only as a scalar quantity but also as a vector quantity by taking both the magnitude and direction into account Surface wind is generally measured as a horizontal flow of atmosphere as the vertical component is insignificant compared with the horizontal component Types of instruments 1 Wind vanes The most commonly used instrument for measuring wind direction is the weathercock vane Two or three axis ultrasonic anemometers are now used in some cases 2 Anemometers There are various types of anemometers These differ by measuring method The main types are shown below Cup anemometer The cup anemometer invented by Robinson in 1850 is called the Robinson anemometer It consists of hemispherical or conical cups and a vertical shaft Originally it was designed with four cups and a long radius of rotation to gain as much torque as possible Because of its poor performance however the four cup anemometer was redesigned For greater efficiency it was made smaller and more lightwe
118. culated on the basis of the vertical profile of soil temperature However measurement using a heat flux plate is easier and thus more common Instruments The heat flux plate Photos 3 5 5 and 3 5 6 operates based on the principle that the temperature difference between the two sides of a thin plate thermal resistance plate with a given thermal conductivity is proportional to the amount of passing heat Heat flux is obtained by dividing the output value of a heat flux plate mV by a sensitivity constant mV Wm7 y 149 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 50mm Photo 3 5 5 Heat flux plate PHF 100 PREDE Photo 3 5 6 Heat flux plate MF 180M EKO Photograph courtesy of PREDE CO LTD Photograph courtesy of EKO INSTRUMENTS CO LTD Measurement A heat flux plate should be installed horizontally Photo 3 5 7 To measure the heat flux of the ground surface it is better to install the plate at a shallow depth because the amount of heat stored in the soil above the heat flux plate is ignored But if the measuring depth is too shallow errors may occur because the plate prevents water movement and because solar radiation affects measurements Although there is no determined practice plates are mostly embedded 1cm to 3cm below the surface Close contact of the plate with soil should be assured Photo 3 5 7 Embedded heat flux plate Kawagoe forest meteorology research site The method of
119. d calibration the solenoid valves are controlled automatically with a PC or a data logger Check the data from the time during which calibration gas was flowing and use the calibration data for data calculations 3 Tips The prices of solenoid valves vary according to the material of their main bodies Fluorine resin is chemically stable and weather resistant Therefore when the valves are used for measuring reactive gaseous constituents or for continuously flowing atmospheric air fluorine resin material such as Teflon is frequently used for valve components In terms of chemical reactivity CO is only weakly reactive to many materials Therefore when solenoid valves are used for measurements of CO valves with gas contact parts made of metal can be used When selecting solenoid valves for use it is also desirable to select those of an appropriate size with respect to the flow rate Refer to orifice size and or valve flow coefficient in catalogs as a guide for selecting an appropriate size The bigger the values of these variables the larger the flow rate that the valves can accommodate On the other hand large valves require large operating power and their inner volumes are large Because of their large inner volumes the displacement efficiency of large valves at the time of flow path switchover is low which needs to be taken into consideration for selecting the size of valves to be used for measurements Furthermore solenoi
120. d of its operational lifetime and the whole pump should be replaced 73 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 y Tips The wear and tear of a diaphragm changes according to the use conditions Even when the flow rate of a pump does not decline it is advisable to replace the diaphragm regularly e g schedule a replacement once a year Although the operational lifetime of the pump is also expected to change according to the use condition the investigator should refer to the operational lifetime of the pump suggested by the manufacturer Note In most cases it is likely that pumps can be used for a longer time period than the operational lifetime suggested by the manufacturer There are numerous diaphragm pump manufacturers The author has used pumps manufactured by Enomoto Micro Pump and ULVAC KIKO Inc Japan These manufacturers distribute pumps as well as only the consumable parts The consumable parts of pumps manufactured by KNF Neuberger GmbH Germany and Gast Manufacturing Inc US can also be purchased from the manufacturers Tips 2 3 5 4 Tips Due to the degradation of the diaphragm or the pump structure itself air leakage sometimes occurs inside a pump As a result air from the surroundings of the installation site of the pump sometimes gets drawn into the pump In order to check for air leakage the following simple method can be used Seal the inlet of the pump with a cap such as that ma
121. d valves are available in AC and DC types and also in a number of voltage ratings thus the investigator should select appropriate valves according to the power source of the measurement system A variety of solenoid valves are available not only in different materials but also with different numbers of valves 2 way and 3 way and different combinations of NO and NC thus it is suggested that the investigator order catalogs from the manufacturers While a number of manufacturers produce solenoid valves the author frequently uses those manufactured by CKD Corporation Japan In addition to CKD solenoid valves are available from TAKASAGO ELECTRIC INC Japan SMC Corporation Japan and KOGANEI CORPORATION Japan Tips 2 3 4 3 Pumps characteristics and structure While a large number of pump structures and types are available diaphragm pumps which are frequently used for flux observations will be discussed below In a diaphragm pump such as those manufactured by Enomoto Micro Pump Mfg Co Ltd Japan fluid is extracted and delivered with the use of intake and exhaust valves that work in conjunction with a rubber diaphragm Two pump drive systems for diaphragm pumps are motor based and electromagnetic based types Because larger flow rates and higher pressures can be achieved by motor based diaphragm pumps than by electromagnetic based diaphragm pumps the use of 72 2 3 Closed path CO gas analyzers motor based diaphragm pumps is recom
122. d with a contact 148 Photo 3 5 4 Underground section where a thermocouple thermometer left of the stick and a soil moisture meter embedded Kratie Cambodia right of the stick are seasonal forest of 3 5 Soil temperature and soil heat flux thermometer the sensor should be the smallest possible and it should be installed as close to the surface as possible The sensing unit is usually installed such as not to be directly exposed to solar radiation y Tips One is often confused about which cable is connected to which sensor after all the sensors are embedded at several depths in a place It is convenient to attach tags with the information of measuring depth at the ground surface and to the logger junctions for maintenance Tips 3 5 1 4 Tips Cables can be laid in a spiral tube or resin pipe for protection against gnawing by mice and other animals Tips 3 5 2 3 Tips A waterproof data logger that is equipped with a thermo sensor may perform poorly as a result of condensation on the instrument base Such malfunction can be prevented by placing silica gel inside the logger and sealing it tightly The silica gel should be replaced occasionally Tips 3 5 3 3 5 2 Soil heat flux Soil heat flux on the ground surface represents the magnitude of heat exchange between soil and atmosphere which is expressed in Wm Because soil heat flux is proportional to the temperature gradient at a given depth it can be cal
123. deviation differs between instruments zero point output should be confirmed during installation to give a zero point adjustment to the output voltage values that are acquired Where a wind tunnel is available tests can be undertaken with real wind velocities that are obtained with the help of a Pitot tube which measures the wind velocity based on the pressure differential inside 132 3 2 Wind direction wind velocity and outside the tube Photo 3 2 2 and Fig 3 2 1 By the side of the anemometer that is to be calibrated the Pitot tube is placed such as not to hinder the air flow While the wind velocity in the tunnel is being varied comparison and calibration are carried out based on measurements checked at ten or so points The dynamic pressure the difference between total pressure and static pressure measured by the Pitot tube which is measured beforehand with a differential pressure gauge and the air density which changes in response to temperature and therefore should be measured simultaneously with temperature are input into Bernoulli s equation in order to calculate the wind velocity 12 y 0 080424 0 988317 x R 0 999449 10 Wind velocity measured by Pitot tube 6 l o T T T T T T T 0 2 4 6 8 10 12 d Wind velocity measured by anemometer Photo 3 2 2 Inspection of an ultrasonic Fig 3 2 1 Wind velocity real calculated through the anemometer in a wind tunnel dynamic pressure of the Pitot tu
124. direction In the case of no wind blowing the calm value is expressed by or 00 2 Wind velocity Wind velocity can be an instantaneous reading or an average Unless otherwise specified the wind velocity is the average of wind velocity measurements for a given period Regarding instantaneous wind velocity there is no clear definition of instantaneous in terms of seconds and the observed value differs depending on responsiveness and recording procedure of each anemometer 134 3 3 Air temperature 3 3 Air temperature Air temperature is measured with a thermometer Thermometers are substantially affected by radiation For accurate measurement they should be installed within a shelter to avoid radiation Because temperature can fluctuate widely with time and location a proper thermometer and proper measuring procedures must be chosen to satisfy the observation objectives In selecting a thermometer factors including the following should be fully examined time constant of the temperature sensing unit durability required calibration frequency installation location number of installation locations and measured range In the International System of Units K is the designated measurement unit of temperature C is used in usual temperature measurement Appendix 3 3 1 Types of instruments There are various types of thermometers as Table 3 3 1 indicates For long term meteorological observation platinum res
125. disturbing the sampled air during its passage through the pump To avoid this circumstance the pump can be placed downstream of the analyzer With this method the entire system is under negative pressure Because concentration measurements are made prior to the passage of the sampled air through the pump there is no influence of the disturbance of the sampled air by the pump on the concentration measurement If the tubing for drawing in the sampled air is long e g as in a forest suction resistance becomes large and the pressure inside the tubing becomes low The value of the negative pressure becomes large When the negative pressure becomes large it becomes more likely that the air surrounding the tubing leaks into the tubing through the tubing junctions Therefore if the tubing length of the system is long it is recommended to set the pump upstream of all the branching points If the observational site is agricultural land or grassland and a short length of tubing can be used for observation the pump can be placed downstream of the analyzer However make sure to minimize the number of branches and connections due to solenoid valves and tubing connectors 82 2 3 Closed path CO gas analyzers v Tips For the measurement of CO concentration small leakages of sampled air under positive pressure reduce the flow rate of the sampled air by only a small amount and thus the influence of the leakages on the measurement is not large In c
126. ds to be filled with CO free gas LI 6262 manual LI COR There are two major methods to keep the reference cell free from CO Refer to Fig 2 3 1 In the first method gas free of CO and H20 e g pure nitrogen is flushed into the reference cell In order to keep the cell constantly filled with nitrogen gas the gas has to be supplied into the cell continuously However only a small flow rate is required for the gas supply In Fig 2 3 1 the flow rate is set to 20 mLmin as an example The second method uses chemicals LI 6262 manual LI COR In the LI 6262 soda lime and magnesium perchlorate are used to produce air free of CO and H20 This procedure is as simple as adding bottles containing the chemicals directly to the inlets and outlets of the reference cell Though replacement of the chemicals may require some effort the present method is a simple and convenient one for short term 70 2 3 Closed path CO gas analyzers measurements and for sites into which the transportation of cylinders of standard gas is not easily feasible In the case of the LI 6262 if observations are made only for CO the second method requires only the addition of the chemical bottles to the reference cells However if simultaneous observations of H2O concentration are also required a pump induced forced circulation is necessary LI 6262 manual LI COR In the LI 7000 air free of CO and H2O is produced with similar chemicals i e soda lime or Ascarite
127. e vertical path orthogonal probe evergreen forest in Kompong Thom Province Cambodia c SONIC SAT 540 slanted path omni directional probe evergreen forest in Kompong Thom Province Cambodia d Campbell CSAT3 slanted path boom probe Kahoku Experimental Watershed Tips All the 3D SAT models in Table 2 1 1 output the upward vertical component of the wind velocity as positive values However the sign convention of the horizontal wind velocity components varies among the models Fig 2 1 1 shows the sign convention of the horizontal coordinate system of some of the SATs in Table 2 1 1 Tips 2 1 2 31 Practical Handbook of Tower Flux Observation Ver 1 00 Chapter 2 K Style Probe i Campbell SONIC CSAT3 DA 600 el i l ee ee ee EE l ainin a EG X i Front side of the sensor i For omni directional probes i side labeled with the letter N Po g i i WindMaster R3 i 7 HS Back side of the sensor i a Fig 2 1 1 Sign conventions of widely used SATs Deployment Selection of deployment location When a SAT probe is installed on a tower in order to avoid the influence of the tower and the SAT itself on the wind velocity measurements the following precautions need to be taken into account 1 Deploy the SAT probe on the top of the tower or on a long boom to keep the SAT probe away from the tower 2
128. e Alternatively air samples can be brought back to a laboratory with the use of canisters and the samples can be analyzed after moisture is selectively removed with a three stage trap This method has enabled the analysis of alcohols which are water soluble 100 2 5 Relaxed eddy accumulation REA method constituents and were previously difficult to analyze The time required for an analysis with a GC MS is no different from the time required for analysis with a GC FID which utilizes capillary columns However the maintenance cost of a GC MS is relatively high compared to that of a GC FID due to the need to replace turbo molecular pumps Soft Ionization Mass Spectrometer A proton transfer reaction mass spectrometer PTR MS is a type of soft ionization mass spectrometer and ionizes pure water vapor for the primary ion source The PTR MS is able to detect alkane ethylene propylene and acetylene which are characterized by lower affinity for protons than water The PTR MS can detect various other organic gases and hydrogen sulfide When injecting air samples into the PTR MS no pre processing is required for the air samples such as condensation of the trace gas of interest Quantitative analyses with a PTR MS are less prone to measurement errors than those with a GC MS A PTR MS is also capable of continuous and high accuracy analyses and consecutive quantitative measurements of multiple VOCs at intervals of a few seconds Recently based on
129. e 2 1 1 the Model 81000 manufactured by R M Young Company US and the USA 1 previous model manufactured by Metek Meteorologische Messtechnik GmbH Germany Boom probes include the CSAT3 manufactured by Campbell Scientific Inc US Table 2 1 1 Photo 2 1 1 d and the HS manufactured by Gill Table 2 1 1 3 Tips Slanted path probes were developed subsequent to vertical path probes Slanted path probes were designed to minimize the disturbance of the horizontal wind the magnitude of which is usually larger than that of the vertical wind However because the three components of the wind velocity are calculated from the outputs from all three sets of sensors the failure of any one set of sensors may lead to a loss of data for the sonic virtual temperature and all of the x y and z wind velocity components Hirano and Saigusa 2007 Tips 2 1 1 Table 2 1 1 Specifications of widely used SATs Path length nfi ti le bet horizontal Prob ight Pi Manufacturer Model probe ed Configuration ang i Lice auanicanet ee Output SARA Flow distortion references m plane and vertical wind sensor path kg consumption 5 Kondo and Sato 1982 Hanafusa Vertical path 90 120 bet th Shi k DA 600 TR 61A 0 2 ertical path pieces 43 Digital Analog lt 30W etal 1982 Wieser et al 2001 horizontal wind sensor paths Ito et al 2001 etal DA 600 TR 61B 0 2 Slanted path omni directional pro
130. e across the semipermeable membrane moisture in the 77 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 sampled air passes through the membrane and is extracted from the sampled air stream When sampled air flows inside the tubing of the dryer moisture removal takes place at high speed thus the air flow is not disrupted Note that the moisture removal efficiency decreases when the flow rate is high Furthermore the recommended flow rate of the purge gas is twice to five times the flow rate of the sampled air For purge gas gas in a cylinder or air that has been filtered through a desiccant e g silica gel can be utilized Finally the use of a heatless dryer such as the HD 0 5 manufactured by CKD Corporation enables the production of dry air without maintenance for several years The closed path gas analyzers of the present day are able to simultaneously measure CO and H30 Therefore when these analyzers are used moisture removal from the sampled air does not need to be performed in some cases However when moisture flux can be measured with the use of a separate instrument it is recommended that a closed path gas analyzer is used for only CO measurements to eliminate the influence of water vapor concentration fluctuations on the CO concentration fluctuations In this case remove moisture from the sampled air with a semipermeable membrane dryer lt Tips Even when a dehumidifier that uses semipermeable membrane
131. e comma separated value CSV format allows easy storage and backup of data Logger types Data loggers can be classified roughly into two types those which first digitalize analog voltage data and record the digitalized data and those which directly record digital output data Some data loggers are able to accommodate both logging modes Storage capacity varies among data loggers Some of them are equipped with internal memories and others record data on compact flash storage cards or MO discs Table 2 6 1 Data logging for turbulence measurements requires a high speed logging function and a large memory size For data loggers that are used for other micrometeorological measurements refer to Section 3 9 Data logger Because turbulence and micrometeorological measurements require different sampling intervals it is recommended to log the data using two separate data loggers in order to avoid problems In this case the clocks of the two data loggers need to be synchronized so that the two data sets are synchronized in time Incidentally recent models can be networked for time synchronization When values of a physical variable are logged as analog output it is necessary to be aware of the conversion relationship between the voltage and the value of the physical variable With this relationship the ranges of measurements and data logging need to be optimized in advance so that accurate measurements can be made Because most instruments for me
132. e flux measurement height Because the vertical distribution of CO concentration in the 86 2 4 CO storage change vegetation layer is not uniform CO concentration must be measured at multiple heights When a single closed path gas analyzer is used two measurement techniques can be used for evaluating CO storage change 1 CO2 concentration can be measured sequentially at each measurement height In this technique air is sampled through inlets at multiple heights by switching flow pathways with the use of pumps and solenoid valves and 2 CO concentration of a mixture of air sampled from multiple measurement heights is measured An advantage of the former method is that it provides information on the CO concentration at individual measurement heights Disadvantages of the former method include a somewhat complex controlling system for switching the flow paths as well as a prolonged time interval between measurements Although these disadvantages can be eliminated by the use of multiple CO analyzers frequent calibration is required to correct for errors that arise from variations among instruments Determination of measuring points the number of measuring points It is desirable to measure CO concentration at as many heights as possible so that the spatially averaged value of CO concentration can be evaluated However when CO concentration is measured sequentially at each measurement height the measurement interval the period between
133. e gases Common balance gases include nitrogen N balance and air air balance For CO concentration measurements in the atmosphere it is advisable to use a CO standard gas in which air is used as the balance gas This choice is recommended because the absorption characteristics of infrared radiation by the gas mixture vary according to the balance gas Tips 2 2 4 Zero CO and zero H O gases can also be produced with chemical scrubbers A number of chemical scrubbers are considered appropriate for producing zero gases and their characteristics are summarized in LI COR 2003 LI COR 2003 recommends a combination of soda lime and magnesium perchlorate for removing CO and H20 from the air to produce zero gases The air needs to pass through the chemicals in the correct order the soda lime first and subsequently the magnesium perchlorate Pressure regulator It is recommended to use a pressure regulator with two adjustment screws that can adjust the gas pressure from the cylinder to approximately 0 1 MPa 1 1 kgfem or 15 psi Prepare tube fittings appropriate for the tubing to be used for calibration Tubing Tubing that is made of fluoroethylene resin such as Teflon and is either 6 mm or 1 4 inch in the outer diameter is frequently used for calibration Choose appropriate tube lengths to facilitate ease of use Minimize the length of the tubing for H20 calibration to avoid condensation inside the tubing Flow meter Select
134. e interval should be collected in a bucket and the collected water should be subsequently measured with a graduated cylinder When employing a water level sensor calibration needs to be performed in advance with the above mentioned calibration procedure for water level sensors It is also effective to check the water level and flow rate outputs while the sensor is deployed at the site 165 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 3 9 Data logger Unlike in the case of using the turbulent fluctuation method to measure flux Chapter 2 micro meteorological observations require no high speed sampling data loggers Data loggers are chosen by taking into account factors such as kinds of signal output from the sensors and power consumption Types of instruments Data loggers are roughly classified into two types a multi channel type that handles various output signals e g voltage and pulse sent from a sensor and a single function type that is equipped with a sensor or that registers one kind of signal Multi channel data loggers are commercially available from many manufacturers in various styles among which are the CR800 and CR1000 both by Campbell Scientific Inc US the CADAC2 previous model and CADAC21 both by Eto denki Coporation Japan and GL220 and GL820 both by GRAPHTEC Corporation Japan The CR1000 CADAC21 and GL 820 are introduced below CR1000 Its power consumption is quite low 0 6 mA fo
135. e is adopted to extract the constituents that are eluted at and near the peak of N2O on the chromatograph and the extracted constituents are analyzed with the detector In addition the GC ECD is highly sensitive in detecting electrophilic substances such as halide and nitro compounds and is also used for analyzing methyl bromide CH3Br which is subject to regulations under the Montreal Protocol GC ECDs can be classified into two types radioactive and non radioactive GC ECDs Use of the former type requires compliance with laws and regulations concerning the conditions for use and storage of radioactive materials Gas Chromatograph Mass Spectrometer A gas chromatograph mass spectrometer GC MS is a highly sensitive analyzer and thus is often used for qualitative and quantitative analyses of atmospheric trace gasses One of the distinguishing characteristics of a mass spectrometer is that it provides mass spectra that include information on the chemical structure of the trace gas of interest For the analysis of a trace gas with an extremely low concentration the gas needs to be pre concentrated in advance In VOC flux observations using the REA method air sampling tubes containing adsorbent are frequently brought back to a laboratory for desorption with a thermal desorption unit A GC MS analysis is conducted after the air sample is concentrated by cooling the air sample with a cold trap called a cryofocus trap and heat is added to the air sampl
136. e pipe PanaFleki DM316 23 mm Panasonic Electric Works Co Ltd Japan http panasonic denko co jp in Japanese 3 5 Regulated DC Power Supplies PS series TEXIO NIKKE TECHNO SYSTEM CO LTD Japan former Kenwood http www nikketechno jp in Japanese 3 3 Sampling tube Daiki Rika Kogyo Co Ltd Japan http www daiki co jp en 3 6 Sealant BATHCAULK 50 g transparent CEMEDINECo ltd Japan http www cemedine co jp e 3 1 3 5 Self fusing tape Hi Bon NO 2 0 5 mmx19 mmx10 m Hitachi Chemical Co Ltd Japan http www hitachi chem co jp english 3 1 3 3 3 4 Silica gel Blue coloured medium grain 500 g Kishida Chemical Co Ltd Japan http www kishida co jp english 3 5 Spiral wrap RPST 20 HIRAKAWA HEWTECH CORP Japan http www hewtech co jp e 3 5 3 6 Spiral wrap tubing Waytek Inc US http www waytekwire com 3 5 3 6 Washing bottle SANPLATEC CORPORATION Japan _http www sanplatec co jp en 3 4 Weather resistant banding band 7 4 mmx250 mm 2 5 72 mm HellermannTyton UK http www hellermanntyton com 3 3 175 176 Literature cited Literature cited ADC 2003 OP 2 Open path CO2 H20 Analyser Instruction Manual ADC BioScientific Ltd 25pp Advanet 1996 Instruction manual of E009B carbon dioxide and water vapour meter the first edition 13pp Albrecht B Poellot M and Cox S K 1974 Pyrgeometer measurements from aircraft Review of Scientific Instruments 45 33
137. e the vertical distribution of average humidity it is recommended that air samples be collected from each elevation and measured with the same analyzer This method however has the disadvantage of not being able to carry out continuous measurement at one point Also it is relatively difficult to provide maintenance in a remote place For these reasons more than one instrument in the HMP45 series which is easy maintain is placed and regularly calibrated at the same elevation y Tips For a ventilated psychrometer enough gauze should be prepared for frequent replacement A wash bottle with a capacity of 500 ml may be useful for cleansing gauze and supplying water to the tank Tips 3 4 1 3 Tips For easy replacement of the sensory unit the HMP45 series is designed to be insertable Structurally as the cable disconnects when tensed special care should be directed to wiring The cable near the sensor may be wound into one or two loops and then fixed Tips 3 4 2 Calibration Active sensors need to be periodically corrected using a reference instrument placed at the same level Sensors packing materials and joints that have deteriorated over time must be replaced To calibrate the reference instrument a chloride saturated solution is poured in a test chamber which is then covered with a lid and left at room temperature for at least one hour so that the test can be carried out under the condition of fixed relative humidity Appendix 3
138. e tubing The sample air is drawn into the analyzer with a pump The length of tubing between the measurement point and the pump is determined based on the deployment location of the analyzer 67 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 Flow path of sampled air Regarding the flow path of sampled air see Fig 2 3 1 sampled air is first drawn in by a pump from the measurement point negative pressure The moisture in the pumped air is removed with a membrane dehumidifier made of resin After the flow rate of the dried air has been regulated by a mass flow controller the dried air is sent into the sample cell of the CO analyzer e g LI 6262 or LI 7000 manufactured by LI COR Inside the sample cell CO2 concentration of the dried air is measured and the dried air is released out of the analyzer In the system shown in Fig 2 3 1 the moisture in the sampled air is removed However when H2O concentration is simultaneously measured for evaluating the moisture flux no moisture is removed from the sampled air In this case omit the dehumidifier shown in the schematic of the sampling system of the closed path gas analyzer Fig 2 3 1 and directly bypass the dehumidifier with a tube When no dehumidifier is used caution is necessary as the likelihood of condensation within the sampling system increases according to the temperature and pressure changes within the pathway of the sampling system The suction flow rate for
139. easure photosynthetically active radiation incident on a forest canopy a sensor should be placed horizontally and higher than the canopy The amount of radiation absorbed by a forest canopy absorbed PAR APAR umolm s can be obtained as follows In remote sensing research the balance between downward PAR PAR above umolm s measured above a forest canopy and reflected PAR PART above umolm s is calculated as APAR APAR PARL 3 1 5 a PART ab above In research on agriculture forest meteorology and ecology more rigorous calculations may be worked out by taking the PAR veiow wmolm s and PART be1ow molm s under a canopy into account APAR PARV part below z PART PART above above below 3 1 6 Generally as the value of PART below in a closed forest during a growing season is small it may be ignored in some cases It is desirable to obtain an average value of measurements from more than one point because values vary widely from place to place when sensors are placed below a forest canopy Two of most commonly used instruments are introduced below One is the LI 190SA LI COR Inc US 125 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 which has an exposed diffuser panel on the surface and the other is the ML 020P EKO which has a glass dome over a diffuse panel to collect radiation LI 190SA 1 The sensor outputs the curren
140. ectively In this case the use of a self recording inclinometer is recommended to record the tower tilt and or vibrations y Tips A bubble level is equipped on the probe of both the CSAT3 manufactured by Campbell and the DA600 TR 61A manufactured by SONIC An inclinometer is built into the probes of the R3 100 R3A 100 and HS manufactured by Gill An inclinometer can be added as an option for the R3 100 or R3A 100 Tips 2 1 4 Data acquisition The output values of a deployed SAT can be recorded by connecting its signal cable to a data logger and setting the data logger appropriately For setting the data logger refer to Section 2 6 Data logger Depending on the model of the SAT its output can be acquired either as an analog voltage signal or as a digital signal Digital signal outputs can be acquired using the Campbell SDM port or the RS 232C port Many SAT models are able to output both analog and digital signals An advantage of analog signals is that they can be easily acquired and recorded by a large number of data loggers On the other hand an advantage of digital signals is that the output values are subject to less noise than those acquired as analog signals In Appendix 2 1 1 a sample program is given for acquiring digital data with a CR1000 from an ATI K Style Probe In this example pin numbers 3 and 2 of the RS 232C connectors are connected directly to the C1 and C2 ports of the CR1000 respectively The sample p
141. ed for flux analysis In particular variables that are ranked as essential in this section are necessary for checking the quality and interpolation of CO flux and of the amount of net ecosystem CO exchange Radiation Although it is best to measure upward and downward shortwave longwave and photosynthetically active radiations PARs as well as radiations over and under the canopy measurement of radiation over the canopy takes priority over the other measurements Table 1 3 1 Net radiation can be calculated by subtracting the sum of the upward short and long wave radiations from that of the downward short and long wave radiations Moreover a spectroradiometer or radiation meter for a certain frequency domain can be set up for ground based verification using remote sensing technology 21 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 1 Basic micrometeorological variables Air temperature humidity wind velocity and wind direction at about the same height as the point of the eddy covariance measurement over the canopy are indispensable Measurements of the amount of precipitation and of the shallow ground temperature are also required Profile vertical distribution measurement variables Table 1 3 2 shows the profile vertical distribution measurement variables To calculate CO storage change the CO profile needs to be measured the CO storage change is required for the calculation of the net ecosystem
142. eed to conduct joint research and development in 2007 in order to promote shared use of observation data for which the reliability has been ensured and quality control has been performed The observation data under consideration concern exchanges of energy and mass such as CO between terrestrial ecosystems and the atmosphere the exchanges for which worldwide observation networking has been promoted A micrometeorological observation and analysis technique called the eddy covariance method has become very common in recent years as a result of the development of measuring instruments with a relatively high response time and improvements in computational processing speed This technique has enabled continuous acquisition of ecosystem production data as well as ecosystem atmosphere mass and energy exchange flux data without damaging the ecosystem under observation Data acquisition with the eddy covariance method has in turn allowed clear evaluations of the diurnal annual and inter annual variations of energy and mass e g CO2 exchanges contributing significantly to improved understanding of ecosystem carbon dynamics and energy budgets Unlike general surface observations of meteorological variables the micrometeorological technique does not require uniform conditions for the observation site and instrumentation Therefore while the micrometeorological technique offers various advantages the data acquired with this technique have been subject to mea
143. eeeeees YASUDA Yukio FFPRI 2 4 COd Storage Change ccececcsessescsseseescsseseeeenseaeeeceeeaeeeceeeaeneeaeerenee KITAMURA Kenzo FFPRI 2 5 Relaxed Eddy Accumulation REA Method ee eeeeseeeeteeeeneeees MIYAMA Takafumi FFPRI ZOD ata LOS GE ss Lvs aati ealsews Mae alden elena TAKANASHI Satoru FFPRI 2 7 Detection and Reduction Of Noise ccccccescsccesessesscceseesessseeseeeees YAMANOI Katsumi FFPRI 31 Radiation siere einer ni u e eraai ner Ee se E eich aan MIZOGUCHI Yasuko FFPRI Appendix 3J lrini eiaa a a REEE MIZOGUCHI Yasuko FFPRI OHTANI Yoshikazu FFPRI Appendix 3 2 orres o aaee OEE EE SERET MIZOGUCHI Yasuko FFPRI 3 2 Wind direction Wind velocity cecceseeeceesceeseeeneeeeeeeeeeeeeeeeenseens TAKANASHI Satoru FFPRI 3 3 Alr TeMpPenatre neinni ea aesa aE aias MIYAMA Takafumi FFPRI 3 AUT ty eadarra uspe ee e rE ieaS EASES MIYAMA Takafumi FFPRI 3 5 Soil temperature and soil heat flux sseeeeeeeeeeseerererereerereersrrrrreerees TAMAI Koji FFPRI 36 Soil MOIStUPEs eine a a A TAMAI Koji FFPRI 3 7 Precipitation Snow Water Equivalent Snow survey eee KOMINAMI Yuji FFPRI 3 8 Water level Water temperature Irrigation and Drainage ONO Keisuke NIAES SO ID Ata JOS BER mananan naaa a ERE MIZOGUCHI Yasuko FFPRI TAKANASHI Satoru FFPRI 194 List of authors Authors used the following figures and photographs by courtesy of researchers and sensor manufacturers Photo 123s eoe eae
144. een the sensor head and the control box even when the type of control box itself remains the same before and after the change in combination Refer to pp 3 18 3 20 of the product manual for the LI 7500 Rev 4 LI COR 2004 for details on changing the sensor head Appendix 2 2 2 High frequency flux loss When the measurement sensor for the vertical wind velocity and that for a scalar quantity CO in the present section are separated by some distance the sensor separation changes the cospectral shape frequency response characteristics Numerous observations and studies have been conducted on the effect of the sensor separation in the horizontal plane horizontal direction on the cospectral shape and satisfactory methods for correcting the change in the cospectral shape have been established e g Moore 1986 Massman 2000 However the influence of vertical separation between the two sensors on the frequency response characteristics is not fully understood When flux loss due to the vertical separation of the sensors is corrected a technique such as the band path method which is often applied for flux measurement with a closed path analyzer e g Watanabe et al 2000 should be adopted The methods for correcting flux loss due to the sensor separation described here are discussed in the analysis edition of the present manual Appendix 2 2 3 The influence of heating by the open path gas analyzer on flux calculation When CO fluxe
145. emains unchanged before and after the calibration The advantages of such a mounting method include that the characteristics of flux losses remain the same between pre and post calibration and that the measurement of the sensor separation distance does not have to be repeated Method for securing the sensor head and installation angle In addition to the cautions related to the SAT as discussed above the method for securing the sensor head and the installation angle of an open path gas analyzer need to be considered for its installation Because vibrations of the sensor head at certain frequencies will influence the measurements of an open path gas analyzer LI COR 2004 the open path gas analyzer needs to be secured in such a way as to inhibit sensor head vibrations y Tips The sensor head of an LI 7500 is equipped with a mounting post and a bolt for installation LI COR 2004 However the use of the mounting post and bolt is insufficient to secure the open path gas analyzer firmly To ensure a secure mounting it is advisable to use additional parts such as the crossover Nu Rail fitting as in Campbell 2006 a cross over plate as in Photo 2 2 1 or a U bolt Tips 2 2 3 The installation angle of the sensor head of an open path gas analyzer can be classified into 4 options 1 vertical 2 slightly tilted 10 to 15 degrees 3 tilted and 4 horizontal The author recommends 2 slightly tilted among these options The advantag
146. ement may be highly affected by the radiometer itself 4 Tips The thermal converter IRI 01 PREDE for the PIR instrument amplifies the thermopile voltage by a factor of 1000 with an amplifier and outputs the amplified voltage The use of an amplifier often produces noise and sometimes induces errors due to the amplification process The output from the amplifier needs to be checked with a DC reference voltage generator e g 3K02 NEC Avio Infrared Technologies Co Ltd Japan Tips 3 1 3 Calibration Sensors need to be inspected regularly as their sensitivity changes with time The difference between upward and downward longwave radiation is not as large as the difference between upward and downward solar radiation Therefore in order to avoid the influence of difference among radiometers on the radiation measurements difference among the radiometers need to be examined in advance 121 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 3 1 3 Net radiation Radiation over the entire wavelength range combining both solar radiation and longwave radiation is called all wave radiation The difference between the downward and upward all wave radiation is called net radiation Types of measuring instruments There are two types of net radiometers net pyrradiometers and four component radiometers The former output net radiation directly The latter physically combines downward upward shortwave radiometers and
147. enoid valve Standard switching of the measurement points for sample air intake 5 heights mi P1 SV1 P2 S V2 P3 SV3 P4 5V4 P5 SV5 SVa SVb i 0 i i 0 Sample taken in 1 i i 0 Sample taken in V 0 Lo J 0 0 0 Sample 3 taken 0 0 0 1 i 0 Sample taken 1 0 Sample taken i i 0 h h h h h h h h r Er Ss SS SS SS H e e O O O e e 00 02 04 06 08 10 12 0 1 0 i 0 0 Sample taken 0 0 1 i 0 Sample taken gas calibration 0 0 0 0 0 gas calibration 0 0 0 0 0 Fig 2 4 2 An example of a control system for the sampling system shown in Fig 2 4 1 Number of measurement points 5 frequency of measurement height switchover every 2 min time required for a single measurement cycle of the entire profile 10 min 93 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 It is recommended that the system for measuring the CO concentration profile be built so that both automatic and manual control of the system are possible Such a system allows ease of maintenance and response to abnormalities When a data logger with an output port e g CR1000 Campbell Scientific Inc US is used the output values from the CO analyzer can be recorded simultaneously with the switchover of the measurement heights In this case mis synchronization between the time on the data logger and t
148. ense light between 400 and 700 nm Spectroradiometers One all weather spectroradiometer is the MS 700 EKO which is of the diffraction grating type and it measures wavelengths between 350 and 1050 nm For use of the MS 700 a personal computer PC or a logger with a digital I O port e g CR1000 Campbell Scientific Inc US is necessary to control measurements and save data Spectroradiometers are also able to figure out the normalized difference vegetation index NDVI which is commonly used in remote sensing research to indicate the wavelength properties of plant leaves This particular subject is not addressed in this handbook Quantum sensors As Table 3 1 5 and Photo 3 1 7 show there are many types of quantum sensors Unlike pyranometers for which the World Radiometric Reference WRR was established quantum sensors have no global standards and therefore observation results of sensors differ between manufacturers Even among sensors of the same type instrumental error and age related changes are significant For this reason it is necessary to set up a reference instrument and exercise periodic calibration to correct for instrumental error and age related changes 124 3 1 Radiation Table 3 1 5 quantum sensors Model Manufacturer LI 190SA LI COR ML 020P EKO IKS 27 KOITO PQS 1 Kipp amp Zonen PAR O1 PREDE SKP215 Skye Photo 3 1 7 Quantameters Left LI 190 LI COR Right ML020P EKO Measuring method To m
149. ensure that the sampling rate does not exceed the capacity of the sampling tube At the same time in order to avoid the influence of wind velocity fluctuations the air Electromagnetic valve togs Photo 2 5 1 A SAT ir inlet i REA intake rate needs to be maintained at a constant value owe os and an ais imlek used aim an a i h sit 4 Lmin or larger and a bypass needs to be included a Keemashine serest nyaroloRy Reseach site 97 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 VOC collection tube for positive w MFC Tedlar bag for positive w 3 way Solenoid valve 3 way Air inlet l Solenoid Air inlet 3 way electromagnetic valve valve Solenoid valve Tedlar bag for negative w VOC collection tube for negative w MFC Fig 2 5 1 Configuration of an REA system for methane Fig 2 5 2 Configuration of an REA system for VOCs within the measurement system Additionally for the purpose of keeping the pressure constant in the system during the solenoid valve switching the system is equipped with a three way solenoid valve When the sampling air inlet is closed VOC free air that has been filtered through activated carbon is supplied to the gas sampling tube instead of the sampled air A programmable data logger such as the CR1000 is used for 1 controlling the solenoid valves 2 recording the wind velocities and temperature and 3 determining the sign positive or negative
150. ently 3 calibration of an E 009 and an OP 2 will be discussed In this section the sensitivity is defined as the ratio of the change in the indicated quantity output value to the change in the measured quantity the value of the mixing ratio of CO in the calibration cylinder The units of sensitivity are non dimensional or V mol CO m In addition the offset is defined as the value output value indicated at the time of zero gas supply The units of offset are ppm mol CO m or volts 49 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 1 Equipment required for calibration Standard gas for calibration For calibration three cylinders with the following concentrations of CO are required 0 ppm i e zero CO gas approximately 300 350 ppm and approximately 500 700 ppm Cylinders with more than 3 different CO concentrations can also be used In this case make sure to include cylinders with at least the following 2 different CO concentrations 0 ppm and approximately 500 700 ppm or 400 500 ppm for studies in forests The concentration of H O in the standard gas is usually zero thus the above mentioned cylinders with the standard gas for CO can also be used as zero H2O gas As for the balance gas the use of an air balance is recommended over the use of pure nitrogen 4 Tips CO standard gas is a gas that has been certified for a specific concentration All other gases besides CO are called balanc
151. ep 2 The goal of Step 2 is to modify the calibration coefficients stored in the control box of the LI 7500 This procedure is identical to the calibration procedure discussed in Section 4 Calibration of the product manual LI COR 2004 Because Step 2 modifies the calibration coefficients Z and S that are stored in the control box both before and after Step 2 make sure to record the old and new values of these two coefficients either in a field notebook or on a PC in case these values are needed in the future After recording the old values of the coefficients supply zero H O and CO gases to the calibration tube When the output stabilizes perform zero adjustments on the HO and CO channels with the use of the LI 7500 software The zero adjustments are performed for HO first and then for CO2 Next a span adjustment is performed on the H2O channel For this adjustment provide H2O gas to the calibration tube from the dew point generator The dew point temperature setting should be 3 to 5 C lower than the ambient air temperature When the output reaches a steady value span the H2O sensor using the LI 7500 software controls Finally the CO2 sensor is spanned Supply CO gas of high concentration 500 700 ppm for analyzers used over farmland and grassland and 400 500 ppm for analyzers used over forests to the calibration tube When the output is stabilized span the CO sensor with the LI 7500 software controls In Step 2 zero calibrat
152. equations used in this method were derived for vertically deployed open path analyzers and there remain some uncertainties arising from some of the simplifying assumptions While the correction method proposed by Heusinkveld et al 2008 requires iterative calculations it takes into account the latent heat term which evaluates the amount of water condensed on the lenses at the ends of the measurement path the difference between the temperature of the measurement path of the SAT and that of the open path analyzer and other factors This method is applicable for open path analyzers that are deployed either horizontally or vertically However the method is not applicable to analyzers which are deployed with a tilt a commonly adopted deployment style for flux observations In the session titled Barriers in Flux Measurements at AsiaFlux Workshop 2009 discussions were held on the effect of instrument surface heating with Dr Burba one of the investigators who have proposed a correction method for this effect In this session it was brought up that the correction term may underestimate the necessary correction in a low temperature environment a brief summary of the content of the discussion is reported in Ohkubo et al 2009 In the Workshop a simulation study was presented indicating that the correction term of Burba et al 2008 overestimates the necessary correction in high wind speed conditions Ono et al 2009 Currently there is no agree
153. er equivalent snow survey Standard rain gauge A cylindrical water bucket is buried and rainwater entering from the intake mouth is collected in a container within the bucket The water is then gauged with a graduated measuring cylinder As is the case of rainfall snowfall is measured by a tipping bucket rain gauge which however requires devices for melting snow and preventing the snow volume from being underestimated under the influence of wind Spilt water tipping bucket To measure snowfall the bucket is filled with heated water on which snow falls and melts The amount of water spilt from the bucket is measured by the tipping bucket to determine the water equivalent of the snow The bucket must be provided with oil regularly to prevent heated water from evaporating from the surface Measuring method A rain gauge must be installed such that it is level and at least four times as far away from any objects e g buildings trees as the objects are high Such a requirement is difficult to satisfy in a forest To address this problem trees are usually felled But in the case where trees are felled the growth of surrounding trees likely triggers a drastic change in rainfall measurements For this reason age related changes are monitored and effects of environmental changes on installation places are evaluated by placing an auxiliary tipping bucket in the mid section of a meteorological observation tower where the observation is little af
154. erating cost For the analyses of methane and VOCs an activated carbon packed column and a capillary column are used respectively The time required for methane analysis is a few minutes On the other hand the analysis time required for VOCs is longer than that for methane In a temperature programmed analysis in which the column temperature is raised for analyzing the high boiling point component cooling time is also required after the analysis In qualitative analyses no information other than the retention time of the separated trace gas can be obtained Therefore additional information needs to be acquired from a reference substance and a gas chromatograph mass spectrometer Because leakage of the hydrogen gas which is required for the analyses may cause an explosion safety measures should be taken in advance These measures include the use of a safety device such as an alarm and an automated ventilator for sufficient ventilation Gas Chromatograph Electron Capture Detector As a measurement principle a gas chromatograph electron capture detector GC ECD depends on the change in the base current which takes place when a chemical compound captures free electrons GC ECDs are used for detecting nitrous oxide N20 a greenhouse gas that is regulated by the Kyoto Protocol Because the atmospheric concentration of N20 is very low 310 ppb the analysis of N20 is affected by the peaks of atmospheric N and O2 Therefore the heart cut techniqu
155. ers Boundary Layer Meteorology 93 227 236 Suyker A E and Verma S B 1993 Eddy correlation measurement of CO flux using a closed path sensor Theory and field tests against an open path sensor Boundary Layer Meteorology 64 391 407 Tsukamoto O 1986 Dynamic response of the fine wire psychrometer for direct measurement of water vapor flux Journal of Atmospheric and Oceanic Technology 3 453 461 van der Molen M K Gash J H C and Elbers J A 2004 Sonic anemometer co sine response and flux measurement II The effect of introducing an angle of attack dependent calibration Agricultural and Forest Meteorology 122 95 109 van Dyk A Kohsiek W and de Bruin H A R 2003 Oxygen sensitivity of Krypton and Lyman alpha hygrometers Journal of Atmospheric and Oceanic Technology 20 143 151 Watanabe T Yamanoi K and Yasuda Y 2000 Testing of the bandpass eddy covariance method for a long term measurement of water vapour flux over a forest Boundary Layer Meteorology 96 473 491 Webb E K Pearman G I and Leuning R 1980 Correction of flux measurements for density effects due to heat and water vapour transfer Quarterly Journal of the Royal Meteorological Society 106 85 100 Wieser A Fiedler F and Corsmeier U 2001 The influence of the sensor design on wind measurements with sonic anemometer systems Journal of Atmospheric and Oceanic Technology 18 1585 1608 Wyngaard J C and Zhang S F 1985 Transducer shadow effects
156. es of a slightly tilted installation angle can be summarized as follows 1 Flow disturbance related to the measurement by the open path gas analyzer is small Accurate measurements are possible for any wind direction 45 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 2 Rain water can run off easily Little rain water accumulates on the lens that is located at the end of the measurement path 3 The frequency response characteristics due to path length averaging are well understood For the frequency response characteristics the sensor head can be considered to be oriented vertically in an approximate sense 4 Ifan LI 7500 is used for observation and the analyzer can be assumed to be vertically oriented the correction formula due to instrument surface heating of Burba et al 2008 is applicable Refer to Appendix 2 2 3 for the issue of instrument surface heating The disadvantages of installing an open path gas analyzer with a slightly tilted are the following 5 When wind flows from the open path gas analyzer to a SAT the SAT measurement is disturbed This disadvantage can be minimized if the open path gas analyzer is installed by taking into consideration the prevailing wind direction 6 When an LI 7500 that was manufactured prior to the one with serial number 0282 is used direct solar radiation influences the measurement Refer to Appendix 2 2 1 If an open path gas analyzer is installed vertically
157. essary at the time of calibration and measurement for LI 7500 with certain serial numbers These precautions are briefly summarized below Because the product will likely continue to be modified in the future it is advisable to visit the web site of LI COR regularly to check the latest information 1 For all serial numbers Upgrade the firmware for the control box LI 7500 Instrument Embedded Software the PC software LI7500 exe and obtain the latest product manual for the LI 7500 The latest versions as of Nov 2008 of the firmware PC software and product manual are Ver 3 0 1 Ver 3 0 2 and Rev 4 respectively 2 LI 7500s manufactured prior to serial number 75H B 0282 When an LI 7500 manufactured prior to the one with serial number 75H B 0282 is exposed to direct solar radiation it affects the ends of the paths of the analyzers and changes the output LI COR 2002 To avoid this effect the sensor head of the LI 7500 needs to point north in the northern hemisphere and also needs to be tilted according to the latitude of observation For example for an observation at 35 N tilt the sensor head by about 35 degrees to the north For an observation at 40 N tilt the sensor head by about 30 degrees to the north 3 LI 7500s distributed earlier than around July 2003 The firmware for the control box with version numbers Ver 1 0 0 2 0 4 is used for LI 7500s that were distributed earlier than around July 2003 The time lag of the
158. eteorological Environment Forestry and Forest Products Research Institute iii Practical Handbook of Tower Flux Observation Ver 1 0 Preface to English edition A half century ago Dr Eiichi Inoue a pioneering scientist of turbulence in the atmospheric boundary layer and famous for his studies on Honami waving plants tried to measure carbon dioxide CO2 fluxes over crop fields by applying the aerodynamic method He dreamed that a sensor similar to a heat flux plate could be developed in the future he named the sensor the CO flux plate and that by merely setting the plate horizontally we could easily measure the CO flux from the difference between the concentration of CO at the upper side of the plate and that at the lower side of the plate We may say that his dream partially came true with the development of the eddy covariance system consisting of a sonic anemometer a fast response infrared gas analyzer and a data logger Now the eddy covariance system is used for monitoring fluxes of CO as well as those of water vapor and sensible heat in various terrestrial ecosystems throughout the world However the measurement of CO flux using the eddy covariance system is not as easy as and actually far different from that using the CO flux plate which Dr Inoue dreamed of a half century ago It is certain that open and closed path infrared gas analyzers as well as sonic anemometers and data loggers have recently been much i
159. eved for observation sites at which the wind direction remains relatively constant 3 Tips It is advised that an open path gas analyzer not be mounted behind the structure of a SAT and be mounted at some distance away from and behind the measurement paths of the SAT Refer to Photo2 2 1 or Figure 3 p 5 of the operator s manual from Campbell Campbell 2006 Tips 2 2 2 43 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 Photo 2 2 1 An example of a deployed open path sensor LI 7500 LI COR Mase paddy flux site A SAT DA 600 SONIC CORPORATION Japan can be seen behind the open path sensor Because the prevailing wind direction of this site is easterly to southerly the open section of the SAT is pointed to the south at this site With this set up the influence of the LI 7500 on the wind velocity measurements is small even when the wind is easterly Easterly wind blows from the back to the front through this photo Occurrence frequencies of northerly from the back side of the DA 600 and westerly from the direction of the LI 7500 winds are low at this observation site Alternatively Campbell Scientific Inc US recommends that an open path gas analyzer to be mounted horizontally underneath the measurement paths of the SAT Campbell 2006 With this method the influence of the open path gas analyzer on the wind velocity measurement is small Therefore this method is considered effective for
160. f flow distortion when using a vertical path probe in which two pairs of sensors are placed on a horizontal plane On the other hand when a slanted path probe is used it is likely that the supporting post and frame which support the sensors induce flow distortion mostly in the vertical wind velocity Generally flow distortion is evaluated using wind tunnel experiments The results of wind tunnel experiments for some of the SAT probes can be found in the references given in Table 2 1 1 However it remains controversial whether the results of wind tunnel experiments on flow distortion can be applied to observational data collected in field experiments While a number of applications of the results of wind tunnel experiments to field observations have been reported e g Kondo and Sato 1982 Kaimal et al 1990 Nakai et al 2006 Saitoh et al 2007 studies opposing such applications have also been published e g Hanafusa et al 1982 Ito et al 2001 Ishida et al 2004 Model recommended for its small measurement errors All the commonly used SATs have achieved an acceptable level of reliability Particularly the models listed in Table 2 1 1 have earned good reputations in terms of reliability Of these models the CSAT3 manufactured by Campbell due to its small intrinsic errors and high measurement accuracy is currently considered the most trusted SAT model e g Mauder et al 2007 No formula is yet available for flow distortion correct
161. fected by trees and by carrying out observations at more than one point The smooth movement of a tipping bucket rain gauge must be ensured Pulse data put out at each tip are confirmed Regular maintenance should be exercised by lubricating junctions and moving parts In a snowy region rain gauges need to be protected from snow by removing snow during the winter or by installing a gauge at a height above the snow cover When the heater cannot melt snow fast enough to keep up with extremely heavy snowfall the bucket top may become filled with snow to which close attention should be paid particularly in a deep snow covered area Once the bucket top is filled up with snow data are unobtainable for a long time When heavy snowfall is expected the heater should be set at a higher temperature In seasons other than winter the spilt water tipping bucket may become infested with bugs if it is filled with water which hampers operation Except in winter measurement should be performed with an ordinary tipping bucket rain gauge 157 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 4 Tips The tipping bucket sends a switch controlled rectangular wave signal which is prone to noise As a chattering prevention measure a small capacity condenser is put between the two output terminals Or to deal with chattering noise data registered on the data logger continuously in a short time approx 1 sec can be regarded as one datum
162. ference is too large the burden on the pump becomes large and water condenses inside the piping Thus it is suggested that the pressure be set to a value slightly larger than the value of the required minimum pressure difference Tips 2 3 11 6 Dehumidifier The process of moisture removal from the sample air for gas analyzer needs to be carried out without disrupting the gas composition or the air flow For this process the use of a dehumidifier that employs a semipermeable membrane such as Perma Pure dryer Perma Pure LLC US equipped with Nafion tube DuPont US is recommended This dehumidifier consists of a dual tube structure the inner tube is made of a membrane material that is selectively permeable to water vapor Furthermore semipermeable membrane dryers are classified into two types The first type is made of a single semipermeable membrane tube and the second type is made of a bundle of semipermeable membrane tubes The former is well suited for drying small volumes of gas while the latter is well suited for drying large volumes of gas Use the former type i e single tube type such as the MD Series manufactured by Perma Pure for an observational system in which a closed path analyzer is used for the eddy covariance method In single tube type dryers sampled air air containing water vapor flows through the inner tube and dry air purge gas flows through the outer tube According to the difference in water vapor pressur
163. forts to mitigate global warming at the societal level call for a rapid implementation of systems that quantitatively evaluate the carbon dioxide CO2 budgets for forests croplands grasslands and other terrestrial ecosystems For observational studies of carbon budgets for terrestrial ecosystems tower based micrometeorological CO flux observations conducted at the interface between the atmosphere and terrestrial ecosystems have attracted attention as an approach that allows direct measurements of the amount of CO absorbed by the terrestrial ecosystems from the atmosphere Such CO flux observations have been taking place at more than 200 locations worldwide Furthermore efforts to integrate studies from tower based observations on CO and energy fluxes and those on the carbon dynamics and energy budgets of terrestrial ecosystems are currently in progress with the goals of improving the parameterization of ecosystem models relevant to global warming research and elucidating the influences of natural and anthropogenic disturbances e g typhoons and land use changes respectively on the dynamics of diverse terrestrial ecosystems With this background four research institutes Forestry and Forest Products Research Institute National Institute for Agro Environmental Sciences National Institute of Advanced Industrial Science and Technology and National Institute for Environmental Studies which have conducted long term tower observations within Japan agr
164. from the measurement heights In this method 3 minute average values at the beginning and end of the flux averaging period are used in order to reduce random errors y Tips As shown above the method for calculating the CO storage change F varies among research groups giving the impression that no standardized calculation method has yet been established However the following equation is used in every evaluation of the CO storage change F 07 Pg gt AP a where At flux averaging period AQ change in the CO concentration of the air layer i over the flux averaging period Az thickness of the air layer i and n the number of measurement heights Tip 2 4 3 95 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 2 5 Relaxed eddy accumulation REA method The eddy covariance method requires a small number of assumptions for flux observations over the ground surface thus it is considered to be the most direct flux observation method When the eddy covariance method is used for flux observations of trace gasses such as methane or volatile organic compounds VOCs the fluctuating component of the trace gases needs to be measured with a high response time Such measurements are necessary in order to match the fluctuating vertical wind velocity w which is measured by an ultrasonic anemometer thermometer SAT usually at a sampling rate of approximately 10 Hz However when a gas chromatograph GC is used
165. g is rarely used for tower based CO flux observations Instead pipework that is based on PTFE tubing is frequently used for tower based CO flux observations with closed path analyzers As for the inner diameter of the tubing 4 8 mm is typically used Properties of PTFE include excellent chemical resistance heat resistance and weather resistance PTFE is also nonhygroscopic and non water absorbing For tower flux observations it is necessary to place tubing in an outdoor environment in which the tubing is likely to be exposed for a long time to ultraviolet radiation and reactive gases such as atmospheric ozone Therefore the heat resistant weather resistant and nonhygroscopic properties of PTFE are highly beneficial for use in tubing for tower observations Polyethylene tubing is more elastic easier to handle and less expensive than PTFE tubing However the weather resistance of polyethylene tubing is inferior to that of PTFE tubing and polyethylene tubing needs to be checked and replaced regularly Short tubing length is often used for observations at sites with short plant canopies such as farmland or grassland In contrast long tubing length is often used for observations at sites with tall plant canopies such as forests Even for measurements above forests if the measurement system as in Fig 2 3 1 can be established in the middle of the observation tower the tubing length can be made short When an observation hut is situated at the botto
166. g weir The flow rate is calculated from the amount of water that spills out of the notch and the water level in the weir Photo 3 8 2 The water level sensor should be selected according to the weir depth The relationship between the water level and the flow rate is determined by the notch shape Flow rate formulas for triangular weirs that is weirs with a right triangular shaped notch and for rectangular weirs that is weirs with a rectangular shaped notch are provided in the Japanese Industrial Standards JIS JISK0094 http www jisc go jp For irrigation and drainage measurements a tank with a notch is usually deployed For example in direct irrigation from a pipeline water flowing out of the spigot is stored temporarily in this tank and the water level in the tank is measured Parshall flume flow meter Parshall flume flow meters are also used for open channel flow rate measurements The Parshall flume is a Japanese hand drum shaped structure and the flow rate is measured using the property that the water surface becomes elevated within the narrow segment of the flume Photo 3 8 3 Because the configuration of the Parshall flume does not allow much dirt to accumulate it requires less maintenance than tank style weirs Capacitive water level meter am Photo 3 8 2 An example of drainage Photo 3 8 3 An example of installation of a discharge measurements with the use of Parshall flume for the measurement of the flow
167. ger on types of input signals Many handy single function loggers are commercially available at reasonable prices The Data Mini series Hioki E E Corporation Japan is introduced briefly below Data Mini There are several models of Data Mini such as the VOLTAGE LOGGER 3635 discontinued model LR5041 LR5042 LR5043 and the Pulse Logger LR5061 Some are equipped with temperature and humidity sensors TEMPERATURE LOGGER 3632 LR5011 and LR5001 thus different loggers can be used for different tasks Measuring intervals can be adjusted easily by the button on the face of the logger or by the software provided by the manufacturer To recover data however they have to be collected from each logger by means of a dedicated data collector COMMUNICATION BASE 3911 3912 COMMUNICATION ADAPTER LR5091 and DATA COLLECTOR LR5092 and fed into a PC Tips To carry out measurement extensively using a small output sensor such as a PAR sensor the VOLTAGE LOGGER 3645 discontinued model is used Setting the measuring range to 50 mV indicated resolution of 0 01 mV and turning off the preheat signal function realize cost effective multi point observations with a short cable Tips 3 9 1 Selection point Generally the output range of pyranometers and other radio meters such as PAR sensors is as low as between 0 and 10mV Data loggers that have accuracy to accord with them should be selected The quantum sensor LI 190B produced by LI C
168. ght The specifications of a tower for flux observations between the atmosphere and ecosystem in forests grasslands or agricultural lands are determined by the construction budget and on site conditions however the tower must be at least higher than the surrounding vegetation There have been cases e g Laubach et al 1994 where measurements taken from observation points that were 3 higher than the surrounding vegetation were not very different from those taken from observation points that were 50 70 higher than the surrounding vegetation Thus observations are possible at any height provided the observation site is slightly higher than the surrounding vegetation However measurements taken at a lower site tend to be influenced more strongly by the surrounding vegetation So it is necessary to check whether the observed values are representative of those of the surrounding vegetation Footprint analysis prior to observation is an efficient means of verification e g Schuepp et al 1990 Rannik et al 2000 Kormann and Meixner 2001 Okada 2002 However along with such ex ante analysis it is recommended that site inspections be performed at various observation heights depending on on site conditions In such cases the tower must be higher than the surrounding vegetation with a certain allowance Also if long term observations are performed at a height close to the vegetation height then the vegetation will grow and approach the measu
169. gy research site 18 1 2 Building infrastructure 4 Tips Measurement boxes should be sealed as tightly as possible to keep out rain insects and humidity Holes for wires should be filled in with clay putty and the desiccant in the box should be replaced regularly A closet dehumidifier can also be used if there is enough space in the box Photo 1 2 13 Tips 1 2 9 1 2 6 Other Paths For the conservation of vegetation and soil paths should be established for routes that are frequently used by people such as paths between the hut and the tower from the parking area to the hut or tower and for approaches to observation equipment installed on the ground Paths are indispensable in wetlands or rice paddies where a boardwalk is often installed Photo 1 2 14 Careful consideration of factors such as whether a boardwalk is required or not is also needed in a forest site to ensure conservation of soil and vegetation around the tower over the course of time An important point to remember while maintaining facilities on an agricultural land is to avoid losing tools and metal fittings clamps bolts nuts arms piles that are used for fixing and supporting the tower and for measuring appliances and cables in the fields Lost items such as these can hinder agricultural work damage agricultural machinery and possibly injure workers Even in an area where a rental fee is paid disruption to crops and soil should be minimized It is
170. he ambient air temperature This dew point temperature setting is necessary to avoid condensation inside the tubing 8 Occasionally the output of the LI 7500 suddenly changes by a few ppm after the passage of some time approximately 5 min to hour following the initiation of calibration gas supply The change in the output of the LI 7500 is accompanied by a change in the cooler voltage of the LI 7500 During calibration particularly in Step 2 closely monitor the output displayed on the PC to make sure that no sudden change occurs in the output 9 The sensor head of the LI 7500 analyzer is internally equipped with two plastic bottles containing soda lime and magnesium perchlorate that keep the detector free of CO and H20 The product manual LI COR 2004 recommends that the bottles be recharged with fresh chemicals once a year After recharging the analyzer needs to be operated for at least 4 hours in warm up mode It has been the experience of the CO flux observational group of NIAES that the chemicals degrade at a slow rate and replacing the chemicals once every 2 to 3 years is sufficient The group has also found that the analyzer needs to be operated in warm up mode for to 3 days to achieve a stable zero output after exchanging the chemicals 10 After the completion of calibration apply water repellant e g Rain X on the lenses located at the ends of the measurement path to prevent adhesion of rain drops The individual steps of
171. he data loggers manufactured by Campbell 3 Tips The sub sampling method is used to set the flow rate between the inlet for air sampling and the pump to the maximum value By including an exhaust outlet after the pump in the sampling system excess gas can be removed and a large flow rate can be achieved This method helps suppress the attenuation of CO concentration fluctuations and the time delay caused by the transport of sampled air within the tubing Suyker and Verma 1993 Tips 2 3 13 4 Tips Photo 2 3 2 shows the control board of a CR1000 and a solenoid valve control which is based on a mechanical relay Fig 2 3 2 is an example program prepared with the CRBasic software In experiments by the author solenoid valve control has been successfully achieved However this success does not necessarily guarantee the success of all future solenoid valve controls by other investigators thus the example shown in the figure should be used only as a reference The program example is for switching on control port 1 i e port C1 turning on the solenoid valve for 10 minutes between 11 50 and 12 00 and between 23 50 and 24 00 Incidentally in some cases the use of Photo MOS relays which have recently become available allows direct control of the relay with a control port Tips 2 3 14 79 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 CR Basic for CR1000 Main Program BeginProg If IfTime 710 1440 Min
172. he object Despite its advantage of noncontact observation its accuracy is plus or minus 2 C which makes it inferior in accuracy to contact sensors Photo 3 5 3 Radiation thermometer IR SA CHINO Right with telescope attached Photograph courtesy of CHINO CORPORATION Measuring method The shallower is the soil depth is the greater are the time variation and vertical change of soil temperature T K Thus thermo sensors need to be placed densely in the shallow layer As one installation procedure after a hole is excavated the thermo sensor is thrust into an undisturbed section of the soil Photo 3 5 4 and then the hole is refilled In another method a narrow vertical hole is dug into which a thermo sensor is inserted and the hole is refilled with the same soil In the former procedure because the surrounding soil is disturbed the hole has to be carefully refilled The latter method is applied to the observation of a shallow layer because it is difficult to ensure that the sensor contacts the soil properly in a deep hole In either case the waterproof efficiency of sensors and cables should be taken into consideration One important factor in flux measurement is the temperature of heat gas exchange surface including ground surface A method for measuring surface temperature is explained here To measure surface temperature the use of a surface thermometer is most convenient and reliable When surface temperature is measure
173. he same way as during the time of the measurements of the sampled air Make sure to set up the measurement system in such a way that the opening and closing of the solenoid valves or the turning off and on of the pump takes place at a fixed time Time control can be achieved using 78 2 3 Closed path CO gas analyzers a relay control with a PC Alternatively relays containing microcomputers such as programmable relays OMRON Corporation Japan can now be used for time control In recent years these relays have become available at low cost and programs created by the investigator allow easy time control of the relays without a PC Solenoid valve control by a PC or a programmable relay takes place independently from the data logger thus cannot be synchronized perfectly with the data recording The issue of synchronization can be resolved with the use of a data logger manufactured by Campbell Scientific Inc US e g the CR1000 and CR3000 which allow digital outputs with programmable control When the control port of one of the above mentioned data loggers is on five volts are output This voltage output can be used to control the relay which in turn opens and closes the solenoid valves Therefore the use of one of these loggers enables synchronized data recording and solenoid valve control without the need for additional equipment Finally the above mentioned control is possible with any data loggers with functions similar to those of t
174. he temperature change inside the analyzer Optically the analyzer is designed to reduce the radiation effect Because the analyzer is also slim it causes less disturbance to the wind velocity field thus the sensor separation distance between the SAT and the analyzer can be reduced The sensor separation distance is 6 cm when used together with the CSAT3 When CO flux is evaluated with an open path analyzer high frequency flux loss see Appendix 2 2 2 is generally most attributable to sensor separation Therefore the slimmer analyzer not only reduces the effect of instrument surface heating on the flux measurement but also reduces the magnitude of the flux 61 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 loss correction term that is reduction of uncertainties Furthermore the EC150 is equipped with a feature to enhance water vapor evaporation subsequent to rainfall and diminish water condensation on the lenses at the ends of the measurement path with the use of heaters This feature reduces the occurrence of missing values in the data acquired by the analyzer Finally the third measure addresses the effect of instrument surface heating without the need to use H in the process of CO flux calculations H is the temperature fluctuation term that is required in the mass conservation equation for dry air Webb et al 1980 and does not have to be considered for closed path measurements because air temperature fluctuatio
175. he three way valves are equipped with three ports COM NO normal open and NC normal close When no voltage is supplied no electric current the COM and NO ports are connected When voltage is supplied the COM and NC ports are connected When three way valves are used connect the COM port to the tubing that leads to the analyzer the NO port to the tubing that originates from the sample air inlet and the NC port to the tubing that leads to the calibration gas When two kinds of calibration gas i e zero gas and span gas are used for calibration connect two three way valves in series with the COM port of the upstream valve connected to the NO port of the downstream valve For steady sampling of atmospheric air no electric current is sent to the valves In this state air that is taken in from the sample air inlet is drawn through the pump into the analyzer In order to draw in calibration gas supply electric current to the valve which is connected to the gas to be drawn in Then the NC port of the valve to which electric current has been supplied opens and calibration gas flows into the analyzer and the NO port closes which shuts off the air flow from the sample air inlet If zero gas and span gas two point 71 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 calibration gases with two different CO concentrations are drawn through the system with this procedure the analyzer can be calibrated In the case of automate
176. he time of the measurement height switchover can be eliminated When the system for the measurement height switchover is not linked to the data logger the voltage of the solenoid valve and the output values from the CO analyzer should both be recorded in order to identify the actual measurement height at which CO concentration was measured 2 Examples of other types of systems The measuring system described above uses the same number of pumps for drawing in sample air as the number of measurement heights The vertical profile of CO concentration can also be measured by a single pump if it is installed downstream of the location at which flow path switching takes place However in this set up air cannot be drawn in from the next height for measurement in advance As a result at the time of the sampling height switchover the measurement delay will be larger than that in the system described in 1 Control system method Given this background Xu et al 1999 created a system that uses two pumps for high speed sampling of concentration profiles Furthermore Ohtani et al 2005 proposed a system that specializes in the measurement of CO storage changes and does not measure concentration profiles This system takes in air samples simultaneously at six measurement heights within a forest canopy The average CO concentration of the forest canopy is evaluated by mixing the air samples from the six measurement heights The proportion of sampled air
177. hecking the output of a radiometer with small output values Tips 3 1 2 Calibration Because the amount of solar radiation is a key element for studying the terrestrial energy balance meticulous care is necessary to maintain the sensor accuracy A radiation sensor can be calibrated by comparing the measurement values from the sensor to those from a highly reliable radiometer around solar noon Appendix 3 1 1 Because of the deterioration of the heat plate coating the accuracy of radiation sensors used to drift significantly with time and it was recommended earlier that radiation sensors be inspected every two or three years The accuracy drift of radiation sensors distributed currently is smaller than that of older sensors 3 1 2 Longwave radiation The radiation emitted by the atmosphere or the Earth s surface is called longwave radiation or infrared radiation The wavelengths of the radiation are 3 100 um longer than those of solar radiation Measuring instruments As with a heat sink type pyranometer an infrared radiometer measures the temperature difference between the light receiving surface and the heat sink with a thermopile The protective dome of an infrared radiometer is made of silicon rather than glass The silicon dome window reflects solar radiation and allows only longwave radiation to pass through As the sensing element emits radiative energy according to the 119 Practical Handbook of Tower Flux Observa
178. hout the use of stays However when the height of the tower greatly exceeds the top of the forest canopy metal stays and an anchor of appropriate size are required oar re Photo 1 2 2 Scaffolding tower with access Photo 1 2 3 Ladder tower with a ladder like part stairs Kahoku Experimental Watershed for easy access Kampong Thom Province Cambodia Photograph courtesy of Shimizu Akira Photo 1 2 4 Monorail used for transporting construction materials Yamashiro forest hydrology research site Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 1 Transporting construction materials Since usually a high tower is constructed in a forest and most of the construction work is done in the mountains the transport of construction materials is arduous Use a monorail to effectively transport materials in large amounts while minimizing damage to the forest floor Photo 1 2 4 The price of a monorail car is about three million yen and the costs of laying the rail is about 30 40 thousand yen per meter Tower maintenance Maintenance of an observation tower is essential to ensure that observers working at the tower are safe If a tower is constructed with a strong foundation using materials that have been chosen based on suitable calculations of their strength it can last for more than ten years unless damaged by a natural disaster However even when it does not experience strong winds or a severe earthqu
179. ical information This proposal aims to contribute to the construction of a system that provides an improved estimate of the amount of CO absorbed by terrestrial ecosystems which is relevant in the mitigation of global warming In the regions centered around Asia tower based observation sites within terrestrial ecosystems to be used for the purpose of validating various models remain scarce Without detailed technical information such as that provided in this manual it may be nearly impossible for a research team to start and operate a new observation site alone Because detailed technical information such as that described above is inseparably linked to the development of observation and analysis techniques this information has been made available on the internet which allows for relatively easy update of information an advantage of the internet Because the information included in this manual is published on paper at this time the inability to easily update the information is one of the biggest concerns Nonetheless publication of the present manual is valuable in that it provides a record of the current state of observations and analyses from a technical point of view It is our hope that the present manual will serve in transferring various techniques to the science communities in Asia and contribute to the efforts to mitigate global warming through the expansion of tower observation August 2011 OHTANI Yoshikazu Director Department of M
180. ies Inc US ATI A measuring and control unit together with a TR probe is identified by the model number DA 600 Of the probes listed above the TR 61C and the K Style Probe are orthogonal probes Slanted path 3D SAT Some 3D SATs are equipped with three pairs of sensors which are arranged in such a way that the upper sensors of all three pairs are on the vertices of an equilateral triangle as are the lower sensors of all three pairs Furthermore the sensors are attached so that the measurement paths are slanted from the vertical axis and the center of the three measurement paths intersect See Photo 2 1 1 These 3D SATs are 29 Practical Handbook of Tower Flux Observation Ver 1 00 Chapter 2 called slanted path 3D SATs here and can be classified roughly into two types The first type is called an omni directional probe The supporting post of the omni directional probe is located underneath the sensors and the probe is rotationally symmetrical around an axis in the vertical direction In contrast the sensors in the second type referred to as boom probes here are supported by arms from the top and the bottom the supporting arms meet at a height that is mid way between the upper and lower sensors Examples of omni directional probes are the TR 61B Table 2 1 1 an option with the DA 600 and the SAT 540 550 Table 2 1 1 Photo 2 1 1 c manufactured by SONIC the WindMaster and the R3 manufactured by Gill Instruments Ltd UK Tabl
181. ies on the infrared absorption characteristics of HO molecules for the measurement principle One advantage of the use of this measurement principle is that it allows a simultaneous measurement of CO with an interference filter that transmits radiation with particular frequencies Accordingly open path H2O CO infrared gas analyzers referred to as an open path IRGA hereafter are currently as of 2008 the most commonly used analyzers in the field of research flux observations Other factors that make open path IRGAs the number one choice for H2O flux i e latent heat flux observations are their widespread availability and the abundance of information on using them for measurements and flux calculations In addition to open path IRGAs open path ultraviolet gas analyzers are also open path HO gas analyzers The measurement principle of open path ultraviolet gas analyzers is based on the ultraviolet absorption characteristics of HO molecules Thermocouples are also sometimes used for measuring H2O although they are not strictly open path gas analyzers However the use of these non IRGA instruments is not widespread and some aspects of these instruments are not well suited for long term continuous observation Except for cases with special research objectives and needs that call for the use of non IRGA instruments an open path IRGA is recommended for constructing a new observation system Types of available analyzers Open path gas analyzers
182. igh voltage electric power line 12 horizontal vertical advection 86 hot wire anemometer 131 hour angle 128 hydrostatic water depth meter 162 IMR MS see ion molecule reaction mass spectrometer influence of heating by open path gas analyzer 59 64 66 infrared absorption 41 56 infrared gas analyzer 56 57 infrared radiation 41 50 56 57 70 119 120 instantaneous power failure 106 107 instantaneous wind velocity 134 insulation resistance 106 107 International Organization for Standardization ISO 76 116 117 117 117 first class pyranometer second class pyranometer secondary standard pyranometer 117 ion molecule reaction mass spectrometer IMR MS 101 Practical Handbook of Tower Flux Observation Ver 1 0 irrigation planning 160 ISO see International Organization for Standardization Krypton hygrometer 57 ladder tower 8 9 LAI see leaf area index land consolidation 160 land improvement organization 5 land use map 2 leaf area index LAI LI 6262 LI COR Inc 88 LI 7000 LI COR Inc 24 61 68 69 70 71 81 82 68 69 70 71 82 88 lightning shielding transformer 15 107 litterfall 24 logger 16 18 124 126 138 148 149 166 167 104 119 121 122 124 148 logging interval longwave radiation low pass filter 107 Lyman alpha hygrometer 57 magnesium perchlorate 50 52 70 71 mass flow controller 68 73 76 77 88 89 91 97 102 measurement box 19 measuremen
183. ight by reducing the number of cups to three and by shortening the arms As the cup anemometer has the advantage of being turned regardless of the horizontal direction in which air flows past the cups it is widely used for determining the average wind velocity With regard to the wind velocity at which the cups start rotating the lower it is the better Attention should be paid to excessive rotation due to the inertia of the cups in motion Windmill anemometers Unlike the cup anemometer which has a vertical axis of rotation this propeller anemometer has a horizontal axis of rotation that makes the propeller anemometer capable of measuring the wind velocity in the direction parallel to the axis of rotation Most are integrated with a wind vane so that the instrument always faces windward 130 3 2 Wind direction wind velocity Ultrasonic anemometers Ultrasonic anemometers measure wind velocity based on the time of flight of sonic pulses between pairs of transducers which face each other Sound waves that are emitted in the same direction as the wind are faster than those emitted against the wind therefore there is difference in the travel time of sound waves between receivers The difference in travel time is proportional to wind velocity so the wind velocity can be determined by measuring the time difference electrically Unlike cup anemometers or windmill anemometers this type does not suffer from the inertia of wind catchers and it i
184. ion for the CSAT3 that is based on a wind tunnel experiment Therefore when flow distortion corrections are necessary for the measurements made by a CSAT3 the investigator may need to conduct his or her own wind tunnel experiment Furthermore when wind flows from the backside of the CSAT3 probe the wind velocity field is disturbed by the boom that supports the probe Christen ef al 2001 Thus the influence of the boom on CSAT3 measurements needs to be taken into consideration 37 Practical Handbook of Tower Flux Observation Ver 1 00 Chapter 2 Correction of SAT measured temperature Correction of horizontal wind contamination The variable c in Equations 2 1 1 and 2 1 3 is strictly the speed of sound waves that are measured in the path of a SAT The actual distance traveled by the sound waves along the path becomes longer than the path length due to the wind component normal to the path cross wind v ms Kaimal and Finnigan 1994 Accordingly the values of cs in Equations 2 1 1 and 2 1 3 are smaller than the actual true speed of sound c ms The actual sonic virtual temperature Tw K is the temperature that is evaluated from the value of c Therefore in order to calculate Tw corrections are required for the cross wind effect The following relationship holds between c and c with the presence of a cross wind vy C C Vv 2 1 4 Therefore the following can be obtained 2 2 2 pct Cr el ee 2 1 5 403 4
185. ion needs to be performed prior to span calibration Because the presence of H2O influences the CO output H2O calibration should be performed prior to CO calibration as a precaution The gas used for CO calibration contains no H2O thus the order of calibration should not influence the calibration results in principle However a large offset may exist in the H2O channel thus it is recommended that calibration of the H2O channel be performed first Step 3 Step 3 consists of two sub objectives 1 checking the calibration coefficients stored in the control box that were modified in Step 2 that is to check if Step 2 is finished successfully or not and 2 performing a set of calibrations to be used as a reference in Step 1 of the next round of calibration in the future In Step 3 as in Step 1 the CO and H O outputs are checked after supplying zero gas and more than one kind of appropriate span gas to the calibration tube of the LI 7500 If the calibration in Step 2 has been 53 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 carried out properly the difference between the stated value of the concentration of the calibration gas and the output of the LI 7500 will be small For CO the difference should be smaller than 1 ppm for H20 the difference in dew point temperature should be less than 0 2 0 3 C When the calibration gas used in Step 2 is re used in Step 3 the difference between the stated value of the c
186. ion rate For drainage however water is disposed of not only by surface drainage but also by subsurface drainage through permeation Accordingly it is not easy to figure out the drainage rate for farmlands unless underdrain systems such as closed conduits are sufficiently developed 160 3 8 Water level water temperature irrigation and drainage 3 8 1 Water level Types of instruments There are two methods of measuring water level One is to measure the distance from a reference point above the water surface to the water surface the other is to measure the distance from a reference point below the water surface up to the water surface Float water level meter The water level is determined by the motion of the float Because the up and down motion of a float can be converted into the rotation of a pulley shaft continuous measurement is possible using a simple instrument The instrument requires frequent maintenance to ensure its accuracy as it contains many moving parts Ultrasonic water level meter The distance to the water surface is figured out based on the reflex time of an ultrasonic pulse that is shot at the water surface The instrument has no moving parts so it requires little maintenance Even so regular inspections must be conducted to ensure that the ultrasonic path is unobstructed Because acoustic waves are used corrections may need to be made by understanding the temperature dependence of the acoustic velocity but a
187. ion requires measurements of the fluctuating component of the vertical wind velocity w ms w ms In order to accurately estimate the exchange of energy and scalar quantities by turbulence the observation system needs to be capable of measuring w at a sampling rate of approximately 10 Hz or higher The observation instrument also needs to be able to make measurements without drifting on the time scale of at least several days and needs to be durable enough to make field observations for a year to several years Ultrasonic anemometer thermometers SATs hereafter are currently the only sensors available that meet the above mentioned requirements Principle of measurement The principle of measuring the wind velocity components and the sonic virtual temperature using a SAT is explained below A SAT measures the wind velocity and the speed of sound in the air c along the straight line path between a pair of sensors transducers that face each other The path length of a SAT typically used in field observations span length is approximately 0 05 0 20 m The pair of sensors are internally equipped with transceivers made of acoustic elements Acoustic signals are transmitted from one transceiver to the other in both directions From the time required for an acoustic signal to travel between the transceivers in two directions f s and f s the wind velocity component parallel to the path va ms and the speed of sound cs ms
188. ire is joined at one end by means of electric welding silver brazing or soldering Temperature can be measured by a thermocouple together with a data logger into which a cold junction circuit is built There are various compensation lead wires of different diameters Those as thick as a few millimeters are strong and they easily handle the large time constant of soil The waterproof efficiency of a thermocouple can be enhanced by putting it into a metal pipe that is one size larger than the thermocouple and then adding sealant A thermistor is a thermo sensor that takes advantage of the proportionality between temperature and 147 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 electric resistance of a conductive substance Because the proportionality factor differs between substances a thermistor and its connecting logger are usually sold as a pair Platinum resistors are basically either three wire or four wire Being little subject to age related changes platinum resistors are well suited for soil temperature sensors that are hard to replace frequently The radiation thermometer is another type of instrument that is often used to measure ground surface temperature Photo 3 5 3 From the surface of any object longwave radiation corresponding to its surface temperature is emitted The radiation thermometer captures this longwave radiation and converts it into temperature to indicate the surface temperature of t
189. istance thermometers and thermocouple thermometers are most commonly used These are equipped with a sheath in which a temperature sensing unit is loaded and sealed with insulation The characteristics of thermometers that are generally used for continuous measurement are discussed in this section Table 3 3 1 Thermometers Name Principle Characteristics Electrical resistance thermometer Thermocouple thermometer Radiation thermometer Self registering metallic thermometer Fluid filled thermometer Ultrasonic anemometer thermometer Temperature change in electrical resistance Thermo electromotive force Thermal radiation Metallic expansion Fluid expansion Ultrasonic Doppler effect Easy to handle The temperature sensing unit is larger than that of a thermocouple The size of temperature sensing unit can be minimized Each junction needs to be maintained carefully for accurate measurement Wide range remote measurement is possible although it is difficult to maintain the measurement accuracy Self registering driven by a spring The measurement accuracy is low Low priced instrument It is high in accuracy but it needs a reader Appropriate for measuring sensible heat flux the instrument is expensive and requires calibration 135 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 Thermistor thermometers This thermometer contains a metalli
190. istics of Small CO Sensors and an Improved Method Based on the Sensor Response Journal of Agricultural Meteorology 61 4 217 228 in Japanese with an English abstract Monrcieff J B Massheder J M de Bruin H Elbers J Friborg T Heusinkveld B Kabat P Scott S Seogaard H and Verhoef A 1997 A system to measure surface fluxes of momentum sensible heat water vapour and carbon dioxide Journal of Hydrology 188 189 589 611 Philip J R 1963 The damping of a fluctuating concentration by continuous sampling through a tube Australian Journal of Physics 16 454 463 Suyker A E and Verma S B 1993 Eddy correlation measurement of CO flux using a closed path sensor Theory and field tests against an open path sensor Boundary Layer Meteorology 64 391 407 Wilczak J M Oncley S P and Stage S A 2001 Sonic anemometer tilt correction algorithms Boundary Layer Meteorology 99 127 150 Yasuda Y and Watanabe T 2001 Comparative measurements of CO flux over a forest using closed path and open path CO analyzers Boundary Layer Meteorology 100 191 208 109 Practical Handbook of Tower Flux Observation Ver 1 0 Devices and instruments 2 1 Ultrasonic anemometer thermometers SATs R M Young Company US Model 81000 Product list Price list Campbell Scientific Inc US CSAT3 2 2 Open path CO H O gas analyzers LI COR Inc US LI 7500 family ADC
191. ive and three new models were brought to market in 2010 based on the second and third measures The first measure instead of aiming to minimize or eliminate AH calculates CO flux from the directly measured value of Hop rather than the value of H Grelle and Burba 2007 placed a fine wire thermometer of 0 1 mm diameter fine wire Platinum Resistance Thermometer on one of the support rods of the measurement path of an LI 7500 in order to measure the air temperature fluctuations within the measurement path The CO flux calculated with the sensible heat flux from this thermometer Hop agrees well with that evaluated from a closed path analyzer LI 6262 LI COR suggesting that this measure is effective for addressing the effect of instrument surface heating This measure which utilizes a fine wire thermometer or a thermocouple is applicable for other conventional open path analyzers in addition to the LI 7500 Furthermore the thermometer can be installed by an investigator and the system can be constructed at a relatively low cost However this measure is not well suited for stable continuous observations extending over a long period as being made of fine wires the sensing element of the thermometer deteriorates with age and is easily damaged by high speed winds and rainfall Such disadvantages of this measure are probably among the reasons that no analyzer models based on this measure are commercially available at the present time The second
192. ke sure to select an analyzer that can provide reliable values of the absolute magnitude of CO number density If the use of a closed path analyzer is not feasible the use of a humidity sensor such as the HMP45 manufactured by Vaisala Oyj Finland can be used instead as proposed by Serrano Ortiz et al 2008 In this method the time averaged values of the atmospheric water vapor content obtained from the humidity sensor are compared to those obtained from the open path gas analyzer From this comparison the amount of dust and dirt on the lenses is estimated and the offset in the absolute magnitude of CO number density measured by the open path gas analyzer can be corrected Calibration As discussed in the beginning of this section the variable measured by an open path gas analyzer is CO number density mol CO m On the other hand the unit of mixing ratio ppm is usually used to label the cylinder that contains the CO gas used for calibration Refer to Appendix 2 2 6 Therefore in order to calibrate an open path gas analyzer the mixing ratio of CO in the calibration cylinder needs to be first converted into units of CO number density with the use of the temperature and pressure within the 48 2 2 Open path CO H O gas analyzers sample cell The obtained value of the CO number density is compared to the output value from the open path gas analyzer to determine the offset value and sensitivity of the analyzer The calibration
193. llow According to past research it is ideal for the length on a side of a snow pillow to correspond to the maximum snow water equivalent The length of the snow pillow should be based on expected value of maximum snow weight Calibration Melting snow creates gaps around snow gauging posts and poles which causes measurement errors The snow depth should be gauged with a sounding rod and any necessary measurement corrections must be made 159 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 3 8 Water level water temperature irrigation and drainage In a flooded area or where the groundwater table is high changes of water level and water temperature substantially affect ground surface characteristics In an aqueous system with a shallow bottom the heat capacity of the system increases with increases in the water level In a high moor apparent changes in the aerodynamic characteristics and evaporation efficiency of the ground surface are observed along with the rise and fall of the water level To calculate the heat storage rate of a water body water level and water temperature must be measured Abrupt changes in these provide information on the horizontal movement of water For irrigated farmlands the amount irrigated or drained for the evaluation of water budget has to be understood beforehand For some systems the inflow and outflow of dissolved or non dissolved carbon and nitrogen that results from irrigation or d
194. lok HellermannTyton UK and vinyl tape while making sure that the bends in the cables do not get damaged by vibrations caused by strong wind Furthermore secure the cables running along the tower at appropriate intervals so that large tension loads are not placed on the cables themselves Leveling adjustment and tilt check In principle the SAT probe should be deployed in such a way that the z axis component of the wind velocity is parallel to the direction of gravity The x y plane of the SAT probe is horizontal The time and effort to adjust the leveling of the SAT can be reduced significantly if a simple level is added to the above mentioned base used for installing the SAT See above section on Probes and parts Nonetheless the horizontal deployment of a SAT may not be strictly feasible in some cases When flux measurements are made over sloped topography and the blow up and blow down angle of the wind velocity for the site is known from preliminary measurements the SAT may be tilted by that angle for deployment In either case the tilt of the SAT should be measured with an inclinometer after the SAT has been stabilized so that the measured vales of the tilt can be used to correct the wind velocity and direction as necessary Sometimes 33 Practical Handbook of Tower Flux Observation Ver 1 00 Chapter 2 the tower tilt or tower vibrations may be of concern because of the weight of workers on the tower or strong wind resp
195. lyzer data are available compare the H O output by the open path gas analyzer to the water vapor content measured by a separate humidity sensor From this comparison the temporal change in the offset value of the CO data can sometimes be evaluated Refer to Measurement method 4 Measurement of the absolute magnitude of CO number density or Appendix 2 2 5 If none of the above mentioned methods can be used follow a procedure similar to that for adjusting data for the change in sensitivity of the open path gas analyzer 55 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 4 Tips If the calibration results sensitivity and offset change significantly over a specific observational period calculate the flux values with both sets of calibration results to evaluate the difference in the flux values caused by the difference in calibration results It is also advisable to plot the relationship between the calculated flux values and a meteorological factor e g the relationship between solar radiation and CO flux This plot sometimes reveals a change in both the flux values and the meteorological factor after a particular time which helps the investigator determine the time period in which the changes in the sensitivity and offset values occurred Tips 2 2 5 2 2 2 Measurement of fluctuating H2O concentration by an open path gas analyzer The measurement of water vapor H20 by an open path gas analyzer rel
196. m of a tower the measurement system is sometimes installed inside the hut instead of in the middle of the tower Although the maintenance of the measurement system in this case becomes easier the tubing length becomes longer than it would be in the case with the measurement system installed in the middle of the tower 3 Tips Make sure to use appropriate tubing connectors for connecting tubing sections For connection points that need to be disconnected after the initial deployment the use of one touch connectors e g products of NIHON PISCO CO LTD Japan is convenient For connection points that will not need to be disconnected after the initial deployment a permanent connection should be selected with the use of fittings such as Swagelok tubing fittings When tubing connectors are fixed with screws e g connections between a connector and a pump or between a connector and a valve it is recommended that thread seal tape be wrapped around the junctions to avoid leakage Tips 2 3 7 75 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 4 Tips Some tubing e g PTFE tubing is sometimes difficult to purchase in large lengths For example when the author intended to purchase PTFE tubing with a 6 mm inner diameter and an 8 mm outer diameter for drawing sample air 100m rolls were the next longest size available after 50 m rolls As only 53 m of tubing was needed 47 m had to be left unused Of course the
197. mber of CO molecules per unit volume CO number density mol CO m with the use of the calibration coefficients determined by the manufacturer or the user Therefore the user needs to be aware that the physical variable being measured is CO number density rather than the mixing ratio ppm or mol CO mol dry air which is used to label the calibration gas and also to calculate the fluxes The general characteristics of an open path CO gas analyzer open path gas analyzer hereafter relative to a closed path gas analyzer Section 2 3 are as follows 1 the response time of an open path gas analyzer to the fluctuating CO is faster 2 an open path gas analyzer requires less power 3 the overall configuration i e the analyzer and its peripheral components of an open path gas analyzer is simpler 4 the volume of the sensor head is larger for an open path gas analyzer The sensor head becomes an obstruction to measurements at the measurement height 5 automated calibrations of an open path gas analyzer are difficult 6 accurate measurements of air temperature and pressure within the open path are not easily obtained and also the magnitude of the correction term of the so called WPL correction Webb et al 1980 is larger Characteristics 1 to 3 are generally considered advantages of an open path gas analyzer while characteristics 4 to 6 are generally considered disadvantages Types of available open path gas analyzers Table 2 2
198. measure is based on the notion of minimizing AH as much as possible AH is generated as a result of the open path analyzer being a heat source which is attributable mainly to heat generation from the interior of the analyzer or longwave or shortwave radiation striking the analyzer or both While heating by the former cause can be reduced by cutting down the power consumed by the analyzer heating by the latter cause radiation can be reduced by adjusting the analyzer configuration specifically for example by cutting down the area that receives radiation With this in mind LI COR has produced the LI 7500A as a successor to the LI 7500 The LI 7500A is equipped with an internal temperature setting function allowing the temperature to be set either at 5 C or 30 C according to the air temperature LI COR 2011a By adjusting the temperature setting appropriately for summer winter and other seasons the analyzer can be operated with a power consumption of 12 W in the normal air temperature range 20 to 40 C The analyzer can also be operated at a minimum power consumption of 8 W depending on the conditions For details contact the distributors Campbell has developed an open path analyzer the EC150 which can be used together with the CSAT3 the SAT available from the same corporation Operation of the EC150 requires low power consumption 4 1 W at a temperature of 25 C The analyzer outputs measured values which have been corrected for t
199. measurements at a particular measurement height becomes larger with an increasing number of measurement points These factors need to be taken into account when determining the number of measurement points CO concentration varies significantly near the soil surface and near leaves or forest canopy in the case of a forest Therefore the heights and number of measurement locations need to be determined appropriately by taking into account the structure of the plant canopy of interest The effects of the heights and number of measurement locations on the evaluated values of the CO storage change are discussed in Yang et al 1999 and Yang et al 2007 Measurement system Fig 2 4 1 illustrates an example of a measurement system which measures and records CO concentration by sequentially sampling air at multiple measurement heights with a closed path gas analyzer In this example the number of pumps used in the system is the same as the number of measurement heights 87 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 Data logger Sample Air Sample Air Sample Air x O E Inlet 1 Inlet 2 E Inlet n Air Inlet Branch Sample Air z O Port Reference gas P P 1 EA P P 2 noes P P n a i Silencer i Silencer i Silencer z amp By Choice Dehumidified Air i X X TTET X Silica gel E ce i i Bottle HB Silencer Control Line i H f i i a F COM Silencer om Silencer tes Silencer Dehumidified Air nc LNO i nc
200. mended for measurements with a closed path system A motor based diaphragm pump sharply reduces the volume of the pump chamber by flexing a diaphragm At the pump inlet a one way valve is attached so that it allows air to flow only in the direction of the pump chamber At the exhaust outlet a valve is attached to allow the air to flow only out of the pump chamber Thus these valves ensure that the air flows only in a given direction in response to the flexing motion of the diaphragm Because there exists no mechanical sliding component at the interface between the fluid air in the present case and the portion of the pump that meets the fluid no fluid leaks out of the pump which is considered an advantage of diaphragm pumps Diaphragm pumps are available for a number of driving voltages voltage ratings therefore select one for use according to the circumstances of the power source available at the field site of interest Brushes are used for electric contacts inside many of the DC motors that are used for generic mini pumps This type of pump frequently produces electronic noise and can fail as a result of brush abrasion when operated continuously over a long period If a DC driven pump is used it is suggested that a brushless DC motor be used provided such an option is available A diaphragm pump due to its structure tends to induce flow rate pulsation Pressure variations that result from the flow rate pulsation sometimes affect the measurement v
201. ment on the method for evaluating AH Amiro 2010 for example calculated the cumulative CO flux for two cases that is using the correction term as is and using the correction term reduced by 50 and compared the two values Furthermore the effect of instrument surface heating that is the difference between the air temperature within the measurement path of an open path analyzer and the actual air temperature becomes large in a low temperature environment Burba et al 2005 showed that the temperature difference can become 4 C or 10 12 C at an air temperature of 10 C Therefore in practice the correction method of Burba et al 2008 is applied only to data colleted at air temperatures below 0 C or below 10 C or alternatively missing values are assigned to these data Mkhabela et al 2009 Amiro 2010 As discussed above it has become commonly acknowledged that conventional measurements with open path analyzers are subject to the effect of instrument surface heating however this issue is being handled on a trial and error basis as of today 2011 In parallel with the efforts to clarify the effect of instrument surface heating by researchers efforts have been made by manufacturers to address the effect by improving existing open path analyzers In order to 60 2 2 Open path CO H O gas analyzers address the effect of instrument surface heating non zero AH the following three measures are considered effect
202. metric water content can be figured out with reasonable accuracy 155 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 3 7 Precipitation snow water equivalent SWE snow survey snow depth snow weight Precipitation is the quantity of condensed atmospheric water vapor that is deposited on the earth s surface within a given time usually expressed in height above a flat surface Precipitation occasionally distinguishes between rainfall in water form and snowfall in snow form Although snowfall is the process of solid snow precipitating its quantity is converted into the amount of water and expressed in mm as for rainfall Snow that does not melt but accumulates on the ground constitutes snow cover As snow cover exerts substantial effects on the surrounding environment various observations are carried out on snow cover This chapter discusses the snow depth and the snow weight 3 7 1 Precipitation rainfall snowfall Types of instruments Tipping bucket rain gauges and standard rain gauges are used commonly for measuring precipitation Tipping bucket rain gauge Rainwater entering from a cylindrical intake mouth is poured through a funnel into a tipping bucket Precipitation is measured by the tip frequency Photo 3 7 1 Tipping bucket rain gauge Intake mouth Funnel gg Tipping bucket Photo 3 7 1 Appearance and structure of a tipping bucket rain gauge 156 3 7 Precipitation snow wat
203. mproved and have become more sophisticated so that we can operate those advanced instruments more easily than two decades ago In addition as the number of users of the eddy covariance system increases manufactures and their agents are providing detailed instruction manuals technical notes and even training courses However these resources are not enough for someone who is going to start flux observations using the eddy covariance system because these materials and activities generally focus on how to use the individual instruments or the eddy covariance system at best but do not discuss practical issues related to eddy covariance flux observation such as constructing an observation site including a tower and related facilities setting up the eddy covariance instruments in the field and conducting the micrometeorological observations that are inseparable from the eddy covariance flux observations AsiaFlux has also had several training courses including lectures on the theory of flux observation but could not spend much time on the above mentioned practical issues which are really required for newcomers especially those without expertise in micrometeorology As shown by its title the Practical Handbook of Tower Flux Observation focuses on the practical issues in eddy covariance flux observation and includes a substantial amount of useful knowhow and unique sections such as lightning surge countermeasures and detection and reduction of
204. n 1 2000 e water vapor pressure Pa ea Saturation deficit Pa s Saturation vapor pressure Pa AE thermopile output voltage mV F CO flux mgm s F vertical flux of a trace gas mgm s F CO storage change mgm s Fg radiant flux density Wm FE radiant flux density of single wavelength 4 Wm Fo molar photon flux density molm s FQ molar photon flux density of single wavelength 1 molm s h Planck s constant 6 626 10 Js H sensible heat flux Wm Hody sensible heat flux generated at the instrument surface Wm Hoy sensible heat flux measured by the open path gas analyzer Wm AH Difference of sensible heat flux measured by SAT from one measured by opne path gas analyzer H H Wm J number of days elapsed since 0 00 Jan 1 k thermopile sensitivity mV Wm ka dome coefficient Lt downward longwave radiation Wm LI downward longwave radiation Wm 184 Me Ma Mw n P Pc PAR aove PAR selow PAR above PARA beiow q Q Q Ro R 100 Ra Rnet ST Sl List of symbols molecular weight of CO kgmoI molecular weight of dry air kgmol molecular weight of water vapor kgmol the number of measurement heights atmospheric pressure Pa partial pressure of CO Pa reflected PAR measured above forest canopy umolm s reflected PAR measured under forest canopy umolm s downward PAR measured above forest canopy molm s downward PAR measured under
205. n While plywood is easy to fabricate it can warp and deform Thus when the base is used for long term observation metal such as stainless metal or aluminum is recommended for the base Alternatively sufficiently dried solid timber can be used if appropriate corrosion protection is applied Some models of SATs come with signal converters that are separate from the probes For these models additional installation space and fittings are required for the signal converters y Tips The DA 600 TR 61A B and C manufactured by SONIC consists of a probe a signal conversion box waterproofed and an output unit non waterproofed The CSAT3 manufactured by Campbell consists of a probe and a signal conversion box waterproofed Waterproofed SAT components are usually deployed outdoors while non waterproofed SAT components are usually placed inside a sheltered space such as a hut in which the components are protected from rainfall Tips 2 1 3 Cables The signal cables of SATs are usually made of 5 to 20 cores thus the weight of a signal cable can become large depending on the length of the cable and the SAT model For example the signal and power cables of the DA 600 manufactured by SONIC weigh about 150 gm It is desirable to determine the appropriate cable length in advance so that it will not be heavier than necessary for hauling and handling Secure the bends in the cables to the tower with weather resistant cable ties e g Insu
206. n case of Pt100 between resistances of Rioo Q at 100 C and Rg Q at 0 C the ratio Rjoo Ro is 1 3850 which conforms to the standard of the International Electrotechnical Commission IEC Because the standard Rjo9 Ro 1 3916 specified in the Japanese Industrial Standards JIS before 1989 was different from the IEC s the standard before 1989 is distinguished as JPt100 Tips 3 3 2 Thermocouple thermometers When metal gains a thermal gradient thermo electromotive force is generated within the metal as a result of a difference in density of free electrons If two different kinds of metal wires that generate different electromotive forces at the same temperature are joined at their ends to form a circuit thermocouple a current flows in a certain direction as long as a disparity of temperature is maintained between the two points of contact This is called the Seebeck effect and it is used by the thermocouple thermometer for temperature measurement Fig 3 3 1 The instruments are relatively simple in structure moderate in price standardized and therefore compatible with each other The point that is connected to a data logger is called a reference junction or a cold junction and its temperature is referred to by the sensor as a base value of temperature The data logger determines the temperature of the measuring point by sensing the terminal temperature with a thermistor To avoid the occurrence of temperature difference between
207. nal variation of vertical integrated value gt LAI Vertical distribution profile Phenology observation Canopy surface image Hemispherical image from forest floor Amount of litterfall Soil survey Inventory to estimate above ground biomass Survey of tree roots Amount of agricultural products removed at harvest Amount of organic materials applied e g compost Amount of crop residues burnt in the field Leaf photosynthetic characteristics w W gt gt Ar w a ane Nitrogen content of tree leaves 24 Related information for chapter 1 Related information for chapter 1 Further reading AmeriFlux Standards Guidelines SOPs http public ornl gov ameriflux sop shtml Fluxnet Canada Measurement Protocols Working Draft Version 1 3 http www fluxnet canada ca pages protocols_en measurement 20protocols_v 1 3_background pdf Devices and instruments 1 2 Monorail O Koei Sangyo Co Ltd Japan http www koei m co jp in Japanese Tower O Nippon Light Metal Company Ltd Japan Nikkei Forest Tower http www nlmetal com http www nikkeikin co jp pages products products_p4 4b 4b_040 html in Japanese CQ Tagami Corporation Japan Wireless antenna tower ht p www cq tagami jp in Japanese Eagle Clamp Co Ltd Japan Fall prevention devices http www eagleclamp co jp english Electrical construction O Kandenko Co Ltd Japan http www kandenko co jp en Undergro
208. nce of snow accretion can also be mitigated if the snow is not wet Pyranometers of various grades are commercially available ISO secondary standard pyranometers the highest accuracy available ISO first class pyranometers ISO second class pyranometers and simplified pyranometers Table 3 1 1 Characteristics of commonly used pyranometers Model Manufacturer Sensitivity Spectral range ISO classification mV kWm nm MS 802 EKO 7 305 2800 Secondary Standard PSP EPPLEY approx 9 285 2800 Secondary Standard CMP 21 Kipp amp Zonen 7 14 310 2800 Secondary Standard MS 402 EKO 7 305 2800 First Class SR11 Hukseflux 15 305 2800 First Class CMP 6 Kipp amp Zonen 5 16 310 2800 First Class MS 601 EKO 7 300 2800 Second Class LP02 Hukseflux 15 305 2800 Second Class CMP 3 Kipp amp Zonen 5 15 310 2800 Second Class ML020VM_ EKO approx 7 400 1100 SP Lite2 Kipp amp Zonen 60 100 400 1100 PCM 01 PREDE 7 or 10 305 2800 a 27 Ad io SS lt Photo 3 1 1 Examples of commonly used pyranometers Left MS 402 EKO Photograph courtesy of EKO INSTRUMENTS CoO LTD Right CMP 6 Kipp amp Zonen Photograph courtesy of Kipp amp Zonen B V Pyrheliometers Commercially available pyrheliometers include the MS 56 EKO INSTRUMENTS CO LTD Japan the CHP 1 Kipp amp Zonen B V Netherlands and NIP THE EPPLEY LABORATORY INC US In order to eliminate the influence of circumsolar radiation a cylinder is
209. nces between an IMR MS and a PTR MS have become smaller than earlier Tunable Diode Laser Spectrometer In a tunable diode laser spectrometer TDLS two high reflectance mirrors are set face to face in order to obtain an optical path of several kilometers Within the optical path laser beams are reflected multiple times and the attenuation and decay time of the laser intensity are measured Adjustments for the alignment of the mirrors and the optical source which were required for proper TDLS operations used to be major issues of observations away from laboratories However in recent years these issues have been resolved for some analyzers with the application of optical measures which rely on the use of lenses Methane analyzers are an example of such analyzers Regarding the Fast Methane Analyzer DLT 100 Los Gatos Research Inc 101 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 US due to its structural feature of having a lens the volume of the analyzer cell is large 408 ml thus more suitable for REA method compared to eddy covariance Therefore air samples need to be drawn in with a large vacuum pump within a short time interval As for the methane analyzer G2311 f Picarro Inc US which is designed for the eddy covariance method the volume of the cell of the analyzer is small and it is able to measure HO and CO simultaneously using another laser spectroscopy cavity ring down spectroscopy CRDS Laser spect
210. necessary to correct for the mis synchronization of the signals The maximum communication speed of SDM SDM clock rate changes according to the number of sensors that are connected the scan interval and the cable length Thus according to the measurement system to be used the SDM clock rate needs to be set to an appropriate value in order to avoid communication errors Tips 2 1 5 Maintenance Generally a SAT requires very little maintenance after its deployment Even when the coating material on the SAT becomes discolored or peels off due to its deployment outdoors the influence of these coating modifications on the measurement result is extremely small if it exits at all The data output can be influenced by nearby lightning strikes or instantaneous power outages as well as rain drops within the measurement paths or on the sensors In these cases the data output is characterized by abnormal values However as long as no similar abnormality can be detected in the data from a few days without rain after the occurrence of the abnormality the SAT measurement can be continued without any adjustment On the other hand if abnormal values occur intermittently and their cause is unknown turn in the SAT to the manufacturer for repair and replace it by a backup SAT immediately Unless data abnormalities such as those discussed above are observed the following procedures are sufficient for routine SAT maintenance O If objects such as spider we
211. ners of the tower and are fixed to the buried concrete anchor An anchor is important for ensuring adequate protection against strong winds so sometimes a large anchor is buried deep in the ground e g an anchor of more than 1 m is buried at a depth of more than 1 m In snowy areas where snow load such as weight on the metal stays and settling force can be significant a scaffolding tower without stays is possibly chosen In such cases it is necessary to have a large base area and to use reinforcing materials that are selected on the basis of their strength to withstand the snow season A scaffolding tower that uses ordinary scaffolding pipes and clamps is treated as a temporary construction at a general construction site whereas a tower used for long term observation must have an appropriate distribution of stiffened elements based on specifications such as the tower height and it should be designed and constructed using strength calculations based on the planned height of the tower and properties of the construction materials From the perspective of construction and maintenance using strong lightweight materials such as aluminum is preferable but the material costs rise steeply Many ladder towers consist of triangles or quadrilaterals of about 10 cm on one side Photo 1 2 3 These towers are used for radio and cell phone communications and materials and strength calculations are often set as standards Since telecommunication towers a
212. ng the manual valves too much as this will cause an insufficient flow rate The valves should be disassembled and cleaned once a year If silencers are added to the exhaust outlets the silencers should be replaced periodically approximately once a year so that clogging of the silencers does not reduce the flow rate of excess air discharge 89 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 Solenoid valves switching between air samples from various measurement heights SV 1 SV 2 SV n 0 0 Solenoid valves are used for switching between air samples from various measurement heights Prior to opening a solenoid valve it is recommended that air be drawn in up to the location of the solenoid valve remove the stagnated air in the tubing between the air inlet and the solenoid valve in order to shorten the time delay in the measurement due to the distance between the air inlet and the sample cell For this purpose create branched tubing between the pump and the solenoid valve for ventilating the excess air Air is ventilated out of the branched tubing until the solenoid valve is opened The investigator should be aware of the operational lifetime of the solenoid valves Details of solenoid valves can be found in Section 2 3 Closed path CO gas analyzers 2 Solenoid valves Air filters Air filters should be included in order to avoid problems caused by dust and dirt accumulating in the flow path
213. nic anemometer thermometer SAT and 2 the distance between the open path gas analyzer and the SAT should be minimized in order to minimize the loss of fluxes in the high frequency range Often these two factors are at odds with each other For the deployment of an open path gas analyzer the characteristics of the individual observation site e g the prevailing wind direction and the range of expected wind directions also need to be taken into consideration Therefore no standard or formulated method of deployment exits Here an example of a deployed open path gas analyzer will be introduced in order to elucidate the principles of deploying an open path gas analyzer Method for deploying sensor head Photo 2 2 1 shows an open path gas analyzer that was deployed by a research group from the National Institute for Agro Environmental Sciences NIAES If the configuration of a SAT is not rotationally symmetrical the SAT needs to be deployed with the open section front plane pointed into the prevailing wind direction When an open path gas analyzer is deployed it should not be placed behind the SAT structure The open path gas analyzer should also be mounted on the side of the SAT sensors that is downwind of the prevailing wind In other words the mounting position of the open path gas analyzer needs to be selected in such a way that air parcels passing the open path gas analyzer only occasionally flow through the SAT This goal is most easily achi
214. nn C Snijders W Valentini R and Vesala T 2000 Estimates of the annual net carbon and water exchange of forests the EUROFLUX methodology Advances in Ecological Research 30 113 175 Businger J A and Oncley S P 1990 Flux measurement with conditional sampling Journal of Atmospheric and Oceanic Technology 7 349 352 Hamotani K Uchida Y Monji N and Miyata A 1996 A system of the relaxed eddy accumulation method to evaluate CO flux over plant canopies Agricultural and Forest Meteorology 52 135 139 Lenshow D H and Raupach M R 1991 The attenuation of fluctuations in scalar concentrations through sampling tubes Journal of Geophysical Research 96 D8 15259 15268 Leuning R and Judd M D 1996 The relative merits of open and closed path analyzers for measurement of eddy fluxes Global Change Biology 2 241 253 Leuning R and Moncrieff J 1990 Eddy covariance CO flux measurements using Open and Closed path CO analysers Corrections for analyser water vapour sensitivity and damping of fluctuation in air sampling tubes Boundary Layer Meteorology 53 63 76 Massman W 1991 The attenuation of concentration fluctuations in turbulent flow through a tube Journal of Geophysical Research 96 D8 15269 15273 McMillen R T 1988 An eddy correlation technique with extended applicability to non simple terrain Boundary Layer Meteorology 43 231 245 Mizoguchi Y and Ohtani Y 2005 Comparison of Response Character
215. ns become attenuated in the course of drawing the sample air However because the degree of attenuation is influenced by factors such as tube configuration tube length and drawing rate the combination of these factors needs to be selected appropriately For details refer to Clement et al 2009 LI COR has created a new product the LI 7200 by covering the measurement path of the LI 7500A with a PVC hood which is low in temperature conductivity and allows little water to adhere and thus converting the instrument into a closed path analyzer With the combined use of an LI 7200 a pump exclusive for the LI 7200 and a flow rate control unit CO flux can be calculated using the calculation procedure for closed path analyzers that is without using H Conventional closed path analyzers tend to be complex in terms of the configuration of the system because they are required to be installed indoors or in shelters to address the influence of rainfall and changes in the surrounding environment particularly temperature However the open path analyzer LI 7500A was adopted for the basic measurement component of the LI 7200 Because the pump and flow rate control unit of the analyzer are also designed to be weather resistant despite being a closed path analyzer the LI 7200 can be deployed outdoors The design of the LI 7200 reduces missing data during a rainfall event and as reported by Nakai et al 2011 it also allows evaluation of the pressure correla
216. nt in all your dealings with them While proceeding with the procedures for acquiring permission for land use you should begin the necessary construction and survey work If the observation site is situated in an area designated as a national park a protected forest or an erosion control area then you need to obtain permission from the proper authorities to use the land Details are explained below Agricultural land When you set up an observation station on an agricultural land you must first obtain permission from the land owner to use his land for the study Towers tend to be rather small when built on agricultural lands compared to these in forest and the impact of tower and facilities on cultivation should not come to an issue However constructing objects such as towers in the middle of fields can adversely affect the efficiency of agricultural work especially work done by tractors and machinery When negotiating the rent with the land owner this point should be taken into consideration Although installing a tower in an agricultural field rarely affects the surrounding fields the consent of neighboring land owners must also be acquired for managing the observation site The consent can be acquired through a land improvement organization or other local organizations It is always important to maintain amicable relation with neighboring land owners as they might also provide information that is useful for your study Special areas
217. nufactured by Swagelok Company US and attach a flow meter to the outlet of the pump Operate the pump and check the flow meter reading If the air leakage is large the surrounding air is drawn into the pump through the leak and the flow meter reading becomes different from zero and indicates the degree of air leakage Note that the proposed method is unable to detect small air leakages Finally when the pump operation required for the above mentioned method is performed over a long time the burden on the pump becomes large Thus caution is necessary while examining the pump for air leakage Tips 2 3 6 4 Tubing When a closed path gas analyzer is used for eddy covariance measurements air is sampled through tubing For this purpose a variety of tubing has been used and the tubing length has varied between a few meters to 50 m or more according to the field site Typical tubing that is used with closed path analyzers includes PTFE tubing polyethylene tubing stainless steel tubing polyethylene coated aluminum tubing e g Decabon tubes Hagitec inc Japan and plastic tubing e g Bev A Line tubing Thermoplastic Processes Inc US For measurements of the 74 2 3 Closed path CO gas analyzers atmospheric background COs stainless steel tubing is often adopted as little CO is adsorbed and penetrates into the tubing However stainless steel tubing is hard to work with when it is deployed on a tower thus stainless steel tubin
218. o the agricultural work manually in the vicinity of the tower Even when the latter option is chosen it is better to pull down the tower once in several years to ensure cultivation of the entire agricultural field 1 2 3 Electric power supply Commercial power supply Wherever possible the use of a commercial power supply is recommended as is the introduction of a facility that has considerable capacitance A back up power supply should be maintained for the event of power loss and the observation system should have automatic data saving and power restoration features To install a commercial power supply at the newly set up experimental site certain steps have to be followed by an electrical contractor who is affiliated with the power company based in each region For example Kandenko Co Ltd in the region around Tokyo Locally registered electricians can be recruited through the local office of the power company in each region If there are residential area close to where power is to be installed setting up the power supply can be done free of charge for a certain distance from such area When a meteorological observation tower is installed it is often several kilometers away from the residential area there will be indispensable expenses for its installation including the installation of electric poles and electric wires Rental expenses will accrue when electric poles are present on private land 3 Tips Comprehensive discussions with pe
219. of sealant to the sensor bottom particularly to the cable connection area Tips 3 1 6 4 Tips Caution is called for when the temperature of the body case decreases An ice film may form over the diffuser panel if it is cleansed with Kimwipes or cotton that has been soaked in pure water Tips 3 1 7 ML 020P 1 The current output from the sensor is converted into the voltage output by the resistor which is inserted in the radiometer When a long cable is used a drop in output voltage has to be taken into consideration 2 The glass dome should be regularly cleansed with Kimwipes or cotton soaked in alcohol Tips The weight of snow may cause the sensor table to tilt In a snowy area an installation table should be reinforced such that it can remain level during the snowfall and snowmelt seasons It is necessary to confirm that the table is level after the snowmelt season Tips 3 1 8 Calibration Because of large instrument error the sensor needs to be rechecked before measurement Because age related changes are also noticeable regular instrumental check ups by the manufacturer or with the reference meter are recommended 127 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 Appendix 3 1 1 Necessary factors to obtain the solar position The followings are the calculations of factors necessary to obtain the solar position at a given time in a given place Equation of time 2 h the diffe
220. oil in such a situation ground bars should be buried 2 m apart and wired in parallel It is also preferable to wire the ground with electrical cables that are as close as possible to the grounds of the connected device r ener OOE R PARRAKAKARAKAAAKAKK 40cm or more V RRRRRRRRRRRRRRRRRR PARARAKAARAAAAARAR RA v2 Beeccracccraraurceccecccaee AA KKRRRAAR RRA vr vn I vr vr vn vn gn 4 or NY SSD SS S SS SS S X SX X N S9 WWW WWW X NY SW WY Ww SINIIIINE ISISI ANNAN SWWVy7y q NY X X X SS X Photo 1 2 11 Ground bar Fig 1 2 2 Installing the ground bar Other matters The most effective lightning countermeasures are cutting off the equipment power and unplugging the power and communications cables Instantaneous failure of a power line can occur during a lightning storm and an operational check of the observation equipment should be performed once it is safe to do so It is also very important to avoid working at or near a high tower when lightning strikes are likely 4 Tips Telecommunication appliances such as telephones modems and computers connected to the two types of electric lines power cables and telecommunications lines are the items most likely to be damaged by lightning This is because of electrical surges that enter one line and exit by passing through another such appliances This can occur in electrical as well as ground lines Therefore
221. omated calibration advantage 2 is possible with a closed path gas analyzer because of its automatic switch over function which allows a standard gas to flow into the flow path of the analyzer The disadvantages of a closed path gas analyzer include 1 its cumbersome and complex measurement system and 2 attenuation of fluctuations of CO concentration during the sampling procedure Under some observational conditions the use of a closed path gas analyzer may be better suited for the eddy covariance method than the use of an open path gas analyzer Ono et al 2007 Thus it may be to the investigator s advantage to acquire an understanding of the use of closed path gas analyzers for the eddy covariance method so that this technique becomes an option for measuring CO fluxes The discussions in this section will mainly focus on CO concentration measurements by closed path gas analyzers although recently designed closed path gas analyzers are capable of measuring both CO and H2O concentrations in the sampled air 1 Summary of the air sampling system that includes a closed path gas analyzer Fig 2 3 1 shows a schematic of an air sampling system that includes a closed path gas analyzer A photo of the air sampling system in Fig 2 3 1 is shown in Photo 2 3 1 In flux measurements with a closed path gas analyzer CO concentration measurements are made on the sample air that is collected at the measurement point and sent to the analyzer through th
222. on that is slightly higher than that at the observational site of interest The calibration method is the same as that in which a zero gas is used However with the use of two span gases the range of CO concentrations to be calibrated can be set according to the CO concentration to be observed and a more accurate calibration is possible than in the case in which a zero gas and a span gas are used for calibration 80 2 3 Closed path CO gas analyzers 4 Tips Even if a CO analyzer is calibrated frequently the calibrations are meaningless if a standard gas with low accuracy is used Thus it is desirable to use standard gas the accuracy of which is higher than that of the CO analyzer In addition stability of the standard gas over time is also important Generally the concentration of the gas in the cylinder increases with a decrease in the residual pressure thus the gas cylinder needs to be replaced before the residual pressure becomes too low if possible before the residual pressure becomes less than 3 MPa Air air balance is recommended as the balance gas for the CO gas Here balance gas means the same as base gas or carrier gas Although nitrogen is also used as the balance gas for the CO gas standard gas with air balance is recommended for measuring CO concentration in the air For details refer to Pearman 1977 Pearman and Garratt 1975 Griffith 1982 Griffith et al 1982 Nakazawa 1982 and Murayama 2001
223. on by an open path gas analyzer eeeeeeeeeeeeeeeeees 41 2 2 2 Measurement of fluctuating H20 concentration by an open path gas analyzer seeeeeeeereereeeeese 56 2 2 3 Recent progress in addressing the effect of surface heating of open path analyzers as of 2011 59 Appendix 2 2 1 Serial number specific characteristics of the LI 7500 LI COR Inc U S A 63 Appendix 2 2 2 High frequency flux loss 0 00 00 ie 64 Appendix 2 2 3 The influence of heating by the open path gas analyzer on flux calculation 64 Appendix 2 2 4 Issues associated with horizontally deployed open path gas analyzers 65 Appendix 2 2 5 Influence of dirt and dust accumulated on the lenses of the open path gas analyzer on CO number density measurements 0sseeeeee teeter tees eens 65 Appendix 2 2 6 Density and mixing ratio 0 6 666s eee 65 Appendix 2 2 7 Literature which reports a negligible effect of instrument surface heating on open path analyzer measurements sseseeeeeeeeeseeeeeeeeeeneeeessenessenssasaeesenees 66 2 3 Closed path CO gas analyzers sssssssesseeeseeeseeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeessensnenseensnenanas 67 Appendix 2 3 1 References on corrections for high frequency signals sreeeeee ee eeeee reece 85 vi Contents 2 4 CO storage change sn Dutenairie ani nati tone oa ase euk onan temnietimeansnmaieieie 86 2 5 Relaxed eddy accumulation REA method
224. on turbulence spectra measured by sonic anemometers Journal of Atmospheric and Oceanic Technology 2 548 558 Xu L K Matista A A and Hsiao T C 1999 A technique for measuring CO and water vapor profiles within and above plant canopies over short periods Agricultural and Forest Meteorology 94 1 12 Yang B Hanson P J Riggs J S Pallardy S G Heuer M Hosman K P Meyers T P Wullschleger S D and Gu L H 2007 Biases of CO storage in eddy flux measurements in a forest pertinent to vertical configurations of a profile system and CO density averaging Journal of Geophysical Research 112 D20123 Yang P C Black T A Neumann H H Novak M D and Blanken P D 1999 Spatial and temporal variability of CO2 concentration and flux in a boreal aspen forest Journal of Geophysical Research 104 D22 27653 27661 183 Practical Handbook of Tower Flux Observation Ver 1 0 List of symbols A Avogadro s number 6 023107 mol APAR radiation absorbed by a forest canopy umolm s b empirical coefficient in REA method c velocity of light 2 9979x108 ms on speed of sound ms Ct actual speed of sound ms C temperature in Celsius C Ca dry bulb temperature C Cap dew point temperature C C volume heat capacity of soil Jm gt C Cw wet bulb temperature C d span length m dP the difference between total pressure and static pressure Pa D 2000 0 magnetic declination at 0 00 on Ja
225. onal site is explained below Based on the purpose of individual stages of calibration the entire calibration procedure can be roughly classified into 3 steps which will be referred as Step 1 Step 2 and Step 3 In this subsection precautions regarding the preparation and the entire procedure for calibration will be discussed first Subsequently the work sequence within each step will be explained Preparations and important reminders for the calibration procedure 1 If the equipment necessary for calibration can be taken out to the observational site calibration can potentially be conducted outdoors However outdoor calibration is subject to changes in the external environment during the calibration and other uncertain factors that influence the calibration results Therefore the user is advised not to calibrate the LI 7500 outdoors and to calibrate it indoors instead by removing the sensor head and control box from the observation stand 2 Make sure that there is no leakage at the tubing junctions when connecting the tubing to the calibration equipment When zero CO gas is flowing through the sensor head and tubing junctions breath on these parts to ensure there is no leakage i e ensure that the CO output does not change 3 Check the AGC output on the PC when the calibration tube is not mounted on the analyzer Subsequently place the calibration tube on the analyzer and make sure that the value of AGC does not change If the mounting
226. oncentration of the calibration gas and the output of the LI 7500 is expected to be small However when a calibration gas other than that used in Step 2 is used in Step 3 the difference between the stated value of the concentration of the calibration gas and the output of the LI 7500 will sometimes be large For example consider the case in which a calibration gas of 700 ppm is supplied in Step 2 and a calibration gas of 350 ppm is supplied in Step 3 In this case the difference between the concentration of the calibration gas and the output of the LI 7500 can sometimes become as large as 1 ppm When the difference between the concentration of the supplied calibration gas and the output of the LI 7500 becomes large as a rough guide more than 2 4 ppm for CO and more than 0 2 0 5 C in dew point temperature for H20 repeat Step 2 and Step 3 3 Calibration of the E 009 and OP 2 In principle the E 009 and OP 2 do not require modification of the calibration coefficients stored in the analyzers While the gain of both open path gas analyzers can be adjusted in the control box the analyzers are usually used without adjusting the gain Accordingly only the calibration procedure equivalent to Step 1 for the LI 7500 needs to be performed regularly to determine the sensitivity and offset of the analyzer The preparations and important reminders for the calibration procedure and the procedure outlined in Step 1 for the LI 7500 are all applicable for
227. ontrast leakage of sampled air under negative pressure causes the surrounding air to enter the system which significantly influences the concentration measurement Since the force exerted by negative pressure due to the suction of the pump is larger than one might imagine extreme care is necessary for the tubing joints If the piping for the system becomes complex it is recommended to apply positive pressure pressurization rather than negative pressure to the system for easier maintenance and long term continuous operation In order to check the location of leaks in a pressurized system the use of liquid leak detectors such as Snoop Swagelok is effective Prior to the system operation check for leaks with liquid leak detectors by applying positive pressure to the system including the portions to which negative pressure will be applied during the time of measurement Tips 2 3 17 11 Attenuation of fluctuations of CO concentration of the sampled air When a closed path gas analyzer is used fluctuations of CO concentration in the measured air sampled air are attenuated The magnitude of attenuation increases with increasing frequency This issue is considered the biggest weakness of the eddy covariance method that uses a closed path gas analyzer The attenuation of fluctuations of CO concentration is caused by the transport of air in the tubing and or the response speed of the analyzer The degree of attenuation of the fluctuations
228. option 1 rain drops tend to accumulate on the lens If an open path gas analyzer is installed with a tilt or horizontally options 3 and 4 respectively the interference of the analyzer on the SAT measurement is small if the analyzer and SAT are positioned appropriately With these installation methods the instrument surface heating can also be reduced However the frequency response characteristics of both the spectra and co spectra from a tilted or horizontal open path gas analyzer remain unknown and the ability to correct flux losses at high frequencies becomes limited Appendix 2 2 4 2 Method for recording output signals When output signals are analog recorded in voltage the output signals may be contaminated by noise and low pass and or digital filters are applied to remove the noise as necessary For recording the data output from an LI 7500 the use of the Synchronous Device for Measurement SDM communication protocol of Campbell is highly recommended Unlike analog recording recording with the SDM communication protocol avoids the issue of noise The SDM communication protocol also allows the simultaneous recording of the operation status of the analyzer One of the recorded variables that represents the operation status is the Automatic Gain Control AGC The value of AGC changes according to the presence of objects e g dirt and pollen that are adhered to the lenses and interfere with the measurements in the measurement pa
229. or measurement of snow and ice cover 244pp Hokkaido University Press in Japanese Japanese Industrial Standards JIS Z 8806 2001 Humidity Measurement methods Japanese Standards Association Kondo J ed 1994 Meteorology in water regime water and energy balance on land surface 348pp Asakura shoten in Japanese Kanto Branch of the Society of Agricultural Meteorology of Japan ed 1988 Instruments and measurement techniques in agricultural meteorology 322pp Association of advancement of agricultural science in Japanese Kanto Branch of the Society of Agricultural Meteorology of Japan ed 1997 New edition Instruments and measurement techniques in agricultural meteorology 356pp Association of advancement of agricultural science in Japanese The society for the study of species biology ed 2003 Introduction to plant physiological ecology 319pp Bun ichi Sogo Shyuppan Tokyo in Japanese Suzuki N ed 1996 Meteorological Research Note No 185 Meteorological Instruments Surface Observation 155pp The Meteorological Society of Japan in Japanse Tsukamoto O and Monji N ed 2001 Meteorological Research Note No 199 Methodology of flux measurement on the ground 242pp The Meteorological Society of Japan in Japanse Watanabe I ed 1987 Experimental method in agricultural environment Agricultural meteorology and environmental engineering in agriculture 285pp Science House in Japanese Yoshino
230. ording to the volumetric water content the TDR moisture meter measures the permittivity of soil by the reflection of high frequency electromagnetic waves The TDR moisture meter is capable of measuring a wide range of average volumetric water contents for most soil layers as far as the probe reaches The instrument however is susceptible to variations in temperature and soil salinity which cause some errors Low priced permittivity moisture meters whose measurements are based on static capacitors e g EC 5 Decagon Devices Inc US Photo 3 6 1 which have become 152 3 6 Soil moisture distributed recently have similar problems with temperature and soil salinity The length of the sensing unit varies between sensors ranging from 5 cm to m They need to be used properly depending on soil sections With the aim of measuring the matric potential a tensiometer Photo 3 6 2 is used The unglazed porous cup which is filled with deaerated water is buried to the measuring depth in an augured hole and exposed to the surrounding soil water The pressure sensor measures the force with which water in the cup is attracted to the surrounding water Fig 3 6 1 TDR moisture meter CS616 L Photo 3 6 1 Permittivity moisture meter EC 5 Campbell Illustration courtesy of Campbell Decagon Photograph courtesy of Decagon Scientific Inc Devices Inc Pressure sensor __ Air pool Porous cup lt Photo 3 6 2 Tensiomete
231. orology 149 291 302 178 Literature cited Hayashi M 1988 Measurement of humidity Jn Instruments and measurement techniques in agricultural meteorology Kanto Branch of the Society of Agricultural Meteorology of Japan ed Association of advancement of agricultural science 51 81 in Japanese Heusinkveld B G Jacobs A F G and Holtslag A A M 2008 Effect of open path gas analyzer wetness on eddy covariance flux measurements A proposed solution Agricultural and Forest Meteorology 148 1563 1573 Hignett P 1992 Corrections to temperature measurements with a sonic anemometer Boundary Layer Meteorology 61 175 187 Hirano T and Saigusa N 2007 Flux measurement using eddy covariance method Jn Practice of flux observations in terrestrial ecosystems AsiaFlux Steering Committee ed 3 1 3 22 http www asiaflux net members material html available exclusively for AsiaFlux members Hirata R Hirano T Mogami J Fujinuma Y Inukai K Saigusa N and Yamamoto S 2005 CO flux measured by an open path system over a larch forest during snow covered season Phyton 45 347 351 Hirose Y and Shibata S 2000 Correction of PIR long wave radiometer using conical hollow blackbody first report theoretical considerations Journal of the Aerological Observatory 60 25 34 in Japanese Horst T W and Oncley S P 2006 Corrections to inertial range power spectra measured by CSAT3 and Solent sonic anemometers Path a
232. otecting power lines communication lines and sensor signal lines Lightning rod 1 2 Building infrastructure Installing a lightning rod is the most effective protection against direct lightning strikes An observation tower more than 20 m high is required to have a lightning protection system lightning rod according to Article 88 of The Building Standards Act A lightning rod can be installed by the builder during tower construction Photo 1 2 9 and at the same time a ground with little earth resistance lt 10 Q should also be installed Fig 1 2 1 Even if lightning strikes the lightning rod surge current can be produced by electromagnetic induction in various cables wired to the observation facility and this can damage the observation equipment Thus surge arresters are required even if a lightning rod is installed Photo 1 2 9 A lightning rod left and a ground right installed in an observation tower Sapporo forest meteorology research site Surge arrester Abnormal current flow induced by a lightning surge can damage observation equipments by various routes such as via electric power lines communication lines and sensor signal lines A surge protection device SPD or a surge arrester should be installed between the observation equipment and any line that is wired to the observation hut Countermeasures for power lines Lightning proof transformers or SPDs in power circuits are used as surge protecto
233. output data of the sensor so that problems of the sensor if any can be fixed At a relatively small body of water such as a paddy the water may be blown leeward at times of strong wind For this reason the water level at more than one observation point in a paddy needs to be recorded on each visit to the site Calibration Both ultrasonic and laser water level meters can be calibrated indoors where a proper flat plate is prepared and measurements are taken by varying the distance to the target plate Among capacitive and hydrostatic water level meters those for a small range can be calibrated indoors with the help of a water tank or a bucket For a sensor equipped with a temperature compensation circuit the accuracy should be confirmed by comparing the output data with the water level that is periodically observed onsite by a researcher 3 8 2 Water temperature Types of instruments As is the case for air temperature and soil temperature water temperature is measured mostly by thermocouples thermistors and platinum resistance thermometers The characteristics of each are given in Sections 3 3 Air temperature and 3 5 1 Soil temperature 162 3 8 Water level water temperature irrigation and drainage Measuring method To measure water temperature at a constant water depth below the water surface the sensor is hung from a float To make measurements at a constant water depth above the water bottom a weighted sensor i
234. output signal programmed in the firmware is different from that given in the product manual LI COR refers to this discrepancy in the time lag as timing error This timing error can be eliminated by upgrading the firmware to Version 3 0 0 or later versions 4 LI 7500s manufactured after serial number 75H B 0370 As a result of improvements in the main circuit in the control box LI 7500s manufactured after the one with serial number 75H B 0370 can be used at low air temperatures down to 40 C As long as the calibration coefficients can be transferred properly LI 7500s can be used for measurements even if the serial numbers of the sensor head and the control box do not match However the coefficients determined for a combination of the main circuit of a control box manufactured before the above mentioned improvement and a sensor head cannot be used for a combination of the main circuit of a control box manufactured after the improvement and a sensor head and vice versa Therefore when the sensor head that was used with the old version new version control box is transferred to the new version old version control box calibration needs to be performed for the new combination of sensor head and control box LI COR recommends that calibration be performed prior to the measurements on the sensor 63 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 head combined with the control box when the serial numbers differ betw
235. over Photo 3 3 5 are used in most places A horizontal shelter needs to be installed and its installation must be such that solar radiation will not enter In addition caution has to be taken so that air can blow in the direction where the fan heat does not affect the observation In general meteorological observation temperature is measured in an open observation field without obstacles The standard measuring height specified by the Japan Meteorological Agency is 1 5m above ground snow surface and that of the World Meteorological Organization WMO is between 1 25 and 5 m above ground To continuously observe the vertical distribution of temperature particularly high measurement accuracy is required In evaluating the static stability of atmosphere the potential temperature the temperature which an air parcel would acquire when brought adiabatically to a standard atmospheric pressure is a key factor of the vertical distribution However because the difference in potential temperature is approximately equal to the difference in atmospheric temperature within the surface layer the atmospheric temperature is often employed As for the measuring height in a forest the upper limit is set at a point more than twice the tree height where the vertical gradient of temperature becomes smaller Other measuring points may be two elevation points above the vegetation community one at the tree crown one under the canopy and one near the ground surface I
236. pling Journal of Atmospheric and Oceanic Technology 7 349 352 Campbell Scientific Inc 2006 Open Path Eddy Covariance System Operator s Manual CSAT3 LI 7500 and KH20 Campbell Scientific Inc Christen A van Gorsel E Vogt R Andretta M and Rotach M W 2001 Ultrasonic anemometer instrumentation at steep slopes Wind tunnel study field Intercomparison measurement MAP Newsletter 15 164 167 http www map meteoswiss ch map doc NL15 christen pdf Clement R Burba G Grelle A Anderson D and Moncrieff J 2009 Improved trace gas flux estimation through IRGA sampling optimization Agricultural and Forest Meteorology 149 3 4 623 638 Finnigan J 2006 The storage term in eddy flux calculations Agricultural and Forest Meteorology 136 108 113 Fluxnet Canada ed 2003 Fluxnet Canada Measurement Protocols Working Draft Version 1 3 109pp Fluxnet Canada Network Management Office Giasson M A Coursolle C and Margolis H A 2006 Ecosystem level CO fluxes from a boreal cutover in eastern Canada before and after scarification Agricultural and Forest Meteorology 140 23 40 Grelle A and Burba G G 2007 Fine wire thermometer to correct CO fluxes by open path analyzers for artificial density fluctuations Agricultural and Forest Meteorology 147 1 2 48 57 Grelle A and Lindroth A 1996 Eddy correlation system for long term monitoring of fluxes of heat water and CO Global Change Biology 2 297 308 Griffith
237. ployed Table 3 1 2 lists the commercially available infrared radiometers that are commonly in use and some of their images are shown in Photo 3 1 4 Table 3 1 2 Properties of major infrared radiometers Model Manufacturer Sensitivity Spectral range Window Temperature Measurement heating offset dependency of dome mV kWm nm Wm C temperature MS 202 EKO approx 4 3 000 50 000 yes PIR EPPLEY approx 4 3 500 50 000 1 20 40 C yes CGR4 Kipp amp Zonen 5 10 4 500 42 000 less than 4 1 20 50 C no CGR3 Kipp amp Zonen Sor7 4 500 42 000 less than 15 5 10 40 C no 120 3 1 Radiation Photo 3 1 4 Infrared radiometers Left CGR 4 Kipp amp Zonen Photograph courtesy of Kipp amp Zonen B V Right PIR EPPLEY Measuring method An infrared radiometer needs to be deployed in a location at which it does not get shielded from radiation in any direction For downward radiation measurements the radiometer is deployed horizontally with the sensor side facing upward Similarly for upward radiation measurements the radiometer is deployed horizontally with the sensor side facing downward When upward radiation is measured the measurement height needs to be selected by taking the following factors into consideration if the measurement height is too high the measurement may include the influence of objects other than the target of observation if the measurement height is too low the measur
238. r Tellus 27 62 65 Rannik U Aubinet M Kurbanmuradov O Sabelfeld K K Markkanen T and Vesela T 2000 Footprint analysis for the measurements over heterogeneous forest Boundary Layer Meteorology 97 137 166 Rinne H J I Delany A C Greenberg J P and Guenther A B 2000 A true eddy accumulation system for trace gas fluxes using disjunct eddy sampling method Journal of Geophysical Research 105 24791 24798 Saitoh T M Tamagawa I and Koizumi H 2007 Flux observation and energy balance in steep slope correction of net radiation and sonic anemometer angle of attack Proceedings of 2007 Annual Conference Japan society of hydrology and water resources 118 119 in Japanese Schmid H P 1997 Experimental design for flux measurements matching scales of observations and fluxes Agricultural and Forest Meteorology 87 179 200 Schuepp P H Leclerc M Y MacPherson J L and Desjardins R L 1990 Footprint prediction of scalar fluxes from analytical solutions of the diffusion equation Boundary Layer Meteorology 50 355 373 Serrano Ortiz P Kowalski A S Domingo F Ruiz B and Alados Arboleda L 2008 Consequences of uncertainties in CO density for estimating Net Ecosystem CO Exchange by open path eddy covariance 182 Literature cited Boundary Layer Meteorology 126 209 218 Shimizu T Suzuki M and Shimizu A 1999 Examination of a correction procedure for the flow attenuation in orthogonal sonic anemomet
239. r DIK 3000 series Daiki Rika Kogyo Photograph courtesy of Daiki Rika Kogyo Co Ltd Measuring method In principle soil moisture sensors are installed at the same points where soil temperature is measured In selecting the depth for monitoring soil water flux water conditions in association with plant roots need to be fully taken into account For example in the evergreen forest of the Forestry and Forest Products Research Institute in Kompong Thom Province Cambodia tree roots extend to nearly 2 m below the surface At this 153 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 site observations are carried out at depths of 20 50 100 150 200 and 250 cm Because the soil environment is never spatially uniform it is recommended to repeat observations both area wise and depth wise as thoroughly as possible The sensing unit of a volumetric water content sensor and the porous cup of a tensiometer should be inserted into soil deep enough so as not to leave a gap at the base To install the unit in a deeper section soil is excavated in profile The unit is inserted horizontally Photo 3 6 3 and then the soil is recovered To avoid soil disturbance a vertical hole is dug to a designated depth with an auger Then a sensing unit attached to the tip of an extension rod is inserted into the hole Any gap around the sensing unit and the porous cup should be filled with soil because water may otherwise flow into the gap d
240. r Flux Observation Ver 1 0 Chapter 3 types of instruments require no correction for atmospheric pressure the negative pressure side is open to the atmosphere Inherent to diaphragms is the fact that those with high pressure resistance have poor resolution Measuring method The sensor must be securely fixed to a firm post so that the water current does not cause it to move When using a large temperature dependent sensor devise a sunshade so that solar radiation does not reach the sensor directly For ultrasonic and laser sensors protect the sensing volume with a solid pipe or mesh tube to keep objects such as leaves from entering the space between the sensor and the water surface However especially in the case of the ultrasonic sensor the dimensions of the detection area need to be checked in advance in the operation manual or other resources so that the above mentioned pipe or mesh tube itself does not interfere with the sensing volume Hydrostatic water depth meters that require atmospheric pressure correction measure the atmospheric pressure in addition to the hydrostatic pressure If the water depth is too small for a hydrostatic water depth meter to take proper measurements the apparent water depth can be increased by digging into the bottom surface inserting a solid pipe and deploying the sensor in the hole The water level and the distance from the reference point to the sensor zero point are periodically measured and compared with
241. r a 1 Hz sampling Its memory capacity is 4 MB With an optional compact flash CF module CFM100 data can be stored on a CF card It communicates with a PC through RS 232C or a dedicated cable optional to recover data transfer control programs and adjust settings by means of specific software The logger is able to respond to digital output sensors Under a command of a programming language called CRBasic the measuring interval and applied voltage are controlled at ease The logger is so versatile and extensible as to increase the number of channels and to achieve relay control simply by adding options CADAC21 To activate the logger a scan unit MODEL 9220A 9223A is connected to the main unit 9201A Through RS 232C or an Ethernet connection optional at shipping the logger communicates with a PC for unit control and data transmission The memory capacity is 8MB If there are many measuring channels the volume of data may be excessive in which case the data can be saved on an always connected PC With additional scan units up to 80 measuring channels are available Measuring intervals can be adjusted with the help of supplementary software Even beginners are able to handle the logger without difficulty GL820 A stand alone logger has 20 channels and it is scalable up to 200 channels It is competitive in price comparing to the above mentioned two loggers however its measurement accuracy can be low depending 166 3 9 Data log
242. r the ground When the situation allows unfixed wiring on the ground using protective tubes is favorable for maintenance Photo 1 2 7 When the location is isolated and a commercial power supply is unavailable a dynamo or a power generation system employing solar panels can be used Nowadays many observation sites use a photovoltaic generator based on solar panels When a dynamo is used it should be installed in such a position that its exhausts do not affect flux observations Photo 1 2 6 Aerial wiring in a forest Photo 1 2 7 Unfixed wiring The forest floor Yamashiro forest hydrology research site undulates so it is more practical to use underground corrugated protective tubes for unfixed wiring Yamashiro forest hydrology research site 12 4 Tips When a high voltage electrical power line cannot be extended to the transformer of the utility pole near 1 2 Building infrastructure the observation facility long distance power transmission is needed between the transformer and the observation facility either with an AC 100 V line or with a 200 V single phase three wire system In this case the resistance of the wire extending to the observation facility can cause a voltage drop As a result depending on the electric power required sufficient power supply voltage may not be available for conducting observations Use of a wire with small conductor resistance i e a thick wire helps to minimize the voltage d
243. rainage cannot be ignored in evaluating the water budget for each system The water level is the height of the water surface in relation to a reference surface A method of monitoring a ruler perpendicular to the water surface by visual or by time lapse camera observation is so fundamental and reliable that it can be applied to the calibration of sensor measurements There are various water level sensors that operate on different measuring principles These are used in accordance with the magnitude of the water level fluctuation These instruments are also used as lysimeters and pans to measure the evaporation rate and for hydrological observation weirs to measure the flow rate which is introduced later As in the atmosphere water experiences thermal stratification As is the case of air temperature or soil temperature water temperature measurement needs to take the measuring height depth into consideration Where the water level fluctuates rapidly and substantially the device must allow the temperature detector to move up and down along with the water level A regional estimate of irrigation water is drawn up for a comprehensive irrigation planning Regarding flux observation on individual paddy lots a researcher must measure the amount of irrigation and drainage for each lot In Japan because farmlands where a land consolidation project has been carried through are irrigated directly from water channels by lot it is easy to measure the irrigat
244. ration the mixing ratio of CO in the sampled air can be determined In this case the WPL correction also becomes unnecessary Grelle and Lindroth 1996 Tips 2 3 18 84 2 3 Closed path CO gas analyzers Appendix Appendix 2 3 1 References on corrections for high frequency signals Aubinet M et al 2000 Estimates of the annual net carbon and water exchange of forests the EJROFLUX methodology Advances in Ecological Research 30 113 175 Lenshow D H and Raupach M R 1991 The attenuation of fluctuations in scalar concentrations through sampling tubes Journal of Geophysical Research 96 D8 15259 15268 Leuning and Judd 1996 The relative merits of open and closed path analyzers for measurement of eddy fluxes Global Change Biology 2 241 253 Leuning R and Moncrieff J 1990 Eddy covariance CO flux measurements using Open and Closed path CO analysers Corrections for analyser water vapour sensitivity and damping of fluctuation in air sampling tubes Boundary Layer Meteorology 53 63 76 Massman W 1991 The attenuation of concentration fluctuations in turbulent flow through a tube Journal of Geophysical Research D8 15269 15273 Monrcieff J B Massheder J M de Bruin H Elbers J Friborg T Heusinkveld B Kabat P Scott S Seogaard H Verhoef A 1997 A system to measure surface fluxes of momentum sensible heat water vapour and carbon dioxide Journal of Hydrology 188 189 589 611 Philip J R 1963
245. rature can be converted after the relationship between temperature and resistance of the element possibly provided by the thermistor manufacturer is determined and the voltage supplied from the constant voltage source is measured Tips 3 3 1 136 3 3 Air temperature Platinum resistance thermometer The instruments are standardized with Pt1l00 4 indicating the resistance of 100 Q at 0 C The three and four wire types Photo 3 3 3 that are often used for meteorological observation have high measurement _ JB accuracy as they are capable of offsetting the resistance value of the lead wire by measuring the output voltage of the bridged circuit Thus they are well suited for stable _ Photo 3 3 3 HMP45D of Vaisala long term observation To make wiring resistance platinum thermometer discontinued model replaced by HMP155 uniform lead wires of the same diameter material and length should be used and corrosion prevention must be given to all the connections If wire is extended excessively resistance may increase too much for the data logger to register Because the heat capacity of a resistance element is greater than that of a thermocouple the response speed is accordingly slower The sheathed platinum resistance thermometer is highly resistant to age related changes which makes it well suited to long term observation but it should be handled carefully as it is susceptible to vibration and shock 4 Tips I
246. re and amount of irrigation water B Stem temperature Required to calculate the amount of heat stored in stems and to estimate stem respiratory volume Amount of water snow or other moisture adhering to the canopy C Sap flow velocity or sap flow rate C Amount of rainfall interception throughfall stemflow and associated water quality 7 Amount of runoff and associated water quality C 1 3 3 Structure and basic characteristics of a plant canopy It often requires a great deal of effort to investigate the structure and basic characteristics of an ecosystem especially in a forest of tall trees For measurement variables that display only small secular changes data obtained from a single observation conducted during the measurement period is enough to help clarify the condition of the site To determine the carbon balance of the agricultural ecosystem it is necessary to measure the biomass and carbon content in different parts of each crop in order to estimate the amount of agricultural product removed from the study site at harvest The influx of carbon accompanying the application of organic materials such as compost and the outflow of carbon accompanying the burning of crop residues are essential measurement variables when those management methods are used Table 1 3 4 23 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 1 Table 1 3 4 Measurement variables of an ecosystem Measurement variable Rank LAI Seaso
247. re disadvantages of the use of thermocouple psychrometers 1 thermocouple psychrometers are not well suited for long term observations because of the significant effort required for maintenance and 2 corrections are required on the measurements by the dry bulb and wet bulb thermocouples due to the difference in the response characteristics between the two types of thermocouples Tsukamoto 1986 Therefore the use of thermocouple psychrometers is appropriate when an observational system is constructed for a short term measurement at low cost Measuring HO with a thermocouple and a SAT As discussed in Section 2 1 Ultrasonic anemometer thermometers SATs the temperature measured by a SAT is the sonic virtual temperature that includes the influence of H O in the atmosphere Therefore if the air temperature is measured by another instrument the concentration of H O in the atmosphere can be calculated from the difference between the sonic virtual temperature and the measured air temperature The air temperature can be measured by tungsten resistance wires platinum wires or thermistors as well as 25 50 um diameter thermocouples In theory as long as the sonic virtual and actual air temperatures are measured with high accuracy H O fluxes can also be measured accurately The present method has been adopted for short term observational studies e g Hanafusa et al 2005 However no long term observational study of more than a few months ba
248. re used around the world it is easy even in overseas to construct such a tower as it can be built relatively cheaply according to the local labor costs It is also possible to add an optional electric or manually operated winch or space for working and evacuation which is called a safety box or stage However this type of tower requires greater physical strength of the observer for moving up and down the tower compared with the scaffolding tower Also when working at great heights the sensation of being high above the ground is more intense and this will limit the number of people who can work in such an area It is also difficult to move up and down while holding something 1 2 Building infrastructure so to set up an instrument you need a pulley and a rope as well as a support person on the ground A device for preventing falls when working high above the ground or safety gear used for mountain climbing is indispensable for moving up and down this type of tower Moreover setting up metal frames that are used for climbing greatly reduces the worker s sense of fear when installing and removing safety appliances This type of tower stands like a rod on a base whose area is relatively small with respect to its height So when it is used for long term observations its foundation should be laid very deep in order to prevent it from falling over Also it is possible to build this type of tower depending on the height as a self standing tower wit
249. recording of the determined sign 3 Automatic exchange of air sampling reservoirs or on site automatic analysis of the previously collected air sample during the next sampling period 4 If on site automatic analysis is not performed the air sample reservoirs need to be brought back to a laboratory After the analysis equipment has been calibrated with the use of a calibration gas the air samples are analyzed and the difference in the concentrations of the trace gas is determined between the times with positive values of w and those with negative values of w 5 Calculation of the value of b with the use of the sensible heat flux Types of analyzers Although mainly gas chromatographs have been used for the analysis of trace gasses other types of analyzers have also been used in recent years Various types of analyzers that are used for trace gas flux observations are described below Gas Chromatograph Flame Ionization Detector A gas chromatograph flame ionization detector GC FID reacts only to carbon compounds other than 99 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 CO and CO and is little affected by other constituents of the air A highly sensitive quantitative analysis of a trace gas of interest can be made by separating the trace gas from the rest of the air sample with the use of an appropriate column Advantages of the detector include its simple configuration low price high stability and low op
250. rement level Therefore when a tower is constructed its height should at least be 1 5 2 times that of the surrounding vegetation regardless of the height of the flux observation equipment Tower types and features In grassland or agricultural areas a pole like tower of approximately 3 5 m is used in most cases Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 1 Photo 1 2 1 There is a free standing type of tower which has a pipe driven deep into the ground a reinforced type that is supported by wires and a tripod type j In a forest a higher tower is needed Most common type is the one which the observer can climbs up with the instruments Some of the towers have stairs Photo 1 2 2 here we call it a scaffolding tower and others have ladders Photo 1 2 3 here we call it a ladder tower There is also another tower Photo 1 2 1 A pole like tower Mase paddy type with an elevating table attached to lift up the flux site instruments to the top The advantage of using a scaffolding tower is that it is easy to ensure the safety of the climber It is also easier to go up and down the stairs when holding an instrument in hand So the installation and maintenance of instruments is comparatively easy even when there are few observers In case of a scaffolding tower a four sided tower is built on a comparatively broad yet shallow foundation with metal stays that extend outward from the four cor
251. rence between mean solar time hypothetical hour angle on the assumption that the sun moves over the celestial equator at a constant speed and true solar time actual hour angle of the sun Although there are several estimation equations Matsumoto 2005 a simple equation is introduced below Q 0 528276 cos aa 3 354103 cos 2 0 086077 cos 3a 0 137550 cos 4a 7 341887 sin a 9 338832 sin 2 0 304815 sin 3a 0 170209 sin 4a A3 1 1 where 27 365 or 22 366 and J the number of days elapsed since 0 00 Jan 1 real number e g J 0 5 for 12 00 Jan 1 which is calculated based on 8 year 1998 2005 data from the Chronological Scientific Tables Hour angle the angular displacement of the Earth s rotation after the sun culmination The hour angle at the culmination is 0 The value is negative before the culmination and positive after the culmination increasing at a rate of 15 an hour G 15 t 12 2 7 7 A3 1 2 where standard time h y longitude and yo meridian Declination of the sun 6 the celestial position of the sun 6 0 for the equinox 6 23 44 for the summer solstice and 6 23 44 for the winter solstice A simple equation is introduced below 0 38145 22 95333 cos a 0 38122 cos 2a 0 153343 cos3a 3 77859 sin a 0 034839 sin a 0 078079 sin 3a A3 1 3 which is calculated based on data 19
252. restry and Forest Products Research Institute was hit twice by typhoons with Ma AA E Wa A Fi 4 EOF Z Photo 1 2 5 Trees connected by steel wires at the base left and at 10 m right The red arrows show the connections Kahoku Experimental Watershed 10 1 2 Building infrastructure maximum wind velocities of 50 ms but none of the trees that had been tied together fell and so there was no damage to the tower or the stays and the observations can be continued without interruption At an observation site located on an agricultural land agricultural work such as crop planting harvesting and cultivation is conducted mostly by machines several times in a year These alter the ground surface conditions A tower built on an agricultural field can interfere with agricultural work but observations of upward radiation soil heat flux plant community profile and so on are often carried out in the vicinity of the tower so it is important to ensure the homogeneity of the land even in the vicinity of the tower There are two ways to do this One is to carry out observations by setting up a simplified tower that can be easily transported such as a tripod and pulling down the tower temporarily when there is agricultural work to be done the other is to carry out observations at the permanently installed tower after asking the field administrator to avoid agricultural work around the tower and having the observers themselves d
253. rk and Flux Evaluation 3 4 Mkhabela M S Amiro B D Barr A G Black T A Hawthorne I Kidston J McCaughey J H Orchansky A L Nesic Z Sass A Shashkov A and Zha T 2009 Comparison of carbon dynamics and water use efficiency following fire and harvesting in Canadian boreal forests Agricultural and Forest Meteorology 149 783 794 Monji N 2003 Measurement of turbulence and flux In Plants and Micrometeorology Turbulence and fluxes in plant atmosphere Osaka Municipal University Press 85 124 in Japanese Moore C J 1986 Frequency response corrections for eddy correlation systems Boundary Layer Meteorology 37 17 35 Murayama S 2001 II 1 2 2 Carbon dioxide New technology in measurement of environmental chemicals Miyazaki A ed Realize Science amp Engineering Center 130 151 in Japanese Nakai T Iwata H and Harazono Y 2011 Importance of mixing ratio for a long term CO flux measurement with a closed path system Tellus 63B 302 308 Nakai T van der Molen M K Gash J H C and Kodama Y 2006 Correction of sonic anemometer angle of attack errors Agricultural and Forest Meteorology 136 19 30 Nakazawa T 1982 Fluctuations of carbon dioxide in the atmosphere Geochemistry 16 63 77 in Japanese National Institutes of Natural Sciences National Astronomical Observatory of Japan ed 2005 Chronological Scientific Tables 2006 1015pp Maruzen In Japanese Ohkawara N and Takano M
254. rmed using other micrometeorological methods However the eddy covariance method does require that there is a flat terrain and homogeneous vegetation in the windward side of the observation point Schmid 1997 Preparation Select candidate observation sites based on information collected from the following topographic maps vegetation maps aerial photography satellite images land use maps forest management maps data on climate and hydrological conditions and history of land use and management With respect to climatic conditions studying the speed and direction of prevailing winds and changes in their daily and seasonal patterns helps to determine the most appropriate site for flux measurements and sensor positioning Practically it is necessary to collect information on land ownership land use rights and building restrictions It is also important to find out the social structure and security of the area from people who are familiar with the surrounding region At the same time draw up an observation plan that specifies the observation period methods for managing vegetation manpower requirement methods employed for data collection data usage and procedures for making the data publically available as well as any relation between your study and other flux observation studies 1 1 Selection of flux observation sites 3 Tips Flux measurement studies require two full time staff members for each observation site Baldocchi et al 1
255. rmly fixed 105 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 2 7 Detection and reduction of noise When various sensors are used as in meteorological observations the measurement values are sometimes affected by noise Turbulence observations are particularly susceptible to the effects of noise because the sampling rate is relatively high ranging between a few Hz to a few tens of Hz and because the measurements require resolutions higher than those sought for general meteorological observations The noise that affects turbulence observations can be roughly classified into three types 1 Electrical noise transmitted by signal cables 2 Electromagnetic noise transmitted in the air 3 Noise transmitted by power supply lines AC power supply lines Electrical noise transmitted by signal cables is generated when the insulation resistance or shielding of the sensors is insufficient or when the signal cables are affected by a power line a pump a motor or electromagnetic waves Caution is required when wireless equipment such as cell phones and wireless LANs are used for data transmission and monitoring of observation systems as the use of these kinds of equipment causes electromagnetic noise Noise induced by power supply lines includes instantaneous power failure indicated by zero voltage for a short time interval such as one cycle harmonic current distortion of the original AC waveform due to high frequency current volt
256. rogram may serve as a useful reference for recording digital data outputs from the SATs manufactured by SONIC or Gill However there is no guarantee that the program will work in all situations When data from a CSAT3 are output digitally to a data logger such as a CR1000 an SDM cable can be used for a simple and easy connection between the sensor and the data logger The SDM connection requires less electricity than other connections and a sample program for the operation of the system is available in the CSAT3 manual Although the length of the SDM cable supplied by the manufacturer is normally 7 62 m the user may need to extend its length in some circumstances In this case the numerical value in the parenthesis that follows the control command SDMspeed for Campbell data loggers needs to be set to a larger value The numerical value used for SDMspeed is approximately 30 for an SDM cable with a length of 7 62 m 34 2 1 Ultrasonic anemometer thermometers SATs 4q Tips SDM Synchronous Devices for Measurement is a protocol established by Campbell for improving the communication control between a data logger and peripheral devices Connection of a data logger to peripheral devices via SDM enables synchronized data acquisition at a high speed Therefore the use of SDM is suitable for measurements such as those for the eddy covariance method in which multiple signals are acquired simultaneously at a high frequency and in which care is
257. rop Many measuring instruments that operate normally at 95 V perform unstably at 90 V though the degree of instability depends on the individual measuring instrument Therefore the voltage of the AC power supply that is to be used for the observation system needs to be checked Electric power generated by a photovoltaic power source Tips 1 2 4 Photovoltaic cells on solar panels charge batteries using sunlight During sunshine hours a photovoltaic generator generates more power than what the observation system needs and the surplus is used to charge the battery The charged power is consumed during the night or during non sunshine hours A charge controller is used to prevent the battery from overcharging and also prevents excessive discharge In terms of the charging capacity and durability of the battery it is most appropriate to use a deep cycle battery as it can be used even when fully charged and it also delivers a consistent voltage as it discharge The capacity of the solar panel and the battery depend on power consumption by the observation system and on the amount of available solar radiation For more information on how to calculate capacity please refer to the technical data posted on related websites The available electric power is limited The observation system should have low power consumption itself and equipped with automatic power control functions including saving of on memory data turning off low priori
258. ropriate method is currently available for evaluating and or correcting the smoothing effect Appendix 2 2 5 Influence of dirt and dust accumulated on the lenses of the open path gas analyzer on CO number density measurements When dirt and dust accumulate on the lenses of an open path gas analyzer LI 7500 the CO and H2O outputs are offset Serrano Ortiz et al 2008 According to Serrano Ortiz et al 2008 when the outputs with dust induced offsets are used to calculate fluxes the errors on the calculated fluxes become large when evaluating the long term e g yearly cumulative flux values To minimize such errors the following actions are considered effective 1 measure the absolute magnitude of CO number density mixing ratio with a closed path analyzer 2 compare the H2O output from the open path gas analyzer to that measured by a humidity sensor Apply the result of this comparison to correct the CO output and 3 clean the lenses at the end of the measurement path regularly Although the discussions of Serrano Ortiz et al 2008 are strictly valid only for LI 7500s it is likely that dirt and dust on the lenses of other open path gas analyzers also induce offsets in the CO and H2O outputs Thus the above mentioned actions may be necessary when data are collected by other open path gas analyzers Appendix 2 2 6 Density and mixing ratio CO mass density is defined as the mass of CO that is included in a unit volume of air CO
259. roscopy is expected to be applied in studies of uncovering CO H20 exchange process using stable isotopes Chemiluminescence Analyzer For the measurements of isoprene and ethylene analyzers have been developed with a chemiluminescent method During the operation of an isoprene analyzer air is introduced into a reaction cell that is filled with gas containing a high concentration of ozone Ultraviolet radiation 430 nm which is emitted from the reaction of isoprene with ozone in the cell is selectively filtered and is measured by an electron multiplier An ethylene analyzer depends on a property of ethylene that its chemical reaction with certain other substances causes long lasting chemiluminescence The chemiluminescent emission from chemical reactions with NO and ozone in a mixing chamber is measured Finally chemiluminescent methods are susceptible to the effects of substances that interfere with the chemiluminescent reactions Deployment Selection of deployment location The air inlet of an REA system should be deployed as close to the SAT as possible however in such a way that the air inlet does not affect the vertical wind Furthermore in order to minimize the time delay in measurements due to the switching of flow paths the solenoid valves and their switching system should be placed immediately after the air inlet Sufficiently high suction force is also necessary so that the air inflow rate at the time of suction is not affected by
260. rs for power lines as shown in Fig 1 2 1 SPDs in power circuits are smaller and cheaper than lightning proof transformers thus they are easier to install in a temporary facility such as an observation hut To discharge surge current to the earth 15 lightning surge ground Fig 1 2 1 Comparison of lightning proof transformers and SPDs Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 1 through the ground it is necessary to prepare a good ground that has little earth resistance Preliminary discussion with builders is necessary as these protective devices should be installed at the same time when the power lines are laid Plug in appliances called surge protectors are commercially available and some of these are built into power strips or uninterruptible power supplies and are easy to use Countermeasures for communication lines For communication lines SPD is selected according to the type of line used As with power lines these are installed during line installation and plug in appliances can be used Damage to the network can be reduced by using optical lines Countermeasures for sensor signal lines Sensor signal lines installed in a tower can also serve as discharge paths for surge current A large number of measuring instruments are set up in observation towers so using terminal blocks for these instruments Photo 1 2 10 makes it easier to perform lightning surge countermeasures All signal lines
261. rs measure the snow depth based on the principle light does not penetrate beyond a certain depth 158 3 7 Precipitation snow water equivalent snow survey Photo 3 7 2 Snow depth measured by ultrasonic snow gauge Tohkamachi Experimental Station Snow water equivalent A snow pillow metal wafer containing an anti freezing solution is placed at the measuring site and the snow weight is measured on the basis of the change in pressure on the snow pillow with the help of a snow cover weight meter As another method a cylinder of known cross section is inserted into a snow layer down to the soil boundary Samples collected from all the snow layers are weighed from which the snow water equivalent is calculated Measuring method As is the case of a rain gauge installation site snow cover is observed on the level in an area free from obstructions such as trees In addition to measurement by a stationary snow gauge it is desirable to carry out the periodical multi point measurement using a snow sampler Through multi point sampling spatial variation can be evaluated and the snow density can be determined from snow depth and weight Although various snow samplers are commercially available a handmade device can serve the purpose When using a snow pillow to measure the snow weight the measurement weight may often be underestimated as a result of snow bridging over the pillow if the snow volume is too large for the size of the snow pi
262. rsonnels of an electrical engineering company affiliated with a power company can greatly improve their support level It is important to emphasize the public nature of observations taking the time and making the effort to provide an explanation for your activities and to participate in negotiations on site prior to beginning your study Tips 1 2 3 11 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 1 When installing a power supply line high voltage electric power lines should be laid as close as possible to the observation tower or to the experimental site in the forest and a transformer should be set on the nearest electric pole This avoids problems such as power line noise after the start of the observation and it also makes it easy to change the capacitance As for wiring in a forest in order to prevent the wire from being cut or damaged by falling trees the power supply line should be laid on or under the ground after being placed into protective tubes Products such as corrugated pipe accordion pipe and so on can be used If a power supply line is laid under the ground then maintenance after setup is difficult It requires efforts such as setting up a linkage box midway along the line As for wiring on telephone poles it may be necessary to cut down some trees so that they do not touch wires Photo 1 2 6 When conservation of the forest is a priority it is better to install the power supply line on or unde
263. s are calculated using data collected by an open path gas analyzer the correction term for air density fluctuations dry air flux needs to be evaluated Webb et al 1980 For details of the Webb correction refer to the analysis edition of the present manual The Webb correction requires evaluation of air temperature fluctuations within the measurement path of the open path gas analyzer sensible heat flux Hop In the past Hop was assumed to be the same as the sensible heat flux measured by the SAT However in recent years it has been reported that the difference between the two sensible heat fluxes AH H H cannot be neglected for the Webb correction e g Burba et al 2008 Ono et al 2008 The magnitude of the introduced error depends on the magnitude of AH not that of H That is the issue arises regardless of the absolute magnitude of H The non zero value of AH originates from the open path gas analyzer itself being the source of heating of the air within the measurement path The instrument can be heated due to its internal electronics or by solar radiation Burba et al 2008 proposed a correction method for AH for vertically deployed LI 7500s Thus the correction method is not applicable for LI 7500s that are deployed other than vertically The same method is also not applicable to other open path gas analyzers although they are also likely subject to the heating issue The issue of an open path gas analyzer being the sour
264. s in flux measurements Study group for flux measurement and evaluation The society of agricultural meteorology of Japan ed 22 26 in Japanese Ono K Hirata R Mano M Miyata A Saigusa N and Inoue Y 2007 Systematic Difference in CO Fluxes Measured by Open and Closed path Eddy Covariance Systems Influence of Air Density Fluctuations Resulting from Temperature and Water Vapor Transfer Journal of Agricultural Meteorology 63 139 155 in Japanese with an English abstract Ono K Mano M Hirata R and Miyata A 2009 A validation study of the practical corrections for sensor heating at Open path IRGA surfaces using computational fluid dynamics Proceedings of AsiaFlux Workshop 2009 Integrating Cross scale Ecosystem Knowledge Bridge and Barriers 92 Ono K Miyata A and Yamada T 2008 Apparent downward CO flux observed with open path eddy covariance over a non vegetated surface Theoretical and Applied Climatology 92 195 208 Ono K Miyata A Saito M and Harazono Y 2003 Calibration and inter model comparison of open path IRGA Proceedings of spring meeting of the Meteorological Society of Japan 83 339 in Japanese Pearman G I 1977 Further studies of the comparability of baseline atmospheric carbon dioxide measurements Tellus 29 171 181 Pearman G I and Garratt J R 1975 Errors in atmospheric CO concentration measurements arising from the use of reference gas mixtures different in composition to the sample ai
265. s look clean accumulated fine dirt or dust particles may be influencing the measurement Regardless of whether dirt or dust is apparent on the lenses it is advisable to clean the lenses regularly at a rate of once every 10days to once a month Refer to Appendix 2 2 5 for the effect on the measurement of dirt or dust on the lenses Finally application of water repellent such as Rain X Pennzoil Quaker State Company US on the lenses is recommended 4 Measurement of the absolute magnitude of CO number density The absolute magnitude of CO number density time averaged value is required to calculate CO fluxes from the data acquired by an open path gas analyzer An open path gas analyzer can measure the absolute magnitude of CO number density However because the measurement path of an open path gas analyzer is exposed to the atmosphere the lenses located at the end of the measurement path can easily accumulate dirt and dust The dirt or dust accumulated on the lenses influences the measurement of the absolute magnitude of CO number density See Appendix 2 2 5 for reference Thus if possible it is desirable to measure the absolute magnitude of CO number density or CO mixing ratio with a closed path analyzer Because the measurement with a closed path analyzer is intended for the evaluation of the time averaged values of the absolute magnitude of CO number density an analyzer with a relatively slow response time can be used However ma
266. s not necessary when a cell phone can be used It is even better if there is an Internet connection Data can be retrieved online but for data integrity it is safer to record and store the data onsite 20 1 3 Measurement variables recommendations and order of precedence 1 3 Measurement variables recommendations and order of precedence Measurement variables required for flux measurement and analysis and for the use of flux data are listed below Here the variables are ranked as essential A B or C according to their order of precedence mainly in terms of CO flux measurement Lower ranked variables may be adopted or rejected based on the purpose of the study 1 3 1 Variables essential for eddy covariance flux measurement turbulence fluctuation method The following variables are essential for energy or CO flux measurement 1 Three dimensional wind velocity fluctuation 2 Sonic virtual temperature fluctuation 3 Water vapor density or volumetric mixing ratio fluctuation 4 CO density or volumetric mixing ratio fluctuation 5 Air temperature humidity and atmospheric pressure These must be measured by sensors that have slow but stable responses 1 3 2 Micrometeorological and hydrological variables In addition to the eddy covariance technique the mean value of the following micrometeorological and hydrological variables can be measured Micrometeorological and hydrological variables are us
267. s possibilities such as reconnecting signal cables changing the power supply system and turning off electric devices such as pumps 106 2 7 Detection and reduction of noise Because the power source can easily cause noise and instrument malfunctions it is important to check the condition of the AC power source The power supply voltage can readily be tested with a tester Various types of power supply related noise such as those described above can also be checked with an oscilloscope Measures to reduce noise 1 Signal cables When noise is generated due to insufficient insulation resistance or shielding of a sensor it is recommended that the sensor be replaced with a reliable one When a signal cable transmits noise there are several possible noise suppression measures keep the cable away from the noise source e g electric devices and wireless LANs avoid looping the surplus cable use a twisted pair cable or a shielded cable keep the signal cable and the power transmission line some distance apart and cover the signal cable with metal foil or run the cable through a metal pipe The sampling frequency used for turbulence observations is approximately 10 Hz and high frequency components including the components at the power supply frequency i e 50 Hz or 60 Photo 2 7 1 Low pass filter for Hz or higher are spurious Therefore it is also effective to apply signal cables a low pass filter approximately 25 Hz
268. s suspended in the water with a float In either case the float and the sensor should be covered entirely with a tubular net to prevent wind and current from carrying away the device Also caution should be exercised to keep the sensing unit from touching the net 4 Tips Before the plants in a rice paddy start growing the water temperature is relatively uniform because the water bottom serves as a heat source When plants grow thickly the water surface serves as a heat source which allows thermal stratification to occur in the paddy Measuring the water temperature at more than one depth is useful for analyzing changes in the heat storage flux of a water body Tips 3 8 1 Calibration A water bath is used for calibrating water temperature sensors in a manner similar to that of air temperature sensors See Section 3 3 Air temperature 3 8 3 Irrigation and drainage Types of instruments The flow rate is the basic variable to be measured for studying irrigation and drainage When the flow rate is approximately 1 to 2 Lmin and there exists a sufficient elevation drop the flow rate can be directly measured using a bucket a beaker and a stop watch However long term continuous measurement of the flow rate requires the following instruments 163 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 Weir flow meter Running water is collected in a weir with a rectangular or triangular notch measurin
269. s used Tips 2 1 6 Tips Abnormal output data from SATs are frequently associated with the presence of raindrops When the probe of a slanted path SAT is deployed with its x y plane perpendicular to gravity the sensors are tilted and raindrops can slide off easily which is considered an advantage of slanted path SATs Furthermore as an option to guide raindrops away from the measurement paths mesh fabric called wicks can be placed on the sensors of the CSAT manufactured by Campbell Due to their presence around the sensors wicks may become a source of additional disturbance for the wind in the vicinity of the sensors However from the size of the wicks it is speculated that their influence on the wind is small Although caution is necessary wicks can be added and removed by the user Therefore it is possible to use wicks only during the rainy season in which the influence of rainfall on the sensors is expected to be large In principle the method of raindrop removal with wicks is also applicable to SATs of any other manufacturers Tips 2 1 7 Measurement errors intrinsic to SATs Errors associated with averaging over the measurement path The wind velocity and signal speed speed of sound obtained by a SAT are those averaged over the measurement path Fine scale fluctuations of a variable that occur at scales smaller than the path length are averaged i e path length averaging effect or line averaging effect Fluctuations of a
270. s well suited to the observation of wind velocity fluctuations in a short time span See Section 2 1 Ultrasonic anemometer thermometers SATs for details Those with a higher resolution of wind velocity approx 0 01 ms have come to be available at reasonable prices Hot wire anemometers In this instrument a wire is electrically heated while exposed to the ambient atmosphere Based on the temperature equilibrium between wire heating and wind cooling the wind velocity is calculated Although the instrument has high sensitivity at low wind velocities it cannot be used where rain and snow strike the heating wire and it cannot afford continuous long time measurement Therefore it is mostly used in indoor wind tunnel tests Measuring method Below an altitude of approximately 50 m which is within the surface boundary layer the profile of horizontal wind velocity tends to be logarithmic and vertical transport is approximately constant with height In the surface boundary layer or the canopy layer where substances and energy are directly exchanged the wind velocity distribution is complex For this reason representative values of wind velocity for a given observation point need to be measured above the canopy layer Weather stations carry out regular observations in flat open spaces that are unobstructed by obstacles such as buildings and trees The measuring height specified by the World Meteorological Organization is 10m above gro
271. sed on this method has been reported in the literature In some cases H O fluxes estimated from the difference between the sonic virtual and actual air temperatures differ from those estimated from other methods e g Gunji et al 2008 Matsuoka and Hayashi 2008 The combined use of a SAT and a thermocouple or another temperature sensor for the estimation of H O fluxes is currently under investigation and development Thus the present method cannot be recommended as a method for H O flux measurements at the present time as of 2008 2 2 3 Recent progress in addressing the effect of surface heating of open path analyzers as of 2011 Both the knowledge and technology of open path analyzers have progressed remarkably Three years have passed since this chapter was initially prepared in 2008 In the meantime three new models of analyzers that have overcome measurement difficulties specifically the effect of instrument surface heating on the CO flux measurement have been brought to market and are available for purchase today 2011 In this newly added subsection the recent progress in addressing the effect of the surface heating of an open path analyzer will be briefly described and the three new models together with their individual characteristics will be introduced As discussed in Appendix 2 2 3 the effect of surface heating of an open path analyzer is an issue in which the open path analyzer becomes a heat source creating errors in the CO
272. several wires may be installed around the sensor or fishing lines may be set up at locations on which birds will likely land Tips 3 1 4 Four component radiometers A four component radiometer is equipped with relatively small pyranometers and pyrgeometers Table 3 1 4 and Photo 3 1 6 One pair of sensors faces upward and the other pair of sensors faces downward Net radiation can easily be evaluated by adding the four radiation components For this reason four component radiometers are currently more often used than the above mentioned net pyrradiometers Table 3 1 4 Commonly used four component radiometers Model Manufacturer Spectral range um Temperature sensor of Pyranometer Pyrgeometer pyrgeometer MR 60 EKO 0 305 2 8 5 50 Body CNR l previous model Kipp amp Zonen 0 305 2 8 5 42 Body CNR 2 Kipp amp Zonen 0 310 2 8 4 5 42 None CNR 4 Kipp amp Zonen 0 300 2 8 4 5 42 Body NRO1 Hukseflux 0 305 2 8 4 5 50 Body Photo 3 1 6 Four component radiometers Left CNR 4 Kipp amp Zonen Photograph courtesy of Kipp amp Zonen B V Right MR 60 EKO Photograph courtesy of EKO INSTRUMENTS CoO LTD Measuring method As with other measurements of radiation components four component radiometers are deployed horizontally at a location at which the radiometers are not shielded from radiation in any direction As measurement errors may occur when the polyethylene domes or sensor protective covers
273. ssion 0060600 6600 5 1 2 2 Tower construction and maintenance cececececcecec eee eetece eee eens ee eee eneeeeseneeeneeeeseneneeaeaenens 7 1 2 3 Electric power supply 0106 660 11 1 2 4 Lightning surge countermeasures 0 6666 0 ee 14 12 5 Observation hit eesosa teres eGo wean teen caves Seid lena gee ed Mest deg bad a a ene eed heed 18 L26 Other osier ianei etn ale ain clare waide widen esto du arned Abalone ER EN EATE dint aa eSalecnted s EE RERE 19 1 3 Measurement variables recommendations and precedence seeeeeeeeeee eee eeeteeeeeeee eee e eee 21 1 3 1 Variables essential for eddy covariance flux measurement turbulence fluctuation method 21 1 3 2 Micrometeorological and hydrological elements ttttt tttttttttttttttttttrttttttetterrrrerttttettet 21 1 3 3 Structure and basic characteristics of a plant canopy tttseeettettttttteetesertstreteetesnertrtteteete t 23 Related information for chapter 1 ttsttsssss tstttttttstttstttsttitttitttititttttitttinitetttttitttttetttettntntetntt 25 2 Observation of Turbulence 2 1 Ultrasonic anemometer thermometers SATs eettttttestieestttitesssiieesriitissrrirerrrrriieerrrrernnterret 28 Appendix 2 2 1 Sample program ssssssseesseeseeeseeeeeeeeeeeeeeeeeeeveveveseseeeseseveeeseeeeeeeeeanas 40 2 2 Open path CO H2O gas analyzers sssssssssessseseeeeeeseseveeeeevevevevevevevevevevevevevenesesseeseeens 41 2 2 1 Measurement of fluctuating CO concentrati
274. st work permit Erosion control area The need for observations is not among the reasons for the designation of an erosion control area to be cancelled It is also virtually impossible to build permanent buildings in a location that is designated as an erosion control area This also applies to rivers Building facilities or roads in an area that has been designated as an erosion control area under The Sand Control Act or alongside rivers that have been defined as rivers by The River Act is extremely difficult However it is possible to obtain permission to construct a few temporary buildings in these areas not by obtaining a Construction Permit but by obtaining an Action Permit in an Erosion Control Area and River 1 2 Building infrastructure 4 Tips To renovate a boardwalk or an observation station located in a protected forest or in an erosion control area you must apply for the permits stated above each time Please remember this when you plan to make large scale repairs Tips 1 2 1 y Tips Although an observation facility is usually temporary The Building Standards Law requires you to obtain a construction certificate if you intend to use it for a long time period Besides obtaining land use permissions confirm whether you need to obtain a permit for building a tower and an observation house and if required follow the necessary steps for obtaining these permits Tips 1 2 2 1 2 2 Tower construction and maintenance Hei
275. surement uncertainties associated with variations in the observation location observation method and analysis method since the initial adoption of this technique Currently the observation data sharing that has been promoted by FLUXNET AsiaFlux and other related programs aims to inter compare data through direct means or through indirect means such as model validation and also to achieve an improved understanding of the regional scale carbon budget Therefore great care has been taken in order to eliminate data uncertainties including those associated with the use of the micrometeorological technique For example in Europe and Canada instrumentation and analysis techniques have been standardized by creating manuals since the beginning of the observational efforts Aubinet et al 2000 Fluxnet Canada 2003 and tower observations have been implemented in a systematic manner In Japan under the leadership of the AsiaFlux Steering Committee Current Practice of CO and Other Flux Observations in Measurements for Terrestrial Ecosystems AsiaFlux Steering Committee ed 2003 in Japanese 2007 in English was published which has Preface contributed to the improvement of observation and analysis standards and the establishment of an observation network by illustrating measurement and analysis techniques In 2004 with FLUXNET as the nucleus of the project a handbook with details on a wide variety of topics including the theory and technique of
276. suring instruments When the latter hut is close to the tower it has the advantage of requiring shorter wires The Forestry and Forest Products Research Institute uses commercially available tool sheds placed on a concrete foundation Photo 1 2 12 The floor has to be adequately strong to store heavy items such as gas cylinders For this reason concrete or other sturdy materials are used Steel transportation containers are used as a observation hut in countries where security is poor Many of the present observation sites of the Forestry and Forest Products Research Institute have huts just beneath the tower the reason being that such an installation has little effect on the tower This is particularly true in Japan where the forest canopy tends to be dense In contrast observations near the ground level in a forest should be performed far from the hut or tower When an observation hut is set up on an agricultural land on grassland or in an open forest with little vegetation it needs to be far from the tower When minimal amounts of data are to be collected it may be possible to avoid installing a hut at all in which case data loggers control loggers control equipment and measuring instruments can each be stored in separate measuring boxes Photo 1 2 12 An observation hut close to the tower Photo 1 2 13 A measuring box with desiccant center and a shed for gas cylinders right closet dehumidifier inside Sapporo forest meteorolo
277. t In the use of a voltage logger a precision resistor with a small temperature coefficient 1 kQ of resistance 0 1 accuracy metal film or wire wound resistor is inserted into the logger to convert current to voltage just before the logger Fig 3 1 1 2 Ifan extension cable is required a thick coaxial cable e g RGS8A U standard should be used 3 Because the BNC connector is not water resistant waterproofing measures should be taken to protect the connector by treating it with self bonding tape and then vinyl tape Photo 3 1 8 It is desirable to encase the device such as to avoid direct contact with water 4 Regular maintenance is required for the diffuser panel Alcohol should not be applied Logger resistance gt Logger Fig 3 1 1 LI 190 current output and resistance controlled voltage measurement Photo 3 1 8 Cable extended to LI 190 Left Wrap self fusing tape around BNC connecter to waterproof Right Female cable side and male sensor side connecter 4 Tips When connecting extension cable to LI 190 attach female terminal of BNC connecter BNC R Tips 3 1 5 126 3 1 Radiation 4 Tips The LI 190 has a built in interference filter to allow light of selected wavelength ranges to enter It is generally known that inference filters degrade from exposure to water When the LI 190 is used in a climate of high temperature and high humidity it needs to be waterproofed by the application
278. t is desirable to have as many measuring points as possible The radiation thermometer is suitable for measuring a wide range of vegetation surface temperature For its use caution has to be exercised regarding the influences observation angle radiation and shade made by the thermometer itself quantity and rate of radiation released by substances other than vegetation and the like 139 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 Photo 3 3 5 Shelter y Tips A shelter fan is prone to breakdown by the entry of foreign matter Whether the fan is revolving should always be checked and preparations for replacement in the event of trouble need to be made Particularly during the summer when small bugs are occasionally pulled into a shelter in large quantities a fan and a temperature sensing unit need frequent cleaning The frequency of cleaning can be reduced by installing a net that for a drain or a comer strainer in the kitchen sink over the shelter intake mouth Tips 3 3 4 Calibration Instrument error is simply calibrated with a reference instrument that is placed regularly at the same elevation as the one to be tested The reference instrument should be inspected by the manufacturer and age related changes should also be checked for It is desirable to exercise calibration with a commercially available thermometer test bath A waterproof thermometer is usually tested in a constant temperature water ba
279. t range 82 103 104 135 161 167 memory media 103 micrometeorological method 2 mixing ratio 21 41 48 49 55 65 84 145 National Forest 6 net ecosystem CO exchange NEE 21 22 86 net radiation 21 22 122 123 124 3 12 16 34 46 73 105 106 107 108 119 121 136 138 158 107 108 noise cut transformer 190 offset 117 120 35 36 48 49 52 53 54 55 56 65 80 open path CO gas analyzer 41 42 67 oscilloscope 106 107 paddy 160 162 163 PAR see photosynthetically active radiation parshall flume 164 165 PC see personal computer permeation 160 152 153 personal computer PC 48 51 52 53 63 72 79 97 103 104 105 124 166 167 permittivity of soil photodiode 116 photosynthetic photon flux density PPFD 124 photosynthetically active radiation PAR 21 22 124 125 129 167 photovoltaic cell 13 Pitot tube 132 133 Planck s constant 129 platinum resistance 143 147 thermometer 61 135 137 142 162 polymeric humidity sensor 142 143 power generation system 12 power restoration 11 power supply line 12 106 PPFD see photosynthetic photon flux density precipitation rainfall snowfall 22 23 156 preheat 167 pressure regulator 50 91 prevailing wind direction 2 32 43 44 46 131 134 programmable relay 79 98 protected forest 6 protective tube 12 proton transfer reaction mass spectrometer PTR MS 101 PTFE polytetrafluoroethylene
280. terminals the terminal may be covered to reduce the effects of radiation For the thermocouple thermometer the difference in shape and size between metal components of two different materials little 137 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 affects on the thermo electromotive force But the thermocouple thermometer is characteristically susceptible to noises because of high wire resistance to electromotive force For wire extension a compensation lead wire appropriate for each type of thermocouple should be used to compensate for the thermo electromotive force between thermocouple terminal and logger terminal For observations from a tower the copper constantan thermocouple T type which has high thermo electromotive force and low resistance is often used Because copper readily oxidizes care should be exercised against corrosion around the junctions In tower observations a device with two sheathed thermocouples in a shelter one as a dry bulb thermometer and the other as a wet bulb thermometer is often used for observing vertical distribution of temperature and humidity If high responsiveness is required of temperature measurement the following method can be used the ends of copper wire and constantan wire with a diameter of 0 1 mm or so are polished and applied with electric welding or silver soldering and then the junction is trimmed and covered with thin film insulator Although the device can be made by
281. th The AGC data are particularly useful for quality controlling the acquired data When output signals are recorded caution must be exercised on compensating for the time lag of the signal output After measurements are made by the sensor head of an LI 7500 they are processed in the control box This measurement processing requires time which causes a time lag in outputting the data The duration of the time lag varies according to the specified output format The product manual for the LI 7500 LI COR 2004 provides the following time lags for signal output 0 240 seconds for signal 46 2 2 Open path CO H O gas analyzers output in voltage and 0 186 seconds for sampling with SDM and RS 232C With the LI 7500 software the time lag can be increased in increments of 0 0065 seconds Consider the case in which the output signal is recorded in the SDM format with a time interval of 0 1 seconds If the time lag is increased by 17 units 0 0065 seconds x 17 0 1105 seconds the total time lag of the output signal becomes 0 297 seconds 0 186 seconds 0 1105 seconds which corresponds to three data values 0 297 seconds 0 1 seconds Therefore if the time lag of the SAT is zero the data from the SAT and from the LI 7500 can be synchronized almost perfectly by shifting the time series of data from the LI 7500 forward by three values The remaining slight mis synchronization 0 3 seconds 0 297 seconds 0 003 seconds is considered sufficien
282. th equipped with a water circulator and a temperature control unit 4 Tips For a test in a constant temperature water bath anti freezing solution is added to keep the water from freezing at low temperature Tips 3 3 5 140 Appendix 3 3 1 Unit conversion Conversion between Celsius C C and absolute temperature T K C T 237 15 T C 273 15 Conversion between Celsius C C and Fahrenheit X F 5 C gt X 32 gt xX 32 X 2C4 32 141 3 3 Air temperature Appendix Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 3 4 Humidity Humidity is the amount of water vapor in the air which is expressed by various indexes depending on the study objectives These indexes are mutually convertible although additional data including those on temperature and atmospheric pressure are required It should be noted that technical terms used for some types of humidity differ slightly between academic disciplines Appendix 3 4 1 Types of instruments The following are the main types of hygrometers that are used in most observations With the aim of avoiding radiation effects as in temperature measurement a shelter is used for all hygrometers except infrared ones Usually a thermometer and a hygrometer are placed in a shelter Wet and dry bulb thermometers One of the two juxtaposed thermometers is used as the dry bulb thermometer The other is used as the wet bulb thermometer This one is kept
283. the Earth surface is called shortwave radiation because the wavelengths of the solar radiation range between 0 3 and 3 um or between 0 29 and 3 um Solar radiation is classified into direct and diffuse radiation The direct and diffuse radiation combined together is referred to as global solar radiation Types of measuring instruments The calibration framework for radiation sensors has been established on the basis of the absolute radiometers that are maintained and managed by the World Radiation Center In addition the performance standard for radiation sensors is maintained by the International Organization for Standardization ISO The two main types of radiation sensors are thermopile type sensors and photodiode quantum type sensors The former are commonly used sensors while the latter are simplified sensors Thermopile sensors can be further classified into heat sink type and black and white type depending on how the temperature which is proportional to the solar radiation energy is evaluated Ohtani 1999b Most of the thermopile sensors distributed currently are of the heat sink type Pyranometers Various types of pyranometers are commercially available Table 3 1 1 and Photo 3 1 1 Thermopile pyranometers are equipped with a hemispheric glass dome to cover the heat plate A frost protection fan can 116 3 1 Radiation be installed to eliminate the influence of frost and to mitigate the zero offset problem The adverse influe
284. the high response characteristics of a PTR MS the disjunct eddy covariance DEC technique has been developed Rinne et al 2000 This technique conceptually falls between the eddy covariance method which relies on sensors with a fast response time and the REA method In the DEC technique atmospheric air sampling periods of less than 1 second are separated in time by intervals of no air sampling The values of w are recorded and the air samples are analyzed This technique aims to include the effect of small eddy transport by minimizing the sampling time as much as possible In practical use virtual disjunct eddy covariance VDEC Karl 2002 as modified DEC is also commonly used for flux measurement of several compounds An ion molecule reaction mass spectrometer IMR MS is another type of soft ionization mass spectrometer While an IMR MS is more expensive than a PTR MS the former spectrometer is able to analyze any gasses and the sensitivity of the spectrometer is as high as that of a PTR MS The IMR MS uses three gases Hg Xe and Kr as the primary ion sources Fragmentation i e break up of molecular ions into smaller pieces due to bond cleavage occurs more frequently in analyses with an IMR MS than in those with a PTR MS however an IMR MS can identify a substance by analyzing the fragments using multiple ion sources On the other hand multiple optional ion sources have become available for use in PTR MSs in recent years and the differe
285. the tank with a hose For deployment of a Parshall flume set it directly in an open channel If the channel width is larger than the flume inlet width the channel needs to be narrowed gradually from the upstream region to the flume inlet by creating an embankment or using other means Therefore in general a Parshall flume is not well suited for use in a concrete channel Regardless of whether a weir or a Parshall flume is used it needs to be deployed as designed usually horizontally in order to accurately calculate the flow rate from the water level Furthermore a weir must be securely anchored to a scaffolding pipe or other object so that it will not be shifted by the water flow In this procedure the flow rate during heavy rainfall and the weight of the weir full of water need to be thoroughly taken into consideration As for water meters they should be installed directly to spigots with reducer or increaser pipes or similar devices as necessary The water level in a weir or a Parshall flume should be measured at 10 to 30 minutes intervals using a capacitive or hydrostatic water level meter As auxiliary data record the irrigation and drainage conditions during each site visit Calibration Prior to the use of an unconventional weir create a water level discharge curve by evaluating the relationship between the water level and the discharge based on measurements For measuring the flow rate water that flows out of the weir within a given tim
286. thermometers SATs Water vapor correction Rigorous calculation of the sensible heat flux requires the use of the air temperature T K rather than the sonic virtual temperature Tw that is calculated in Equation 2 1 5 The sonic virtual temperature Tw can be related to the air temperature T as T 1 032 2 1 6 P where p Pa and e Pa are the atmospheric and water vapor pressures respectively If e lt lt p e 1 fi 0 32 z 1 0 32 and also0 32 0 32 0 32g 0 51q Here mg is the molecular P P P p e My weight of dry air kgmol my is the molecular weight of water vapor kgmol and q is the specific humidity kgkg Accordingly the relationship T 1 0 514 r 2 1 7 is a close approximation for Equation 2 1 6 Similarly the fluctuating components of Ta Tu and q can be related to one another as T T 0 51T q 2 1 8 The effect of water vapor on the sensible heat flux evaluated from SAT measurements can be corrected in the following way if the instantaneous values of air pressure and water vapor pressure are available the instantaneous value of T can be calculated from that of 7 and Equation 2 1 6 The calculated instantaneous value of 7 can in turn be used to calculate the sensible heat flux Alternatively the effect of water vapor can be corrected in an approximate sense using Equation 2 1 8 together with the individually calculated values of sonic virtual temperature flux w
287. tic solar tracker average wind direction average wind velocity Avogadro s number back up power supply 11 50 81 133 105 116 126 7 19 balance gas Bernoulli s law binary format black body BNC connector boardwalk 188 calibration 18 41 42 45 48 49 50 51 52 53 54 55 56 57 58 63 67 71 72 80 81 87 116 119 121 124 127 132 133 135 140 142 144 155 158 159 160 162 163 165 135 41 51 52 53 54 71 72 78 88 calibration frequency calibration gas 91 93 99 canister 92 98 100 capacitive water level meter 161 164 cavity ring down spectroscopy CRDS 102 53 82 160 164 165 166 13 channel charge controller 102 55 41 57 67 68 69 70 chemiluminescence closed path CO analyzer closed path gas analyzer 74 78 83 84 87 CO concentration 18 41 50 57 58 65 67 68 70 72 78 79 80 81 82 83 84 86 87 88 90 94 95 measurement 50 67 CO molecule 41 56 CO storage change 22 86 87 94 95 coaxial cable 126 cold junction 137 138 circuit 147 cold trap 100 comma separated value format CSV 103 105 commercial power 3 11 12 compensation lead wire 138 147 correcting flux loss 44 47 64 CRDS see cavity ring down spectroscopy cross sensitivity 41 42 58 cryofocus 100 CSV see comma separated value format 128 130 131 culmination time cup anemometer data logger 18 34 35 40 72 78 79 88 94 98 103 104 105 108
288. tion Ver 1 0 Chapter 3 Stefan Boltzmann law the infrared radiation that passes through the dome Ra Wm can be expressed as follows R gt n oT 3 1 1 k where AE thermopile output voltage mV k thermopile sensitivity mV Wm o Stefan Boltzmann constant 5 67051x10 Wm K and T sensor body temperature K The use of a silicon dome mitigates dome heating caused by the solar radiation absorbed by the dome However dome heating cannot be completely eliminated and accurate measurements sometimes require corrections for the effect of the heated dome The most commonly used correction formula was proposed by Albrecht et al 1974 and can be expressed as AE Ran 408 kat ar 3 1 2 where ka dome coefficient and Ta dome temperature K Furthermore Hirose and Shibata 2000 proposed the following equation for evaluating the infrared radiation passing though the dome R E tkot k oT k o T T 3 1 3 where k k2 k3 coefficients associated with the temperature of the infrared radiometer The values of infrared radiation calculated with Equation 3 1 3 agreed well with the values observed according to the global standard instituted in 2006 Ohkawara and Takano 2008 However because the performance of individual infrared radiometers cannot be easily checked against the infrared radiometer certifying device owned by the Aerological Observatory of Japan either Equation 3 1 1 or Equation 3 1 2 is frequently em
289. tion term which contributes to the CO flux Webb et al 1980 Lee and Massman 2011 These features are advantages of the LI 7200 However caution is necessary because water vapor H20 fluctuations in a similar manner to air temperature fluctuations become attenuated in the process of drawing sample air Because the suction tube of the LI 7200 is short the attenuation of water vapor fluctuations inside the tube is smaller for this model than for other models of closed path analyzers that is approximately 10 of the signal is attenuated LI COR 2011b Nonetheless this value cannot be neglected and adequate corrections are necessary for the attenuated water vapor fluctuations Incidentally Campbell initiated the sale of a closed path analyzer the EC155 which possesses features similar to those of the LI 7200 As discussed above the measurement theory and hardware technology in the field of CO flux measurements with an open path analyzer are in the process of advancement Therefore users need to pay attention to announcements from manufacturers as well as published papers so that newly acquired knowledge can be incorporated into ongoing observations 62 2 2 Open path CO H O gas analyzers Appendix Appendix 2 2 1 Serial number specific characteristics of the LI 7500 LI COR Ever since the LI 7500 became commercially available in 2000 LI COR has been continuously modifying and improving the product Therefore precautions are nec
290. tly small to be neglected for most sites To summarize when an LI 7500 is used for observation the time lag of the signal output needs to be adjusted according to the signal output format the time lag of the SAT and the data recording interval so that the total mis synchronization within the system becomes sufficiently small No descriptions of the time lag of the output signals are provided in the product manuals for the E 009 or the OP 2 When these open path gas analyzers are used the time lag should be considered equal to zero Alternatively cross correlation can be used to estimate the time lag Calculate the cross correlation coefficient of the output signals from the SAT and those from the analyzer as a function of the time lag The time lag at which the cross correlation coefficient reaches the maximum value is used as the time lag of the output signals of the open path gas analyzer with respect to the SAT The use of the latter approach implicitly includes a partial correction of flux losses due to the sensor separation in the along wind direction Therefore when this estimation approach is adopted caution is necessary to avoid over correcting flux losses in the course of the flux calculation The time lag of the output signal influences the flux calculation significantly at sites at which the contribution of the co spectra at high frequencies to the total flux is large e g grassland The issue of the time lag of the output signal needs
291. tp www onsetcomp com Campbell Scientific Inc US 107 L http www campbellsci com Platinum resistance CLIMATEC Inc Japan C HPT 5 JM http www weather co jp in Japanese Radiation thermometer CHINO Corporation Japan IR SAB http www chino co jp english Heat flux transducer 3 6 PREDE CO LTD Japan PHF 100L EKO INSTRUMENTS CO LTD Japan MF 180M http www prede com file 32html htm http www eko usa com Soil moisture sensor Decagon Devices Inc US EC 5 Capacitance Frequency Domain Method http www decagon com Campbell Scientific Inc US CS616 L Time Domain Reflectrometry Method http www campbellsci com Stevens Water Monitoring Systems Inc US Hydra Probe Soil Moisture and Salinity Sensor Amplitude Domain Reflectrometry Method http www stevenswater com Delta T Devices Ltd UK ML2x Sentek Pty Ltd Australia EnviroSCAN 172 http www delta t co uk http www sentek com au Related information for chapter 3 Tensiometer O Daiki Rika Kogyo Co Ltd Japan DIK 3042 http www daiki co jp en O CLIMATEC Inc Japan UNSUC CSK 5500EL http www weather co jp in Japanese O UIZIN Co Ltd Japan UIZ SMT http www uizin co jp in Japanese 3 7 Tipping bucket rain gauge O Yokogawa Denshikiki Co Ltd Japan WBO0011 http www yokogawa com jp ydk O Onset Computer Corporation US HOBO Data Logging Rain Gauge RG 3n http ww
292. tube Use a separate temperature sensor instead to evaluate the temperature inside the calibration tube The 54 2 2 Open path CO H O gas analyzers product manual for the OP 2 ADC 2003 calls for at least 3 point calibration for H O as the H O output is expressed in a quadratic expression Finally application of the calibration results to the observational data is considered Over a period of observation the sensitivity and offset of an open path gas analyzer sometimes change significantly In this case the method of application of the calibration results to the observational data needs to be considered Because the change in the sensitivity of the analyzer influences the flux co variance calculation the sensitivity change cannot be taken lightly If CO number density mixing ratio data have been simultaneously collected with a closed path analyzer the time averaged values of these data can be compared to those of the CO number density from the open path gas analyzer The result of the comparison can sometimes be used to evaluate the temporal change in sensitivity If no CO number density mixing ratio data are available from a closed path analyzer or an evaluation of the temporal change in sensitivity was not possible from the comparison choose either of the following methods 1 apply the new value of the sensitivity since a particular date chosen by the investigator and 2 adjust the data using a mathematical operation that
293. tube for the LI 7500 which is an accessory for the LI 7500 is equipped with a thermistor thus the above mentioned unit conversion for the CO gas in the cylinder can be easily made using the data from the pressure meter inside the control box If a separate pressure meter is available the measurement of the pressure inside the calibration tube can also be made If an E 009 or OP 2 is used for observation a temperature sensor can be attached inside the calibration tube Alternatively the temperature sensor can also be attached to the outside wall of the calibration tube The temperature measured by the temperature sensor and the pressure near the calibration tube or a constant pressure value e g 101 3 kPa are used for the unit conversion for the concentration of the CO gas in the cylinder Frequency of calibration is an important factor to consider The CO flux observational group of NIAES has extensive experience in using the open path gas analyzers listed in Table 2 2 1 When all factors are considered together along with the knowledge acquired from experience the CO flux observational group recommends the following frequencies for calibration once every month to three months for the E 009 and the OP 2 once or twice a year for the LI 7500 The change in the calibration coefficients with time for each of the three analyzers is provided in Ono et al 2003 and Ono et al 2007 When the user has become familiar with the calibration proced
294. tubing is employed all of the moisture in the sampled air cannot be removed completely In order to enhance the efficiency of moisture removal the flow rates of the sampled air and purge gas may be adjusted or multiple dehumidifiers can be connected to the air sampling system Although the adoption of either method does not result in zero water vapor concentration these methods can reduce the water vapor concentration in the sampled air and eliminate almost all of the fluctuations of the water vapor concentration That is the influence of water vapor concentration fluctuations on CO concentration fluctuations can be eliminated Tips 2 3 12 7 System control methodology Changing the flow path with solenoid valves to introduce calibration gas is the minimum system control required for a closed path measurement system for the eddy covariance method In the course of switching to the calibration gas the pump may need to be powered off depending on whether the sub sampling method is used When the sub sampling method is adopted the exhaust vent is available for sampled air upon injection of calibration gas Thus the pump does not need to be powered off On the other hand when the sub sampling method is not adopted the pump needs to be powered off upon the solenoid valve switchover or an exhaust vent is required During the injection of the calibration gas continue recording the output signals from the CO analyzer with a data logger in t
295. ty devices for power saving and restarting of observation The main precautions to take when using solar panels are as follows 1 solar panels should be used so that the wind impact on the flux sensors is minimized 2 the wind resistance of the panel is high so care should be taken that the tower or the panel is not blown away by the wind 3 the electrical resistance of wiring should be small and loss of power should be minimized and 4 care should be taken to avoid electric shocks caused by 13 Photo 1 2 8 A flux observation tower using solar cells Tura Russia Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 1 the electric current in the panel Measures such as light shielding should be taken when work is performed in the vicinity of the panels An example of a flux observation tower using solar cells is shown in Photo 1 2 8 Tips When a lead storage battery becomes overly discharged the precipitated lead sulfate forms hard crystals on anode of the battery This is called sulfation and these crystals have a low solubility which makes it practically impossible to recharge the battery Deep cycle batteries are the same because they are lead storage batteries in principal However their electrode are strengthened to make them more discharge resistant than ordinary lead storage batteries Tips 1 2 5 y Tips Solar panels should be set up to achieve the maximum possible production of electricity Sun
296. ules Open path gas analyzers for HO measurements can be classified into open path IRGA and open path ultraviolet gas analyzers according to the wavelengths of radiation used As described in the beginning of this section open path IRGA are able to measure H O and CO simultaneously and are the main gas analyzers used for flux observations at the present time Unless there exist specific reasons for choosing ultraviolet gas analyzers the use of open path IRGAs recommended for H O flux observations H O flux measurements are also possible with thermocouples Though it is not strictly open path gas analyzer the methodology that involves the use of thermocouples will be introduced briefly in this section The characteristics of each type of sensor are summarized below 1 Infrared gas analyzers Refer to the section on CO measurement Section 2 2 1 Measurement of fluctuating CO concentration by an open path gas analyzer for the methods of deployment maintenance and calibration as well as for the characteristics of open path IRGAs Information on commercially available open path IRGAs can also be found in the same section 2 Ultraviolet gas analyzers The measurements of open path ultraviolet gas analyzers are based on the ultraviolet absorption characteristics of H O According to the particular wavelengths of ultraviolet radiation Lyman alpha radiation or the radiation source Krypton tube that is used for these analyzers open path
297. und Japan s Automated Meteorological Data Acquisition System AMeDAS conducts observations at 6m above ground If research measurement is carried out from a tower it is desirable to install the instrument as far away from the tower as possible with the help of devices such as arms in order to avoid having the tower affect the measurements The tower s effects can be minimized by projecting the instrument in the prevailing wind direction Photo 3 2 1 When a Photo 3 2 1 Installed anemometer Fujiyoshida measurement box is installed in the tower it should be placed at a different elevation from that of the Boney ineteorolagy mca Sel 131 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 anemometer to minimize its influence By observing the wind velocity in a vertical profile with anemometers placed at four or five elevation points above the forest canopy the friction speed can be calculated In this case as the profile of wind velocity above the canopy tends to be logarithmic anemometers should be placed more densely as one moves toward the lower heights to obtain a logarithmic profile of wind velocity with height Anemometers of cup type and windmill type contain moving parts Such anemometers need to be cleaned and lubricated to maintain smooth rotation for long use Electromechanical components must be replaced and recalibrated regularly In cold snowy regions attention has to be paid to snow and i
298. und cable protective tube O Furukawa Electric Co Ltd Japan EFLEX http www furukawa co jp english Power generation system and Power supply devices O Natural sky network Japan http www natural sky net in Japanese Selection of solar power generation system and example of electric power calculation http www natural sky net learn index_study solar html in Japanese Campbell Scientific Inc US http www campbellsci com Lightning surge countermeasures Sankosha Co Ltd Japan YO8U 75B http www sankosha co jp en O Fuji Electric Technica Co Ltd Japan http www fujielectric co jp technica in Japanese O Shoden Co Ltd Japan http www sdn co jp eng Morinaga Electronic Co Ltd Japan http alp plp co jp eng Storerooms Yodogawa Steel Works Ltd Japan http www yodomonooki jp in Japanese INABA SEISAKUSHO Co Ltd Japan http www inaba ss co jp in Japanese 25 26 Observ Turbule Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 2 1 Ultrasonic anemometer thermometers SATs When scalar fluxes are measured using the eddy covariance method the fluctuating components of the wind velocity need to be measured regardless of the type of scalar of interest In the observation of the fluxes across the interface between the Earth s surface and the atmosphere the vertical exchanges of energy and scalar quantities are important Therefore flux observat
299. uple Measuring H20 with a thermocouple psychrometer A pair of dry bulb and wet bulb thermocouples i e a thermocouple psychrometer can be constructed with fine wires 50 100 um in diameter fine wire thermocouples to measure the air temperature The difference in air temperature measured by the pair of thermocouples is used to evaluate H20 concentration A number of combinations of metals can be used to construct thermocouples They include the combinations of copper constantan chromel constantan and chromel alumel Although construction of high quality finished thermocouples may be difficult at first thermocouples can be constructed in house and at low cost by users For methods of constructing thermocouples refer to Section 3 3 Air temperature RAKIZ HAM AYE Handbook of forest environmental survey environmental measurement in forest 1999 in Japanese and 2 4 xAOWP eH EYE Instruments and measurement techniques in agricultural meteorology 1988 in Japanese Other advantages of the use of a thermocouple psychrometer include the following 1 the temperature measurement is highly accurate 2 the measured value is not subject to the effect of line averaging because of the small sensing elements of the thermocouple psychrometer and 3 a thermocouple psychrometer has little influence on the wind velocity 58 2 2 Open path CO H O gas analyzers measurement of a SAT On the other hand the following a
300. ure of an open path gas analyzer only 5 to 6 hours are necessary to complete the entire calibration procedure including the warming up time for the analyzer prior to calibration In this case the open path gas analyzer can be taken back to the laboratory in the evening for calibration After completing calibration during the night the analyzer can be brought back to the observational site for re installation the next morning In contrast if the user is not yet familiar with the calibration procedure multiple attempts may be necessary to carry out the entire procedure and calibration may take up to 1 to 2 days During the calibration period no data can be collected in the field Therefore the timing of calibration should be planned in advance in order to avoid time periods during which flux data are necessary Cleaning of the lenses located at the end of the measurement path is at least as important as the frequency of calibration Refer to Measurement Method 3 Maintenance and Appendix 2 2 5 The offset due to dirt or dust accumulated on the lenses is generally larger than the changes in offset and calibration coefficients of the individual analyzer particularly for the LI 7500 thus the lenses of the analyzer need to be cleaned periodically Here 1 the equipment necessary for calibration and 2 the procedure for calibration will be discussed The discussions will assume the use of an LI 7500 and will include calibration for H O Subsequ
301. uring heavy rainfall wj Photo 3 6 3 Soil profile created for the installation of a soil moisture meter EC 5 Terrestrial Environment Research Center University of Tsukuba Photograph courtesy of Shinichi Iida FFPRI Caution is required to avoid breaking the porous cup of a tensiometer when it experiences stress while being inserted into soil As the water in the tensiometer air pool gradually lessens the air pool needs to be re supplied with water when necessary so that it won t become empty When supplemented water in the porous cup is opened up to the atmosphere and it takes one to 24 hours for the sensor to resume a correct value Caution should be exercised so as to avoid damaging the sensor under excessive pressure when the air pool is capped and installed The above ground components including the pressure sensor should be shaded from the sun If they are directly exposed to sunlight and their temperature fluctuates air expands contracts in the air pool and temperature drift occurs in the sensor output which causes significant measurement errors If the water in the tensiometer freezes the sensor may stop operating During the freezing season observation needs to be suspended after water is discharged With the help of the following soil water characteristic curve equation the volumetric water content and the matric potential are mutually convertible 154 3 6 Soil moisture 0 Y c 3 6 4 alg sat
302. urpose A mass flow controller not only allows highly stable flow rate control but can also suppress pressure fluctuations due to pump pulsation 68 2 3 Closed path CO gas analyzers J Branch gt Sample Air O Port Inlet P 2 R By Choice nnaasnananannnnnnnnsn Sili l 4 Branch port ron Soia ge Solenoid Valve i i Dehumidified Air SK Manual Valve Inside the Main Case z ZN C O LEETE lt lt Control Line H OEL HA umo O f j i Flow Meter AF 1 NO Air Dryer SV 1 Nc NES m com LI Air Filter FM 2 SV 2 NO h ne H F m StdGas Zero l LI 6262 LI 7000 IRGA AF 2 Exhaust MEGA com lt H i Sample cell j i aL mint i Reference cell i S ee rca ee ii i 20mLmin LG TT StdGas Span CO N mansnnannan r De COz2 desiccant assembly ZEN l Programmable Sequence Controller Fig 2 3 1 An example of an air sampling system that includes a closed path CO gas analyzer Figure Ohtani et al 2001 partially modified Photo 2 3 1 The air sampling system that includes a closed path gas analyzer from Fig 2 3 1 69 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 Tips Dust generated from the pump within the air sampling system as well as insects and dust in the air can accumulate in the interior of the system piping and the cell of the CO analyzer To keep the system and cell interior free from d
303. ust and insects the use of an air filter is recommended For better results the air filter should be placed at the inlet of the suction tube immediately after the pump and immediately before the CO analyzer The air filters that come with CO analyzers manufactured by LI COR are PTFE membrane filters with a pore diameter of 1 um Because similar filters are commercially available the investigator can pick any alternatives to the LI COR filters that can be easily handled e g filters manufactured by Toyo Roshi Kaisha Ltd Japan Tips 2 3 1 v Tips When moisture is removed from the sampled air H O concentration in the air cannot be monitored and moisture fluxes cannot be calculated with the closed path gas analyzer Advantages of moisture removal include the elimination of the need for the WPL correction and a reduction in the accumulation of dirt inside the sample cells On the other hand because the sample cells of the LI 7000 can be removed and cleaned the analyzer can be used for long term measurements without removing moisture from the sampled air Tips 2 3 2 Reference cell Closed path gas analyzers LI 6262o0r LI 7000 evaluate the CO concentration or HO concentration of the sampled air from the difference between the infrared radiation absorbed by the air in the sample cell and that absorbed by the air in the reference cell Therefore when the absolute magnitude of the CO concentration is sought the reference cell nee
304. uze for a wet and dry bulb thermometer it has to be boiled well enough to remove accretions such as starch and oil and then it has to be dried cleanly The use of distilled water is desirable to moisten the gauze and the wet bulb should always be kept wet with a thin film of water The wet bulb sensing unit is positioned approximately 2 cm above the tank water surface and the water level is maintained constantly Periodical maintenance is also required to keep the dry bulb from collecting dirt and water droplets The polymeric humidity sensor has its sensing unit stored in a resin case which is equipped with a dust filter to protect the sensor Attention should be paid to dirt on the dust filter and the sensor Distilled water can be used to remove stubborn dirt A humidity measuring chip is particularly fragile and it has to be handled with great care As is true for temperature measurement dirt caught in the shelter should be removed regularly 143 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 3 The cell of an infrared hygrometer has to be kept clean with regular maintenance using a sponge and 50 ethanol If a closed path hygrometer is connected with a tube to intake air samples the tube needs to be regularly inspected cleaned and replaced to prevent leakage staining internal condensation and intrusion of rainwater Instrumental errors between hygrometers are more pronounced than those between thermometers To measur
305. varies among measurement systems and the investigator needs to be aware of the frequency response characteristics of the particular measurement system from the power spectra and other data obtained from the system If the contribution of the attenuated fluctuations to the fluxes is significant corrections need to be made to the CO concentration data high frequency fluctuation correction A number of correction methods have been proposed however the influence of the choice of the correction method is small for observational sites such as forest sites where the periods of fluctuations that contribute to fluxes are relatively long A number of publications are available on high frequency fluctuation correction Refer to Appendix 2 3 1 for some of these publications 83 Practical Handbook of Tower Flux Observation Ver 1 0 Chapter 2 4 Tips When measurements are made with a closed path gas analyzer air temperature fluctuations of the sampled air become attenuated in the course of transportation through the tubing Therefore the influence of the correction for air density fluctuations the WPL correction becomes small The correction amount is small If 1 the tubing is long 2 air temperature fluctuations are negligibly small and 3 moisture has been removed from the sampled air then the WPL correction will not be necessary Suyker and Verma 1993 Furthermore if water vapor concentration is simultaneously measured with CO concent
306. veraging errors Boundary Layer Meteorology 119 375 395 Ishida S Matsushima D Higuchi A Hiyama T Toda M Asanuma J Tamagawa I Miyazaki S Tanaka K Sugita M Nagai H Tanaka H Iida S and Kobayashi N 2004 Intensive Field Campaign 2001 Preliminary Results in Inter comparison of the Turbulent Sensors Journal of Japan society of hydrology and water resources 17 43 60 in Japanese with an English abstract Ito Y Hayashi T and Tamagawa I 2001 Performance test of sonic anemo thermometer TR 61A 120 intersecting probe Annual Report 2000 of research project Accurate evaluation of energy and water balance 1 9 http atmos cc okayama u ac jp flux TR61A PDF in Japanese Japanese Industrial Standards JIS Z 8806 2001 Humidity Measurement methods Japanese Standards Association Kaimal J C and Finnigan J J 1994 Atmospheric boundary layer flows Oxford Univ Press 289pp Kaimal J C Gaynor J E Zimmerman H A and Zimmermann G A 1990 Minimizing flow distortion errors in a sonic anemometer Boundary Layer Meteorology 53 103 115 Kaimal J C and Gaynor J E 1991 Another look at sonic thermometry Boundary Layer Meteorology 56 401 410 Karl T G Spirig C Rinne J Stroud C Prevost P Greenberg J Fall R and Guenther A 2002 Virtual disjunct eddy covariance measurements of organic compound fluxes from a subalpine forest using proton transfer reaction mass spectrometry Atmospheric Chemistry and Ph
307. w onsetcomp com Snow gauge Niigata Electric Co Ltd Japan SDM 301s http www snowcon com in Japanese O SONIC CORPORATION Japan SL 370 http www u sonic co jp english Campbell Scientific Canada Corp Canada SR 50A http www campbellsci ca Snow weight meter O Niigata Electric Co Ltd Japan MN 301s http www snowcon com in Japanese 3 8 Ultrasonic water level meter O Keyence Corporation Japan UD 300 series http www keyence co jp O General Electric Company US PDCR PTX 1730 1740 http www ge mcs com en Capacitive water level meter Unidata Pty Ltd Australia Model 6521 series http www unidata com au Senecom Inc Japan Trutrack series http www senecom co jp in Japanese Hydrostatic water level meter CLIMATEC Inc Japan agency of CSTS series http www weather co jp in Japanese Hydrological observation weir Environmental Measurement Japan CO LTD Japan MIJ 09K http www environment co jp in Japanese Senecom Inc Japan Parshall flume http www senecom co jp in Japanese IKEDA KEIKI MANUFACTURING INC Japan PF series http www ikeda keiki co jp in Japanese Measuring weir in general O Takeuchi Tekkosho Japan ph 81 562 82 7851 3 9 Multi channel data logger O Campbell Scientific Inc US CR1000 CR800 http www campbellsci com Etodenki Coporation Japan CADAC2 CADAC21 CADAC3 http www etodenki co jp
308. wet with gauze applied to a sensing unit and fed with water from a tank Evaporative heat loss causes the wet bulb to cool There is a relationship between the amount of water vapor in the air and the temperature marked by a wet and dry bulb thermometer This relationship is used to determine the humidity To automatically observe the vertical distribution profile of temperature and humidity platinum resistance thermometers and sheathed thermocouple thermometers are most commonly used The Assman ventilated psychrometer incorporates a mercury thermometer which makes the unit portable It also has high measurement accuracy For these reasons it is used as a handy calibration instrument Dew point hygrometers Taking advantage of the electric conductivity of lithium chloride which is highly hygroscopic this hygrometer indicates the resistance value in response to the dew point temperature Under high humidity conditions it is capable of continuous measurement with high accuracy This makes it well suited to observation in snowy areas However it cannot function in low humidity where the equilibrium temperature is below the atmospheric temperature Dew point hygrometers of a cooling type are relatively expensive In this instrument a mirror placed in the air is cooled and temperature is measured when frost forms on the mirror surface Polymeric humidity sensors Moisture sensors made of polymeric organic substances measure humidity by detecting
309. wind velocity fluctuations For this purpose a mass flow controller is used to maintain a constant flow rate Finally care is necessary to prevent water from entering the analyzer and to prevent water vapor from condensing inside the analyzer 4 Tips The Campbell CR1000 is equipped with a terminal with a switch for 12 V DC output SW12 terminal Because the SW12 terminal can supply up to 900 mA of electric current at a temperature of 20 C this terminal can be used for direct control of solenoid valves On the other hand the digital I O ports C1 through C8 can output only up to 2 0 mA of electric current at 3 5 V and thus a relay circuit is necessary for using these ports for control An example of such a circuit is shown in Chapter 5 of the CR1000 Operator s Manual Tip 2 5 1 102 2 6 Data logger 2 6 Data logger When flux measurements are made with the eddy covariance method multiple observational values need to be simultaneously logged at a sampling rate of approximately 10 Hz When turbulence statistics are sought the data storage capacity needs to be sufficiently high so that the values of the fluctuating component of w w and of the fluctuating component of a scalar quantity can be stored for several days The data recorded on the data logger can be transferred to a PC with the use of a communication cable or by swapping the media on which the data are recorded The use of a versatile digital data format such as th
310. ysics 2 279 291 Kelliher F M Leuning R Raupach M R and Schulze E D 1995 Maximum conductances for evaporation from global vegetation types Agricultural and Forest Meteorology 73 1 16 Kohsiek W 2000 Water vapor cross sensitivity of open path H O CO sensors Journal of Atmospheric and Oceanic Technology 17 299 311 179 Practical Handbook of Tower Flux Observation Ver 1 0 Komori D Aoki M Ishida T Suzuki S Satou T and Kim W 2004 Development of an air Sampling system for true eddy accumulation technique Journal of Agricultural Meteorology 60 4 263 272 Kondo J and Sato T 1982 The determination of the von Karman constant Journal of the Meteorological Society of Japan 60 461 471 Kormann R and Meixener F X 2001 An analytical footprint model for non neutral stratification Boundary Layer Meteorology 99 207 224 Kristensen L and Fitzjarrald D R 1984 The effect of line averaging on scalar flux measurements with a sonic anemometer near the surface Journal of Atmospheric and Oceanic Technology 1 138 146 Laubach J Raschedorfer M Kreiletn H and Gravenhorst G 1994 Determination of heat and water vapour fluxes above a spruce forest by eddy correlation Agricultural and Forest Meteorology 71 373 401 Lee X 1998 On micrometeorological observations of surface air exchange over tall vegetation Agricultural and Forest Meteorology 91 39 49 Lee X and Massman W J 2011 A perspective on thirty

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