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User's Guide MICROTOPS II

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1. Menu Enter LJ oO E D Figure 9 Setting the number of top ranking samples 15 3 2 1 5 Restoring factory calibrations The factory calibrations can be recalled in case a change is made that inhibits proper operation of the instrument This operation restores all initial calibrations and measurement settings Restore calibr Yes gt gt The path to the restore screen is shown in Figure 7 The user is presented with the following screen When the above screen is displayed the button triggers the re store operation Escape or Enter buttons leave to upper menu level without restoring the calibrations The current calibration settings can be printed via the serial port using function X in the remote menu see page 27 3 2 2 Data processing The settings that can be modified by the user include scan length the number of samples selected for averaging and the line fre quency of the local power distribution system The first two pa rameters are selected to suit most conditions and should not be changed except under special circumstances Setting the local line frequency affects the internal digital filter s transfer function and enables elimination of line interference 3 2 2 1 Scan length In order to achieve best performance the Microtops II is able to perform a series of rapid samples of all channels within one meas urement scan Processing a series of samples allows for t
2. year Real time and date for the solar zenith angle calculation is provided by the on board clock The in herent accuracy of low power crystal clocks is not adequate for long periods of time therefore a clock trimming mechanism is implemented in the software The user can enter the clock correction in seconds 30 days and the program will periodically skip or add a few seconds in order to main tain the clock accuracy to within 5 seconds 9 3 3 Sun targeting While optionally equipped with the hardware for tripod mounting the MICROTOPS II is designed primarily for hand held operation There was even concern about the accuracy of pointing the meter towards the sun A series of tests indicated that in the hands of a well trained operator the instru ment can move up to 1 off the sun s center Presence of strong wind or cold weather may further degrade the steadiness of the operator s hand To enhance the sun targeting accuracy in the MICROTOPS II an algorithm was implemented that analyzes a series of rapidly repeated measurements A signal strength factor is calculated based on the signal from all 3 UV channels Only the records with highest ranking signal strength factor are averaged and passed for further processing These are the records for the best positioning of the sun s image The total number of samples in a scan as well as the number of samples averaged can be set by the user Figure 29 presents the results of three consecutive
3. 19 22 23 25 26 28 34 solar zenith angle 10 16 17 43 45 SUD target isse NN 5 T time and date 2 e 10 U User calibration eee 33 user Calibrations 12 27 id EE 10 26 45 54 Solar Light Co Inc Instruction Manual Update Version 2 4X Appendix 1 Interpretation of the data The corrected ozone value is based on measurements on two pairs of wavelengths 305 5 312 5 and 312 5 320nm This algorithms reduces the error introduced by aerosol absorption on each UV chan nel For airmass gt 3 the single channel measurement 305 5 312 5 is generally more reliable The formula for corrected ozone calculation in version 2 4X software is as follows e n rs ts me a 0 a o 1 where Io is the extraterrestrial constant of the channel I is the measured signal a and D are the ozone and Rayleigh absorption cross sections respectively m and pare optical airmass for air and ozone and P and Py are the barometric pressure and normal pressure respectively The indexes 1 3 identify the three channels 305 5 312 5 and 320 nm
4. Inc 7 2 Quick start 2 1 Power up To turn ON MICROTOPS II press the ON OFF switch for about 1 2 second It will not react to a brief touch For about 1 second the display shows Hardware test message and the version number of the firmware loaded into the instrument For the next 2 seconds the Initialization keep covered message is displayed Keep the top window cover closed until the display shows RDY ready mode To turn the instrument OFF press the ON OFF button again It will turn off only when in the ready mode Otherwise the ON OFF button is not active To return to ready mode from any other mode press the Scan Escape button until the RDY message appears on the LCD All buttons are inactive during the measurement scan The meter will automatically shut off after 10 minutes of inactivity 2 2 Menu structure All settings for MICROTOPS II are accessible through a tree organized menu At the top of the menu structure is the ready mode where the instrument is prepared to take measurements and dis plays the following information Ready mode indicator RDY Phila ID 01 15Aug96 12 24 45 Universal time If the name of the selected location is 6 characters long or less it will be displayed in its entirety Otherwise only the first 5 characters are displayed followed by two dots indicating continuation The named locations can be set from a PC via the serial port See Remote control on page 24 for more details If a manually ent
5. either isopropyl or ethyl can be used to remove any residue from the window 7 2 Battery maintenance Microtops II operates on four AA alkaline batteries A new set of batteries will last for at least 50 hours of continuous operation Since the measurement requires very little time the effective battery life can be several months Note that AA NiCad batteries will not provide sufficient voltage to run the Microtops II Low battery voltage sensing is built into Microtops II The battery is checked upon power up and every minute thereafter If the battery voltage is below a pre set minimum the message Battery low Enter continue is displayed Pressing Enter resumes operation and no more warning will be displayed until the next power up cycle The instrument will continue to function for a while how ever measurement accuracy might be degraded To replace the batteries the cover of the battery compartment should be pulled towards the bottom and lifted up Pay attention to the polarity of all batteries when replacing them 7 3 Calibration To assure reliable readings the Microtops II should be re calibrated yearly and if possible partici pate in inter comparisons with ozone measuring instruments The calibration procedure is described in Theory of operation on page 39 An experienced user having access to a site with another Solar Light Co Inc 37 ozone measuring reference instrument and a perfectly clear sky for at least half a day
6. over the pressure measurement and the station pressure is stored and used for calculations For unit conversion 1 mB 0 0145 PSI 0 02953 in Hg 0 1 k Pascal 0 75006 mm Hg 3 4 Data logging Microtops II has a non volatile memory buffer for data storage After each measurement scan one record is added to the buffer If the memory space is filled then the Memory full message is dis played on the LCD and the last scan is ignored To store additional records the memory buffer has to be cleared see Clearing the memory buffer on page 21 or some records must be deleted The 20 16 45 56 16 45 40 16 44 12 12Sep96 16 43 38 Ready mode Menu Enter Main menu Clock Main menu Measurement Main menu Location Main menu Data logging Data logging Clear memory 25 scans stored Clear all gt gt Figure 17 Clearing the entire memory buffer O38 corr O3 1 2 O3 2 3 Water 12Sep96 306 5 mes 3004 3064 12Sep96 307 3 1 12Sep96 306 9 300 9 306 8 1 di 305 9 300 8 305 9 1 Figure 16 Viewing the stored data on LCD Solar Light Co Inc qe gt 5 301 6 307 2 42 46 50 43 data from the buffer can be downloaded to a computer via the serial port see Computer communication on page 23 or viewed on the LCD 3 4 1 Viewing the stored data The data browse mode allows inspection of all data stored in me ter s non volatile memory The b
7. support special characters The Microtops II calculates the ozone value based on two pairs of wavelengths channell channel2 and channel2 channel3 The fac tors 012 B12 and L12 correspond to channell channel2 pair while 023 823 and L23 relate to the other pair After the ozone is calculated from the two pairs the corrected ozone is determined with 14 Solar Light Co Inc the help of factor OC The details of the calculations and calibration are presented in section Specifications on page 38 Figure 5 shows the menu path to the ozone calibration factors The number editing rules are de scribed in chapter Irradiance calibration constants on page 12 3 2 1 3 Water vapor calibration constants The calibration constants for water vapor calculation include In V04 the natural logarithm of the extraterrestrial constants for channel 4 for mean sun earth distance In V05 the natural logarithm of the extraterrestrial constants for channel 5 for mean sun earth distance K a constant dependent on the spectral transmission of the channel 4 filter B a constant dependent on the spectral transmission of the channel 4 filter Ready mode Measurement Calibrations lai Calibrations Irradiance Calibrations Ozone cal Calibrations Water cal Calibrations Pressure cal Calibrations Restore calibr Restore calibr Yes gt gt Figure 7 Restoring factory cali bration factors C
8. 14 45 30 and your time zone is Solar Light Co Inc 11 GMT 5 then the UT is 9 45 30 Please note that most countries use Daylight Savings Time during the summer season which is offset by 1 hour from LST 3 1 2 Clock trimmer The absolute accuracy of the low power clocks is not adequate for long term time keeping Thus a software clock trimmer was implemented into the instrument When given the clock s error in seconds 30 days the algorithm periodically skips or adds 5 seconds effectively keeping the clock within 5 seconds from accurate time The residual error would depend mainly on the storage temperature of the instrument To calibrate the trim mer follow these steps 1 Set the clock to an accurate time for example from a radio broadcast Figure 3 Setting the clock trimmer 2 Check the time few a days later at least 5 and note the difference from an accurate time 3 Calculate the time drift in seconds 30days For example if the clock drifted 12 seconds ahead in 9 days 216 hours then the clock drift per 30 days is 30_day_drift 30 days 12 seconds 9 days 40 seconds If the initial setting of the clock trimmer was 0 then setting it to the opposite to clock drift i e 40 seconds 30 days would effectively correct the clock s error In order to set the clock trimmer enter the menu by pressing the Menu Enter button step level down by pressing kor Menu Enter key press w to select the Clock trimmer in
9. 3 2 Coordinates ocation The geographic coordinates in the current location buffer can be pera modified from the keypad Figure 12 The LCD will show Saved location Location Coordinates ibi 40 03 N 75 08 W pr The selected underlined item can be incremented decremented with 4 and w keys and the selection can be changed with and 4 Amd keys The latitude and longitude directions will change N S and WIE respectively Pressing Escape key allows return to higher Figure 13 Setting current location levels and to the ready mode The degrees and minutes 1 altitude 1 60 are modified independently Please note that coordinates are sometimes given in degrees and decimal fraction of a degree In that case proper conversion is necessary An accuracy of a 5 minute angle is adequate for both latitude and longitude Solar Light Co Inc Ready mode Menu Enter A Main menu Clock Main menu Measurement Main menu Location Location Saved location Location Coordinates Location Altitude Location Pressure station pressure Pressure 1013 mB Figure 14 Figure Setting the 19 The change of coordinates is effective immediately It will affect only measurements made after the change 3 3 3 Altitude The altitude is used for the calculation of the radiation effective path 1 through ozone layer Microtops II accepts the altitude in meters above sea lev
10. NMEA 0183 formats versions 1 5 and 2 0 can be read by Microtops II 6 1 Setting up GPS The individual setup procedures vary between receivers The following example is based upon Gar min Model GPS 12 receiver 1 2 cer ace S 10 11 12 Turn the GPS receiver ON Turn the Microtops II ON and set the baud rate to 9600 This is the only Microtops II setting required for GPS compatibility Connect the Microtops II and GPS receiver using the special cable provided by Solar Light Co for the GPS option Go to the MAIN MENU page on the GPS by pressing the PAGE button Using 4 and buttons on the GPS select SETUP MENU Press ENTER to view the SETUP MENU then w to select INTERFACE Press ENTER then e to select the interface mode Press ENTER again to edit the mode and using 4 and e set it to NONE NMEA Press ENTER then w to select the baud rate Press ENTER again to edit the baud rate and using 4 and e set it to 9600 baud Press ENTER when done and return to the page showing satellite signal strength by pressing PAGE Position the GPS receiver so the view of the sky is not obstructed and the instrument can ac quire the satellite information This process may take up to several minutes depending on the satellite configuration and recent location changes Please refer to the GPS manual if the re ceiver is not able to acquire position Once the position is acquired the GPS receiver shows 2D NAV message if the latitude longit
11. aea eed ad cet rette ere eet in 33 6 GPS COMMUNICATI QON 5 5 55e tonic sede neon dese epoca Peace ea ende de nuce te deed gorge oe canino naci 34 6 1 SEHINGUPGPStL ND a FR MM MM UI aaa 34 T MAINTENANCE n a a LINATE anna 36 7 1 CLEANING AND STORAGE ee eege A RIA ie 36 72 BATTERY MAINTENANCE ld 36 73 CALIBRATION irene ie ALA e tA P e e Ces tes P e TR e ET es 36 8 SPECIFICA TIONS 5 ERRO ese ese eege Leto dose depen uos ede ed gogo ese de cede Deuce de eget RARA RAR 38 9 THEORY OF OPERATION 5 ecece cte e cete nose ceno aeo on cetero e cenae aca co toes den eene oe ce noe sede Re eran end 39 9 1 INTROD GTION re eee RR co 39 9 2 Ee ERNEIEREN E CN WEE 40 9 3 INSTRUMENT DESIGN A ad 40 9 3 1 Optical block 3 iei A e e e ee eee need tas 40 9 3 2 Signal conditioning and processing eese tette eterne 42 9 3 3 SSE LAAR M iis o 43 9 4 CALIBRATION AND MEASUREMENT OF OZONE cirie 44 9 5 DERIVATION OF WATER VAPOR ue Seege E AREA A AE AERE A SERE ATE ens 47 9 6 CONCLUSIONS ii A eret eet eb etes EE ad 49 9 7 REFERENCES 8 ciet iere PR NER EUER ERRORES 49 10 TABLE OF ASA RO 51 11 RL DEI 52 Solar Light Co Inc 5 1 Introduction The MICROTOPS II is a hand held multi band sunphotometer capable of measuring the total ozone column and optionally the water vapor column also called precipitable water as well as aerosol optical thickness at 1020nm 1 1 Princ
12. and the data will begin to be inserted into the database 5 3 3 Importing files in data exchange format Database text files can be imported into the database by using the File Import command An open dialog will appear to select the database text file to import into the database After selecting the appropriate file with a dbt extension click OK and the data will begin to be inserted into the database 5 3 4 Exporting in data exchange format Database files can be exported to a database text file by using the File Export command A Save dialog will appear to select the database text file to export to After selecting or typing the appropri ate file with a dbt extension click OK and the data will begin to be exported to the database text file 5 3 5 Data description Every data entry in the database has a data description field which can be used as a user description for the data This field is a 40 character text field which can contain any text the user wishes to store with the data Some uses include the date the data was downloaded or the name of the person who collected the data Every download will result in a prompt for a data description entry which the user can type in This prompt can be disabled by un checking the Data Description Prompt in the Op tions Menu Solar Light Co Inc 5 3 6 User calibration factors Calibration Factors D Query Begin End Serial Number rUser Cal F
13. around and a CR marker is placed where the carriage return character is sent 26 Figure 25 Printout of Microtops II calibration constants 27 Figure 26 MICROTOPS II structure 40 Figure 27 Spectral transmission of UV filters measured using a monochromator with 2 5nm slit width notice bandwidth broadening in order to detect the stray light 41 Figure 28 Signal measured by MICROTOPS II on Mauna Loa May 16 1996 271 DU clear sky 42 Figure 29 Series of consecutive MICROTOPS II measurements of ozone employing three different ways of sun targeting 44 Figure 30 Illustration of the MICROTOPS II calibration procedure 45 Figure 31 Comparison of Microtops II S N 3106 with Dobson instrument 65 in Boulder CO 08 01 96 48 Figure 32 Measurement of ozone over wide range of air mass in Philadelphia PA May 31 1996 48 52 11 Index A air MASS 13 17 19 40 42 47 48 altitude 6 17 18 19 25 27 AVELARIND criticano 15 16 43 B Battery maintenance sissien inisee 36 Bd in a n 22 C calibration 5 11 12 13 14 15 16 19 21 23 27 28 32 33 36 37 39 43 45 47 49 circumsolar radiation 5 12 Clearing data buffer 24 29 Clearing the memory 19 21 clock 10 11 26 35 40 43 45 CLOCK trimme oerte 10 colitis 5 eet Ek LTE 5 40 Computer communication 23 C
14. can attempt the calibration of the ozone and water vapor measurements Calibration of the irradiance can be performed by direct comparison of Microtops II with another sunphotometer The calibration of the 3 UV channels assumes nominal bandwidth of 2 4nm for each channel and the respective nominal center wavelength For example the reading of 305 nm channel corresponds to direct component of the irradiance on a normal surface within a band of 303 8 306 2 nm The calibration of the 2 optional IR channels is based on their nominal bandwidth FWHM of 10nm and respective center wavelengths 38 Solar Light Co Inc 8 Specifications Optical channels 305 0 0 3nm 2 4 0 4nm FWHM 312 5 0 3nm 2 4 0 4nm FWHM 320 5 0 3nm 2 4 0 4nm FWHM OPTIONAL 936 1 5nm 10 1 5nm FWHM 1020 1 5nm 10 1 5nm FWHM Max out of band 305 0nm 10 sensitivity rel to peak 312 5nm 10 transmission 320 5nm 10 936 1020 nm 10 Angle of view 209 Dynamic range gt 3 10 Precision 1 2 Non linearity Max 0 002 Operating environment 0 50 C no precipitation Computer interface RS232 Data storage 800 records Power source 4xAA alkaline batteries Battery life 50hrs min continuous operation 10 min inactivity shutdown Weight 21oz 600 grams Size 4 W x 8 L x 1 7 D 10 x 20 x 4 3cm The irradiance cal factors are derived for the nominal FWHM and center wavelengths listed above Solar Light Co Inc 39 9 T
15. depositing the filter s layers and coatings assures long life and stability The GaP photodetectors used in the MICROTOPS II are characterized by relatively strong sensitivity in the UV region low noise level and low sensitivity above 500nm These characteristics allowed us to relax the out of band rejection above 650nm lowering the production cost of the filters The photodetectors are hermetically packaged to assure long life and stability 9 3 2 Signal conditioning and processing The solar radiation at short UV wavelengths decreases rapidly with increasing air mass Figure 28 The slope increases as the ozone layer increases In order to measure the ozone column the MICROTOPS II measures each wavelength independently and then calculates the ratio unlike the Dobson instrument which benefits from the differential approach In order to perform accurately the MICROTOPS II must be able to measure very weak and very strong signals with adequate signal to noise ratio and high linearity To achieve that goal the following approach was taken e The input amplification stages were optimized to have the lowest noise level The dominant noise source in the most sensitive channels is the thermal noise of the feedback resistance in the amplifier The band width of all amplifiers is reduced to a minimum and is equal for all channels With a band width of just under 10Hz the max RMS amplifier noise is 5 8 pV e A high performance sigma delta A D converter
16. erm Ue E e era b Ges havi ale FOR E EUR He b e Eae a eo 22 4 COMPUTER COMMUNICATION ccsssssssssssssessssssssessesssssessssssssessesssssessessessessessessessessssesses 23 4 1 PAYSICAL CONNECTION cita ee eva be esee Prae ee Lee Pied Lene o o TR RE ERE Re Een 23 4 2 REMOTE CONTROL ilaria aaa anali 24 4 2 1 Listing and setting current location eee eese tentent narran 24 4 2 2 Clearingdata Du ferina iaa uno anios cuasi dins 25 4 2 3 Listing and setting saved locations eese eene ener 25 4 2 4 Downloading data buffer ede ede aos 25 4 2 5 IEN 26 4 2 6 Setting date and TEE 26 4 2 7 Printing calibration con gionts esee eret ener 27 4 Solar Light Co Inc 5 MICROTOPS ORGANIZER SOFTWARE csccsscsssssssssccssscsscssscscccsssssscscscssssscssssssssescsssenscoes 28 5 1 INTRODUCTION o 28 5 1 1 Software installation darla e e 28 5 1 2 Communication UA ea rie 28 52 MICROTOPS OPERATION a a aree RI iii 29 5 2 1 Downloading data resinae i iaia 29 5 2 2 Clearing data DUO te d e edd 29 5 2 3 Modifying saved Microtops II Jocetieons 30 53 DATABASE OPERATIONS Pato ca RSS eov eae E i 31 5 3 1 Changing location names in the computer database 31 5 3 2 Importing text OT 3l 5 3 3 Importing files in data exchange format 32 5 3 4 Exporting in data exchange format eee ee eese tenete tenete nete 32 5 3 5 D t descriptiOnz ee ette Rte tete Rete aa ee ante eie lenge 32 5 3 6 User calibratiomfacfOEs
17. is determined based on measurements at 940nm water absorption peak and 1020nm little absorption by water Both the calculation of ozone column and precipitable water column require knowledge of the actual air mass It is calculated by the MICROTOPS II based on the time from a built in clock and the user entered coordinates of the measurement site 9 3 Instrument design The overall structure of MICROTOPS II is shown in Figure 26 The optical block shapes the field of view of the instrument filtering incoming radiation detecting it and facilitating targeting of the sun Electrical signals from the photodetectors are amplified converted to digital form and numerically processed in the signal processing block 9 3 1 Optical block The success of the instrument depends on its ability to measure ozone column with long term stabil ity under a broad range of air masses and atmospheric conditions The entire instrument and all subsys tems were analyzed in a series of computer simulations The initial de sign goal of an overall precision bet ter than 3 for air mass up to 3 translated into a set of very stringent specifications Several iterations of the process allowed us to find a set of specifications that met the initial cri teria and were realistic at the same 300 0 nm channel 305 5 nm channel 312 5 nm channel 940 nm channel 1020 nm Lampe time channel OPTICAL SIGNA
18. is determined by finding the wavelength at which the slope of the In of the measured signal Figure 30 matches the theoretical slope A The ozone column for calculation of A is taken from a co located independent instrument such as Dobson spectrophotometer Once the A is known the o and B for each channel can be calculated from 8 and 9 For the filters used in MICROTOPS II the effective wavelengths are fraction of a nanometer above the filter s center wavelength Table 4 9 5 Derivation of water vapor Water vapor transmission was studied for almost a century The calibration technique used for MICROTOPS was developed by Reagan et al and further tested by Michalsky et al The water vapor measurement is based on a pair of radiometric measurements in the IR band The 940nm filter 10nm FWHM is located in a strong water vapor absorption band while the 1020nm filter 10nm FWHM is affected only by aerosol scattering For the 940nm channel indexed with 1 located in the water vapor absorption band the Bouguer Lambert Beer law takes the form LR m k um 11 Voi where V is the ground based radiation at 940nm Vo is the extraterrestrial radiation Zu is the aero sol scattering coefficient at 940nm u is the vertical water vapor column thickness m is air mass and k and b are constants numerically derived for the filter For the 1020nm channel there is negligible water vapor absorption and the equation takes t
19. p it yields a value for In I and a total coefficient value for the remaining terms when sub jected to regression analysis That constant must then be broken down into a term for ozone absorp tion and a term for the Rayleigh scattering TERC developed a simple model which assumed that a narrow bandpass filter acts like a filter of a single wavelength This forces an additional constraint on the coefficients to be determined because they must both be appropriate for that wavelength Very helpful is the fact that the and B change differently with wavelength To simplify the deter mination of a and p the wavelength dependencies of these coefficients were calculated with the following two equations derived by fitting the ozone cross sections derived by Molina and Molina and the Rayleigh coefficients of Penndorf a A 2 1349 x 101 e 0 14052 S BO 16 407 0 085284 2 0 00011522 X P where is the wavelength in nm Solar Light Co Inc 47 Substituting 8 and 9 into 7 one can calculate the slope A of the In I vs u line A 1 2 1349 x 1019 e 14952 o 1000 16 407 0 085284 A 0 00011522 22 P P 10 The 1 1000 factor associated with Q Table 4 Effective wavelength vs filter s center wave comes from unit conversion between length Dobson Units and atm cm The effective MICROTOPS II Filter s Typical effective wavelength A of each channel s interfer center wavelength nm wavelength A nm ence filter
20. results was the lack of stable narrow band UV filters with adequate out of band rejection Recent advances in thin film deposition techniques made it possible to produce filters of satisfac tory quality The Total Ozone Portable Spectrometer TOPS project has proven that filters cur rently available can be used to measure the total ozone column accurately Based on prior experi ence a new portable sunphotometer and ozone monitor was developed at Solar Light Company The MICROTOPS II is a 5 channel portable sunphotometer measuring the direct solar radiation at 300 305 5 312 5 940 and 1020 nm Based on these measurements it is possible to calculate the total ozone column and total water vapor 40 Solar Light Co Inc 9 2 Basics of the instrument Ozone absorbs shorter wavelengths of solar ultraviolet radiation much more than longer wave lengths This means that the amount of ozone between the observer and the Sun is proportional to the ratio of two wavelengths of the Sun s ultraviolet radiation MICROTOPS Il uses that relationship to derive the Total Ozone Column the equivalent thickness of pure ozone layer at normal pressure from measurements of 3 wavelengths in the UV region Similarly as in the traditional Dobson in strument the measurement at an additional 3rd wavelength enables a correction for particulate scat tering and stray light The field of view of each of the optical channels is 2 5 The precipitable water column
21. series of ozone measurements performed on a Table 3 Performance of sun targeting methods fairly clear day with the same instru Targeting method Standard deviation mient Each of the measurement series ici 0 87 employs a different sun targeting tech Hand hel d pose 0 18 E nique hand held with targeting en Tripod moune d o ER 3 hancement based on a series of 32 rapid D measurements measurement time 314 approx 10 seconds hand held with just 312 averaging of measurements and the third m series was measured with MICROTOPS a 310 II mounted on a tripod o Se Table 3 shows the standard deviation of 9 306 each measurement series the hand held O 304 with targeting enhancement offering the 302 most repeatable results with a standard ee deviation of 0 18 The targeting en hancement produces results are slightly hand held enhanced e tripod mou ted better than tripod mounted instrument lt a hand Hold no enhancement since it compensates the targeting error due to limited resolution of the instru Figure 29 Series of consecutive MICROTOPS II measure i ment s targeting system ments of ozone employing three different ways of sun target ing 9 4 Calibration and measurement of ozone Calibration of the MICROTOPS II instrument requires that the intensity of radiation measured at each channel be analyzed assuming the validity of the Lambert Beer law which
22. the Clock menu and press kor Menu Enter key to reach the trimmer editing Figure 3 The display will show the current setting of the trimmer Clock trimmer 070 sec 30days One digit within the time correction will be selected underlined by a cursor This digit can be in cremented or decremented by pressing the w and 4 buttons The selection can be changed by press ing and 4 keys If the cursor points at the sign character then the w and A buttons will toggle it between and To go back to the RDY mode press the Escape key 3 times 3 2 Measurement parameters and calibration constants In order to measure the ozone water vapor and irradiance the Microtops II stores a set of calibration factors that relate the electrical signal measured by its A D converter to the physical quantities de sired These factors are described in chapter Calibration constants that follows Other important 12 Menu Enter Ready mode Main menu Clock Main menu Measurement Solar Light Co Inc settings described in chapter 3 2 2 Data processing affect the measurement and data manipulation process 3 2 1 Calibration constants Microtops II stores two sets of calibration factors the factory cali brations FC and user calibrations UC The FC are pro grammed into the instrument during a calibration process and cannot be modified by the user The UC are initially set to equal FC but can be individually modifi
23. the database of saved locations cannot be modified from the instrument s keypad nor Push gt to select 2 Mauna_Loa is the information for calculations fetched directly from this database The location settings for calculations always come from the current location buffer The Saved locations feature only cop les a selected record containing coordinates altitude and pressure from the database to the cur rent location buffer The contents of the current location buffer can be edited from the keypad All location parameters except name are stored with each measurement scan The menu path to selecting a saved location is shown in Figure 11 On the lowest level the user is prompted with the message The top line informs that pushing key will copy the selected location parameters to current loca tion buffer The bottom LCD line shows the record number of the database location currently se lected and the name of the location stored in it There are 6 re cords in the database Initially some of them are named Empty and all location parameters are set to zero The selection can be changed by pressing A or w key The display MenuEnter will scroll through all the records In order to copy the location Man MEn parameters it is necessary to press gt key when pointing at Lk the desired location Scrolling through the database does not Menmenu modify the contents of current location buffer Or Measurement dolida 3
24. with on chip digital filtering is used The high over sampling ratio of this converter eliminates the need for high order anti aliasing filters at the front end The conversion non linearity is less than 0 0015 within the entire input range and the A D conversion noise level is 5 3uV RMS with 2 5V full scale e The A D converter s filter is programmed to reject line frequency interference user select able e Each measurement cycle comprises multiple measurements of all channels that are processed numerically in order to lower noise level and improve overall accuracy e Attention was paid to proper shielding and optimal layout of the amplifiers and the conversion block Overall the dynamic range achieved in the instrument is over 300 000 with excellent linearity leav ing adequate signal to noise margins even for very weak signals To assure long term stability of measurements the electronic circuitry itself has to be very stable both thermally and long term The gain of the amplifiers is determined by a set of precision resis tors with temperature coefficients below 0 005 C The amplifier s offset is automatically com pensated every time the instrument is powered on Both the offset and full scale of the A D con verter are automatically calibrated before each scan The full scale calibration relies on a high per formance voltage reference with the temperature coefficient under 0 001 C and long term stabil ity in the order of 0 005
25. 25995 26003 1995 M Degorska B Rajewska Wiech Airmass Dependent Total Ozone Measurement Errors Pub lications of Institute of Geophysics Polish Academy of Sciences D 40 263 1993 Solar Light Co Inc 51 10Table of figures Figure 1 Simplified Microtops II menu 8 Figure 2 Entering the date and time editing mode 10 Figure 3 Setting the clock trimmer 11 Figure 4 Modifying irradiance calibration factors 12 Figure 5 Modifying ozone calibration factors 12 Figure 6 Modifying water vapor calibration factors 13 Figure 7 Restoring factory calibration factors 14 Figure 8 Setting the scan length 15 Figure 9 Setting the number of top ranking samples 15 Figure 10 Setting the line frequency rejection mode 16 Figure 11 Selecting a saved location 17 Figure 12 Setting current location geographic coordinates 17 Figure 13 Setting current location altitude 18 Figure 14 Figure Setting the station pressure 19 Figure 15 Mean barometric pressure vs altitude 19 Figure 16 Viewing the stored data on LCD 20 Figure 17 Clearing the entire memory buffer 20 Figure 18 Deleting last data record 22 Figure 19 Adjusting serial port speed baud rate 22 Figure 20 Serial communication cable for Microtops II 23 Figure 21 Microtops II remote menu 23 Figure 22 Listing of saved locations database 25 Figure 23 Location input pattern 25 Figure 24 Data transfer format Long lines are wrapped
26. 83 sec Z 1 2 Solar Light Co Inc R h 45 R En Rar sin zl 1 or more conveniently de 1 v sin Z 3 4 where v is a geometric factor for the height of the ozone layer given by R r RA R mean earth radius 6371 km y 5 r height of ozone station above sea level in km and h height of ozone layer above sea level approximated as h km 26 0 1 latitude Sa In general at sea level in the continental United States v 0 99316 The solar zenith angle Z angle of sun with respect to the zenith which is the basis for the calcula tion of p and m is calculated based on the coordinates of the measurement site and universal time UT The algorithm implemented in the MICROTOPS II were tested to an accuracy of 0 03 Extrapolatio to miu 0 2 In 305 5nm signat In 312 5nm signal Figure 30 Illustration of the MICROTOPS II calibration procedure max error for the entire practical range of lati tudes and longitudes for the time period of 1996 2006 The error observed comes partially from simplified algorithms and partially from the use of single precision arithmetic This error causes negli gible effect on ozone calculations The MICROTOPS II is equipped with a real time clock and calendar The coordinates of the location are entered from the keypad GPS receiver or an exter nal computer The theore
27. If there is reason to believe that the last measurement is not correct it can be deleted from memory using this feature Figure 18 illustrates the menu path 22 Ready mode Main menu Clock Menu Enter Main menu Measurement Main menu Location Main menu Data logging Data logging Clear memory Data logging Delete last Figure 18 Deleting last data record Delete scan 25 Solar Light Co Inc The LCD displays Delete scan 25 Yes gt gt The top line indicates the number of scans currently in memory Each key activation will delete one record from memory last measured and the displayed number will decrement by one To withdraw without deleting the data press Escape or Enter 3 5 Baud rate Microtops II can communicate with a computer or GPS receiver via the serial port The speed of that communication link is adjust able from 2400 to 19200 baud Please note that the baud rate should to be set to 9600 if the GPS receiver is connected to Microtops II see GPS Commu nication on page 34 Setting the baud rate to a higher speed quickens the data transfer process and makes the instrument more responsive during remote setup However some slower Ready mode Menu Enter lt Main menu Clock Main menu Measurement Main menu Location Main menu Data logging Main menu Baud rate Baud rate 9600 incr decr Figure 19 Adjusting serial port speed bau
28. L PROCESSING BLOCK Described below are some of the BLOCK critical issues considered during the Figure 26 MICROTOPS II structure design process Solar Light Co Inc 41 e To assure long term stability the opti cal block is machined from a cast aluminum plate e The mechanical alignment of the opti cal channels is better than 0 1 e Internal baffles in each channel pre vent reflections from reaching the photodetectors The internal surfaces of the collimators are lined with a low reflectivity material Transmission e The sun targeting hardware is ma chined from aluminum and directly at tached to the filter block to avoid temperature effects on targeting 280 300 320 340 360 380 400 Wavelength nm 300nm 305 5nm 312 5nm Noise floor Figure 27 Spectral transmission of UV filters measured using a monochromator with 2 5nm slit width notice bandwidth broad ening in order to detect the stray light e The entire optical block is suspended in the enclosure in such a way that a mechanical strain applied to the en closure does not result in substantial strain in the optical block e The sun targeting assembly is laser aligned to within 0 1 from the optical axis of the block e The temperature of the optical block is monitored and logged in order to allow temperature compensation if needed e A built in solid state pressure sensor provides the
29. Letters 20 5 367 370 1993 G J Labow et al Estimating Ozone with TOPS Instruments Practical Operation and Comparisons in press Lawrence E Flynn Estimating Ozone with TOPS Instruments Theoretical Model and Error Analysis in press Basher and R W L Thomas Applied Optics 18 3361 62 1979 D Kohmyr R D Grass and R K Leonard J Geophys Res 94 9847 61 1989 D Kohmyr Operations Handbook Ozone Observations with a Dobson Spectrometer WMO June 1980 J Meeus Astronomical algorithms st ed Willmann Bell 1991s G M B Dobson and C W B Normand Ann Int Geophys Year 5 161 191 1962 S Bannasch G Unger and P Wagoner Preliminary Calibration of TERC Total Ozone Spec trometers TERC private communication L T Molina and M J Molina J Geophys Res 91 14501 508 1986 R Penndorf J Opt Soc Amer 47 176 82 1957 F E Fowle The spectroscopic determination of aqueous vapor Astrophys J 35 149 162 1912 J Reagan K Thome B Herman R Gall Water vapor measurements in the 0 94 micron ab sorption band calibration measurements and data applications Proceedings International Geoscience and Remote Sensing Symposium Ann Harbor 1987 J J Michalsky J C Liljegren L C Harrison A comparison of Sun photometer derivations of total column water vapor and ozone to standard measures of the same at the Southern Great Plains Atmospheric Radiation Measurement site JGR Vol 100 No D12 pp
30. Locations command in the Tools menu A new form will appear Before changing the location names the correct data points must be selected in the database To select data points select the location name which is to be cor rected select lt blank gt for empty location names and optionally type in the latitude and longitude of the location and click the Run Query button All of the data points defined by the above criteria will be displayed in the query results table at the bottom of the form If the correct set of data points are in the query results table then the location names are ready to be changed Select or type in the new location name and then click Update The new location names will be written to the database 5 3 2 Importing text files Microtops data can be imported as a text file with the following format 1 Calibration Constant Header 2 Data This can be accomplished by using Windows Terminal or other communications software 32 Solar Light Co Inc Setup communications protocol port and baud rate Start a log file using a txt extension type X to retrieve the calibration constant header type P to download the data close the log file UI h UN ra This log file can now be imported into the database by using the File Import command An open dialog will appear to select the text file log file to import into the database After selecting the appropriate file with a txt extension click OK
31. PP ree a OL ME 5 Sm Wig screen First is a single digit number Igure isting of save ocations database D 8 of sav of the location that is being changed The max length of location name is 14 characters Only alphanumeric characters a z A Z 0 9 and underscore _ are allowed within the name string The coordinates are in degrees with decimal fraction not minutes Use a period to separate the fraction from the whole number Two decimal places are sufficient for coordinates The direction sign rules described above apply The altitude is in meters and pressure in milliBars Altitude and pressure are stored as whole numbers no fractions Separate all items with one or more space characters and finish the entry with the CR character Enter or Return on the keyboard If all parameters are accepted then the Microtops II replies with Location x saved where x is re placed with the number of the location Otherwise an Input ignored message is returned The Microtops Organizer software ESE ARAR offers an interactive way of updating the Loc Name Lat N Long E Alt m Pres mB instrument s location database see X XXXXXXXXXXXXXX IXX XXX XXX XXX TXXXX XXXX Microtops Organizer Software on page 28 Figure 23 Location input pattern 4 2 4 Downloading data buffer Sending P to the Microtops II triggers data transfer from the instrument s buffer The transmitted data Figure 24 is preceded by a header REC xxxx where the
32. TOPS II Location Settings D Current Microtops Location Settings Loc Name Lat LongGt Al m Pres mB Philadelphia 40 050 75 133 20 Mauna_Loa 19 533 155 583 3397 Empty 0 000 0 000 0 Empty 0 000 0 000 Empty 0 000 0 000 Empty 0 000 0 000 Microtops II internal location database max 6 locations can be viewed and changed by selecting the Change Instrument Locations command on the Tools menu Only legal values will be accepted by the Microtops Retrieve will display all current locations saved in the instrument To change the location setting type in the new data on the appropriate line and click the SET button All of the dis played locations will be saved to the instrument for future use Solar Light Co Inc 31 5 3 Database Operations 5 3 1 Changing location names in the computer database Change Database Location Names D Latitude Longitude 155 583 Location Name Mauna Lo gt To new_tocation _ 2 ETC ETT hoe m 598 Records Found TIME LATITUDE LONGITUDE 0 9 25 96 4 23 05 PM Mauna_Loa 19 533 155 583 3103 8 20 96 1 31 19 PM Mauna_Loa 19 533 155 583 3103 8 20 96 1 31 29 PM Mauna_Loa 19 533 155 583 3103 8 20 96 1 48 14 PM Mauna_Loa 19 533 155 583 3103 8 20 96 1 48 23 PM Mauna_Loa 19 533 155 583 3103 8 20 96 1 48 32 PM Mauna_Loa 19 533 155 583 3103 8 20 96 1 48 41 PM Mauna_Loa 19 533 155 583 Database locations can be changed by selecting the Rename Database
33. This effect contributed to by out of band radiation leaks scattering of diffuse UV radiation into the instrument s field of view and the effect of the finite bandwidth of the filter itself Figure 32 shows a series of measurements performed during a sunny day in Philadelphia PA over a wide range of p The ozone calculations based on a single pair for example 300 305nm or 305 312nm show the air mass dependence effect With the air mass dependence correction the measurements can be made to an air mass of 3 8 The quality of calibration depends strongly on weather conditions when the Langley method is used limiting where and when the calibration can be performed A calibration based on spectroradiometric measurements of individual filters is proposed but more experimental data is needed to test its applicability 9 7 References 1 G P Gaushchin et al Total ozone measuring instrument used at the USSR station network in Atmospheric Ozone edited by C S Zeferos and A Ghazi Reidel Dordrecht 1985 2 A Smajkiewicz Filter durability effect of temperature humidity radiation and time Barr Associates Inc private communication 3 Forrest M Mims III How to Measure the Ozone Layer Science Probe 2 4 45 51 November 1992 50 10 11 12 13 14 15 16 17 18 Solar Light Co Inc Forrest M Mims III and E R Mims Fluctuations in Column Ozone During the Total Solar Eclipse of July 11 1991 Geophysical Research
34. User s Guide MICROTOPS Il Ozone Monitor amp Sunphotometer Version 2 43 Solar Light Company Inc O 2001 Solar Light Company All rights reserved 721 Oak Lane Philadelphia PA 19126 USA tel 215 927 4206 fax 215 927 6347 info Esolar com www solar com Document No MTPOS February 2001 Printed in the United States of America Solar Light Co Inc 3 Contents L SINTRODUG A O O TA 5 1 1 PRINCIPLE ee E 5 1 2 MAJOR FEATURES 5 iiti fi Gn An AWA ANAL ANAL ANAL AHA AHANANAL i 6 2 QUICK RN WEE 7 2 1 POWER UP ie sees siii eii 7 2 2 MENU STRUCTURE eege ee eb He ER Eb E redd 7 23 BEFORE MAKING FIRST MEASUREMENT 8 24 FIRST MEASUREMENT 3 2 Sine hak da loca eere dada a To eve ENEE ate sae haa 8 PRI CN H RE E A O E NANA 10 3 1 REALTIME CLOCK cecilia te 10 3 1 1 Setting the time and date 10 3 1 2 Clock trimester Rio 11 3 2 MEASUREMENT PARAMETERS AND CALIBRATION CONSTANTS eese ener enne nnne 11 3 2 1 Calibration constants ui 12 3 2 2 Data D Feier Een eene Een DEES 15 3 3 LOCATION SETUP irem cete erae n tet e eed ra a eT eed E aee ve be e una ea Doa d 17 3 3 1 Saved LO COLONES XN Xo XO X X NUEVO RO OU OU GR NER OLG OH OUI USO CHO GOOGLE RANI 17 3 3 2 Coordinates cis 18 3 3 3 EE a IO a LIPPE 19 3 3 4 Pre Rea 19 3 4 DATA EL AA ara 19 3 4 1 Viewing the stored dato 20 3 4 2 Clearing the memory buffers uua siii aiii ad 21 3 4 3 Deleting last measurement eese teet teens 21 3 5 BAUD RATE Ll eet
35. a sunny day From the radiation transfer model a relationship between Ta and Ta2 is found for a standard atmosphere and because of a close proximity of the two bands it is assumed constant for other conditions For the filters used in MICROTOPS II the relationship is Tai 1 16 14 From 12 13 and 14 the vertical water vapor column is calculated as 1 b T m 1 no Ye uz 2 01 15 km 9 6 Conclusions The MICROTOPS II is a low cost hand held instrument allowing quick and accurate ozone column and water vapor measurements Tests indicate that the instrument gives reproducible results under various weather and climatic conditions Figure 31 shows the results of a comparison between Dobson spectrophotometer and MICROTOPS II instrument carried out in Boulder Colorado during a demonstration of the Dobson instrument courtesy NOAA Climate Monitoring and Diagnostic Laboratory The MICROTOPS II instrument was previously calibrated in Mauna Loa Hawaii under substantially different climatic conditions Comparisons with other instruments are under way and early data indicate good agreement The typical agreement between multiple MICROTOPS II instruments is within 1 2 The repeat ability of consecutive ozone measurements is better than 0 5 Table 3 Measurements through broken clouds or in very hazy conditions show variability of 1 2 Similarly to other spectrophotometers the MICROTOPS II exhibits some air mass dependency
36. actors 3103 8 20 96 3103 8 20 96 3103 8 20 96 3103 8 20 96 3103 8 20 96 Query Results 591 Matching Records 1 31 19 PM 1 31 29 PM 1 48 14 PM 1 48 23 PM 1 48 32 PM 33 User calibration factors can be changed by selecting the Cal Factors command in the Tools menu A new form will appear Before changing the calibration factors the correct data points must be selected in the database To select data points type in the beginning and end dates for which the data was collected select the appropriate serial number and click the Run Query button All of the data points defined by the above criteria will be displayed in the query results table at the bottom of the form If the correct set of data points are in the query results table then the user calibration factors are ready to be entered Select or type in the new user calibration factors and then click Update The new user calibration factors will be written to the database and a user ozone value will be calcu lated and stored in the database 34 6 Solar Light Co Inc GPS Communication Accurate location parameters can be automatically transferred from a GPS Global Positioning Sys tem receiver to the Microtops II The location is calculated by the receiver based on a combination of signals emitted from satellites orbiting the Earth For commercial use the typical accuracy of GPS positioning is 30 meters Any GPS receiver supporting
37. anu ally Once the GPS is set up for NMEA support it remembers the setting and the whole operation is re duced to turning both instruments on linking them with the supplied cable and waiting for 3 or 5 beeps from Microtops II 36 Solar Light Co Inc 7 Maintenance As with every optical instrument the Microtops II needs to be handled carefully and some mainte nance is necessary for best operation 7 1 Cleaning and storage To assure long term stability the instrument should be stored in a dry dust free place preferably at room temperature Condensation of water may damage the instrument when exposed for a pro longed period of time It is recommended that the instrument be stored in its carrying case Microtops II should be protected from excessive vibrations and shock The hard carrying case with soft foam lining or field carrying case should be used for transportation If the instrument was ex posed to shock was dropped it should be examined carefully and compared with another reference instrument Re calibration might be necessary The front quartz window should be kept clean The window cover should be closed at all times ex cept during measurement Touching the window with your skin will leave an oily residue that will affect the measurements The recommended method for cleaning the window is to use a Q tip to push any lint or dust to one side then remove it with a stream of compressed gas As a last resort only pure alcohol
38. cans stored in me ter s memory Aim the meter towards the sun until the instrument beeps twice and the display shows the RDY message At that time the measurement is complete To view the measurement results press the button The and 4 keys will scroll through the parameters for an individual record one scan or measurement The A and w buttons change the selected record Each record is identified by its date and time in the top LCD line To go back to the ready mode press the Scan Escape button See Viewing the stored data on page 20 for more information 10 Solar Light Co Inc 3 Setup 3 1 Real time clock The Microtops II has an on board real time clock and calendar RTC that provides time for the cal culation of solar zenith angle The software driven clock trimmer enhances the long term accuracy of the clock The current date and time is displayed in the ready mode The settings of the clock calendar and clock trimmer can be modified from the keypad chapter 3 1 1 or remotely via com puter chapter 4 2 6 3 1 1 Setting the time and date To set the RTC enter the menu by pressing the Menu Enter button and then step 2 levels down by pressing kor Menu Enter key twice Figure 2 Adjust clock 13Sep96 12 35 46 The LCD will show the current date amp time with the day item underlined by a cursor see above The selected underlined item may be incremented decremented by pressing the A and Lt w buttons The
39. ch channel 305 312 Ratio between 1 and 2 channel 312 320 Ratio between 2 and 3 channel Coordinates Geographical coordinates of the measurement site in degrees and minutes Alt Altitude of the measurement site in meters above sea level Pressure Barometric pressure at the measurement site Either the measured one or the pre set station pressure see Pressure on page 19 Temp Temperature of the internal optical block in degrees Celsius so the record can be easily identified The normal direct irradiance displayed is not stored in memory Instead it is calculated on the fly when displayed or downloaded based on the raw data in mV and the C1 C5 calibration factors in W m mV described in Calibration constants on page 12 Pressing Escape terminates the browse mode and brings the control back to ready mode 3 4 2 Clearing the memory buffer The instrument s data buffer can be cleared from the keypad as well as from the PC see Remote control on page 24 The menu path to memory clear function is shown in Figure 17 The user is 25 scans stored Clear all gt gt presented with the screen The top line shows the number of data records scans currently in memory The bottom line informs that pressing gt key will clear the buffer and the number of stored scans will change to zero To with draw from the menu without deleting the data press Escape or Enter instead of 3 4 3 Deleting last measurement
40. constants Current calibration constants S N 03106 A1 4 644E 00 A2 2 687E 00 B1 9 100E 02 B2 1 026E 01 L1 4 155E 01 L2 8 353E 01 OC 0 040 C1 9 100E 03 C2 1 580E 02 C3 4 130E 02 C4 1 345E 00 C5 1 657E 00 LNV04 6 618E 00 LNV05 6 280E 00 K 7 049E 01 B 6 107E 01 C 1 16 POFFS 1 502E 01 PSCALE 1 928E 01 Figure 25 Printout of Microtops II calibration constants 28 Solar Light Co Inc 5 Microtops Organizer Software 5 1 Introduction The purpose of the Microtops Organizer is to make the Microtops easier to use and more productive by providing software which will take care of data collection and instrument setup First the data buffer is downloaded to the PC where it is permanently stored into a database in DBase IV format The file DATA DBF is located in the local sub directory to which the Microtops Organizer was installed In addition the software enables the user to set up locations for the instrument and also gives the ability to add calibration factors to the database for further calculations of ozone values 5 1 1 Software installation 1 Insert disk 1 into a 3 1 2 floppy drive and run setup exe 2 Plug the serial cable supplied with the Microtops large end 9 pin to an available serial port on the back of the computer and the small end phono jack to the Microtops II 3 Turn the Microtops II on 4 Microtops Organizer is now ready to transfer data from the Microtops data buffer to your PC 5 1 2 Communication set
41. correction factor between aerosol optical depth at 1020 and 936 nm Detailed description of the algorithms and calibration procedure can be found in Theory of operation on page 39 Figure 6 shows the menu path for editing of the water vapor cali bration factors The number editing rules are described in chapter Irradiance calibration constants on page 12 3 2 1 4 Pressure calibration constants A solid state pressure sensor is built in the Microtops II This type of pressure sensors is characterized by very good linearity and stability but the repeatability of the sensor manufacturing process is poor therefore each sensor needs individual calibra tion The Microtops II sensor is factory calibrated in a pressure chamber with 2point calibration procedure Ignoring the tem perature compensation algorithm the formula used to calculate pressure from the sensor s voltage is Pressure PSCALE mB mV Voltage mV POFFS mV The two calibration factors PSCALE and POFFS are accessible through the menu system Changing them is not desirable since special equipment is needed for proper calibration Solar Light Co Inc Ready mode Processing Scan length bi Scan length 32 scans Figure 8 Setting the scan length Ready mode Main menu Clock Main menu Measurement Measurement Calibrations Measurement Processing Processing Scan length Processing Select top Select top 04 samples
42. current atmospheric pressure needed for the Table 2 UV filters specifications FILTER 1 FILTER 2 FILTER 3 Center Wavelength 300nm 305 5nm 312 5nm 0 3nm 0 3nm 0 3nm FWHM 2 4nm 2 4nm 2 4nm 0 4nm 0 4nm 0 4nm Angle of incidence 0 0 0 Max out of band transmission relative to 10 A lt 650nm 10 lt 650nm 10 lt 650nm 10 A gt 650nm 107 A gt 650nm 10 A gt 650nm peak Min peak transmission 15 Temp coef of center wavelength 0 005 nm C Wet dry shift lt 0 1nm Long term stability lt 0 1nm year Operating environment temp 20 50 C hum 0 100 42 Solar Light Co Inc Rayleigh scattering calculation Special consideration was given to the optical filters and photodetectors par ticularly for the UV channels The most critical and difficult to meet was the requirement for high out of band rejec tion The computer simulation called for leakage no greater than 10 A lt 650nm for 300nm filters Lower wavelength filters have more strict leakage require ments because the in band signal is signal mV H EE 15312 weaker than that at higher wavelengths Figure 28 Signal measured by MICROTOPS II on Mauna Typical shapes of the filters transmis Loa May 16 1996 271DU clear sky sions are shown in Figure 27 The repeat ability of center wavelength and FWHM within a batch was in the order of 0 1nm The novel technology for
43. d by experienced users having a full understanding of the inner workings of the device In case a change is inadvertently made the factory settings can be restored using the Restoring factory calibrations function in the menu see page 15 All settings are retained in the meter s nonvolatile memory and are ef fective until the next change is made 2 4 First measurement Once the initial set up is completed the Microtops II is ready to take measurements The following steps outline the procedure des Solar Light Co Inc 9 Make sure that the top window cover of the Microtops II is closed and then turn the instrument ON When the display shows RDY ready mode you may open the top window cover Point the instrument s window towards the sun and adjust its position so that the image of the sun appears in the Sun target window Center the image of the sun on the bull s eye Best re sults will be obtained during clear conditions with the sun high in the sky Haze and thin clouds will increase the measurement s variability but the ozone readings are still valid However any water vapor measurements taken will be severely affected by clouds and heavy haze and should thereby be treated with caution While keeping the sun s image centered press the Scan Escape button to initiate the scan The meter will beep and the LCD will show Scan 234 Point at the sun The number in the top line is the count of the current scan including all the s
44. d rate computers might not be able to communicate reliably at the highest speed Figure 19 illustrates the menu path to baud rate adjustment The screen will display Baud rate 9600 incr decr The lower LCD line indicates the current setting of baud rate Pressing 4 or w keys will either increase or decrease the serial port s speed The choices available are 2400 4800 9600 and 19200 bits per sec ond Pressing Escape key brings the control back to upper menu levels and ready mode Solar Light Co Inc 23 4 Computer communication Microtops II can communicate with a computer via RS232 serial port using the cable provided with the instrument The data can be transferred from the instrument into the computers memory for ar chiving and processing There is also a number of settings that can be inspected and modified re motely An off the shelf communication software Windows terminal Procomm etc can be used to communicate with Microtops However we recommend the use of Microtops Organizer page 28 a Windows based software that performs data management automatically 4 1 Physical connection The cable connection between Microtops II and the serial port is shown in Figure 20 The DB9 plug should be connected to an available serial DB9 Plug port on the back of the computer The Stereo jack stereo plug should be inserted into the socket located on the side of Microtops OA HH Figure 20 Ser
45. e readily absorbed by ozone than the longer wavelengths in the same UV bandwidth This means that the amount of ozone between the observer and the Sun is proportional to the ratio of two wavelengths of the Sun s ultraviolet radia tion MICROTOPS II uses that relationship to derive the Total Ozone Column the equivalent thickness of pure ozone layer at standard pressure and temperature from measurements of 3 wavelengths in the UV region Similarly as in the traditional Dobson instrument the measurement at an additional 3rd wavelength enables a correction for particulate scattering and stray light The precipitable water column is determined based on measurements at 936nm water absorption peak and 1020nm no absorption by water The aerosol optical thickness at 1020nm is calculated based on the extraterrestrial radiation at that wavelength corrected for the sun earth distance and the ground level measurement of the radiation at 1020nm A more detailed description of the functioning of the instrument along with the calibration proce dures is enclosed in the accompanying paper on page 39 Solar Light Co Inc 1 2 Major features High accuracy High grade filters are embedded in a solid cast aluminum housing that assures accurate stable optical alignment Low noise electronics and a 20 bit A D converter ensure high linearity resolution and dynamic range Ease of use No computer knowledge is necessary to take measurements Once the ge
46. ed from the instrument s keypad should the Irradiance Ch1 cal W m 2 mV user re calibrate the instrument on his own The Restore calibra Irradiance Ch2 cal W m 2 mV tions function copies FC into UC restoring the initial configuration Ch2 cal W m 2 mV 5 345E 04 irradiance Ch3 cal W m 2 mV trradiance Cha cal W m 2 mV L trradiance Ch cal W m 2 mV of the instrument The UC set can be read via serial port using func tion X in the remote control menu See page 27 3 2 1 1 Irradiance calibration constants The calibration factors for irradiance link the measured signal in mV with the absolute radiometric power in W m of the direct solar ra Figure 4 Modifying irradiance calibration factors diation The field of view of the Microtops II is 2 5 therefore larger than the solar disk s subtending angle A small correction for the cir cumsolar radiation is taken into account when the meter is calibrated Ready mode Main menu Clock Main menu Measurement Measurement Calibrations Calibrations Irradiance Calibrations Ozone cal Lo Ozone cal Ozone cal L12 Ozone cal Ozone cal L23 Ozone cal L23 9 029E 02 Ozone cal Ozone cal a 12 Ozone cal Ozone cal a 23 Ozone cal Ozone cal p12 Ozone cal Ozone cal p23 Figure 5 Modifying ozone calibration factors All irradiance calibration factors are derived for the nomi
47. el m a s 1 The altitude in the current location buffer can be modified from the keypad see Figure 13 When editing altitude the number editing rules apply The number editing rules are de scribed in chapter Trradiance calibration constants on page 12 An accuracy of several hundreds meters is sufficient 3 3 4 Pressure Atmospheric pressure affects the absolute air mass that the solar radia tion must travel through before it reaches the instrument Hence it influences the Rayleigh scattering process and should be taken into account when calculating ozone For most applications it is sufficient to enter a mean station pressure Microtops II accepts the pressure in milliBars mB The menu path is shown in Figure The number edit ing rules are described in chapter Irradiance calibration constants on page 12 Pressing Escape after the number is set returns to upper menu levels An accuracy of 20 mB is sufficient Figure 15 shows how the station pressure changes with altitude If the alti tude is not known it can be estimated based on pres sure measurement To facilitate measurements the Microtops can be equipped with an optional pressure sensor In this case the station pressure should be set to zero If the pre set station pressure is not zero it takes precedence altitude 0 1000 2000 3000 Altitude above seal level m 4000 5000 6000 Figure 15 Mean barometric pressure vs
48. en all samples are simply averaged If the scan length is modified so that it is less than the number of top selected records then the number of top selected records is automatically lowered to match the scan length The default setting of 4 samples selected for averaging is good for most conditions The following special circumstances may justify changing this setting e Very large solar zenith angle and weak signal less than 1mV Increasing the number of aver aged samples to maximum reduces the noise level of the measurement e A need to make a rapid measurement series Decreasing both the scan length and number of selected samples will Main menu speed up the measurement process Clock Ready mode Menu Enter lt To change the number of samples selected for averaging fol low the path illustrated in Figure 9 The number editing rules are described in chapter Trradiance calibration constants on Main menu Measurement Measurement page 12 The mstrument does not allow this setting to be E anii lower than 1 or higher than scan length Measurement Processing 3 2 2 3 Line frequency The most common source of interference in sensitive elec tronic equipment is the electromagnetic radiation emitted from power distribution lines The radiation is emitted at the basic line frequency 60Hz in the US 50Hz in Europe as well as at harmonic frequencies multiples of the basic fre que
49. ered unnamed location is used then the location name displays Manual The ID code is a user adjustable number that is stored with each scan This number can be incre mented decremented with the A or w keys when in ready mode Its purpose is to store auxiliary user defined information such as sky conditions during measurement or operator s code etc The menu can be accessed by pressing the Menu Enter key while in the ready mode The simplified structure of the entire menu is shown in Figure 1 Within the same level move with A or w keys Enter a lower level by pressing or Enter and quit to an upper menu by pressing Escape or 4 Es cape only if editing numbers All settings accessible through the menu system are described in chapter 3 Setup on page 10 Ready mode Main Menu Clock Adjust Clock Clock trimmer Main Menu Measurement Calibrations Processing Main Menu Location Saved location Coordinates Main Menu Data logging Clear memory Irradiance Ozone cal Water cal Pressure calibr Restore calibr Scan length Select top Line frequency Altitude Pressure Delete last Main Menu Baud rate 19200 9600 4800 2400 Figure 1 Simplified Micro tops II menu Solar Light Co Inc When editing various settings the general rule is that 4 or w incre men
50. he form RS exp T m 12 Vo 48 Solar Light Co Inc a 400 j 350 BE x 300 5950 k SH f 9200 c R150 C io 50 0 6 0 65 0 7 0 75 0 8 0 85 07 j j j j UT decimal 1 1 5 2 25 3 3 5 4 MICROTOPS Il 3106 Dobson 65 H Figure 31 Comparison of Microtops IS N3106 7 Ozone 300 305 Ozone 305 312 Corrected ozone with Dobson instrument 65 in Boulder CO 08 01 96 Figure 32 Measurement of ozone over wide range of air mass in Philadelphia PA May 31 1996 A radiation transfer model was used to calculate the spectral irradiance around 940nm for standard US atmosphere and various air masses Subsequently the spectral irradiances from the model were multiplied by the 940nm filter s transmission curve producing the theoretical signal from 940nm detector Based on 11 a set of k and b parameters was found that matches most closely the simu lated results The Vo for the instrument is found from an extrapolation to air mass zero of the linearized 11 In V t m 1In V k um 13 The k and b are already known therefore In Vo is the intercept from linear regression of 13 ver b sus m For the water vapor calculation the aerosol scattering coefficient Ta at 940nm is needed In MICROTOPS II the aerosol scattering coefficient Ta2 at 1020nm is first measured based on 12 The Vo is obtained from extrapolation of a Langley plot on
51. he reduc tion of the error associated with sun targeting and the reduction of measurement noise The effectiveness of the method implemented in Microtops II is described in Theory of operation on page 39 Each scan can consist of up to 64 samples from each of the 5 chan nels The samples are taken in a rapid succession at a rate of over 3 samples second one sample contains readings from all 5 chan nels Consequently the maximum time for a single scan is about 20 seconds The number of samples in a scan scan length can be set by the user to a number from 1 to 64 The default value 1s 32 16 Solar Light Co Inc 1s 32 and it is suitable for virtually all conditions Lowering the number of samples per scan may be necessary if only a short time is available for taking the measurement Figure 8 illustrates the path to scan length setting The number editing rules are described in chapter Irradiance calibration constants on page 12 The instrument does not allow setting the scan length to a number lower than 1 or higher than 64 3 2 2 2 Number of averaged samples A signal strength factor is calculated for each sample based on the signal from all 3 UV channels Only the samples with the highest ranking signal strength factor are averaged and passed for further processing The number of top ranking samples selected for averaging can be set by the user to a value between 1 and the scan length If this number is equal to the scan length th
52. heory of operation Note The Appendix contains updated information regarding this topic Design calibration and performance of MICROTOPS II hand held ozonometer Marian Morys Solar Light Co Inc Philadelphia PA 19126 Forrest M Mims III Sunphotometric Atmospheric Network Seguin TX 78155 Stanley E Anderson Westmont College Santa Barbara CA 93108 Abstract MICROTOPS II a 5 channel hand held sunphotometer a narrow band filter for each channel was designed to allow quick and inexpensive measurements of the total ozone column and water vapor column The 2 5nm FWHM for the UV channels was selected to balance noise and ozone measure ment performance The total ozone column is automatically calculated based on measurements at 3 UV wavelengths the site s latitude and longitude universal time altitude and pressure A built in pressure transducer facilitates the measurement Two IR channels allow measurement of total pre cipitable water in the atmosphere Critical aspects of the design described in the paper include stray light rejection thermal and long term stability signal noise optimization collimation targeting and data analysis MICROTOPS II performance is tested by comparing to Dobson spectrophotometers 9 1 Introduction Several attempts have been made to construct an inexpensive portable sunphotometer for the pur pose of total ozone column measurement In the past a major obstacle in producing accurate and repeatable
53. ial communication cable for Microtops II If a third party communication software is used then some minimal setup is neces sary in order to establish communication 1 The serial port should be set to the one that Microtops II is connected to 2 The baud rate of the Microtops II and the computer s serial port must be the same see Baud rate on page 22 The port settings should be 8 Data bits 1 stop bit no parity 4 ANSIterminal emulation is recommended MICROTOPS II Ozone Monitor Sunphotometer Ver 2 43 2000 S N 03686 A show current location B set current location C clear data buffer L list saved locations M modify saved location P print data buffer S initiate scan T set the date and time X print calibration constants Figure 21 Microtops II remote menu 24 Solar Light Co Inc 4 2 Remote control When the setup is completed turn the Microtops II on and wait until the ready mode is reached RDY on display Press Enter on the computer s keyboard The Microtops II responds with the screen shown in Figure 21 The header contains the model number the software version number and the serial number of the instrument The menu that follows is a set of functions that are triggered by pressing the associated key or combination of keys on the computer s keyboard 4 2 1 Listing and setting current location Code a or A sent to Microtops II prompts the instrument to return it
54. iple of operation The instrument is equipped with five 5 accurately aligned optical collimators capable of a full field view of 2 5 Internal baffles are also integrated into the device to eliminate internal reflec tions Each channel is fitted with a narrow band interference filter and a photodiode suitable for the particular wavelength range The collimators are encapsulated in a cast aluminum optical block for stability A sun target and pointing assembly is permanently attached to the optical block and laser aligned to ensure accurate alignment with the optical channels When the image of the sun is centered in the bull s eye of the sun target all optical channels are oriented directly at the solar disk A small amount of circumsolar radiation is also captured but it makes little contribution to the signal Radiation captured by the collimator and bandpass filters radiate onto the photodiodes producing an electrical current that is proportional to the radiant power intercepted by the photodiodes These signals are first amplified and then converted to a digital signal by a high resolution A D converter The signals from the photodiodes are processed in series However with 20 conversions per second the results can be treated as if the photodiodes were read simultaneously The ozone layer a concentration of 3 atom oxygen molecules in the stratosphere is essential to life on Earth Short wavelengths of ultraviolet radiation are much mor
55. nal filter bandwidth and its nominal center wavelength see specifications for details There are 5 irradiance calibration factors C1 C5 corresponding to the nomi nal wavelengths of the instrument s filters Each calibration factor can be individually modified from the keypad Figure 4 illustrates the menu path that leads to the editing of the irradiance calibration factor on channel 2 Once the editing mode is reached the calibration factor is shown in exponential form scientific notation Ch2 cal W m 2 mV 5 345E 04 In this notation 5 345E 04 5 345 10 The instantaneous irradiance is calculated as Irradiance W m signal mV cal_factor W m mV The selected underlined digit can be incremented decremented with 4 and w keys and the selection can be changed with and 4 keys The signs can be toggled between and The exponent indicator E will be skipped automati Solar Light Co Inc 13 cally when changing the selection Pressing the Escape key allows return to higher levels and to the ready mode The number will be automatically converted to its simplest form with the first digit always gt 0 except when the whole number is zero For example 0 234E 04 will automatically become 2 340E 05 This way the best dynamic range for number editing is assured Please note that the absolute irradiance is not stored in memory after each measurement Instead the raw data in mV is stored and the displayed irradiance i
56. ncy While the higher frequencies are effectively filtered out by the analog low pass filter the basic and lower harmon ics get to the input of the A D converter with sufficient ampli Figure 10 Setting the line frequency tude to distort readings The A D converter used in Microtops rejection mode Processing Scan length Processing Selecttop Processing Line frequency Line frequency 60 Hz change Solar Light Co Inc 17 II operates on the principle that discrimination against line frequency and harmonics is obtained by properly setting the digital filter coefficients The path to Line frequency setting is illustrated in Figure 10 After selecting the frequency selection Ready mode Menu Enter lt Main menu Main menu Measurement Main menu Location Location Saved location Dy EN Push gt to select 1 Philadelphia Push gt to select 2 Mauna_Loa Figure 11 Selecting a saved lo cation Ready mode Menu Enter A E E Main menu Clock Main menu Measurement Main menu Location Location Saved location Location Coordinates Coordinates 40 03 N 75 08 W Figure 12 Setting current location geographic coordinates window the user is presented with the following screen Pressing or keys toggles the setting between 50 and 60 Hz Line frequency 60 Hz lt gt change Setting an incorrect freq
57. o graphical coordinates of the measurement site are entered just aim the meter at the sun align the image of the sun with the bull s eye and push the button In seconds the result will be dis played on the LCD Portability A small hand held device is all you need to take measurements No additional computer is necessary Computer interface A serial interface allows for the transfer of data and remote con trol of the instrument from any computer Simple text protocol makes the process easy and dependable Specialized data management software is available as an option GPS interface Microtops II understands the NMEA 0183 communication protocol and can be linked directly to a hand held GPS receiver via serial cable The GPS receiver is op tional Instantaneous results The ozone and total water vapor calculation algorithms are pro grammed in the MICROTOPS II and the results of all stored scans can be conveniently viewed on the LCD The raw data is also stored to allow retrospective adjustments of calibration con stants Non volatile memor y The raw data collected by MICROTOPS II as well as calcu lated results are stored in non volatile memory Each data point is annotated with date time site coordinates solar angle altitude pressure and temperature Low cost By implementing the latest technology instrument cost has been brought below that of comparable ozonometers without sacrificing accuracy or features Solar Light Co
58. oordinates i 18 21 current location 17 18 23 24 D data browse i 20 Data descrpton see 32 data exchange format 32 Data processing coccooccccccncononcnnnnncnanananncnanonooos 15 ELE 19 Database cetro 31 32 digital filten iene 15 16 Downloading of data 29 F factory calibrations 12 14 features Aa 5 Solar Light Co Inc G geographical coordinates 17 GPS cin 6 22 24 34 35 I Importing text essensie 31 irradiance 11 12 13 21 37 38 47 L latitude ili etd tete tret 25 Line freQuency serere 16 Location setup entm 17 Locations canna ene 30 longitude neue 18 M Microtops Organizer 23 25 28 N Non volatile memory 6 number editing 13 14 15 16 19 O optical block 5 21 27 40 41 ozone absorption 13 44 46 OZONE daria conan 5 P precipitable water 5 39 40 Pressure eene 14 17 19 21 24 pressure sensor 14 19 24 27 35 41 Q Query scorie ts 31 R Solar Light Co Inc Remote control 23 Restoring factory calibrations 14 A S an lengtli u eseu 15 Serial cable eos 23 serial port 12 13 15 17
59. rmat will have to be converted into their decimal for mats before being entered In order to enable the internal atmospheric pressure sensor the station pressure entered must be set to 0 Solar Light Co Inc 25 4 2 2 Clearing data buffer The instrument s buffer can be cleared from a computer by sending the C or c character The Mi crotops II responds with the prompt Clear data buffer Y N mon Pressing y or Y confirms the deletion of the stored data from Microtops II 4 2 3 Listing and setting saved locations The contents of the saved locations database see Saved locations on page 17 can be customized from a PC via serial port In response to a letter 1 or L pressed on the computer s keyboard the Microtops II responds with the listing of all saved locations Figure 22 The parameters printed are identified by the header North latitude is positive south negative east longitude is positive west negative To modify any of the 6 locations press Saved locations acts HKN d Loc Name Lat N Long E Alt m Pres mB m or M on the computer s key l Philadelphia 40 050 075 133 20 1013 board The Microtops II replies with 2 Mauna Loa 19 533 155 583 3397 680 the input pattern shown in Figure 23 3 Empty 400 000 000 000 0 1013 4 Empty 00 000 000 000 9 1013 Enter the location parameters follow 5 Empty 00 000 000 000 0 1013 3 h displayed th 6 Empty 00 000 000 000 0 1013 Ing the pattern I
60. rowse mode is initiated by press ing the key while in ready mode The display shows The LCD acts as a single cell window into a large imaginary spread sheet Figure 16 The top LCD line indicates the date and time of the selected record The bottom line shows the name of the parame ter and its value After entering the browse mode the window is always positioned in the upper left corner of the spreadsheet show ing the corrected ozone from the last stored scan The window can be moved through the spreadsheet with the A w and 4 keys The and 4 keys select a parameter to be displayed within one record while the 4 and w keys move the windows be tween records showing the value of the selected parameter in other records other scans top LCD line always shows the date and time 12Sep96 16 45 56 03 corr 306 5DU Solar Light Co Inc 21 Table 1 Memory contents that can be viewed on the LCD Parameter Description O3 corr Corrected ozone column in Dobson Units DU 03 1 2 Ozone column based on the ratio of channels 1 and 2 in Dobson Units DU 03 2 3 Ozone column based on the ratio of channels 2 and 3 in Dobson Units DU Water Precipitable water column in cm AOT1020 Aerosol optical thickness at 1020nm SZA Solar zenith angle in degrees 305 312 320 936 1020 305nm 312nm 320nm 936nm 1020nm Direct irradiance on a normal surface in W m2 at each of the instrument s wavelengths Raw data Signal in mV from ea
61. s calculated based on the recorded voltage and Ready mode Main menu Clock Menu Enter lt Calibrations Irradiance Calibrations Ozone cal Calibrations Water cal Water cal Water In V04 Water cal Water In VO5 Water cal Water cal K Water cal K 3 456E 00 Water cal Water cal B Water cal Water cal C Figure 6 Modifying water vapor calibration factors current calibration factors Consequently a change in the irradi ance calibration factors affects the irradiance values displayed on the LCD but not the ozone and water vapor values 3 2 1 2 Ozone calibration constants There are 7 calibration constants involved in the ozone column calculation 0112 Al difference in ozone absorption coefficients between channels 2 and 1 023 A2 difference in ozone absorption coefficients between channels 3 and 2 B12 BI difference in Rayleigh scattering coefficients be tween channels 2 and 1 B23 B2 difference in Rayleigh scattering coefficients be tween channels 3 and 2 L12 L1 difference of extraterrestrial constants between chan nels 2 and 1 L23 L2 difference of extraterrestrial constants between chan nels 3 and 2 OC a factor determined experimentally and used for air mass dependence correction of ozone Some calibration factors have 2 names associated The second designation is used for serial port communication that does not
62. s current location setup The instrument returns Current location Lat N Long E Alt m Pres mB Loc 40 055 75 131 137 0 256 The latitude and longitude are in degrees and decimal fractions thereof North latitude and East lon gitude are positive South and West are negative Altitude in meters and pressure in milliBars is fol lowed by a number indicating whether the current location is copied from one of the saved and named locations see Saved locations on page 17 If the location was set manually or from GPS the returned code is 256 To set the current location from a PC press b or B Microtops II replies with the following prompt Enter current location Lat N Long E Alt m Pres mB Loc EXX XXX tXXX XXX EXXXX XXXX x If a valid location is entered following the pattern shown on screen then the instrument will ac knowledge acceptance of the settings with OK If one of the values entered is beyond acceptable range then the message Illegal value is returned Too few numbers or incorrect pattern will result in Input ignored message Valid ranges for location parameters are as follows Latitude lt 90 90 gt Longitude 180 180 gt Altitude 1000 20000 Pressure lt 0 1100 Changes in current location are effective immediately All components of current location can be set individually from the keypad of the instrument Note map coordinates in DEG MIN SEC fo
63. selection can be changed by pressing and 4 keys When incremented or decremented each item will as sume values from the range valid for that particular item After setting the time press the Scan Escape button 3 times to re turn to ready mode Adjust clock 13Sep96 12 35 46 Figure 2 Entering the date and time Please note that the Microtops II uses Universal Time UT for editing mode all calculations This time is defined by the Earth s rotation and determined by astronomical observations The UT is related to the zero meridian which passes through the observatory in Greenwich London For ozone measur ing purposes this time can be considered equivalent to UTC Coordinated Universal Time since they do not diverge more than 0 9 second Historically the UT was called GMT Greenwich Mean Time and is being reported as such by some radio stations such as BBC Another synonym for UTC is the Zulu time This arises from the military custom of writing times as hours and minutes to gether and suffixed with a letter designating the time zone For example 2345Z 23 45UTC 23 45UT The desired time accuracy for ozone water vapor and aerosol measurements is 20 seconds The Uni versal Time is broadcast by BBC radio stations The UT can be also calculated knowing the offset between your Local Standard Time LST and UT which is a constant for each time zone and for most places it is a whole hour multiple For example if your LST is
64. site in meters above sea level PRESSURE Either the user preset station pressure or the measured pressure if instrument is equipped with pressure sensor and station pressure is set to zero SZA Solar zenith angle in degrees The SZA is 0 for overhead sun and 90 for sun on the horizon TEMP Temperature of the optical block inside the instrument SIG305 Signals in mV from all 5 optical channels SIG312 SIG320 SIG936 SIG1020 R305 312 Ratio of signals between channels 1 and 2 305 0 and 312 5nm R312 320 Ratio of signals between channels 2 and 3 312 5 and 320 5nm STD305 312 Standard deviation of ratios between channels 1 and 2 within a single scan STD312 320 Standard deviation of ratios between channels 2 and 3 within a single scan OZ305 312 Ozone column in Dobson units based on the 1 2 channels ratio OZ312 320 Ozone column in Dobson Units based on the 2 3 channels ratio OZONE Ozone column in Dobson units based on both ratios and experimentally derived compensation algorithm WATER Precipitable water column in cm AOT1020 Aerosol optical depth at 1020nm 4 2 7 Printing calibration constants All user calibration constants see Calibration constants on page 12 can be retrieved from Micro mom tops II by sending the x or X code The instrument replies with the listing of current settings Figure 25 Please note that the user calibrations are initialized at the factory and are equal to fac tory calibration
65. t decrement a selected usually underlined item while the and 4 keys change the selection 2 3 Before making first measurement To measure the ozone column several MICROTOPS II settings must be properly initialized These include 1 Universal date and time UT By choosing UT for the timing of MICROTOPS II this setting is location independent The desired accuracy is 20 seconds See Setting the time and date on page 10 2 Geographic coordinates of the measurement site Accuracy to a 5 minute angle is adequate for both latitude and longitude See chap ter O on page 17 The geographical coordinates can be picked off a map scale 1 5 000 000 or larger determined using a GPS te ceiver or obtained from a local meteorological office The instru ment s location is initially set for Philadelphia PA 3 Altitude of the measurement site The effect of the altitude setting is minor and an accuracy of several hundred meters is sufficient See Altitude on page 19 4 Atmospheric pressure at the measurement site If the Microtops II is not equipped with the optional barometric pressure sensor then the average station pressure can be used If the pressure sensor is built in then the station pressure should be set to 0 Otherwise the user preset station pressure has precedence over the measured pressure See Pressure on page 19 Other settings should remain a their factory preset state Changing these settings should only be attempte
66. tical expression for the ozone value de rived for any channel pair indexed by 1 and 2 in this paper is as follows 46 Solar Light Co Inc 1000 La dE Dm E 6 OD H where 012 0L 2 the difference in the ozone coefficients for respective channels 1 and 2 B12 Bi B2 the difference in the air scattering coefficients for respective channels 1 and 2 L 12 L1 L2 In T I 2 the combined extraterrestrial constant Figure 30 Note Please see Appendix 2 Interpretation of the Data for the current updated form of equation 6 Luz corresponds to measurement of the incident radiation above the earth s atmosphere no attenua tion from any absorption or scattering process It is obtained by extrapolating a plot or doing a regression analysis of In I Db vs u Langley plot The ozone column thickness is expressed in Dobson units which correspond to milliatm cm Calibration was based on the Langley method which has a long history of application to the Dobson instruments A regression analysis is carried out using the most linear portion of Langley plot u lt 1 75 for each channel and the data is appropriately weighted The intercept gives the extraterrestrial constant for that channel The os and B s for each channel were calculated using a model developed by the TERC project The exponential equation 1 when linearized gives an expression of the form In I In I auQ uP P 7 For m
67. ude is fixed based on the previous altitude information The 3D NAV message appears when the GPS is able to calculate the altitude as well As soon as the location fix is available the GPS receiver sends this information to the Micro tops II via the serial port The Microtops II acknowledges reception of valid latitude longitude Solar Light Co Inc 35 13 14 15 16 and time information by sounding the buzzer 3 times Usually a new fix is sent every 2 seconds and the buzzer will sound again The on board clock of the Microtops II is automatically syn chronized with the accurate time broadcast by GPS satellites Garmin GPS also sends the altitude information if in the 3D NAV mode This information is specific to Garmin only since it is not included in the NMEA standard Microtops II will ac knowledge the reception of altitude information by sounding the buzzer 2 times If all components are received simultaneously latitude longitude time and altitude then the buzzer will beep 5 times 3 beeps immediately followed by 2 When the complete information is sent to Microtops II the GPS receiver can be turned off and disconnected from Microtops II The GPS receiver does not provide local pressure and this setting is not changed by the GPS If the Microtops II is equipped with an optional pressure sensor then leaving the station pressure at 0 will enable the pressure measurement Otherwise the station pressure has to be updated m
68. uency will result in increased variability of measurements in an environment polluted with line emitted noise Pressing Escape traverses the menu structure in reverse order and brings control back to the ready mode 3 3 Location setup Setting the geographical coordinates of the measurement site is essential for ozone and water vapor measurement The location is subsequently used in a routine that calculates the solar zenith an gle and air mass during measurement Other factors that affect the calculation of those two parameters are altitude and baromet ric pressure The currently active settings are stored in a current location buffer The current location buffer can be viewed and edited from a remote computer via serial port chapter 4 2 1 Valid ranges for location parameters are as follows Latitude lt 90 90 gt Longitude 180 180 gt Altitude 1000 20000 Pressure lt 0 1100 3 3 1 Saved locations In addition to the current location buffer the Microtops II con tains an internal database of 6 named locations that can be pro grammed from a PC via the serial port chapter 4 2 3 Any loca tion record from the database can be quickly copied to the cur rent location buffer using the Saved location feature It facili tates the location setup when taking measurements in multiple locations The additional benefit of naming locations is an option 18 Solar Light Co Inc worth considering Please note that
69. up Communications Setup Baud Rate CommPort Auto Detect Auto Detect C 19200 COMI C 9600 C come O 4800 COM3 2400 COM4 The serial port settings com port and baud rate can be set using the Communications command in the Options menu The default settings are Auto Detect for baud rate as well as for com port which will automatically detect the appropriate port and baud rate for the Microtops to communicate with the PC If the port and baud rate are not going to be changed fixed settings can be selected instead of the auto detection process Solar Light Co Inc 29 5 2 Microtops Operation 5 2 1 Downloading data MICROTOPS Il Organizer D File Tools Options Help F connected T Cal factors 0 Records received Baud rate 19200 on Com2 Downloading of data is accomplished by clicking the Download button on the bottom center of the form Be sure that the Microtops is connected to the PC with the supplied cable and is turned on After clicking the Download button the contents of Microtops II data buffer will be copied into the DATA DBF database located in the PC 5 2 2 Clearing data buffer The data buffer of the Microtops can be cleared by selecting the Clear Buffer command in the Tools menu The user will be prompted to make sure that the data buffer should be cleared 30 Solar Light Co Inc 5 2 3 Modifying saved Microtops II locations MICRO
70. use the data capture feature of your communication software Various programs use different ways of initiating data capture Please refer to your program s man ual for specific instructions 4 2 5 Initiating a scan won The measurement scan can be initiated from a remote computer by sending the s or S character via serial port This feature can be used to control the Microtops II when mounted on a tripod or sun tracker Contact Solar Light for details on sun trackers 4 2 6 Setting date and time If the t or T code is received by the Microtops II the instrument replies with the prompt for cur rent universal date and time UT Date amp time UT mm dd yy hh mm ss ENTER If a valid date and time is entered following the displayed pattern then the internal clock is set to that time and the instrument replies with OK If the entry is not valid then the Microtops II will display Invalid message The internal clock can be also set from the keypad see Setting the time and date on page 10 Solar Light Co Inc 27 Table I Contents of Microtops II data buffer Field Comments SN 5 digit serial number of the instrument with leading zeros DATE The universal date of the measurement TIME The universal time of the measurement LATITUDE The latitude of the measurement site in degrees LONGITUDE The longitude of the measurement site in degrees ALTITUDE The altitude of the measurement
71. when applied to ozone absorption and Rayleigh scattering by the atmosphere gives the simple equation I Leger 1 I is the intensity of the light of a particular wavelength before it passes through the atmosphere I the intensity remaining after all processes attenuating the incident radiation have occurred Q is the amount of ozone is the ozone absorption coefficient at that specific wavelength p the ratio of the actual and vertical path lengths of the radiation through the ozone layer P is the pressure of the at mosphere in mB P is standard pressure 1013 25 mB and miis a quantity known as the airmass which is defined as the ratio of the actual and vertical path lengths of the radiation through the entire atmosphere to the detector For m lt 2 the pl and m are virtually identical Other processes including molecular scattering Rayleigh scattering coefficient represented by B by the atmosphere and par ticulate scattering produced by haze water plus atmospheric pollutants of micron particle size are included as shown into the exponent for a complete representation of atmospheric attenuation It is customary to ignore the particulate scattering Studies have shown that even the worst haze condi tions do not effect ozone measurements by more than a few percent and much less under usual con ditions Expressions for u and m quantities are as follows m sec Z 0 0018167 sec Z 1 0 002875 sec Z 1 00080
72. xxxx is the number of records to be 26 Solar Light Co Inc REC 0001 CR FIELDS CR SN DATE TIME LATITUDE LONGITUDE ALTITUDE PRESSURE SZA TEMP SIG305 SIG312 SIG320 SIG936 SIG1020 R3 05_312 R312_320 STD305_312 STD312 320 02305 312 02312 320 OZONE WATER AOT1020 ID CR 03116 10 02 1996 19 43 15 19 533 155 583 3397 680 43 32 27 0 35 01 83 26 124 61 345 24 427 21 0 4205 0 6682 0 003 0 002 298 5 302 2 302 3 1 24 0 123 2 CR END CR Figure 24 Data transfer format Long lines are wrapped around and a CR marker is placed where the carriage return character is sent downloaded The keyword FIELDS in the next line is followed by the list of field names that corre spond to the structure of downloaded data When the transmitted information is captured to a file and subsequently imported to a spreadsheet then these field names appear above the columns of data facilitating data management The field names are also used by the Microtops Organizer software so any changes in data format are accommodated automatically The data fields are separated by commas and records are separated by CR characters This format is accepted by most data processing programs Use comma separated format when importing the data Table 1 contains detailed description of all fields in the downloaded data The transmission is ended by the keyword END followed by CR character To save the transmitted data to a disk

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