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User`s Guide MICROTOPS II

1. D are 2 2 1 Calibration constants leasurement Microtops II stores two sets of calibration factors the factory cali B e brations FC and user calibrations UC The FC are programmed into the instrument during a calibration process and cannot be modi t ppm fied by the user The UC are initially set to equal FC but can be indi vidually modified from the instrument s keypad should the user re DU NH e calibrate the instrument on his own The Restore calibrations func tion copies FC into UC restoring the initial configuration of the in ona ca ao strument The UC set can be read via serial port using function X in eI the remote control menu See page 27 aT NL NN 2 2 1 1 Irradiance calibration constants pem The calibration factors for irradiance link the measured signal in mV MT with the absolute radiometric power in W m of the direct solar radia os cal aa tion The field of view of the Microtops II is 2 5 therefore larger Figure 4 Modifying irradiance than the solar disk s subtending angle A small correction for the cir calibration factors cumsolar radiation is taken into account when the meter is calibrated All irradiance calibration factors are derived for the nominal filter Ready mode bandwidth and its nominal center wavelength see specifications for details Main menu There are 5 irradiance calibration factors C1 C5 corresponding to the nomi Er nal wavel
2. eee 33 user calibrations ssse 12 27 LT sodes E D pd Bat 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 of 2 J 79 3 0 02 2 a a a a 4 where I is the extraterrestrial constant of the channel I is the measured signal a and f are the ozone and Rayleigh absorption cross sections respectively m and p are 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
3. where an a a 2 the difference in the ozone coeffi cients for respective channels 1 and 2 Bi2 Bi B2 the difference in the air scattering coefficients for respective channels and 2 L L1 L2 Ind I 2 the combined extra Figure 30 Illustration of the MICROTOPS II calibration terrestrial constant Figure 30 procedure gt e In 305 5nm signal e In 312 5nm signal Note Please see Appendix 2 Interpretation of the Data for the current updated form of equation 6 46 Solar Light Co Inc Li2 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 re gression analysis of In I 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 a s and f 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 apQ upP P 7 For m pit
4. Baud rate 9600 incr decr crease or decrease the serial port s speed The choices available are 2400 4800 9600 and 19200 bits per second Pressing Escape key brings the control back to upper menu levels and ready mode Ready mode Menu Enter lt Main menu Clock Main menu Measurement Main menu Location Main menu Data logging Main menu Baud rate L Baud rate 9600 incr decr Figure 19 Adjusting serial port speed baud rate Solar Light Co Inc 23 3 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 3 4 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 II If a third party communic
5. Ready mode Menu Enter lt Main menu Clock Main menu Measurement Measurement Calibrations Measurement Processing Ci Processing Scan length bl Scan length 32 scans Figure 8 Setting the scan length Ready mode Menu Enter Main menu Clock Main menu Measurement LJ Measurement Calibrations Measurement Processing L1 Processing Scan length Li Processing Select top EF sess 04 samples Figure 9 Setting the number of top ranking samples 15 restores all initial calibrations and measurement settings The path to the restore screen is shown in Figure 7 The user is Restore calibr Yes gt gt presented with the following screen When the above screen is displayed the gt 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 2 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
6. Inc 37 measuring reference instrument and a perfectly clear sky for at least half a day can attempt the cali bration 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 5 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 sensi 305 0nm 10 tivity rel to peak trans 312 5nm 10 mission 320 5nm 10 936 1020 nm 10 Angle of view 2 95 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 Battery life 4xAA alkaline batteries 50hrs min continuous operation 10 min inactivity shutdown Weight Size 21oz 600 grams 4 W x 8 L x 1 7 D 10 x 20 x 4 3cm The irradiance cal factors are
7. 1 2 Major features i U High grade filters are embedded in a solid cast aluminum housing that e High accuracy High grade fil bedded lid 1 h h Solar Light Co Inc 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 geo 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 de pendable 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 mem
8. 20 5 367 370 1993 5 GJ Labow et al Estimating Ozone with TOPS Instruments Practical Operation and Compari sons in press 6 Lawrence E Flynn Estimating Ozone with TOPS Instruments Theoretical Model and Error Analysis in press 7 Basher and R W L Thomas Applied Optics 18 3361 62 1979 8 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 10 J Meeus Astronomical algorithms 1st ed Willmann Bell 1991s 50 11 12 13 14 15 16 17 18 Solar Light Co Inc 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 absorp tion band calibration measurements and data applications Proceedings International Geo science 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 S
9. DRE ER RERO TARDE ee ERES HAC ROT 10 I UOnn 51 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 opti cal thickness at 1020nm 1 1 Principle 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 reflections 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 sig nals are first amplified and then converted to a digital signal by a high re
10. 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 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 2 1 2 Clock trimmer Clock The absolute accuracy of the low power clocks is not adequate for long term time keeping Thus a software clock trimmer Clock was implemented into the instrument When given the clock s Adjust clock error in seconds 30 days the algorithm periodically skips or adds e 5 seconds effectively keeping the clock within 5 seconds from Clock trimmer accurate time The residual error would depend mainly on the storage temperature of the instrument To calibrate the trimmer follow these steps 070 sev30days 1 Set the clock to an accurate time for example from a radio Figure 3 Setting the clock trimmer broadcast 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
11. 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 1 level down by pressing Eor Menu Enter key press to select the Clock trimmer in the Clock menu and press Xor 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 E and 4 keys If the cursor points at the sign character then the w and 4 buttons will toggle it between and To go back to the RDY mode press the Escape key 3 times 2 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 Solar Light Co Inc Ready mode settings described in chapter 2 2 2 Data processing affect the meas urement and data manipulation process Menu Enter Main menu Clock
12. consecutive series of ozone measurements performed on a fairly clear day with the same instrument Each of the measurement series employs a different sun targeting technique hand held with targeting enhancement based on a series of 32 rapid measure ments measurement time approx 10 seconds hand held with just averaging of measurements and the third series was measured with MICROTOPS II mounted on a tripod Table 3 shows the standard deviation of each measurement series the hand held with targeting en hancement offering the most repeatable results with a standard deviation of 0 18 The targeting en hancement produces results are slightly better than tripod mounted instrument since it compensates the targeting error due to limited resolu tion of the instrument s targeting system Table 3 Performance of sun targeting methods Targeting method Standard deviation Hand held no enhancement 0 87 Hand held enhanced 0 18 0 23 1 4 Calibration and 314 312 measurement of a ozone umm Calibration of the MICROTOPS II in 5 306 strument requires that the intensity of 304 radiation measured at each channel be analyzed assuming the validity of the Lambert Beer law which when applied to ozone absorption and Rayleigh scat tering by the atmosphere gives the sim ple equation I I e ouiO mpP Po 1 Figure 29 Series of consecutive MICROTOPS II measurements m 3 of ozone employing three differen
13. display shows Eg a The LCD acts as a single cell window into a large imaginary spread H measurement sheet Figure 16 The top LCD line indicates the date and time of O the selected record The bottom line shows the name of the parame Location ter and its value After entering the browse mode the window is SZ always positioned in the upper left corner of the spreadsheet show Data logging ing the corrected ozone from the last stored scan GS The window can be moved through the spreadsheet with the 4 w gt Clear memory and 4 keys The K and 4 keys select a parameter to be displayed a within one record while the 4 and w keys move the windows be tween records showing the value of the selected parameter in other Cear al gt gt records other scans top LCD line always shows the date and time Figure 17 Clearing the entire so the record can be easily identified memory buffer The normal direct irradiance displayed is not stored in memory In stead it is calculated on the fly when displayed or downloaded 12Sep96 16 45 56 O3 corr 306 5DU Solar Light Co Inc 21 c viewed on the LCD Parameter Desqription ES Main menu Clock Corrected ozone cc urn in Dousor Units WUJ Ozone column bas 1 n 38 38 ch feidinsa2 E Tem Units DU Ozone column bas 1 on R Tatio of ahannels 2 and 3 in Dobson Units DU Prec pitable water column in cm Main menu Measurement Aerqsol optical thi
14. frequency affects the internal digital filter s transfer function and enables elimination of line interference 2 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 the 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 is 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 avail able for taking the measurement 16 Solar Light Co Inc 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 2 2 2 0 Number of averaged samples A signal strength factor is calculated for each sample base
15. in data exchange format 5 3 4 Exporting in data exchange format 5 3 5 Data description sie ie tei ee PRESE ota ERR ERE REPRE EE iiia 5 3 6 User calibration actors 3 cokes creer oa Voted escalate SO I RU vin cates Sonu dU US 6 GPS COMMUNICATION eeenen serata eee ereer eee eee 34 6 1 SETTING UP GD5 a Dg e RR p RD 34 7 MAINTENANCE cccssssssssssscessessssscssssssssssessssessssscssssessevessssessssesscsessassesessssesssssssssassesessesesees 36 7 1 CLEANING AND STORAGE 5 ettebelt eee e iuret tie tete e ED e Cadet LEDS EATS TD eaae dues s 36 7 2 BATTERY MAINTENANCE ccccssssscesssssccssscsccssscsccsssceccsseesesesssececseeecesssescsesseecessseecesssecessneeecses 36 7 3 CALIBRATION ettces ensi sete tb oto at etat ted ree ee 36 ENUOn M 38 9 THEORY OF OPERATION eere eeen senos tatnen tata stata eers 39 9 1 INTRODUCTION inea shel beds o Ere e ERE en ERE E ee Pre REALE Re REST 9 2 BASICS OF THE INSTRUMENT 9 3 INSTRUMENT DESIGN si 3 tania ot oi pe NOUIS 9 3 1 Optical block ii steterit datgaqnb i REDE 9 3 2 Signal conditioning and processing 9 3 3 Sun targeting onte tette eene 9 4 CALIBRATION AND MEASUREMENT OF OZONE 9 5 DERIVATION OF WATER VAPOR sees enne nennen enne nnn sse Enaria en inar ina iaer Eoas epai naiean 9 6 CONCLUSIONS e 9 7 REFERENCES e duet P
16. position 11 Once the position is acquired the GPS receiver shows 2D NAV message if the latitude longitude is fixed based on the previous altitude information The 3D NAV message appears when the GPS is able to calculate the altitude as well 12 As soon as the location fix is available the GPS receiver sends this information to the Microtops II via the serial port The Microtops II acknowledges reception of valid latitude longitude 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 synchro nized with the accurate time broadcast by GPS satellites Solar Light Co Inc 35 13 Garmin GPS also sends the altitude information if in the 3D NAV mode This information is spe cific to Garmin only since it is not included in the NMEA standard Microtops II will acknowl edge the reception of altitude information by sounding the buzzer 2 times 14 If all components are received simultaneously latitude longitude time and altitude then the buzzer will beep 5 times 3 beeps immediately followed by 2 15 When the complete information is sent to Microtops II the GPS receiver can be turned off and disconnected from Microtops II 16 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 press
17. sec Z 1 0008083 sec Z 1 2 KLH H S aren 3 R h R ry sin Z 1 or more conveniently U T aa 4 vl v sin Z where v is a geometric factor for the height of the ozone layer given by R cT Vee 5 R h R mean earth radius 6371 km 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 7 5a 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 calculation 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 40 03 max er ror for the entire practical range of latitudes 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 negligible 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 external computer The theoretical expression for the ozone value derived for any channel pair indexed by 1 and 2 in this paper is as follows P 0 Extrapolation mmi nG n L to miu 0 Q DU 2 Ai H 6
18. 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 scans stored in me ter s memory 4 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 5 To view the measurement results press the E button The K and 4 keys will scroll through the parameters for an individual record one scan or measurement The 4 and 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 2 Setup 2 1 Real time clock The Microtops II has an on board real time clock and calendar RTC that provides time for the calcu lation 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 calen dar and clock trimmer can be modified from the keypad chapter 2 1 1 or remotely via computer chapter 3 5 8 2 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 bor Menu Enter key twice Figure 2 Adjust clock Ready mode 13Sep96 12 35 46 The LCD will show the current date amp time with
19. yields a value for In 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 a and B change differently with wavelength To simplify the determination 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 4 2 1349 x 10 9 e 0 14032 8 BA 16 407 0 085284 A 0 00011522 1 9 where A is the wavelength in nm Substituting 8 and 9 into 7 one can calculate the slope A of the In I vs p line A 1 2 1349 x i05 e 0140529 4O 1000 16 407 0 085284 A 0 00011522 47 P P 10 The 1 1000 factor associated with Q Table 4 Effective wavelength vs filter s center wavelength comes from unit conversion between Dob MICROTOPS II Filter s Typical effective son Units and atm cm The effective wave center wavelength nm wavelength nm length XA of each channel s interference 300 8 filter is determined by findi
20. 3 Location input pattern 25 Figure 24 Data transfer format Long lines are wrapped 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 271DU 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 47 Figure 32 Measurement of ozone over wide range of air mass in Philadelphia PA May 31 1996 _ 48 52 1 Index A air mass eee 13 17 19 40 42 47 48 altitude s 6 17 18 19 25 27 averaging 15 16 43 B Battery UEO 36 Batid TTT 22 C calibration5 11 12 13 14 15 16 19 21 23 27 28 32 33 36 37 39 43 45 47 49 circumsolar radiation ss 5 12 Clearing data buffer Clearing the memory 19 21 collimator collimators Computer communication Coordin tes isenana current location see D data bro
21. 8 533 155 583 3103 8 20 96 1 31 18 PM Mauna Loa 18 533 155 583 3103 8 20 96 1 31 28 PM Mauna Loa 18 533 155 583 3103 8 20 96 1 48 14 PM Mauna Loa 18 533 155 583 3103 8 20 96 1 48 23 PM Mauna Loa 18 533 155 583 3103 8 20 96 1 48 32 PM Mauna_Loa 18 533 155 583 3103 8 20 86 1 48 41 PM Mauna Loa 18 533 155 583 Database locations can be changed by selecting the Rename Database 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 blank 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 13 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 37 Solar Light Co Inc Setup communications protocol port and baud rate Start a log file using a txt exte
22. Micro tops II menu Solar Light Co Inc When editing various settings the general rule is that 4 or w incre ment decrement a selected usually underlined item while the gt and 4 keys change the selection 1 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 0 on page 17 The geographical coordinates can be picked off a map scale 1 5 000 000 or larger determined using a GPS receiver or obtained from a local meteorological office The instrument s lo cation 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 Pressu
23. User s Guide MICROTOPS II Ozone Monitor amp Sunphotometer Version 2 43 Revision C Solar Light Company Inc 2001 Solar Light Company All rights reserved 100 East Glenside Avenue Glenside PA 19038 USA tel 215 517 8700 fax 215 517 8747 info solarlight com www solarlight com Document No MTPOS October 2011 Printed in the United States of America Solar Light Co Inc 3 Contents 1 INTRODUCTION e ca ckasc acces es ego ropa cero cepe reo seno ee vo eoe Deos eaae sovevecsesevocsassdesecsveadescesssscotectes 5 1 1 PRINCIPLE OF OPERATION 5 creer tied ee enne teen eere REY Ee aS eee roS ETENEE a EEES EEKi en 5 1 2 MAJOR FEATURES iuit eere rin Ple ete teen ee He eee ea eae RENE SERAIS SERE 5 2 QUICK STAR Tirana aiiiar iini iieiaei 7 2 1 POWER 91 octo ied T A TTT 2 2 MENU STRUCTURE 2 3 BEFORE MAKING FIRST MEASUREMENT sese eee 8 2 4 FIRST MEASUREMENT 9 TTT Nee Ett aE RE teed 8 3 SETUP EETA E E A TE T 10 3 1 REALE TIME CLOCK 5 eicere E PR RR EAR RO RD ERA T 3 1 1 Setting the time and d te iua eie tle dieere 3 1 2 Clock trimm r osc eS P ER NAAR RE EEE AES EEE ERE CLONE T Y S 3 2 MEASUREMENT PARAMETERS AND CALIBRATION CONSTANTS 3 2 1 Calibration Constants ui t Oe EE RAI PU DUE PNIS 3 2 2 Data processing 3 3 LOCATION SETUP 3 3 1 Saved locations 3 3 2 Coordinates 3 3 3 Altitud sa eia eigene e ae etae e p ema 3 3 4 OAAR A ANAE E ENA EAT RERO P
24. aded data When the transmitted information is captured to a file and subsequently imported to a spreadsheet 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 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 accom modated 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 use the data capture feature of your communication software Various programs use different ways of initiating data capture Please refer to your program s manual for specific i
25. adiation 7 is the aerosol 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 the form Bn exp 7 m Voz 12 48 A radiation transfer model was used to calculate the spectral irradiance around 940nm for stan dard 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 simulated results The Vo for the instrument is found from an ex trapolation to air mass zero of the linearized 11 In V 7 n lt 1n V4 k um 13 The k and b are already known therefore In V is the intercept from linear regression of 13 versus m Solar Light Co Inc Ozone 300 305 Ozone 305 312 Corrected ozone Figure 32 Measurement of ozone over wide range of air mass in Philadelphia PA May 31 1996 For the water vapor calculation the aerosol scattering coefficient T at 940nm is needed In MICROTOPS II the aerosol scattering coefficient z at 1020nm is first measured based on 12 The Vo is obtained from extrapolation of a Langley plot on a sunny day From the radiation transfer
26. ation software is used then some minimal setup is necessary 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 3 The port settings should be 8 Data bits 1 stop bit no parity 4 ANSI terminal 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 3 5 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 3 5 3 Listing and setting current location Code a or A sent to Microtops II prompts the instrument to return its current location setup The instrument returns Current location Lat N Long E Alt m Pres mB L
27. b bu bet Da MM E etes 3 4 DATA LOGGING eene 3 4 1 Viewing the stored data 3 4 2 Clearing the memory buffer riasin anea esset eene tnnt ether tne Tonie 3 4 3 Deleting last measurement eese 3 5 BAUD RATE eei re PERI EDINSEA 4 COMPUTER COMMUNICATION eene etna ntn tts tn senos east n state tata son eee 23 4 1 PHYSICAE CONNECTION s iiti ot SE REPRE ES to ret EE E EE 23 4 2 REMOTE CONTROL s 4 2 1 Listing and setting current location sss sese 24 4 2 2 Clearing data buffer er RR RD ERE e enge aei 4 2 3 Listing and setting saved locations 4 2 4 Downloading data buffer 4 2 5 Initiating a scan esee 4 2 6 Setiing date nd Wne snos ro prO pn ibd 4 2 7 Printing calibration constants essent nennen enne 5 MICROTOPS ORGANIZER SOFTWARE esee eee enses en enntnsnattstn ansia ereenn 28 4 Solar Light Co Inc 5 1 INTROBUGTION 5 eiecti teri ater Ies TT ses free Ie eee NUM eds 5 1 1 Software installation 5 1 2 Communication setup 5 2 MICROTOPS OPERATION 5 2 1 Downloading data ee oaa ED omen ed odi 5 2 2 Clearing dat buffer 4 e e ee het re eee E EE Eee EO Pa eet 5 2 3 Modifying saved Microtops II locations 5 3 DATABASE OPERATIONS i iie o Du DRE ER NER TOI RN OE EA 5 3 1 Changing location names in the computer database eee 5 3 2 Importing text files sss sees eee eee 53 3 Importing files
28. button the contents of Microtops II data buffer will be copied into the DATA DBF database located in the PC 1 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 1 2 3 Modifying saved Microtops II locations MICROTOPS II Location Settings Current Microtops Location Settings loc Name Lat N Long e Att 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 0 Empty 0 000 0 000 0 Empty 0 000 0 000 0 Retrieve 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 1 3 Database Operations 13 1 Changing location names in the computer database l Change Database Location Names Latitude Longitude Location Name Bj 0 quem rue R99 e 598 Records Found LATITUDE LONGITUDE 0 3 25 96 4 23 05 PM Mauna Loa 1
29. c 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 is calculated based on the recorded voltage and 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 um lal 2 2 1 2 Ozone calibration constants There are 7 calibration constants involved in the ozone column calculation Main menu Measurement a12 AI difference in ozone absorption coefficients between channels 2 and 1 a23 A2 difference in ozone absorption coefficients between Calibrations irradiance channels 3 and 2 Cameos B12 B1 difference in Rayleigh scattering coefficients between channels 2 and 1 Calibrations Water car p23 B2 difference in Rayleigh scattering coefficients between channels 3 and 2 Water cal Water In vos L12 L1 difference of extraterrestrial constants between chan Water cal nels 2 and 1 Water In V05 L23 L2 difference of extraterrestrial constants between chan nels 3 and 2 ae OC a factor determined experimentally and used for air mass ater cal 3 456E 00 dependence correction of ozone Some calibration factors have 2 names associated The second Water cal Water cal B R l i designation is used for serial
30. cation ID code 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 Oth erwise 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 entered 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 4 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 4 or w keys Enter a lower level by pressing E 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 chap ter 2 Setup on page 10 Ready mode Main Menu Clock Adjust Clock Main Menu Measurement Calibrations Scan length Select top Line frequency Main Menu Location Main Menu Data logging Clear memory Delete last Main Menu Baud rate Figure 1 Simplified
31. ckness at 1020nm Main menu Solaf zenith angle in degrees Location FT N x 7 d Dirett irradiance on a normal surface in W m2 at each of the instrument s wavelengths 305nm 3 2j Main menu Raw data Signal in mV from each channel Data logging 936nm 1020nnt 305 312 4 F HpRatie between 1 and 2 channel t Data logging 312 320 Clear memory Rati between 2 and 3 channel Coordinates Data logging Geographical coordinates of the measurement site in degrees and minutes Delete last E E Alt eee aS _lAltithde of the measurement site in meters above sea level Pressure L etric pressure at the measurement site Either the measured one or the pre set station Delete scan 25 Mure see Pressure on page 19 Yes gt gt Temp 18 Deletine last d Temperature of the internal optical block in degrees Celsius cord 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 2 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 presented with the screen The top line shows the number of data records scans currently in memory The bott
32. d 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 then 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 se lected samples will speed up the measurement process 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 Irradiance calibration constants on page 12 The instrument does not allow this setting to be lower Main menu Sick than 1 or higher than scan length Main menu Measurement 2 2 2 3 Line frequency The most common source of interference in sensitive elec tronic equipment is the electromagnetic rad
33. derived for the nominal FWHM and center wavelengths listed above Solar Light Co Inc 39 1 Theory 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 precipi table 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 1 1 Introduction Several attempts have been made to construct an inexpensive portable sunphotometer for the purpose of t
34. e database does not modify the contents of current location buffer Head d 2 3 2 Coordinates mag The geographic coordinates in the current location buffer can be modified from the keypad Figure 12 The LCD will show Main menu Main menu Measurement Coordinates Mial 40 03 N 75 08 W ain menu Location n 5 The selected underlined item can be incremented decremented with 4 and keys and the selection can be changed with E and 4 CE keys The latitude and longitude directions will change N S and WIE respectively Pressing Escape key allows return to higher Locati E La RUE levels and to the ready mode The degrees and minutes 1 60 are modified independently Please note that coordinates are prre sometimes given in degrees and decimal fraction of a degree In that case proper conversion is necessary An accuracy of a 5 min ute angle is adequate for both latitude and longitude Altitude 0345 m a s l The change of coordinates is effective immediately It will affect Figure 13 Setting current location only measurements made after the change altitude Solar Light Co Inc 19 2 3 3 Altitude The altitude is used for the calculation of the radiation effective path u through ozone layer Microtops II accepts the altitude in meters Ready mode Menu Enter Mein monu above sea level m a s 1 The altitude in the current location buffer can i be modified from the k
35. e sensor the station pressure entered must be set to 0 Solar Light Co Inc 25 3 5 4 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 3 5 5 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 Loc Name Lat N Long E Alt m Pres mB m or M on the computer s key Ls Philadelphia 40 050 075 133 20 1013 S s 2 Mauna Loa 419 533 155 583 3397 680 board The Microtops II replies with 3 Empty 00 000 000 000 0 1013 the input pattern shown in Figure 23 4 Empty 400 000 000 000 0 1013 5s Empty 00 000 000 000 0 1013 x 6 ed 100 000 000 000 0 1013 Enter the location parameters follow ing the pattern displayed on the screen First is a single digit number of the location that is being changed The max length of location name is 14 characters Only alpha
36. engths of the instrument s filters Each calibration factor can be ae individually modified from the keypad por Figure 4 illustrates the menu path that leads to the editing of the irradiance calibration factor on channel 2 Calibrations irradiance Once the editing mode is reached the calibration factor is shown in exponen tial form scientific notation Calibrations Ozone cal Ozone cal Ozone cal L12 E Ch2 cal W m 2 mV Ozone cal L23 45 345 E 04 CI Ozone cal L23 49 029E 02 In this notation 5 345E 04 5 345 10 The instantaneous irradiance is Oro ad a12 calculated as osea um Irradiance W m signal mV cal factor W m7 mV Ozone cal Ozone cal p12 The selected underlined digit can be incremented decremented with 4 and oor cl F23 w keys and the selection can be changed with and 4 keys The signs can be Figure 5 Modifying toggled between and The exponent indicator E will be skipped automati ozone calibration fac tors 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 dynami
37. er of 0 005 year Real time and date for the solar zenith angle calculation is provided by the on board clock The inher ent 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 sec onds 30 days and the program will periodically skip or add a few seconds in order to maintain the clock accuracy to within 5 seconds 13 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 instrument 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 aver aged and passed for further processing These are the records for the best positioning of the sun s im age 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
38. eypad see Figure 13 When editing altitude the Main menu number editing rules apply The number editing rules are described in chapter Irradiance calibration constants on page 12 An accuracy of several hundreds meters is sufficient Measurement Main menu Location Location Saved location Location Coordinates Location Altitude Location Pressure Pressure 1013 mB Figure 14 Figure Setting the station pressure 2 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 in fluences the Rayleigh scattering process and should be taken into ac count when calculating ozone For most applications it is sufficient to enter a mean station pressure Microtops II accepts the pressure in mil liBars mB The menu path is shown in Figure The number editing rules are described in chapter Irradiance calibration constants on page 12 Pressing Escape after the number is set returns to upper menu lev els An accuracy of 20 mB is sufficient Figure 15 shows how the sta tion pressure changes with altitude If the altitude is not known it can be estimated based on pressure measurement To facilitate measurements the Microtops can be equipped with an optional pressure sensor In this case the station pres sure should be set to zero If the pre set station pres sure is not zero it takes precedence over the pres
39. he field of view of each of the optical channels is 2 5 The precipitable water column 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 1 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 1 3 4 Optical block The success of the instrument depends on its ability to measure ozone column with long term stability under a broad range of air masses and atmospheric conditions The entire instrument and all subsystems were analyzed in a series of computer simulations The ini tial design goal of an overall precision better than 346 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 criteria and were realistic at the same time 300 0 nm Described below are some of the criti channe cal issues considered duri
40. hm WATER Precipitable water column in cm AOT1020 Aerosol optical depth at 1020nm ID User defined identification code see Menu structure on page 7 3 5 9 Printing calibration constants All user calibration constants see Calibration constants on page 12 can be retrieved from Micro 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 constants Current calibration constants S N 03106 Al 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 1 Microtops Organizer Software 1 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 in stalled In addition the software enables the user to set up locations for the instrument and also g
41. iation 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 frequency Broess While the higher frequencies are effectively filtered out by the Scan length analog low pass filter the basic and lower harmonics get to Poean the input of the A D converter with sufficient amplitude to Select top distort readings The A D converter used in Microtops II op Processing erates on the principle that discrimination against line fre Line frequency quency and harmonics is obtained by properly setting the digi tal filter coefficients EH Line frequency 60 Hz lt gt change Figure 10 Setting the line frequency rejection mode Solar Light Co Inc 17 The path to Line frequency setting is illustrated in Figure 10 After selecting the frequency selection window the user is presented with the following screen Pressing or 4 keys toggles the setting between 50 and 60 Hz Setting an incorrect frequency will Ready mode Menu Enter lt Main menu Clock Main menu Measurement Main menu Location Push gt to select 1 Philadelphia Push gt to select 2 Mauna_Loa Figure 11 Selecting a saved loca tion Main menu Clock Main menu Measurement Main menu Location Location Saved location Location C
42. ides the current atmospheric pressure needed for the Rayleigh scattering calculation Special consideration was given to the optical filters and photodetectors particularly for the UV channels The most critical and difficult to meet was the requirement for high out of band rejection The computer simulation called for leakage no greater than 107 A lt 650nm for 300nm filters Lower wavelength filters have more strict leakage requirements because the in band signal is weaker than that at higher wavelengths Typical shapes of the filters transmissions are shown in Figure 27 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 Max out of band transmission relative 107 2 lt 650nm 10 3 650nm 10 2 lt 650nm to peak 10 A gt 650nm 10 A gt 650nm 10 A gt 650nm Min peak transmission 1576 Temp coef of center wavelength 0 005 nm C Wet dry shift 0 1nm Long term stability 0 1nm year Operating environment temp 20 50 C hum 0 100 42 Solar Light Co Inc repeatability of center wavelength and FWHM within a batch was in the order of 0 1nm The novel technology for deposit ing the filter s layers and coatings assures long life and stability 10000 0 1000 0 T 100 0 The GaP photodetectors used in the MICROTOPS II are characterized by
43. ives the ability to add calibration factors to the database for further calculations of ozone values 1 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 1 1 2 Communication setup Communications Setup r Baud Rate Comm Port Auto Detect Auto Detect C 19200 COMI C 9600 C COM2 C 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 1 2 Microtops Operation 1 2 1 Downloading data File Tools Options Help 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
44. ma delta A D converter 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 3u V RMS with 2 5V full scale e The A D converter s filter is programmed to reject line frequency interference user selectable 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 leaving 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 resistors with temperature coefficients below 0 005 C The amplifier s offset is automatically compensated every time the instrument is powered on Both the offset and full scale of the A D converter are automati cally calibrated before each scan The full scale calibration relies on a high performance voltage ref erence with the temperature coefficient under 0 001 C and long term stability in the ord
45. model a relationship between Ta and 7 2 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 Tal 1 16 Ta2 14 From 12 13 and 14 the vertical water vapor column is calculated as V Voz 7 m 1 116 of lb V S km 1 6 Conclusions 15 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 Comment MM1 From i user marian mtops observ TARGE TARGETING 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 cour tesy NOAA Climate Monitoring and Diagnostic Laboratory The MICROTOPS II instrument was previously calibrated in Mauna Loa Hawaii under substantially different climatic conditions Com parisons 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 repeatabil ity 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 spectr
46. ng the de 305 5 nm sign process channe Sa e To assure long term stability the 312 5 nm optical block is machined from a chang cast aluminum plate 940 nm channe e The mechanical alignment of the optical channels is better than 1020 nm 0 1 channe OPTICAL SIGNAL PROCESSING BLOCK e Internal baffles in each channel PLOCK prevent reflections from reaching Figure 26 MICROTOPS II structure the photodetectors The internal surfaces of the collimators are lined with a low reflectivity material e The sun targeting hardware is ma chined from aluminum and directly at tached to the filter block to avoid tem perature effects on targeting lon e The entire optical block is suspended in the enclosure in such a way that a mechanical strain applied to the enclo sure does not result in substantial strain in the optical block m e o a ru E o c c he LE e The sun targeting assembly is laser aligned to within 0 1 from the optical Wavelength nm axis of the block 300nm 305 5nm 312 5nm Noise floor e The temperature of the optical block is Figure 27 Spectral transmission of UV filters measured using a monitored and logged in order to al monochromator with 2 5nm slit width notice bandwidth broaden A UE 3 low temperature compensation if ing in order to detect the stray light P P needed s A built in solid state pressure sensor prov
47. ng the wave 306 0 length at which the slope of the In of the 312 6 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 a and f for each channel can be calculated from 8 and 9 Solar Light Co Inc 0 6 0 65 0 7 0 75 0 8 0 85 UT decimal x MICROTOPS II 3106 e Dobson 65 Figure 31 Comparison of Microtops II S N 3106 with Dobson instrument 65 in Boulder CO 08 01 96 Lambert Beer law takes the form Vi 01 47 For the filters used in MICROTOPS II the effec tive wavelengths are fraction of a nanometer above the filter s center wavelength Table 4 1 5 Derivation of water vapor Water vapor transmission was studied for almost a century The calibration technique used for MICROTOPS was developed by Reagan eLa and further tested by Michalsky et al The wa ter vapor measurement is based on a pair of ra diometric 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 exp T m k um 11 where V is the ground based radiation at 940nm Vo is the extraterrestrial r
48. nsion type X to retrieve the calibration constant header type P to download the data close the log file Pe Ta 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 ap propriate file with a txt extension click OK and the data will begin to be inserted into the data base 1 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 ap propriate file with a dbt extension click OK and the data will begin to be inserted into the data base 1 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 1 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 d
49. nstructions 3 5 7 Initiating a scan ngon 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 3 5 8 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 1 Contents of Microtops II data buffer Field Commens CC pressure sensor and station pressure is set to zero SZA SIG305 Signals in mV from all 5 optical channels SIG312 SIG320 SIG936 SIG1020 Ratio of signals between channels 1 and 2 305 0 and 312 5nm Ratio of signals between channels 2 and 3 312 5 and 320 5nm 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 column in Dobson units based on both ratios and experimentally derived compensa tion algorit
50. numeric 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 Alti tude 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 replaced with the number of the location Otherwise an Input ignored message is returned Figure 22 Listing of saved locations database The Microtops Organizer software offers an interactive way of updating the instrument s location database see Microtops Organizer Enter new location Software on page 28 Loc Name Lat N Long E Alt m Pres mB X XXXXXXXXXXXXXX EXX OXXX XXX XXX IXXXX XXXX Figure 23 Location input pattern 3 5 6 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 xxxx is the number of records to be downloaded The keyword FIELDS in the next line is followed by the list of field names that correspond to the structure of downlo
51. oc 40 055 75 131 137 0 256 The latitude and longitude are in degrees and decimal fractions thereof North latitude and East longi tude 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 re turned 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 Loci LIXX OXXX XXX XXX XXXX XXXX x If a valid location is entered following the pattern shown on screen then the instrument will acknowl edge acceptance of the settings with OK If one of the values entered is beyond acceptable range then the message Ilegal value is returned Too few numbers or incorrect pattern will result in In put 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 format will have to be converted into their decimal formats before being entered In order to enable the internal atmospheric pressur
52. ocation 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 NMEA 0183 formats versions 1 5 and 2 0 can be read by Microtops II 3 1 Setting up GPS The individual setup procedures vary between receivers The following example is based upon Gar min Model GPS 72 receiver 1 Turn the GPS receiver ON 2 Turn the Microtops II ON and set the baud rate to 4800 This is the only Microtops II setting re quired for GPS compatibility 3 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 Select SETUP and press ENTER to view the SETUP menu Scroll across to the INTERFACE tab Set Serial Data Format to NMEA Set the baud rate to 4800 SE 9 OR LT etis cde Press PAGE when done to return to the page showing satellite signal strength 10 Position the GPS receiver so the view of the sky is not obstructed and the instrument can acquire 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 receiver is not able to acquire
53. om line informs 25 scans stored Clear all gt gt that pressing K 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 E 2 4 3 Deleting last measurement 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 The LCD displays 22 Solar Light Co Inc The top line indicates the number of scans currently in memory Each E 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 2 5 Baud rate Microtops II can communicate with a computer or GPS receiver via the serial port The speed of that communication link is adjustable from 2400 to 19200 baud Please note that the baud rate should to be set to 9600 if the GPS receiver is connected to Mi crotops II see GPS Communication 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 computers might not be able to commu nicate reliably at the highest speed Figure 19 illustrates the menu path to baud rate adjustment The screen will display The lower LCD line indicates the current setting of baud rate Pressing 4 or w keys will either in
54. oordinates bi Coordinates 40 03 N 75 08 W Figure 12 Setting current location geographic coordinates Line frequency 60 Hz lt gt change 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 2 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 barometric pressure The currently active settings are stored in a current loca tion buffer The current location buffer can be viewed and edited from a remote computer via serial port chapter 3 5 3 Valid ranges for location parameters are as follows Latitude 90 490 Longitude 180 4 180 Altitude 1000 420000 Pressure lt 0 1100 2 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 3 5 5 Any loca tion record from the database can be quickly copied to the current location buffer using the Saved location feature It facilitates the location setup when taking measuremen
55. ophotometers the MICROTOPS II exhibits some air mass dependency This effect contributed to by out of band radiation leaks scattering of diffuse UV radiation into the in strument 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 w 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 ap plicability 1 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 Asso ciates Inc private communication 3 Forrest M Mims III How to Measure the Ozone Layer Science Probe 2 4 45 51 November 1992 4 Forrest M Mims III and E R Mims Fluctuations in Column Ozone During the Total Solar Eclipse of July 11 1991 Geophysical Research Letters
56. ory 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 Inc 7 1 Quick start 1 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 in active during the measurement scan The meter will automatically shut off after 10 minutes of inac tivity 1 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 displays the following information Lo
57. otal ozone column measurement In the past a major obstacle in producing accurate and repeat able results was the lack of stable narrow band UV filters with adequate out of band rejection Re cent advances in thin film deposition techniques made it possible to produce filters of satisfactory quality The Total Ozone Portable Spectrometer TOPS project has proven that filters currently available can be used to measure the total ozone column accurately Based on prior experience 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 1 2 Basics of the instrument Ozone absorbs shorter wavelengths of solar ultraviolet radiation much more than longer wavelengths This means that the amount of ozone between the observer and the Sun is proportional to the ratio of 40 Solar Light Co Inc two wavelengths of the Sun s ultraviolet radiation MICROTOPS II 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 instrument the measurement at an additional 3rd wavelength enables a correction for particulate scattering and stray light T
58. outhern Great Plains Atmospheric Radiation Measurement site JGR Vol 100 No D12 pp 25995 26003 1995 M Degorska B Rajewska Wiech Airmass Dependent Total Ozone Measurement Errors Publi cations of Institute of Geophysics Polish Academy of Sciences D 40 263 1993 Solar Light Co Inc 51 1 Table of figures Figure 1 Simplified Microtops II menu 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 21 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 2
59. ownloaded 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 33 1 3 6 User calibration factors cenar Query Begin End Serial Number Query Results 591 Matching Records 3103 8 20 96 1 31 19 PM 3103 8 20 96 1 31 29 PM 3103 8 20 96 1 48 14 PM 3103 8 20 96 1 48 23 PM 3103 8 20 96 1 48 32 PM 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 se lected 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 calculated and stored in the database 34 Solar Light Co Inc 3 GPS Communication Accurate l
60. port communication that does not support special characters Figure 6 Modifying water vapor The Microtops II calculates the ozone value based on two pairs of calibration factors wavelengths channell channel2 and channel2 channel3 The fac tors 0 12 B12 and L12 correspond to channell channel2 pair while 23 823 and L23 relate to the other pair After the ozone is calculated from the two pairs the corrected ozone is determined with the help of factor OC The details of the calculations and calibra tion are presented in section Specifications on page 38 14 Solar Light Co Inc Figure 5 shows the menu path to the ozone calibration factors The number editing rules are described in chapter Irradiance calibration constants on page 12 2 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 dis tance In V05 the natural logarithm of the extraterrestrial constants for channel 5 for mean sun earth dis tance 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 C 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 opera tion on page 39 Figure 6 show
61. re on page 19 Other settings should remain at their factory preset state Changing these settings should only be attempted 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 14 All settings are retained in the meter s nonvolatile memory and are effec tive until the next change is made 1 4 First measurement Once the initial set up is completed the Microtops II is ready to take measurements The following steps outline the procedure 1 Make sure that the top window cover of the Microtops II is closed Solar Light Co Inc 9 and then turn the instrument ON When the display shows RDY ready mode you may open the top window cover 2 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 results 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 3 While keeping the sun s image centered press the Scan Escape button to initiate the scan The meter will beep and
62. relatively strong sensitivity in the UV region low noise level and low sensitiv ity above 500nm These characteristics allowed us to relax the out of band rejec 300 nm 305 nm 312 nm tion above 650nm lowering the produc tion cost of the filters The photodetectors are hermetically packaged to assure long life and stability signal mV Figure 28 Signal measured by MICROTOPS II on Mauna Loa May 16 1996 271DU clear sky 1 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 ampli fier 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 84 V e A high performance sig
63. s 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 Ready mode Menu Enter lt Main menu 2 2 1 4 Pressure calibration constants Maln meny A solid state pressure sensor is built in the Microtops II This type Measurement i of pressure sensors is characterized by very good linearity and stability but the repeatability of the sensor manufacturing process Measurement Calibrations is poor therefore each sensor needs individual calibration The Calibrations Irradiance Microtops II sensor is factory calibrated in a pressure chamber with 2 point calibration procedure Ignoring the temperature com pensation 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 Calibrations Ozone cal Calibrations Water cal Calibrations Pressure cal Calibrations Restore calibr GI Restore calibr Mas 2 2 1 5 Restoring factory calibrations Figure 7 Restoring factory cali bration factors The factory calibrations can be recalled in case a change is made that inhibits proper operation of the instrument This operation Solar Light Co Inc
64. solution 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 more 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 radiation 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 procedures is enclosed in the accompanying paper on page 39
65. sure 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 1100 21000 o 200 8 800 a 2 700 2 amp 600 2 O E 500 lt 400 o wo aw m w wo wo 24 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 displayed 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 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 Figure 15 Mean barometric pressure vs alti tude 20 Solar Light Co Inc 4 O3 corr O3 1 2 O3 2 3 Water 12Sep96 306 5 300 4 306 4 16 45 56 12Sep96 306 9 300 9 306 8 16 45 40 12Sep96 307 3 301 6 307 2 1 1 1 5 16 44 12 12Sep96 305 9 300 8 305 9 1 16 43 38 Figure 16 Viewing the stored data on LCD 42 46 50 48 2 4 41 Viewing the stored data The data browse mode allows inspection of all data stored in me 4 ter s non volatile memory The browse mode is initiated by pressing jA Man mony the K key while in ready mode The
66. t ways of sun targeting I is the intensity of the light of a particu lar wavelength before it passes through the atmosphere I the intensity remain ing after all processes attenuating the incident radiation have occurred Q is the amount of ozone a 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 m is 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 2 the p 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 conditions do not effect ozone measurements by more than a few percent and much less under usual conditions 302 300 amp hand held enhanced tripod mounted m hand held no enhancement Expressions for u and m quantities are as follows m sec Z 0 0018167 sec Z 1 0 002875
67. the day item underlined by a cursor see above The selected underlined item may be incremented decremented by pressing the 4 and w buttons The selection can be changed by pressing and 4 Clock keys When incremented or decremented each item will as Adjust clock 9 sume values from the range valid for that particular item After L A setting the time press the Scan Escape button 3 times to return Adjust clock to ready mode 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 measuring 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 writ ing times as hours and minutes together and suffixed with a letter designating the time zone For ex ample 2345Z 23 45UTC z 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
68. to one side then remove it with a stream of compressed gas As a last resort only pure alcohol either isopropyl or ethyl can be used to remove any residue from the window 4 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 dis played until the next power up cycle The instrument will continue to function for a while however 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 4 3 Calibration To assure reliable readings the Microtops II should be re calibrated yearly and if possible participate 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 ozone Solar Light Co
69. ts in multiple loca tions The additional benefit of naming locations is an option worth considering Please note that the database of saved locations cannot be modi fied from the instrument s keypad nor is the information for cal culations fetched directly from this database The location set 18 Solar Light Co Inc tings for calculations always come from the current location buffer The Saved locations feature only copies a selected record containing coordinates altitude and pressure from the database to the current location buffer The contents of the current location buffer can be edited from the keypad All Push gt to select 2 Mauna_Loa 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 K key will copy the selected location parameters to current location buffer The bottom LCD line shows the record number of the database location currently selected and the name of the location stored in it There are 6 records 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 4 or w key The display will scroll through all the records In order to copy the location parameters it is necessary to press K key when pointing at the de sired location Scrolling through th
70. ure at 0 will enable the pressure measurement Otherwise the station pressure has to be updated manu 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 30 Solar Light Co Inc 4 Maintenance As with every optical instrument the Microtops II needs to be handled carefully and some mainte nance is necessary for best operation 4 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 prolonged 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
71. ws sees esse eee eee Data description data exchange format Data processing sss sees eee RE ETT Database TEST Downloading of data sss F factory calibrations sss 12 14 Teanireg scs s zavo s enaa teens tentat tena shi naan 5 Solar Light Co Inc G geographical coordinates 17 GPS can 6 22 24 34 35 I Importing text eese irradiance L s tenete Line frequency Location setup IEoCatlOlsza ne eie eren longitude oops M Microtops Organizer 23 25 28 N Non volatile memory 6 number editing 13 14 15 16 19 0 optical block 5 21 27 40 41 ozone absorption sese eee eee 13 44 46 ozone layer etn 5 P precipitable water e 5 39 40 PrGSRIITG sax sc z g o itinin 14 17 19 21 24 pressure sensor 14 19 24 27 35 41 Q QUE iret ete a ees 31 R Rayleigh scattering Remote control esses Solar Light Co Inc Restoring factory calibrations 14 S Scan lengthy uie etii 15 serial Cable a ERE RC hes 23 serial port 12 13 15 17 19 22 23 25 26 28 34 solar zenith angle 10 16 17 43 45 riui m 5 53 T time and date centena 10 U User calibration

User`s Guide MICROTOPS II

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