1. Flight Tests of the Novel TechSat Satellite Ozone Meter Algorithms and Measurement Processing Results M. Guelman, F. Ortenberg, B. Wolfson Asher Space Research Institute, Technion, Haifa, 32000, Israel 40th Israel Annual Conference on Aerospace Sciences, Tel Aviv, February 23,24 2000

2. The filter photometer, which measures the solar backscattered ultra-violet (SBUV) radiance in nadir direction, is intended for measuring atmospheric ozone concentration. “Small SBUV” main characteristics: Spectral region 252.0 - 340.0 nm, Spatial resolution 170 km x 70 km, Footprint height in atmosphere 0 - 55 km, Weight 1.9 kg, Power consumption < 2 W THE OZONE METER OPTICAL HEAD

3. OZONE METER

4. TECHSAT SATELLITE AND OZONE METER INTEGRATION The OM was successfully launched aboard TechSat (10.07.98) on a sun-synchronous, circular orbit (altitude 820 km, inclination 98 o and local time of the descending node 10 h). After the launching of the satellite the OM was turned-on, while moving in the illuminated part of the orbit. Measured results were registered by the on-board computer and data was sent via the down-link during the subsequent orbits.

5. OZONE METER FILTERS ARRANGEMENT AND FIELD STOP POSITION

6. EARTH FOOTPRINT AREA

7. MAIN GOALS OF TECHSAT "SMALL SBUV" OZONE METER FLIGHT TESTS Study the instrument's capability to measure the ozone profile and its total column content; Develop algorithms for OM data processing; Use flight results to improve the accuracy of the OM instrument; Define the applicability of OM for studies of latitudinal, seasonal and planetary scale ozone variation.

8. SOLAR BACKSCATTERED ULTRAVIOLET RADIATION AT A GIVEN WAVELENGTH ORIGINATES MOSTLY FROM A LIMITED-ALTITUDE REGION OF THE ATMOSPHERE Ozone profile * Results of measurements on four short wavelengths of 252.0nm, 273.5nm, 283.0nm, 292.0nm (filters 1-4) are used for estimating the ozone profile above the ozone density peak at 20-25 km. * Radiation on the wavelength 301.9nm (filter 5) provides profile information near and below the peak. * Wavelengths 320.0nm and 340.0nm (filters 6-7) are used to register backscattering photons originating in the lower troposphere. Total ozone Values of total ozone are derived using OM measurements on two longest wavelengths (filters 6-7).

9. 1-5 filters 6-7 filters OZONE'S PROFILE AT LATITUDE 50 o, LONGITUDE 137 o IN APRIL 1999.

10. THE OZONE METER RESULTING DAILY COVERAGE OF THE EARTH`S SOUTHERN HEMISPHERE Measurements were made in the following way: after switching on the device, results of photoelectron count were introduced into the device computer up to the point of memory fill and then transferred into the on-board computer memory; at this stage no measurements were carried out by the device. After device memory reset, measurements were resumed and continued up to full memory capacity, etc. Thus, the results of measurements were actually a set of cycles (5-6 cycles per orbit) separated by gaps, corresponding to periods of data rewriting.

11. SOLAR BACKSCATTERED ULTRA VIOLET RADIATION Where: I(l,q) - backscattered atmospheric radiance (erg/cm 2 secAstr) F o (l) - extraterrestrial solar irradiance (erg / cm 2 sec); b l - atmospheric scattering coefficient (atm -1 ); X p - amount of ozone above pressure (atm.cm); a l - ozone absorption coefficient (atm. cm) -1 ; q - solar zenith angle; p - atmospheric pressure (atm);

12. Total ozone measurement processing  = Ln (I 6 /I 7 ) K 67. Mapping of total ozone in Dobson Units [D.U.] Ozone profile retrieval by approximation of n 1 :n 7 as a polynomial function on (Ln (p)). Ozone mixing ratio [ppmv.] vs. atmospheric altitude [km.]  St - standard total ozone column month average data from TOMS http://toms.gsfc.nasa.gov/ Computation of calibration coefficient for filters 6-7: K 67 (  ) =  St / Ln (I 6 /I 7 ). Total ozone Measurement processing n i (  )= I i (  ) K i ( ,  ); (i=1-5); n 67 (  )=Ln(I 6 /I 7 ) K slope (p-p 0 ). data: I, , t, , l. Measurements Processing Computation of K slope - slope coefficient of ozone profile, for atmospheric pressure: 70<p<100 mb., for filters 6-7 K slope = Standard Slope / Ln (I 6 /I 7 ). Approximation of monthly intensity for first five filters as function of zenith distance for south and north hemisphere separately: I = Acos (  +  0 ) +C, where A,  0, C are constants. Computation of calibration coefficients for filters 1-5: K i ( ,  )= n St (  ) / (Acos (  +  0 ) +C) Calibration n St - standard ozone profile month average data from SBUV ftp://wrabbit.gsfc.nasa.gov ftp://wrabbit.gsfc.nasa.gov Telemetry: Intensity (I) for filters 1-7, time. Zenith distance , latitude , longitude l. Ozone profile Input BLOCK DIAGRAM OF OZONE METER DATA PROCESSING

13. RADIATION MEASUREMENT RESULTS AS A FUNCTION OF ZENITH DISTANCE, RECEIVED FROM FIRST FILTER FOR NORTH HEMISPHERE Zenith distance [deg.] Intensity (counts) For calibration the Ozone Meter measurements are approximated by function, where A = 1601.4  0 =-0.8 o ; C = 184.9; standard deviation  = 3.0%

14. Latitude [deg.] N6 ( =320) - N7 ( =340) AN EXAMPLE OF OM MEASUREMENTS FOR FILTERS 6,7 AS A FUNCTION OF SUBSATELLITE LATITUDE, CARRIED OUT IN APRIL 1999. STANDARD DEVIATION  =8%.

15. Ozone Meter TOMS COMPARISON OF TOTAL OZONE COLOR MAPS MEASURED BY INSTRUMENTS: OM AND TOMS IN APRIL 1999

16. 1-5 filters 6-7 filters OZONE'S PROFILE AT LATITUDE 50 o, LONGITUDE 137 o IN APRIL 1999.

17. ESTIMATION OF OZONE PROFILE RESULT ACCURACY

18. OZONE DETERMINATION ACCURACY AND RESULT VALIDATION The ozone values derived from Ozone Meter measurements are subject to three types of uncertainties: uncertainties in the basic measurements, uncertainties in a priori quantities needed to retrieve ozone values, and those associated with the mathematical procedure used to derive ozone values The presented evaluation of precision in ozone determination shows that the overall error in the derived ozone profile should be in the 10-20% range, whereas the error in the derived total ozone content should be less than 10%. A number of OM ozone data sets were compared with measurements performed by TOMS, GOME and SBUV instruments. The comparison showed that ozone profile differences are less than 10% at high altitudes and reach 20% at lower atmosphere altitudes; the standard deviation is about 15% for all the altitudes. Comparison of OM data with results produced by the above mentioned instruments show that the estimated error in total ozone measurements is about 10%.

19. OZONE DETERMINATION ACCURACY AND RESULT VALIDATION (cont.) Intercomparison ozone profiles and total ozone data sets of the Ozone Meter with other ozone measurements confirm the validity of developed algorithms and processing software. OM ozone measurements are subject to global coverage spatial limitations. Measurements over the higher latitudes cannot be processed, as well as those taken over regions where ozone changes are substantial and irregular, during the year, and from year to year. Additional sources of OM errors brought about by the absence of pre-launch and in-flight radiance and irradiance calibration can be easily excluded in future models of the small OM by incorporating a calibration unit without substantial changes of device dimensions and power consumption. After modernizing the device enhancing spatial and temporal coverage, accuracy, as well as overall performance, the small OM are expected to be as good as other SBUV instruments.

20. Flight tests of the new Ozone Meter, installed on board the microsatellite TechSat, have been completed. An optimal procedure for acquisition of vertical ozone profiles and total ozone content, using OM measurements of Solar Backscattered Ultra-Violet radiation, has been implemented. The statistical method was applied to obtain ozone data from both the measured radiation and a priori information. In these algorithms the climatology data is based primarily on previous satellite measurements. The monthly averages of ozone mixing ratio and total ozone are used for Ozone Meter measurement calibration. SUMMARY

21. An operational version of the profile and total ozone algorithm or the processing of OM data has been developed. The algorithm for ozone profile essentially retrieves a 7-node natural polynomial spline curve in the following coordinate system: ozone-mixing ratio in ppmv vs. the altitude (logarithm of pressure). Values of total ozone are read out in Dobson Units (DU) in accordance with subsatellite latitude and longitude, and are applicable for color map generation. This algorithm was used to produce a 10-month data set of global ozone profiles and total ozone values on the basis of OM instruments. SUMMARY (Cont.)