N95- 11128 POST LAUNCH PERFORMANCE OF THE METEOR-3/TOMS INSTRUMENT Glen Jaross, Zia Abroad, and Richard P. Cebula Hughes STX Corporation Lanham, Maryland 20706, USA Arlin J. Krueger NASA Goddard Space Flight Center Greenbelt, Maryland 20771, USA Abstract The Meteor-3/TOMS instrument is the sec- ond in a series of Total Ozone Mapping Spectrome- ters (TOMS) following the 1978 launch of Nimbus- 7/TOMS. TOMS instruments are designed to mea- sure total ozone amounts over the entire earth on a daily basis, and have been the cornerstone of ozone trend monitoring. Consequently, calibration is a crit- ical issue, and is receiving much attention on both instruments. Performance and calibration data obtained by monitoring systems aboard the Meteor-3 instru- ment have been analyzed through the first full year of operation, and indicate that the instrument is per- forming quite well. A new system for monitoring in- strument sensitivity employing multiple diffusers has been used successfully and is providing encouraging results. The 3-diffuser system has monitored changes in instrument sensitivity of a few percent despite de- creases in diffuser refiectivity approaching 50 percent since launch. Introduction The Meteor-3/TOMS instrument was launch- ed aboard a Soviet Meteor-3 spacecraft on August 15, 1991. The TOMS instruments are part of a class of ozone monitoring instruments which measure at- mospheric albedo through the Backscatter Ultravi- olet (BUV) technique (Klenk et al. 1982). As with other BUV instruments, M3/TOMS is in a polar orbit (82.5 ° inclination), though at the somewhat higher altitude of 1200 km. Unlike other BUV instrument platforms, the orbital plane of the Meteor-3 space- craft precesses relative to the sun-earth vector with a period of approximately 212 days. This rapid pre- cession rate impacts the ability to monitor and cali- brate the instrument, as well as having implications for ozone retrieval. With the exception of its solar diffusers, the TOMS instrument optics are identical to those of its predecessor (NT/TOMS) aboard the Nimbus-7 space- craft (Heath et al. 1975). While some of the elec- tronics have been updated, major features such as the spectrometer design, wavelength channels, cross- track scanning, and field of view remain unchanged on the newer instrument. Three major calibration and monitoring functions are used aboard both in- struments. Two of these, the wavelength and elec- tronic calibration systems are completely unchanged on M3/TOMS. The principles of solar irradiance mea- surement are the same as on N7/TOMS but are func- tionally different with a change from one to three diffuser plates. Since this change represents a sig- nificant improvement over N7/TOMS for calibration of instrument sensitivity, and hence in the accuracy of ozone measurements, a more detailed discussion of the solar irradiance measurements will follow. Wavelength Calibrations The wavelength calibration system is designed to monitor the wavelength stability of the spectropho- tometer. Entrance slits separate from those used for 942