RADIOMETRIC CALIBRATION TRACKING OF THE VACUUM-ULTRAVIOLET SPECTROMETER SUMER DURING THE FIRST YEAR OF THE SOHO MISSION

Detailed radiometric calibration tracking of the vacuum-ultraviolet sp ectrometer SUMER (from solar ultraviolet measurements of emitted radia tion) was performed during the first year of the Solar and Heliospheri c Observatory (SOHO) mission and will continue. In view of the flight history of many previous solar UV instruments, the stability of calibr ation of the extreme-ultraviolet instruments on SOHO has been a major concern. Results obtained during the first year of operation show that excellent radiometric stability has been achieved with SUMER. These r esults were accomplished by stringent cleanliness and contamination-co ntrol procedures during all phases of the project;. We describe the st rategy and results of the in-flight calibration tracking program perfo rmed with SUMER. (C) 1998 Optical Society of America.