THE SOLAR ULTRAVIOLET SPECTRAL IRRADIANCE MONITOR (SUSIM) EXPERIMENT ON BOARD THE UPPER-ATMOSPHERE RESEARCH SATELLITE (UARS)

The state of solar ultraviolet in-irradiance measurements in 1978, whe n NASA requested proposals for a new generation of solar ultraviolet m onitors to be flown on the Upper Atmosphere Research Satellite (UARS), is described. To overcome the radiometric uncertainties that plagued the measurements at this time, the solar ultraviolet spectral irradian ce monitor (SUSIM) instrument design included in-flight calibration li ght sources and multichannel photometers. Both are aimed at achieving a maximum precision of the SUSIM measurements over a long period of ti me, e.g., one solar cycle. The design of the SUSIM-UARS instrument is compared with the original design specifications for the UARS instrume nts. Details including optical train, filters, detectors, and contamin ation precautions are described. Also discussed are the SUSIM-UARS pre flight calibration and characterization, as well as the results of the inflight performance of the instrument during the first 3 months of o peration. Finally, flight operations, observation strategy, and data r eduction schemes are outlined.