Ultimate determination of ScaRaB flight model 2 channel gains

The Scanner for Radiation Budget (ScaRaB) instruments are a series of Earth Radiation Budget (ERB) radiometers of which the first flight model (FM1) was launched on a Russian METEOR satellite in 1993. A second model (FM2) was launched on the Russian RESURS satellite in July 1998. The FM2 instrument worked perfectly until the failure of the platform transmitter in April 1999. Considering both missions, ERB data were obtained over sixteen months with ScaRaB. In order to obtain a good correlation between calibrations on the ground and in space in the long-wave spectral domain, the spectral response has been re-estimated using an original method. As the solar ground calibration and the integrating-sphere calibration are conducted in an enclosure purged with dry nitrogen, the detector gain differs from the gain under vacuum, and a correction factor must be applied. A new correction coefficient has been determined through analysis of the ScaRaB data sets, leading to satisfactory agreement between long-wave vacuum calibration and solar calibration.