The ScaRaB instruments are a series of Earth Radiation Budget radiometers of which the first flight model (FM1) was launched on a METEOR satellite on 25 January 1994. A second model (FM2) was launched on the Russian Resurs satellite in July 1998. Results obtained from FM1 indicated the need for more accurate ground calibration for FM2 and the spare model. Besides spectral response characterization (from 0.2 µm to 50 µm), channel gains and absolute filtered radiance of the on-board lamps and on-board black bodies have been measured, using different reference sources: laboratory black bodies, an absolutely calibrated integrating sphere, and the Sun. The black bodies ensure the validity of the calibrations in the long-wave spectral domain, while the Sun and the integrating sphere check the short-wave spectral domain. After a brief description of the ScaRaB instrument and its main characteristics, this paper describes the procedures and results, including the associated uncertainties, for the measurements of the broadband channel gains: these need to be accurately calibrated and compared. Points of interest and also weaknesses of the three methods are compared in order to lead to the most realistic uncertainty budget.
Scarab (SCAnner for Radiation Budget) Flight Model 1 (FM1) is a four channels scanning radiometer, launched in February 1994, with the same ERBE scientific mission. It worked perfectly during one year, aboard a Russian satellite, METEOR 3 N°7. Data were very consistent with ERBE results. Calibration of FM2 and Spare Model (SM) is described (one model will be launched aboard a Russian platform, RESURS, by the end of 1997). The calibration comprises three phases S solar/diffuser short wave source (will not be discussed in this article). blackbodies long wave sources under vacuum S integrating sphere short wave source Results are described and a comparison between the two last methods is established.
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