Comparison of ScaRaB ground calibration in the short-wave and long-wave spectral domains

The ScaRaB instruments are a series of Earth Radiation Budget radiometers o f 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 sa tellite 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 mu m to 50 mu m), channel gains and abs olute filtered radiance of the on-board lamps and on-board black bodies hav e been measured, using different reference sources: laboratory black bodies , an absolutely calibrated integrating sphere, and the Sun. The black bodie s ensure the validity of the calibrations in the long-wave spectral domain, while the Sun and the integrating sphere check the short-wave spectral dom ain. After a brief description of the ScaRaB instrument and its main charac teristics, this paper describes the procedures and results, including the a ssociated uncertainties, for the measurements of the broadband channel gain s: 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 t he most realistic uncertainty budget.