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The French-Russian-German 4-channel ScaRaB (Scanner for Radiation Budget) instrument operated on board the Russian
Meteor-3/7 satellite from February 1994 to March 1995. Earth Radiation Budget (ERB) detenninations depend on the two
broad-band channels -an unfiltered total (TW) channel sensitive from 0.2 to at least 50 gm, and a short-wave (SW) channel
in which a fused silica filter cuts off sensitivity at about 4 jim. In-flight SW calibration depends on lamp sources which may
drift or fluctuate. Because daytime LW determinations depend on a weighted subtraction of SW from LW measurements,
SW calibration errors will affect the results and can induce a spurious diurnal cycle in the LW. The relative SW sensitivity
of the TW and SW channels can be checked, independently of on-board SW lamp sources, by using the ScaRaB JR window
(IRW : 1O.5-12.5jim) channel and insisting on diurnal/nocturnal LW consistency. Both the IRW channel and the LW
portion of the TW channel are calibrated by reliable on-board black bodies. Results for the first several months of ScaRaB
operation are presented, considering also the difficulties arising from the thermal radiation in the near-IR portion of the SW
channel. These results are compared with those obtained using the on-board lamp sources. They show that these two
methods are complementary: iamps allow accurate monitoring of short-term gain fluctuations while the geophysical method
ensures reliability oflamp calibration over the monthly time scale.
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