Vicarious calibration of the Meteosat visible channel

Abstract

Postlaunch calibration of the Meteosat visible (VIS) channel has been performed with Meteosat-1, Meteosat-2 and Meteosat-4. The radiance at the satellite radiometer aperture has been determined by independent means and has been related to the simultaneous satellite radiometer count. This technique has been named vicarious calibration. Airborne radiance measurements over homogeneous targets (two land surfaces, clear ocean, and stratiform clouds) have been performed. The derived calibration factors are scene dependent because of the nonrectangular shape of the Meteosat VIS channel spectral responsivity curve. The latter and, hence, the scene dependence, slightly differs between the three satellites. Therefore, the calbiration factors also differ within ±15%. Average values of the calibration factors are about 1.1 W m-2sr-1 per count for land surfaces and clouds and about 1.5 W m-2sr-1 per count for ocean. -Authors