A New Concept for the In-flight Calibration of Large-Aperture Satellite IR Radiometers with Respect to METEOSAT

Past investigations by several authors have shown that in-flight calibrations should of necessity include not only the detectors but also the complete optical system of satellite scanning radiometers. Based on calibrations made by the German Aerospace Research Establishment (DFVLR) with airborne radiometers, a calibration concept is proposed which makes use of an additional calibration radiometer on board the spacecraft. This supplementary radiometer should be equipped with identical spectral channels but with a wider field of view (FOV) than the scanning radiometer, making absolute calibration relatively simple. In the proposed procedure, the absolute radiance detected by the calibration radiometer is related to the mean radiance from all pixels inside the wider FOV. This concept can be extended to a scanner with multiple defector arrays. Recent investigations have led to a simplification of the instrumentation by using the same detector-filter package for the calibration radiometer and the scanner.