Radiometric calibration of the MOMS-2P camera

Kurzfassung

For the radiometric calibration of the MOMS-2P camera on board of the Russian MIR-station an inflight sun calibration method using a diffuser plate in front of the optics is applied. By tilting the diffuser plate by 20 degrees with respect to the entrance optics the direct sunlight is reflected into the optics. Prior to the absolute radiometric calibration of every pixel the image has to be corrected for relative radiometric disturbances along the scan lines. The reasons are the odd/even effect and the CCD typical non-uniformity. To correct for these effects relative calibration tables, derived from the diffuser plate calibration, are applied to the image. The applicability and stability of these tables is only given to an accuracy of about 1-2% in the nominal case. Therfore the remaining disturbances, probably caused by deficiencies of the internal electronic amplifier circuits and temperature variations, are removed using empirical methods. To correct for these random type of image failures, a digital filter in the spatial domain was developed. It is based on an averaging technique that acts in a large kernel size. Since there seems not to be complete linearity for very high and very low brightness levels, these levels have to be excluded from the averaging procedure. The image contrast and information content is less influenced than with other known filter techniques. In this paper the procedure to derive the level L1A Data in shown. After correcting for the relative radiometric differences the measured solar irradiance values can also be used for absolute calibration because the extraterrestrial spectrum of the sun is very well known. The methods to derive the absolute calibration factors are described and first results are presented.