Inter-calibration of Meteosat Imagers and Iasi

EUMETSAT has initiated routine inter-calibration of the infrared channels of Meteosat imagers and the Infrared Atmospheric Sounding Interferometer (IASI) on Metop-A, based on the regression of collocated radiance observations, weighted according to their spatial variability. This paper describes the algorithm and presents key results for Meteosat-7, -8 and -9 during 2007. These demonstrate the reliability of the inter-calibration method and show it can be used to monitor the gradual change in calibration bias of the 13.4 μm channel of Meteosat-9. This is shown to be consistent with the build up of ice contamination on the instrument’s optical elements and can be reduced by performing periodic decontamination processes – warming the instrument’s optics to drive off condensates. The modelling of this process, together with the inter-calibration monitoring can help understand the mechanism responsible for the changing biases and develop and validate operational corrections.