2013-09-30: Inter-calibration of polar imager solar channels using SEVIRI

Accurate calibration of satellite imagers is a prerequisite for using their measurements in climate applications. We have developed a method for the inter-calibration of geostationary and polar-orbiting imager solar channels based on regressions of collocated near-nadir reflectances.

The method is used to calibrate the solar channels of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on the geostationary Meteosat satellite with corresponding channels of the Moderate Resolution Imaging Spectroradiometer (MODIS) on the polar-orbiting Aqua satellite. The SEVIRI operational calibration is found to be quite stable during the years 2004 to 2009, but offset by -8, -6, and +3.5 % for channels 1 (0.6 µm), 2 (0.8 µm), and 3 (1.6 µm), respectively. A specific application of our method is the inter-calibration of polar imagers using SEVIRI as a transfer instrument. This offers an alternative to direct inter-calibration, which in general has to rely on high-latitude collocations. Using this method we have tied MODIS-Terra and Advanced Very High Resolution Radiometer (AVHRR) instruments on NOAA satellites 17 and 18 to MODIS-Aqua for the years 2007 to 2009.
Time series of inter-calibration slopes for SEVIRI-Meteosat-8 and -9 against MODIS-Aqua for three solar channels. Black (red) symbols and lines correspond to data that have (have not) been corrected for differences in spectral response between SEVIRI and MODIS. The inter-calibration slopes are defined with respect to the operational SEVIRI and MODIS calibrations.