MSG-SEVIRI solar channels are calibrated against the MODIS instrument following the methodology outlined in Meirink et al. (2013). This calibration has been extended to the full MSG era and updated using Aqua-MODIS Collection 6.1 reflectances as a reference.
The figure below shows the resulting calibration slopes for the 0.6 (top), 0.8 (middle) and 1.6 (bottom) micrometer SEVIRI channels from 2004 to 2020. Aqua-MODIS collocations for the months April and October of each year have been considered (symbols). Linear trend fits for the four satellites Meteosat-8 to Meteosat-11 are shown by the solid lines, and the coefficients of these fits are indicated (D - D1/1/2000 denotes the number of days since the beginning of 2000). The EUMETSAT operational calibration slopes are shown by dashed lines. In general, these are found to be on the order of 5-10% too low for the 0.6 and 0.8 micron channels, and about 3% too high for the 1.6 micron channel.
Meirink, J.F., R.A. Roebeling and P. Stammes, 2013: Inter-calibration of polar imager solar channels using SEVIRI, Atm. Meas. Tech., 6, 2495-2508, doi:10.5194/amt-6-2495-2013