Calibration of Meteosat water vapor channel observations with independent satellite observations

The objective of this study is to identify potential problems of and increa se confidence in the operational calibration of the water vapor channel of the Meteosat Visible and Infrared Radiation Imager (MVIRI). First, the oper ational vicarious calibration method of the MVIRI water vapor channel is an alyzed. This is done through a comparison of the operational calibration co efficient with a calibration coefficient derived from collocated satellite observations taken by water-vapor-sensitive channel 12 of the High Resoluti on Infared Sounder (HIRS) on NOAA 14. The analysis suggests a relatively la rge difference between the two calibration coefficients, the operational ca libration coefficient being 10-15% larger than the one from the intersatell ite calibration. Second. no such difference is found to exist between the M VIRI operational calibration coefficient and an intersatellite calibration coefficient derived from collocated GOES 8 water-vapor-sensitive channel 3 observations. Third, it is shown that the operational calibration coefficie nt for the MVIRI water vapor channel on Meteosat 7 is consistent with its b lackbody calibration. At the present stage of the research no definite conc lusions can be made. The results support the previously documented accuracy of 5% for the operational calibration coefficient of the MVIRI water vapor channel.