Calibration Assessment of ISCCP Geostationary Infrared Observations Using HIRS

Abstract Infrared window (∼11 μm) brightness temperatures from global geostationary meteorological instruments were calibrated using the High Resolution Infrared Radiation Sounder (HIRS) as an independent analysis of the satellite intercalibration performed by the International Satellite Cloud Climatology Project (ISCCP). Criteria for matching geostationary observations with HIRS from previous literature were inadequate to analyze a shift in calibration due to the limited range of resulting temperatures. The result was an inability to determine the impact of a calibration error on observations of cold clouds. To better understand the calibration error, a new set of matchup criteria that collected targets at all temperatures proportionately showed a significant shift in the ISCCP calibration. Using the new criteria, it became apparent that observations of cold temperatures were biased too cold. A correction based on these results removed the bias between the geostationary and HIRS observations.