Inter-Calibration of Geostationary Imager Infrared Bands Using a Hyperspectral Sounder on the Same Platform

Geostationary (GEO) imager Infrared (IR) bands are often intercalibrated with hyperspectral IR sounders onboard low earth orbit (LEO) satellites. Due to viewing geometry and time differences between GEO and LEO, the inter-calibration is limited to certain viewing angles and times. When a GEO hyperspectral IR sounder and GEO imager are on the same platform, the inter-calibration can be conducted from all angles and at all times. In this study, the Geostationary Interferometric Infrared Sounder (GIIRS) is used to inter-calibrate the Advanced Geosynchronous Radiation Imager (AGRI), both onboard FengYun-4A. Radiance inter-comparisons between GIIRS and AGRI under homogeneous scenes, including both clear and cloudy situations, indicate that the differences are within 1 K. The differences have obvious dependence on scene radiance, less dependence on the cloudy situation, and the local zenith angle when it is less than 70 degrees. However, they exhibit significant diurnal characteristics.