GPM Microwave Imager on-orbit radiometric calbration using a satellite deep space calibration maneuver

The Global Precipitation Measurement (GPM) Microwave Imager (GMI) is designed to be the radiometric calibration standard for a group of satellites with passive microwave instruments known as the GPM constellation. Because GMI is the transfer standard, it is crucial to vet its calibration accuracy in an extensive post-launch Calibration/Validation campaign. One important element of this campaign is a special set of satellite maneuvers known as Deep Space Calibration (DSC). During the DSC maneuver, the satellite pitch attitude is adjusted to cause the microwave instrument to view space, which is an isotropic non-polarized scene of known brightness temperature. Because of the delay in the GPM launch and the associated DSC, this paper focuses on the predecessor TRMM Microwave Imager (TMI) DSC maneuvers to gain insight into the GMI DSC results.