Radiometric Inter-Calibration of Microwave Imagers Over Homogeneous Warm Scene Targets

Abstract

Conventional satellite intercalibration for microwave imaging radiometers involves a linear two-point calibration approach, over cold ocean scenes and warm ends of the scene brightness temperatures, traditionally over tropical rain forest. Unfortunately, this approach ignores the possibility of non-linear radiometer transfer function, which is often important. This paper discusses a new tool developed to identify large-scale homogeneous desert scenes as possible third calibration targets with brightness temperatures that fall between the conventional cold and warm earth scenes. Previously a prototype “ShowMask” procedure was developed over continental Australia using 10, 18 and 37 GHz Vertical and Horizontal polarized brightness temperatures from GPM Microwave Imager (GMI) data. This paper focus on extending this tool to global scale and including 89 GHz channel in the analysis. Further, by applying the mask, we examine intercalibration results over selected desert targets using GMI-TMI and GMI-AMSR-2 match-ups. Initial results indicate a scene temperature dependence of calibration factor particularly for horizontally polarized channels.