A comparison OF GPM Microwave Imager (GMI) high frequency channel brightness temperatures to the Advanced Technology Microwave Sounder (ATMS)

A direct comparison of top-of-atmosphere brightness temperatures for the 183.31 and 166 GHz channels is given in this paper between the Global Precipitation Measurement (GPM) Microwave Imager (GMI), the Advanced Technology Microwave Sounder (ATMS), and the Microwave Humidity Sounder (MHS) on MetOp-A. As far as is possible, differences in polarization and earth incidence angle are accounted for by properly selecting the data around the GMI incidence angle and rotating the polarization of the dual-pol channels. A sensitivity analysis using a radiative transfer model shows that the comparison should be valid to within +/-0.5K for moist atmospheric conditions. Results are shown before and after antenna pattern corrections applied during the on-orbit calibration/validation period. Except for very dry atmospheric conditions and for convective rain events, the comparison is stable over brightness temperature and atmospheric water content. The GMI brightness temperatures are within about 1K of the ATMS and about 0.5K of MHS on MetOp-A.