Cloud Height-Parallax Correction of GPROF Rainfall Product Improves General Accuracy of Retrievals over CONUS

Satellite rainfall retrieval algorithms whose measurement instruments are tilted respect to the zenith line, are subject to a space mismatch between the theoretical ground coordinates and the actual coordinate pair corresponding to the top of the cloud sending spectral signals to the satellite. This is the case of the rainfall retrievals of the GPM Passive Microwave Imagery (GMI) on board of the core satellite of the Global Precipitation Mission (GPM) that generates the Goddard Profiling Algorithm (GPROF). Up to date, there is no geometrical correction of GMI retrievals which makes them dependent on cloud height. Therefore, GPROF comparisons with ground truth are spatially offset especially for tall cloud systems (i.e. typical of summer convective events). GPROF rainfall retrievals over the three different atmospheric regime regions of the U.S. (Arizona, Washington and Oklahoma states) are analyzed with the support of ground-validated Multi-Resolution Multi-Sensor (GV-MRMS) system and simultaneous multi-level atmospheric temperatures from ERA5 reanalysis. Results (see figure attached) applying this parallax correction show improvements in the overall retrieval accuracy of GPROF by simply finding a single cloud height that consistently (over one year and multiple regions) minimizes the biases of GPROF. Further CONUS analysis by seasons should reveal how this parallax correction could be applied before any other bias correction strategy is adopted.