Comparison of instantaneous TRMM satellite and ground validation rain rate estimates

Space-borne rain rate estimates derived from data collected with two remote sensors aboard the Tropical Rainfall Measuring Mission (TRMM) satellite were compared against ground-based estimates inferred from radar data at several Ground Validation (GV) sites. The satellite rain rates were generated from the TRMM Microwave Imager (TMI), Precipitation Radar (PR) and Combined (COM) rain algorithms. The GV rain rates were obtained from the TRMM 2A53 rain maps. The first part of the study compared 0.5° x 0.5° gridded data extracted from the TRMM 3G68 product with GV data gridded at the same scale. The second part of the study compared satellite and GV rain rates at the nominal scale of the TMI footprint. The matching criteria constrained the comparisons to the intersection of the PR orbital track with the GV radar domain, defined as within 100 km of the radar location. The matching PR, COM and GV rain rates were then averaged within a 7 km radius of each TMI footprint. Both analyses were made at the same spatial and temporal scales in order to eliminate sampling biases in the comparisons and utilized data covering the period from 1999 to 2004. The results show that the respective rain rate estimates agree well, with some exceptions, which were associated with heavy rain events in which one or more of the algorithms failed to properly retrieve these extreme events. Also, it is shown that there is a preferred mode in the TMI rain rate distributions over the ocean at or near 2 mm hr^-1, which is not evident in any of the other distributions. This mode was noted over ocean areas of Melbourne, Florida and Kwajalein, Republic of the Marshall Islands, and was also present in TMI tropical-global ocean areas..