Next generation of NOAA/NESDIS TMI, SSM/I, and AMSR‐E microwave land rainfall algorithms

Abstract

Revised versions of previous passive microwave land rainfall algorithms are developed for the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI), the Special Sensor Microwave/Imager (SSM/I), and the new Advanced Microwave Sounding Radiometer‐Earth Observing System (EOS) (AMSR‐E). The relationships between rainfall rate and 85 GHz brightness temperature are recalibrated with respect to previous algorithms using collocated TMI and TRMM Precipitation Radar (PR) data. Another new feature is a procedure to estimate the probability of convective rainfall, as convective/stratiform classification can reduce the ambiguity of possible rainfall rates for a given brightness temperature. These modifications essentially eliminate the global high bias found in studies [e.g., McCollum et al., 2000; Kummerow et al., 2001] of previous versions of the SSM/I and TMI algorithms. However, many regional and seasonal biases still exist, and these are identified. The applicability of the new features to the other microwave sensors is studied using SSM/I data, and a correction is developed to account for the differences in footprint resolution between the TMI and SSM/I. The AMSR‐E algorithm is the same as the TMI, as the footprint resolutions and frequencies of these instruments are very similar. The TMI algorithm will be used in the land portion of the official version 6 TMI instantaneous rainfall rate product, to be released in 2003, while the AMSR algorithm will be used in a similar manner for future AMSR‐E products.