Improved Correction of Beam Mismatch of the Precipitation Radar After Orbit Boost of the TRMM Satellite

One effort in developing the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) data processing algorithm is to correct the PR received power for mismatched-beam data after the orbit is boosted. The current standard algorithm employs a beam-mismatch correction algorithm based on the rain-echo radar equation (Takahashi's method). However, there remains a need for improving the estimated power of the mismatched-pulse echo returned from the Earth's surface and weak rain because the echo is represented with the surface-echo radar equation and the noise-power level. The error in Takahashi's method causes a negative bias (around 1 dB) in the PR received power near the main lobe clutter. This paper formulates an improved estimate of the mismatched pulse based on the rain-echo radar equation and the surface-echo radar equation for a flat-Earth surface. The improved estimate is then evaluated numerically and experimentally with the actual data obtained by TRMM/PR for observations over the ocean. The consistency of TRMM/PR data sets between preboost and postboost was improved by eliminating the negative bias (around 1 dB) in the PR received power. The mean rain rate near the surface-echo range increases by 10%, and the angle-bin asymmetry of the mean rainfall rate, which is present in the postboost data corrected by Takahashi's method, is resolved.