How TRMM precipitation radar and microwave imager retrieved rain rates differ

Analysis of the collocated rain retrievals from Tropical Rainfall Measuring Mission's precipitation radar and microwave radiometer reveals that their difference depends on the intensity and the type of rain - the radiometer-derived rain rates vary from higher to lower than the radar-derived ones as rain rate or convective fraction increases. To better understand how this difference occurs, the relations between the two leading EOFs (Empirical Orthogonal Functions) of the observed brightness temperatures and the radiometer- or radar-derived rain rates were examined for convective, mixed and nonconvective rain categories. In all types of rain, the two EOFs respond to the variation of the radiometer- and radar-derived rain rates in a similar fashion in low rain rates, while they respond quite differently in high rain rates.