Rain-profiling algorithm for the TRMM precipitation radar

This paper describes the Tropical Rainfall Measuring Mission (TRMM) standar d algorithm that estimates the vertical profiles of attenuation-corrected r adar reflectivity factor and rainfall rate. In particular, this paper focus es on the critical steps in the algorithm. These steps are attenuation corr ection, selection of the default drop size distribution model including ver tical variations, and correction for the nonuniform beam-filling effect. Th e attenuation correction is based on a hybrid of the Hitschfeld-Bordan meth od and a surface reference method. A new algorithm to obtain an optimum wei ghting function is described. The nonuniform beam-filling problem is analyz ed as a two-dimensional problem. The default drop size distribution model i s selected according to the criterion that the attenuation estimates derive d from the model and the independent estimates from the surface reference w ith the nonuniform beam-filling correction are consistent for rain over oce an. It is found that the drop size distribution models that are consistent for convective rain over ocean are not consistent over land, indicating a c hange in the size distributions associated with convective rain over land a nd ocean, respectively.