Analysis of Surface Normalized Radar Cross Section for the Improvement of the TRMM Precipitation Radar Algorithm PART II : Over the Land

Abstract

The Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) standard algorithm 2A21 produces the surface normalized radar cross section (NRCS) values under no rain conditions as functions of the incidence angle and surface physical parameters which affect surface scattering. These NRCS values are used as the reference values to calculate the path integrated attenuation (PIA) values in the surface reference technique (SRT) to perform the rain attenuation correction. This paper (Part II) shows the relation between the land surface NRCS values and the three land surface physical parameters which are NDVI (Normalized Differential Vegetation Index), the surface roughness, and the soil moisture over the land for each of the incidence angles and tries to improve the methods to calculate reference NRCS values over the land.
We calculate the correlation coefficients and derive the linear regression equation between the land surface NRCS and each of the tree land surface physical parameters for each of the incidence angles, respectively. The present PR 2A21 version 6 algorithm uses the temporal reference method to calculate the reference NRCS as a function of incidence angle only over the land. We apply the multiple regression analyses between the NRCS and all of the tree land surface physical parameters at a time and derive the new equations which express the NRCS by the tree land surface physical parameters for each of the incidence angles. This equation is expected to improve the reference NRCS in the temporal reference method over the land.