A simulation of air/space-borne radar rain path attenuation estimation using the mirror image radar return

The mirror image rain echo, received through the double reflection of the radar from the surface, may provide useful information in estimating the rainfall rate from airborne and spaceborne weather radars. As the TRMM spaceborne weather radar has been successfully launched recently, issues regarding the utility of this measurement are pertinent and timely. In this study, having described a mirror image model, which yields the co- and cross-polarized components of the mirror image and bistatic returns as a function of the radar parameters and the scattering properties of the rain and surface, several algorithms to estimate the path attenuation based on the mirror image returns are constructed. These methods generally use a difference (in dB) between the direct and mirror image radar returns where the returns are taken at equally distant ranges above and 'below' the surface. In some implementations of the algorithm the return power from the surface is used as well. To test the accuracy of these algorithms, the direct, mirror image and surface return powers are generated from measured raindrop size distributions, a surface scattering model and a mirror-image scattering model. These models can be used to control the characteristics of the rain profiles (rain intensity and vertical structure) as well as the surface scattering characteristics. Comparisons between the mirror-image and the surface reference techniques are made for various rain intensities, vertical rain profiles and surface scattering characteristics. In the final part of the paper, some preliminary results of comparisons of the mirror image algorithms with the surface reference technique are given using data from the TRMM Precipitation Radar.