Simultaneous Ocean Cross Section and Rainfall Measurements from Space with a Nadir-Looking Radar

Abstract

In the case of a nadir-looking spaceborne or aircraft radar in the presence of rain the return power corresponding to secondary surface scattering may provide information on the properties of the surface and the precipitation. The object of the study is to evaluate a method for determining simultaneously the rainfall rate and the back-scattering coefficient of the surface, σ0. The method is based upon the mirror-reflected power, Pm, which corresponds to the portion of the incident power scattered from the surface to the precipitation, intercepted by the precipitation, and again returned to the surface where it is scattered a final time back to the antenna. Two approximations are obtained for Pm depending on whether the held of view at the surface is either much greater or much less than the height of the reflection layer. Since the dependence of Pm on the backscattering coefficient of the surface differs in the two cases, two algorithms are given by which the path-averaged rain rate and σ0 can be deduced. We also discuss the delectability of Pm, the relative strength of other contributions to the return power arriving simultaneously with Pm, and the validity of the approximations used in deriving Pm.