Influence of Scattering from Rough Ocean Surface on Rain Measurements with Microwave Radiometry

Abstract

Rain measurements are being conducted by microwave passive techniques from air as well as from space. Microwave radiometry is also applied to ocean surface measurements. They are usually examined separately, and the rain and ocean surface roughness due to wind are regarded as a perturbing factor to each other's objectives. From a standpoint of rain measurements, however, ocean surface condition is important, since it determines the lower boundary condition for microwave radiative transfer. In this paper, an influence of ocean surface roughness on microwave passive measurements of rain from an airborne platform is evaluated by a numerical computation. A two-scale rough surface model is adopted to characterize the microwave scattering signature from a rough ocean surface. The results of computation show that the nadir-looking configuration minimizes the influence of ocean surface roughness on rain measurements. The influence can be partly reduced by using excess brightness temperatures for rain rate estimation. A comparison between the theoretical results and the measurements is also made.