Evaluating the effect of rain on SeaWinds scatterometer measurements

Abstract

A simple wind/rain backscatter model is used with co-located precipitation radar (PR) data from the Tropical Rainfall Measuring Mission (TRMM) satellite to evaluate the effect of rain on SeaWinds on QuikSCAT σ° observations. The model incorporates wind-induced surface scattering, the surface rain perturbation, and atmospheric rain attenuation and scattering. The co-located PR measurements afford direct computation of SeaWinds-scale averaged rain rate and atmospheric rain attenuation and scattering. An estimate of the wind-induced surface backscatter is computed via numerical weather prediction (NWP) winds. By synergistically combining the SeaWinds, NWP, and PR data, estimates of surface rain perturbation and combined surface/atmospheric scattering are made as a function of PR-derived rain rate. The scattering from rain is dominated mainly by the surface perturbation low rain rates, and by atmospheric scattering at high rain rates. The backscatter model estimates 94% of the observed rain-contaminated SeaWinds on QuikSCAT σ° values to within 3 dB. Using the model, the conditions are determined for which it is possible to estimate rain from scatterometer measurements and where wind retrieval is not possible. Copyright 2004 by the American Geophysical Union.