Evaluating the effect of rain on SeaWinds scatterometer measurements

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 sigmadegrees 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 sigmadegrees 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.