Overview of surface wind speed retrieval from C-band SAR images: Empirical and electromagnetic approaches

In spite of the difference in description, it is reasonable to compare sea surface wind speed estimates based on empirical (EP) and electromagnetic (EM) approaches, since both of them describe the relation between radar backscattering and wind parameters, directly for EP models and via sea surface roughness spectrum for EM models. For EP approach, two methods are presented for wind speed estimation: scatterometry and model without wind direction input. For EM approach, the approximation models, i.e. small-slope approximation (SSA) and resonant curvature approximation (RCA), are presented since they can calculate radar backscattering close to that given by the EP models. The comparison between EP and EM models demonstrate that estimated wind speeds by two approaches are quite similar, especially for radar incidence angles below 40°.