Quantitative Evaluation of the Effects of Large-Scale Sea Wave Components on Microwave Backscattering From Ocean Surface

This article quantitatively examined the effect of these long-wave components with wavelength larger than the Bragg component on radar backscattering using the series-expanded first-order small-slope approximation (SSA-1) and the Hwang sea wave spectrum model. First, some roughness with various scales is constructed using different long-wave sea spectrum components and, subsequently, is cast into SSA-1 to obtain the corresponding normalized backscattering cross section (NBCS) at different radar frequency, incidence angles, and wind speeds, respectively. Then, the effect of large-scale wave components on radar backscattering is revealed by analyzing the NBCSs with different roughness. Finally, the existing wavelength filtering theory explained the effect of large-scale waves on radar backscattering. It was also verified by another scattering model, i.e., the advanced integral equation model and radar measurements. Besides, we also investigate the effects of sea states and swell waves on the numerical simulation results. The effect of long-scale waves on NBCS clarifies the source of backscattering from the multiscale sea surface, which is helpful for both analytical and numerical scattering models to explore the sea surface scattering properties and better interpret the radar sensing of sea surface. Also, the examination of the effect of sea states and swell waves on radar backscatter is instructive for reducing the inversion errors of sea surface wind speed from radar measurements by means of configuring the appropriate radar parameters (e.g., high frequencies and large-incidence angles)