Study of Microwave Backscattering From Two-Dimensional Nonlinear Surfaces of Finite-Depth Seas

This paper presents a study of the microwave backscattering from 2-D time-evolving nonlinear surfaces of a sea with finite depth by using the second-order small-slope approximation. According to the shallow-water dispersion relation, the revised nonlinear hydrodynamic choppy wave model in connection with an experiment-verified sea spectrum for finite-depth water is employed to construct the wave profiles in the finite-depth sea. The numerical results show that the discrepancy between the choppy surfaces of the infinite-depth sea and their finite-depth counterparts for monostatic normalized radar cross section is much smaller than that between the linear surfaces and the nonlinear choppy surfaces. Furthermore, the comparison of the Doppler spectra of the backscattered echoes from the linear and nonlinear choppy sea surfaces shows that the nonlinear hydrodynamic features significantly impact the Doppler spectrum. In particular, the Doppler spectrum for nonlinear finite-depth sea presents much higher second-order peaks and increased spectral amplitudes in the frequency range around the Doppler peak frequency, which reiterates the importance of the role that the nonlinear hydrodynamic effect of waves played in the interpretation of backscattering from finite-depth nearshore seas from the qualitative point of view.