Numerical simulation of backscatter from linear and nonlinear ocean surface realizations

Abstract

In this paper, numerical simulations of the scattering from time‐dependent realizations of one‐dimensional ocean surface waves are described. A new technique is used that allows efficient generation of ocean surface realizations that preserve the dominant nonlinear hydrodynamic characteristics. Thus unique scattering effects of real ocean surface waves can be explored. Until very recently, numerical simulations of rough‐surface scattering were used mainly to test and/or improve theoretical models that predict the average bistatic scatter cross section. We carry the simulations further by generating Doppler spectra from dynamically evolving surface realizations. Doppler spectra of signals scattered from the ocean surface are affected by both hydrodynamic nonlinearities and higher‐order scatter terms. The simulated Doppler spectra from nonlinear surface realizations reproduce the measured characteristics of ocean and wave‐tank data for low and high wind conditions. We also show that the results are essentially reproduced by the second‐order Kirchhoff approximation.

Investigation on Doppler Spectral Characteristics of Electromagnetic Backscattered Echoes From Dynamic Nonlinear Surfaces of Finite-Depth Sea

“…h (x,t) exp (−jζx)dx (13) P is the incident wave power captured by the sea surface. The details of kernel functions of the integral, B and M , can be found in [25], here, we safely omit it for the sake of brevity.…”

“…Unfortunately, beyond their applicable range of angles, as low-grazing angles (LGA), their predictions are inaccurate to some extent. Rino et al [13] comparatively studied the backscattering and the Doppler spectra from one-dimensional (1-D) time-varying linear and nonlinear Creamer sea surfaces [14] for the first time. Toporkov and Brown [15] made a comprehensive study of the Creamer nonlinear surface scattering characteristics using the method of ordered multiple interactions (MOMI).…”

Sea Surface Microwave Scattering at Extreme Grazing Angle: Numerical Investigation of the Doppler Shift

“…This corresponds to a surface being invariant along one direction, e.g., the y direction, with an elevation z = η(x). With the radio waves propagating much faster than water waves, the surface can be frozen at any given time t from a scattering point of view [14]. Time dependence of the surface height and horizontal displacement D(x) are thus neglected in the derivations of this section.…”

“…In the last decade, significant progresses have been made in numerical and physical modeling of the microwave Doppler spectra. It has become clear that a rigorous electromagnetic approach [14]- [19], combined with nonlinear hydrodynamic models [20]- [22], is necessary to reproduce, at least qualitatively, the observed phenomena. In the reference paper [23] and its follow-up [24], a systematic numerical computation of Doppler spectra under different wind conditions has been conducted using a rigorous electromagnetic method and the weakly nonlinear Creamer model.…”

Rough Surface Models Implemented Within the Split-Step Parabolic Equation Algorithm

“…As a second validity check for MLAYER, a height/range profile was created for one realization of a random sea surface using the Pierson-Moskowitz ocean wave spectrum [12]. This profile was used as input to TPEM (Terrain Parabolic Equation Model) [3], which models radiowave propagation over variable terrain.…”