Doppler Properties of Sea Backscatter Simulated with Creamer or Choppy Wave Surface Models

The accuracy of sea scattering simulations depends on both the robustness of the chosen electromagnetic model and the adequate description of the ocean surface itself. The latter consideration is particularly relevant for Doppler simulations that are sensitive to hydrodynamic (non-linear) effects in surface propagation. There are two commonly used approaches to introduce such non-linearities – the Creamer transform and the Choppy wave model. We compare these two models and their impact on the Doppler characteristics of the computed backscattered signals using Monte Carlo simulations in the 2-D space. The electromagnetic part of the problem is solved exactly using a boundary integral equation technique. Significant differences in Doppler centroids corresponding to the two models are observed for intermediate to large incidence angles, with the Creamer transform producing larger shifts. The widths of the spectra are more consistent, with the Creamer model leading to somewhat larger values. Possible reasons for the discrepancies are discussed.

1. INTRODUCTION

Numerical Monte Carlo simulations have been an important tool in sea scattering studies. The procedure of obtaining an ensemble member naturally splits in two tasks: generating a representative, sea-like surface realization, and then calculating the field scattered by this profile with a direct electromagnetic solver or an approximate scattering model. For Doppler simulations, a surface realization needs to be evolved in time. The accuracy and relevance of the simulation results depend on the fidelity of the electromagnetic scattering model and on the adequate representation of the rough scattering interface and its behavior. This study focuses on the latter aspect.