Accuracy of the Coherent Two-Scale Model in Predicting Doppler Moments and Cross-Section of Sea Backscatter as a Function of Scale Separation Length and Incidence Angle

This paper examines errors in commonly used sea backscatter characteristics, such as the normalized radar cross section (NRCS) and first moments of the Doppler spectrum, when calculated using the Two-Scale Model (TSM). The latter is used in its “deterministic” or “coherent” formulation that allows evaluation of the complex scattered field for any given surface profile. The average quantities of interest are compute in the two-dimensional space using large-scale Monte Carlo simulations at X band. These descriptors are benchmarked against their “exact” counterparts obtained from a Method of Moments (MoM) solution for the same surface realizations. The calculations cover incidence angles from 0 to 85° and scale separation lengths from 0.5 to 8 electromagnetic (e-m) wavelengths. The produced error maps in these two variables look very different for the NRCS and for the Dopple moments. The error landscape for the latter is rather complex, but a depression is discernable where the separation length is inversely proportional to the sine of the incidence angle. Picking this path, however, is not optimal for the NRCS and would lead to large errors at smaller incidence angles. For the angle-independent choice, various optimization approaches suggest the best separation value to be around one e-m wavelength for all considered quantities.