Full-Polarization Modeling of Monostatic and Bistatic Radar Scattering From a Rough Sea Surface

Abstract

Fully polarimetric radars have advantages compared to more conventional single-polarization radars when measuring ocean wave characteristics. However, the theoretical analysis of full-polarization radar scattering frequently presents a challenge. For example, the classical composite model fails to correctly predict the cross-polarization components of the normalized radar cross section (NRCS). The new version of the numerical implementation of the small slope approximation of the second order, the SSA2, is presented in this paper. The SSA2 correctly predicts the behavior of out-of-plane bistatic scattering for an arbitrary set of polarization indices. The SSA2, as contrasted with the composite model, accounts for Bragg scattering of the second order which is essential for modeling cross-polarization scattering. We present the results of numerical simulations of both monostatic and bistatic cross sections and scattering amplitude correlators for various ocean conditions and transmitter-receiver geometries using the SSA2. We compare them with available experimental data and other modeling results.Index Terms-Electromagnetic (EM) scattering by rough surfaces, polarimetric radar, sea surface electromagnetic scattering.

Circularly Polarized Wave Scattering From Two-Dimensional Dielectric Rough Sea Surface

“…The small-slope approximation (SSA) [25] theory consists of a basic approximation of the theory (SSA-I) and second-order corrections to it (SSA-II) and represents a systematic expansion of a scattering amplitude with respect to slopes of rough surface, which has been successfully applied to evaluate microwave scattering from rough sea surfaces [22,26]. Although SSA-I is much more efficient than SSA-II, it cannot predict the depolarization of wave scattering from rough surfaces in the plane of incidence.…”

“…The two scale model (TSM) [18][19][20][21] also known as composite surface model underestimates the cross-polarized components due to the neglect of second-order Bragg scattering. In comparison with the classical model such as SPM, KA and TSM, the modern analytical approximate model of second-order small-slope approximation (SSA-II) takes into account the mutual transformation of the two linear polarization states caused by facets tilts as well as the second-order Bragg scattering [22], and thus can predict the depolarized scattering from rough sea surface both in and outside the plane of incidence.…”

Second-Order Perturbative Solution of Scattering From Two Rough Surfaces With Arbitrary Dielectric Profiles

“…Active-passive soil moisture estimation algorithm [4], polarization features [5], [6], fast and efficient numerical techniques [7]- [9], semi-analytical methods [10], low frequency analytical derivations [3], [11], [12], high frequency analytical solutions [13], [14], and higher order perturbative procedures [15]- [17] are examples of publications in the last three years.…”

Sensitivity of modeled polarimetric radar ocean scattering to wind direction

“…Here, our intention is to analyze how well the small slope approximation model of the second order (SSA2) can reproduce the behavior of polarimetric radar signal, and how it is sensitive to the choice of ocean surface spectrum. It was demonstrated that the SSA2, as contrasted with the smallslope approximation of the first order SSA1 (and with the composite (two-scale) model) accounts also for Bragg scattering of the second order which includes a contribution from resonant terms responsible for Wood's anomaly [9][10][11]. Even though there is a qualitative agreement between the SSA2 predictions and the measured polarized backscattering cross sections and other complex entries of the correlation matrix, still, significant quantitative differences remain between the SSA2 predictions and experimental data.…”

“…Recent wind retrieval algorithms which employ cross-polarization radar signal (VH) rely on an assumption that VH is independent on azimuthal and incidence angles and driven mainly by wind speed [12]. However, azimuthal and incidence angle dependences of the VH return are predicted by the SSA2 [11] and clearly visible in airborne and satellite data [1][2][3][4][5][6][7][8]. Evidently, both measured co-pol and cross-pol radar cross sections manifest the directionality of the ocean surface roughness and wave breaking.…”