OcLAGRS-Wind: A Fully Polarized GNSS-R Ocean Surface Scattering Model Based on Modified Kirchhoff Geometric Optics Approximation for Wind Field Retrieval

Abstract

Global navigation satellite system reflectometry (GNSS-R) has demonstrated substantial potential for ocean surface wind field retrieval over the past three decades, owing to its all-weather capability, global coverage, and cost-effectiveness. Polarization signals are physically sensitive to sea surface winds due to wind-modulated ocean mean square slope and depolarization, and cross-polarized channels improve wind detection performance under high wind speeds. However, most existing ocean scattering models are designed primarily for single-polarization operations—typically left-hand circular polarization (LHCP) reception with right-hand circular polarization transmission—and provide limited consideration of full polarization characteristics, including hybrid compact polarization (HCP). Conventional Fresnel reflection coefficients for LHCP in both transmission and reception exhibit an unphysical decreasing trend with increasing sea surface salinity, which contradicts observational evidence and established physical expectations. Moreover, most models rely on a single wave spectrum, limiting robustness across diverse sea states. To address these limitations, this article develops OcLAGRS-Wind, a fully polarized GNSS-R ocean surface scattering model for wind field retrieval, as a specialized module within the OcLAGRS framework. Based on a modified Kirchhoff geometric optics approximation, the model incorporates multiple directional wave spectra (Elfouhaily, Durden–Vesecky, Kudryavtsev, and Donelan–Banner), adapts seawater Fresnel coefficients via a full-polarization Mueller matrix approach (inspired by Umich4PolR), and supports multifrequency, multiconstellation simulations including BeiDou. Particular emphasis is placed on HCP modes relevant to emerging missions such as China’s Tianmu-1 commercial constellation and ESA’s HydroGNSS. This end-to-end simulator enables comprehensive analysis of polarization effects, wave spectrum influences, and geophysical sensitivities in delay-Doppler maps and waveforms. OcLAGRS-Wind will serve as a vital mechanistic tool for novel sensor design, multiparameter wind retrieval, and mission planning in next-generation GNSS-R systems.