Radiative Transfer Modelling of Ka-band Microwave Interactions with Snow-Covered Freshwater Ice: Implications for SWOT KaRIn Property Retrieval

Abstract. Snow cover on lake ice plays an important role in regulating lake ice thermodynamics, making its characterization essential for understanding lake climatology and cryospheric processes. However, remote sensing studies of snow-covered lake ice remain limited, and the physical understanding of high-frequency radar backscatter from the coupled snow–ice system remains unclear. This study investigates the interactions between Surface Water and Ocean Topography (SWOT) Ka-band Radar Interferometer (KaRIn) observations and snow-covered lake ice by examining how snow and ice properties, together with radar acquisition geometry, influence the relative contributions of different scattering mechanisms. A field campaign was conducted on Kluane Lake, Yukon, during the winter season of 2026, where in-situ snow and ice properties were measured coincident with eight SWOT acquisitions from five orbital passes. The Snow Microwave Radiative Transfer (SMRT) model was used to simulate Ka-band backscatter and perform sensitivity analyses of snow/ice properties and sensor configurations. A second-order iterative scattering solver was implemented to quantify backscatter contributions from individual snow and ice layers and to investigate the evolution of the dominant scattering mechanism. Modelled and observed backscatter showed good agreement, with RMSEs of 1.14 dB using smooth snow configurations and 1.08 dB for using rough snow configurations and Pearson correlation coefficients of approximately 0.95 at both configurations. Results indicate that the ice surface generally dominates KaRIn backscatter over snow-covered lake ice, while the relative contributions of the snow surface and snow volume increase under specific combinations of incidence angle, snow depth, and snow microstructure. These findings demonstrate the importance of explicitly considering snow–ice interactions when interpreting Ka-band observations and provide a physical basis for developing snow and ice retrieval approaches from current and future Ka-band satellite missions.