| 22 May 2026
Soil microwave background retrieval and snow sensitivity from multi-frequency SAR observations over an agro-forested environment in northern Ontario
Abstract. Accurate retrieval of Snow Water Equivalent (SWE) using Synthetic Aperture Radar (SAR) requires effectively decoupling the signal contribution of the snowpack from that of the underlying soil. This study evaluates a multi-frequency soil parameter inversion methodology using Snow Microwave Radiative Transfer (SMRT) model in a temperate, agro-forested environment in Powassan, Ontario. Using multi-frequency observations from Cryospheric SAR (CryoSAR) (L-band), Radarsat Constellation Mission (RCM) (C-band), and TerraSAR-X (TSX) (X-band) acquired during the 2022/2023 winter season, soil roughness and permittivity were jointly inverted to reproduce observed backscatter. The inversion strategy, which optimizes a single time-invariant roughness per site alongside time-varying permittivity, achieved strong agreement between simulated and observed signals across frequencies (Global R2 = 0.87, RMSE =1.25 dB). Sensitivity analyses reveal a clear frequency-dependant hierarchy of controls: surface roughness dominates L-band backscatter (particularly in VV polarization), soil permittivity governs C- and X-band responses, and extending the analysis to explicitly include snow properties shows that the dominant controls progressively shift to snow microstructure and depth toward Ku-band. Comparisons with in situ measurements indicate that inverted parameters represent effective values at the radar scale; specifically, inverted roughness differs from LiDAR-derived topography, suggesting the influence of basal snow layer properties. Despite complications arising from spatial heterogeneity of soil properties including freeze/thaw cycles, the results demonstrate the feasibility of retrieving soil background parameters to support future multi-frequency snow missions such as Terrestrial Snow Mass Mission (TSMM).
Competing interests: At least one of the (co-)authors is a member of the editorial board of The Cryosphere.
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