A Sentinel-1 Dual-Polarimetric Scattering-Regime Framework with AMSR2 Consistency Assessment for Interannual Sea Ice Characterization in the Southern Sea of Okhotsk

Passive-microwave sea ice concentration (SIC) products, such as AMSR2, provide broad coverage but limited spatial detail in coastal and marginal ice zones. This study presents a Sentinel-1 IW-mode dual-polarimetric framework for interannual sea ice characterization in the Southern Sea of Okhotsk. Twenty Sentinel-1 SLC scenes acquired during February–March 2022–2026 were aligned to a common SAR footprint and restricted to an ocean-only domain using a temporal σVV0-based land/ocean mask. Open water was separated using an incidence-angle-normalized σVV, norm0 threshold; the correction was evaluated through leave-one-scene-out analysis, and threshold robustness was assessed through sensitivity testing. The remaining ice-candidate pixels were partitioned into surface-like, mixed, and random/dipole-like scattering regimes in H–α space. Sentinel-1-derived ice fractions were compared with temporally collocated AMSR2 Level-2 SIC. The comparison showed a moderate positive association at the scene-mean level (R2 = 0.277, RMSE = 24.85%, bias = +0.13%) and footprint scale (R2 = 0.429, RMSE = 29.98%, bias = −0.11%). The large RMSE values indicate weak absolute agreement, particularly at the footprint scale. The framework provides higher-resolution information on sea ice coverage and scattering-regime composition, but Sentinel-1-derived ice fraction and AMSR2 SIC should not be interpreted as interchangeable quantities.