Snow Depth on Arctic Sea Ice Retrieval Using a Synergy of Sentinel‐3's Active and Passive Microwave Instruments

Abstract Snow depth remains one of the largest sources of uncertainty in satellite‐derived sea ice thickness (SIT). Here, we introduce the novel N a dir R adiometer and R adar S ynergy ( NaRRS ) method that combines data from Sentinel‐3's Microwave Radiometer (MWR) and Synthetic Aperture Radar Altimeter (SRAL) to retrieve Arctic snow depth on sea ice. The resultant snow depths are co‐located with SRAL‐derived radar freeboard, reducing spatio‐temporal mismatches in SIT processing. NaRRS achieves an of 0.72 and RMSE of 0.05 m in cross‐validation against Operation IceBridge snow depth data, and better matches IceBird observations than the modified Warren Climatology (mW99). Ice drafts estimated from coupled snow depth and freeboard align with mW99 against Beaufort Sea moorings but reduce bias by up to 50% against Fram Strait moorings. This work provides a proof‐of‐concept for simultaneous, co‐located snow depth and SIT retrievals, paving the way for next‐generation satellite missions and retrieval frameworks.