Synoptic Variability in Satellite Altimeter-Derived Radar Freeboard of Arctic Sea Ice

Satellite observations of sea ice freeboard are integral to the estimation of sea ice thickness. It is commonly assumed that radar pulses from satellite-mounted Ku-band altimeters penetrate through the snow and reflect from the snow-ice interface. We would therefore expect a negative correlation between snow accumulation and radar freeboard measurements, as increased snow loading weighs the ice floe down. In this study we produce daily resolution radar freeboard products from the CryoSat-2 and Sentinel-3 altimeters via a recently developed optimal interpolation scheme. We find statistically significant (p < 0.05) positive correlations between radar freeboard anomalies and modeled snow accumulation. This suggests that, in the period after snowfall, radar pulses are not scattering from the snow-ice interface as commonly assumed. Our results offer satellite-based evidence of winter Ku-band radar scattering above the snow-ice interface, violating a key assumption in sea ice thickness retrievals.