Publication

Abstract : The geophysical properties of the snow cover on first-year sea ice play a significant role in the growth, evolution and decay of Arctic sea ice. Snow salinity, which occurs on first-year sea ice, has been shown to reduce the penetration depth of Ku-band microwaves and causes a vertical shift in the main scattering horizon of up to 7 cm above the snow/sea-ice interface. A vertical shift in the scattering horizon leads to overestimated sea ice thickness from spaceborne radar altimeter retrieval approaches. In this study, field measurements of snow thermophysical properties from several sites in the Canadian and the Norwegian Arctic over the past 25 years are used to evaluate the effect of snow brine volume on Ku-band scattering. Estimates of the main scattering horizon, using a semi-empirical approach, are then used to assess potential errors in Ku-band derived sea ice freeboard and ice thickness. Using the freeboard-to-thickness hydrostatic equilibrium, differences between corrected and uncorrected thicknesses, based on assumed (snow-ice interface) and radar (vertically shifted) scattering horizons, are evaluated. We find that brine-wetted snow covers under both cold and warm conditions shift the Ku-band main scattering horizon upwards within the snow volume, over estimating ice thickness retrievals. The largest error of up to 200% is found from warm, brine-wetted snow overlaying thin sea ice observed in the Canadian Arctic; the error decreases with an increase in sea ice thickness. Similar errors are observed from sites in the Norwegian Arctic, where thicker snow cover induces negative sea ice freeboard and causes formation of highly saline snow-ice near ice surface. This work also highlights the need for direct measurements of Ku-band scattering from saline and complexly layered snow packs to address first-year sea ice thickness uncertainty.