Snow wetness and density retrieved from L-band satellite radiometer observations over a site in the West Greenland ablation zone

Abstract

We demonstrate a novel method to retrieve snow liquid water content and density over a site in the ablation zone of the Western Greenland Ice Sheet from L-band radiometer data measured by the Soil Moisture and Ocean Salinity (SMOS) satellite. Previous demonstrations using ground-based close-range radiometry separately retrieved snow density and snow wetness over frozen and thawed ground. We apply similar techniques over the ice sheet to simultaneously retrieve snow density and wetness at the location of “Swiss Camp” from June 2010 through August 2018 at nearly daily temporal resolution. Achieved results are compared to in-situ air temperature data and to a well-known 19 GHz and 37 GHz passive-microwave melt characterization technique known as the cross-polarized gradient ratio (XPGR). The L-band based snow wetness retrievals often detect the onset of seasonal melt earlier than the XPGR algorithm without the need for empirically tuned thresholds. We also demonstrate the performance of the SMOS based snow wetness retrievals based on error statistics compared with an air temperature melt proxy. By applying temporal averaging to the SMOS based snow density retrievals, we achieve reasonable agreement with in-situ observations from May 2014 and May 2018. The demonstrated retrieval algorithm shows potential as a future SMOS data product for ice-covered regions of the cryosphere.