Ice sheet height retrievals from Spire grazing angle GNSS-R

Global Navigation Satellite System-Reflectometry (GNSS-R) leverages signals of opportunity for remote sensing, such as for mapping sea surface topography. This study investigates Grazing angle observations of GNSS-R (GG-R) to systematically retrieve ice sheet surface height in Greenland and Antarctica using Spire Global, Inc. CubeSats. Over a nine-month period, approximately 7800 coherent segments have been processed over the polar regions to compute relative height of the ice sheet above the WGS84 reference ellipsoid under grazing angle geometries. The retrieval of surface height is based on using ionosphere-free phase measurements from both the direct and reflected signals. Digital Elevation Models (DEMs) were used for the relative height adjustment and the validation of the GG-R retrievals, which presented a root mean square error (RMSE) of ∼1.7 m for both regions. Furthermore, the collocated GG-R profiles manifest good agreement among each other and reveal systematic behavior in the height residuals that might be caused by the DEMs. The results presented in this study demonstrate the potential of dual-frequency GG-R for measuring ice sheet surface heights.