Preliminary GNSS-R Altimetry in the Hudson Bay Based on Spire Grazing Angle Measurements.

This paper presents high-precision phase altimetric retrievals using the GNSS reflected signals off of sea-ice under grazing angle geometries collected by the Spire Global, Inc. satel-lite constellation. The region and period selected for this study (Hudson Bay and James Bay from January to March 2021) were determined to be the most suitable and steady region as the starting point for the analysis of sea-ice cov-ered areas. The difference between grazing angle GNSS-R retrievals from more than 500 coherent reflection profiles and a reference surface (composed of the DTU mean sea surface and TPXO ocean tide model) has a root-mean-square er-ror (RMSE) of 16.4 cm. This demonstrates that consistently meaningful altimetry retrievals can be achieved under grazing angle GNSS reflectometry (GG-R) geometries using dual-frequency phase measurements collected by nanosatellites in low-Earth orbit over sea-ice covered areas.