Data-driven Tide Correction for SAR-derived Ice Velocity Measurements on Antarctic Ice Shelves

Abstract. Synthetic Aperture Radar (SAR) offset tracking is widely used to measure ice velocity on floating ice shelves, however, vertical displacement caused by ocean tides projects into the radar-range direction, introducing apparent horizontal motion unrelated to true ice flow. Here, we develop an observation-driven tide-correction for SAR-derived ice speed measurements using differential range offset tracking (DROT) applied to Sentinel-1 SAR data. The method estimates spatially and temporally varying tidal response coefficients directly from observed radar-range displacement variability and an ocean tide model. Application of the method to SAR-derived ice velocity measurements on Antarctic Ice Shelves shows spatial variability in the magnitude of the tide-induced ice-speed correction, with an Antarctic-wide mean tide-correction range of 106 m/yr, a standard deviation of 71 m/yr and maximum values exceeding 300 m/yr. The largest tide correction range predominantly occurs on freely floating ice shelves in regions of strong tidal forcing, particularly in the Weddell Sea and Antarctic Peninsula. Smaller tide corrections are observed near grounding zones and pinned regions where tidal motion is mechanically constrained. Time-series analyses show that the tide correction systematically reduces non-physical temporal variability in SAR-derived ice velocity products while preserving the large-scale spatial structure of ice flow. Independent validation using GNSS observations on Brunt Ice Shelf shows improved agreement between tide-corrected satellite-based ice speed and in situ measurements. Our results demonstrate that tide-induced apparent motion is a source of variability in SAR-derived ice velocity products on floating ice shelves, highlighting the importance of applying a correction when tide-induced signals are not required.