Investigating the Utility of Swath Mode CryoSat Data for Determining Ice Sheet Grounding Line Locations

Abstract:

Surface elevation measurements derived from Swath Mode processing of CryoSat data are examined to determine their utility for measuring ice sheet grounding line locations. Ice sheet grounding lines are the boundary between floating ice in hydrostatic equilibrium with the ocean, and grounded glacial ice. In reality grounding lines are a transitory feature with a location that can fluctuate on short, sub-daily timescales due to the effect of ocean tides, and long, decadal timescales due to the effect of ice mass loss. Grounding line retreat is a key indicator of change in mass balance and internal instability in marine terminating ice masses therefore it is important to develop new techniques to measure change in this important geophysical parameter. As part of the ESA STSE CryoTop project, Synthetic Aperture Radar Interferometer (SARIn) mode CryoSat data was processed in ‘Swath Mode’, which uses the full altimeter waveform to retrieve surface elevation measurements at a fine spatial resolution across the CryoSat ground track. This results in a narrow digital elevation model for each CryoSat ground track with a high density of points relative to traditional pulse limited altimetry. As part of the ESA STSE GLITter project, Swath Mode CryoSat data was differenced from tracks acquired at different times. The resulting surface elevation difference is caused by variation in the ocean tide amplitude which we use here to determine the ice sheet grounding line location. Our CryoSat grounding line location result is inter-compared with a cotemporaneous grounding line location derived from the established technique of differential interferometry (DInSAR).