GPS for ice sheet movement monitoring and grounding line detection

Abstract

The velocity field of outlet glaciers at the grounding line is a critical parameter, together with ice thickness, in determining the ice discharge rate for the Antarctic Ice Sheet. Moreover the position of the grounding line is very sensitive to changes in the mass balance of the ice sheet. Data on ice velocities have been obtained with remote sensing and GPS measurement techniques on the David Glacier-Drygalski Ice Tongue, Priestley and Reeves Glaciers. A measurement technique particularly suitable for glacier monitoring is the satellite GPS technique, due to the environmental conditions and the accuracy that can be achieved in positioning. GPS static, fast-static and kinematic applications have been used since 1989 and repeated five times for ice stream velocity field determination, floating glacier undulation determination under sea tidal effects and grounding line detection (Capra et al., 1996,Frezzotti et al., 1997). The GPS measurements made on the David Glacier-Drygalski Ice Tongue are presented with particular attention to the method used and data analysis. On two floating glaciers, Drygalski and Hells Gate (a small ice shelf that seems to be particularly sensitive to changes), different in size and shape, GPS techniques were used for the floating glacier undulation determination under sea tidal effects (Bondesan et al., 1994) and kinematic profiles were obtained for grounding line detection (Capra et al., 1996). The GPS instruments used were the Geodetic L1/L2 Trimble model 4000 SSE and all the data were processed with the Geotracer software v. 2.25 and GPSurvey software v.2.0.