MONITORING CHANGES OF ICE STREAMS USING TIME-SERIES OF SATELLITE-ALTIMETRY-BASED DIGITAL TERRAIN MODELS

The Antarctic Ice Sheet plays a major role in the global system, and t he large ice streams discharging into the circumpolar sea represent it s gateways to the world's oceans. Satellite radar altimeter data provi de an opportunity for mapping surface elevation at kilometer-resolutio n with meter-accuracy. Geostatistical methods have been developed for the analysis of these data. Applications to Seasat data and data from the Geosat Exact Repeat Mission indicate that the grounding line of La mbert Glacier/Amery Ice Shelf the largest ice stream in East Antarctic a, has advanced 10-12 km between 1978 and 1987-89. The objectives of t his paper are to explore possibilities and limitations of satellite-al timetry-based mapping to capture changes for shorter time windows and for smaller areas, and to investigate some methodological aspects of t ile data analysis. We establish that one season of radar altimeter dat a is sufficient for constructing a map. This allows study of interannu al variation and is the key for a time-series analysis approach to stu dy changes in ice streams. Maps of the lower Lambert Glacier and the e ntire Amery Ice Shelf are presented for austral winters 1978, 1987, 19 88, and 1989. As a first step toward understanding the dynamics of the ice-stream/ice-shelf system, elevation changes are calculated for gro unded ice, the grounding zone, and floating ice. In the absence of (su fficient) surface gravity control for the Lambert Glacier/Amery Ice Sh elf area, altimetry-based maps may facilitate improvement of geoid mod els as they provide constraints on the terrain correction in the inver se gravimetric problem.