Mapping Ice-Sheet Margins from Radar Altimetry Data

Abstract

The Seasat radar altimeter, which was designed to measure ranges to the sea surface, has also provided the most accurate available maps of ice-sheet elevation. Seasat operated for three months during the austral winter of 1978, when Antarctica was girdled by sea ice. As the satellite approached the continent from the ocean, the altimeter obtained very strong reflections from the sea ice, and it continued to measure ranges to the sea ice even for a short time after passing over the ice front. The measured ranges are oblique distances to the nearest portion of sea ice, and the sequence of oblique ranges gives the position of the sea ice along the ice front. After the satellite crossed the ice front travelling seaward, oblique ranges were measured to the nearest portion of ice shelf. Examples are given from Seasat orbits crossing the Amery and Fimbul ice shelves. The entire Seasat data set provides an opportunity for mapping most of the East Antarctic coastline to an absolute horizontal accuracy of ±(0.1 → 1) km. The resulting map would effectively be an instantaneous view of the ice margin, requiring no adjustment for ice movement during the survey period.