Elevation changes on the East Antarctic ice sheet, 1978-93, from satellite radar altimetry: a preliminary assessment

Abstract

Radar altimeter data from Seasal (1978), Geosat (1985-88) and ERS-1 (1991—93) are employed to estimate multi-year mean changes of the surface height throughout a region on the East Antarctic ice sheet (EAIS) extending to 72.1° S, the southernmost limit of coverage for Seasat and Geosat altimetry, and above 1500 m elevation, using orbit crossover analysis. The changes are estimated on a same-season (austral late-winter (ALW) toALW) basis, where ALW is the 10 July 9 October time-frame of the Seasat altimetry. Altimeter data corrected for slope-induced errors are used. Altimeter data not corrected for slope-induced errors are also used, for comparison. Intersatellite orbit bias, combined with the effect of other radial errors such as instrumental bias, is estimated using crossover differences on the offshore ALW sea ice, which is employed as a geoid-parallcl reference surface. If similar intersatellite radial biases are characteristic of the continental Antarctic ice-sheet altimetry to 72.1° S, the results of all crossover analyses adjusted for this intersatellite bias — suggest that the mean rate-of-change of the surface height between Seasat and Geosat for ALWs 1978 to 1986-88 was with in the range +11 to -11 mm a−1. The bias-adjusted results of all crossover analyses between Seasat and ERS-1 suggest that the mean rate-of-change of the surface height between ALWs 1978 and 1991-93 was with in the range-17 to-55mma−1 (maximum intersatellitc bias estimate) or 0 to -40 mm a−1 (minimum bias estimate), suggesting that the surface may have lowered slightly during this time interval. The inconsistency of the adjusted Seasat to Geosat vs Seasat to ERS-1 results, however, may be an indication that orbits more accurate than JGM-2 are needed for estimation of regional multi-year mean changes of elevation on the EAIS. Alternatively, it may be a reflection of the differing orbit inclinations of Seasal and ERS-1.