Recent elevation increase on Lambert Glacier, Antarctica, from orbit cross-over analysis of satellite-radar altimetry

The mean rate-of-change of the surface elevation on lower Lambert Glacier is measured with satellite-radar altimetry from the Geosat Exact Repeat Mission (ERM) (1987 89) and Seasat (1978), using orbit cross-over analysis. The measurement region extends 190km in the along-flow direction from 72.1° to 70.4° S, an area that includes the grounding zone of Lambert Glacier. The Geosat ERM and Seasat altimetry are referenced to GEM T2 orbits. The random-noise levels in the data are reduced by low-pass filtering. The orbit bias between the two satellites is estimated from cross-over differences over sea ice seaward of the calving front of the Amery Ice Shelf. The results show a mean rate of increase of the surface height on lower Lambert Glacier of 31±10 mm year -1 during the decade from 1978 to 1987–89. The computation is also carried out independently using data not low-pass filtered but with orbit bias minimized by adjusting the Seasat and Geosat ERM orbits into a common ocean surface. The latter analysis shows a mean rate of increase of the surface height of 83 ± 9 mm year -1 during the same time period. Cross-over analyses carried out using altimetry not low-pass filtered and with orbits not adjusted into a common ocean surface yield intermediate results. Taken together, the cross-over analyses show that the surface height on lower Lambert Glacier increased at a mean rate within the range 20–90 mm year -1 during the decade 1978 to 1987–89.