Greenland ice sheet elevation change since 1978 from radar and laser altimetry1

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Abstract
Repeat satellite radar altimetry gives estimates of surface elevation change for the southern half of the Greenland ice sheet between 1978 and 1988, and repeat aircraft laser altimetry gives equivalent estimates for 1993–1998. Over large areas away from the coast, the two data sets show the ice sheet to be in balance, but with localized zones of significant thickening or thinning. Rates of surface elevation change derived by comparing localized 1980 ground surveys with 1993–1994 laser surveys show excellent agreement with the 1978–1988 radar results, suggesting that the radar altimeter provides reliable estimates of elevation change when data are averaged over areas of ice sheet with low surface slopes. Regions where there are significant differences between the 1978–1988 and 1993–1998 results can be explained either by changes in near‐surface snow conditions that affect the radar reflecting horizon, or by temporal variability in snow accumulation rates.