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

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.

Elevation change of the southern Greenland ice sheet from 1978 to 1988: Interpretation

“…In addition, the spatial pattern of elevation change from the 1978-1988 radar altimeter and 1993-1998 laser altimeter surveys were found to be in qualitative agreement over large areas of the southern ice sheet Davis et al, 2000]. A more detailed and quantitative comparison of the elevation change results from the radar and laser altimeter studies is given by Thomas et al [1999].…”

Surface elevation and velocity changes on the south-central Greenland ice sheet: 1980–2011

“…Elevation change is more uniform across the central cluster. Thomas and others (1999) found that the ice thickened by 0.094 AE 0.04 m a -1 through 1993/94. Through 2005, the average thickening rate is slightly less, 0.08 AE 0.02 m a -1 .…”

“…Repeated measurements were used for estimating surface displacement and accumulation. Aircraft laser altimeter flights were also designed to resurvey the sites (Krabill and others, 1995a; Thomas and others 1999). The most recent of these missions was part of the Arctic 2011 Operation IceBridge campaign.…”

“…Several of the central and western sites were reoccupied during June 2003, 2004 and 2005, and surface gravity, position and elevation were remeasured by the author using GPS instruments and gravimeters. All of the original cluster sites have been overflown on an opportunity basis by the Wallops Flight Facility Airborne Topographic Mapper (ATM) (Krabill and others, 1995a;Thomas and others, 1999). The last overflight occurred in 2011 as part of NASA’s Operation IceBridge, which is tasked with assuring continuity of the ice-sheet elevation change record during the period between ICESat and ICESat-2.…”

Retrieving snowpack properties and accumulation estimates from a combination of SAR and scatterometer measurements

“…Overcoming these uncertainties and recovering spatiotemporal ice sheet volume variations have become a major goal of current spaceborne Earth observation methods, in the first instance carried out by passive [5], [55] and active microwave instruments [6], [8], [11], [30], [47], [48], [53]. Although much effort has been done to assess the principles of microwave interaction with snow and ice, they are not yet completely understood in all their complexity [1].…”