C43D-05
Two Decades of Elevation Changes of the Greenland Ice Sheet from Radar and Laser Altimetry.

Thursday, 17 December 2015: 14:40
3007 (Moscone West)
Louise Sandberg Sorensen1, Rene Forsberg2, Kirill Khvorostovsky3, Rakia Meister2 and Sebastian B. Simonsen4, (1)DTU Space, Lyngby, Denmark, (2)Technical University of Denmark - Space, Kongens Lyngby, Denmark, (3)Nansen Environmental and Remote Sensing Center, Polar Environmental Remote Sensing, Bergen, Norway, (4)DTU Space, National Space Institute, Geodynamics, Kongens Lyngby, Denmark
Abstract:
The Greenland Ice Sheet has been mapped by radar altimetry since the launch of ERS-1 in 1991, which was followed by ERS-2, Envisat and currently CryoSat-2. For the period 2003-2009 the ice sheet topography was also mapped by laser altimetry by the ICESat mission.

Here, we apply suitable elevation change algorithms to radar data from ERS-1, ERS-2, Envisat, and CryoSat-2 data, with the goal to derive continuous, ice sheet-wide elevation changes for the period 1992 to 2015. This analysis has been made possible through the recent release of data from the REAPER project, in which ERS-1 and ERS-2 radar have been reprocessed in a consistent way to that used for Envisat data.

Over this 23-year period, the pattern of elevation changes varies significantly. Whilst thickening and thinning can both be observed during different periods, the overall trend of the elevation of the ice sheet is negative, i.e. an overall lowering can be seen during the two decades studied. This work is part of the ESA Greenland Ice Sheet CCI project.

We compare elevation changes derived from radar and laser altimetry (2003-09) and find a complex pattern of difference between the two sensor types, and we explain how some of this pattern can be explained by changes in firn compaction and accumulation rates, obtained from a regional climate model and an offline firn model. Also we show how this pattern changes if using differently retracked Envisat data.

A special focus will be on results obtained from the CryoSat-2 measurements that provide radar heights of unprecedented coverage and resolution. Here we present the results of a validation exercise carried out as part of the ESA-funded CryoVAL-LI project in which the accuracy of the CryoSat-2 measurements of land ice is assessed.

The results presented here signify an important milestone in measuring the surface elevation of the ice sheet: providing us with an insight into past as well as recent changes, providing up-to-date information on the behaviour and evolution of the ice, and hence associated sea level alterations.

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