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Surface topography and massflux of the Antarctic ice sheet in western Dronning Maud Land, derived by differential SAR interferomety

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Drews, R. , Rack, W. , Wesche, C. and Steinhage, D. (2008): Surface topography and massflux of the Antarctic ice sheet in western Dronning Maud Land, derived by differential SAR interferomety , EGU General Assembly 2008. .
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Abstract:

Considerations on mass balance in Antarctica are of high interest in recent debatesabout the influence of the cryosphere and its response to climate change. Antarcticaplays an important role in the earths overall radiation budget, the development of themean sea level, and, as an excellent climate archive, it enables paleoclimatic researchand improved understanding of the climate system. In order to address those questions,a detailed knowledge of the ice sheets topography and its dynamics is crucial.Space borne interferometric synthetic aperture radar (InSAR) offers high resolutionmapping of displacement fields with large spatial coverage. For this process, a detaileddigital elevation model (DEM) with both vertical and horizontal resolution isneeded. Since the existing DEMs in the study area of western Dronning Maud Landhave a relatively crude resolution, we derived a new DEM through a differential In-SAR approach (DinSAR) in combination with new IceSAT laser altimeter data. Forthe processing we used a commercial software package. The calculated displacementfields were combined with ice thickness maps from an airborne Radio Echo Soundingsystem to measure the mass flux into the Ekströmisen ice shelf as well as to estimatethe accumulation rate on the higher elevated areas by means of mass conservation.The newly deduced DEM was compiled from acquisitions of the European RemoteSensing Satellites ERS-1 and ERS-2 from 1994 to 1996, where 116 scenes have beenused. The spatial extent is approximately 135 thousand square kilometres. In largeareas of the mosaicked DEM stacking of up to 19 independently derived DEMs waspossible in order to reduce noise. The concurrently received difference field does notshow systematic deviations apart from the south-eastern area, where we believe thatatmospheric conditions are responsible for a larger error. The comparison of the DEMwith additional IceSAT data and available GPS measurements on a 50x50 meter gridrevealed the accuracy to be approximately 7 meters in areas of high coherence, whichmakes it a high quality DEM in both vertical and horizontal dimension. We allocatederrors both due to physical parameters, as for example a varying penetration depthand an unknown atmospheric contribution, and errors due to an imprecise processing.The latter becomes evident when comparing overlapping parts of adjacent framesoriginating from the same raw data.By a combination of ascending and descending orbit, fully 3D-velocity fields wereused for the mass flux estimate. An estimate for accumulation was derived by calculatingthe divergence of mass flux in a closed box within the velocity field. A positivedivergence is attributed to accumulation, a negative to ablation in the respective area.Limiting factors are the unknown horizontal velocity profile with depth and the availabilityof highly resolved ice thickness maps. However, a comparison of our resultswith a new accumulation map from in situ data shows good agreement.

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