Mapping of Arctic Glaciers in the Barents Sea by using TanDEM-X: DEM Analysis for Observing Current Variations
Breunig, Markus1; Wagenbrenner, Susanne2; Wendleder, Anna1; Wessel, Birgit1; Roth, Achim1

The tandem constellation of ERS-1 and ERS-2 between August 1995 and May 1996 was a milestone in mapping the Arctic land surface. For the first time it had been possible to derive digital elevation models (DEM) of glaciered regions in the Arctic and Antarctic using repeat-pass SAR interferometry [1], [2] and no ERS-comparable tandem formation was realised thereafter [3]. However, it is only since December 2010 that the two German satellites TerraSAR-X and TanDEM-X are operating jointly in a helix tandem formation [4]. The primary mission goal of the TanDEM-X mission is the generation of a seamless global multi-coverage DEM using single-pass interferometry in bi-static mode. The outstanding quality and resolution of the DEM will allow topographical applications at an unprecedented level of detail, therefore the possibility of monitoring the Arctic land surface with up-to-date and high resolution DEM is given. Thus, the purpose of this paper is to analyze glacier variations using different acquisitions of the TanDEM-X dataset. The approach shows the benefit of DEM data for Arctic applications including both natural short-time variations and long-term impacts e.g. of the global warming on this ecosystem. As demonstration sites the archipelagos of Svalbard, Francis-Joseph's-Land and Novaya Zemlya in the European and Russian Arctic have been chosen (see Fig. 1).

The methodology is involving TanDEM-X mission data that has been acquired operationally since December 2010. The base idea of the presented approach is the usage of separately generated intermediate DEM. For this purpose, both coverages of winter seasons 2010-2011 and 2011-2012, with most of the Arctic Ocean being frozen, were taken independently from each other for DEM mosaic production. Accordingly, the datasets are showing the Arctic land surfaces under same physical conditions at two different acquisition times making them usable for comprehensive high-resolution analysis like DEM change comparisons. Therefore, the data has been processed operationally, i.e. interferometric phase unwrapping [5], DEM inspection, water detection [6], height comparison with ICESat data, calibration including tilt and offset correction in order to provide a homogenous dataset for a regional mosaic [7]. Furthermore, first and second TanDEM-X coverages are regarded as single mosaicked datasets that are compared to one another.

In a first step glacier height variations on a regional scale are identified. Due to the comprehensive TanDEM-X data availability it is possible to process DEM data for a larger region, i.e. the introduced study area, and there exists no limitation to single scenes. In a second step the glaciological deformation areas that are indicating a significant change in height values within the time span of data acquisition are analyzed in detail. On a local scale the glaciological characteristics like inter-annual fluctuations and spatial variations in glacier movement are evaluated, e.g. pattern phenomena like a surge at Polakkbreen and Nathorstbreen in Van Keulenfjorden located at Sor-Spitsbergen National Park. Therefore, values like mass balance are derived and classified from indicators like glacier height and extent changes (see Fig. 2). To validate and compare these results both historical and current reference data provided by ESA, ICESat or GLIMS Glacier Database [8] are used. Third, the local results are compared at an interregional context to distinguish different glacier activities and their spatial distribution in the European and Russian Arctic. Thus, trends can be detected regarding the behaviour of glaciers for the entire region for a specific time span.

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Figure 1: Location of the demonstration sites: the archipelagos of Svalbard (left), Francis-Joseph's-Land (middle up) and Novaya Zemlya (middle-down).
Figure 2: Calculation of glacier variations by using single coverages of TanDEM-X DEM: Polakkbreen, Nathorstbreen and adjacent glaciers in Van Keulenfjorden located at Sor-Spitsbergen National Park, Svalbard.