About the Potential of TanDEM-X to Assess Complex Topographic Changes
Kubanek, Julia; Westerhaus, Malte; Heck, Bernhard

The innovative bistatic TanDEM-X mission consists of the two nearly similar satellites TerraSAR-X and TanDEM-X which build a large single-pass Synthetic Aperture Radar (SAR) interferometer enabling to acquire highly accurate across-track interferograms. These bistatic interferograms can be successfully used to generate digital elevation models (DEMs) without the characteristically negative effects typical for repeat-pass interferograms like temporal decorrelation and atmospheric disturbances. Highly accurate DEMs are a great advantage in volcano research, especially in addition to repeat-pass interferometry. Many studies have shown that the latter can be successfully used to observe small deformations at active volcanoes. However, considering fast changing environments, like dome building volcanoes, repeat-pass InSAR soon reaches its limits: large changes in the observed surface lead to strong temporal decorrelation, which further results in lacking coherence, preventing an interferometric analysis. To overcome these difficulties, we apply the bistatic TanDEM-X data to monitor large deformations at dome building volcanoes. We chose Merapi on Java, Indonesia as test site. During the last big eruption which took part in 2010, the volcano dome was destroyed, built up and destroyed again. As a consequence, the topography of the summit area changed dramatically. We analyzed the volume change due to this eruption using a time series analysis of DEMs generated from the bistatic TanDEM-X data recorded before and after the eruption. As a result of the strong explosions during the eruption, the topography of Merapi now consists of steep slopes, which are a challenge for SAR data acquisition. We therefore further analyze the applicability of the TanDEM-X data in such a steep terrain and highlight errors influencing the DEM generation and hence the volume estimates.