The TanDEM-X Global Water Body Layer

The interferometric SAR dataset acquired by TanDEM-X to generate a global Digital Elevation Model, covering at least twice the complete Earth's landmasses, represents a unique data source to derive geo-information products at a global scale. In the bistatic TanDEM-X system, characterized by the absence of temporal decorrelation, the interferometric coherence adds valuable information to the common amplitude images, typically acquired by monostatic SAR systems. Using the interferometric coherence of TanDEM-X acquisitions as the main input feature, we have generated a new global Water Body Layer. This paper reports on the developed activities at DLR for achieving this task. The proposed approach takes into account the geometric properties of SAR acquisition scenes, in order to mitigate the effects of geometric distortions, such as shadow and layover, and to improve the discrimination between water bodies and vegetated areas characterized by low coherence. Taking advantage from the two global coverages of TanDEM-X data, it is possible to determine the minimum and maximum areas of extent of the different water bodies, as detected by TanDEM-X during the acquisition period. At a local scale, it is even possible to monitor water bodies' extension variability and their seasonality.