Generation of a New Global Water Bodies Layer from TanDEM-X Data

Abstract

In this paper we propose a new method for extracting water bodies from TanDEM-X bistatic SAR images, aimed at generating a new global water bodies layer. A reliable detection of water bodies from SAR Remote Sensing images is useful for many scientific purposes, such as water extent monitoring, flood monitoring, digital elevation models editing, flow modeling, runoff estimation, coastal and shoreline monitoring, and agriculture sustainability assessment. SAR images can provide reliable information on all-weather and all-day conditions and the global coverage of TanDEM-X represents a high valuable data set for the generation of large-scale geomaps. The iterative algorithm that we developed is based upon the segmentation algorithm called “Watershed”, taking as input the interferometric coherence derived from a single bistatic TanDEM-X acquisition. The “Watershed” algorithm begins from an arbitrary group of well-known seeds called “markers”, and from these seeds it iteratively segments the entire image into different connected and homogeneous group of pixels. In order to successfully exploit such an algorithm, the choice of the “markers” is crucial; this operation has been performed through an ad-hoc training process of the input data. The algorithm allows for the preservation of water bodies borders even if they have complex shapes, leading to the generation of highly precise water masks. Then, once a fully segmented image has been returned, the analysis continues with different refinement steps in order to mitigate the effects of geometric distortions, such as Shadow and Layover, caused by the side-looking nature of the SAR system, and with a threshold-based final classification. In the final paper we will present an analysis of the algorithm’s performance using full-resolution bistatic TanDEM-X data acquired over Pennsylvania, USA, and over the Berchtesgaden Alps, Germany, together with the first results from a global processing of TanDEM-X quicklook data, at 50 meters resolution, for the generation of a new global water bodies binary layer.