Sentinel-1 satellite constellation offers enough Synthetic Aperture Radar (SAR) images for long-term water monitoring, due to its relative large swath, great revisit frequency and high resolution. The middle and upper Yangtze River suffers serious flood disaster in 2016. It is significant to detect water and its changes of Poyang Lake, since it is one of the important flood storage lakes along the Yangtze River mainstream. However, the traditional segmentation algorithm has shortage in edge preservation and the accuracy of water detection, especially in the case of Poyang Lake, which is widely distributed and has more complex background, weak edges and blurred edges. A new Active Contour Model (ACM) algorithm based on local narrowband is proposed to solve these problems, and it is applied to Sentinel-1A observations related to Poyang Lake. First, a cascade two-level Otsu approach is adopted to obtain the initial contour. Second, the local narrowband is built along the initial contour to reduce the calculating time. Finally, a region-based ACM is introduced into the local narrowband to stop the contours at weak or blurred edges. Experiment results show that the new method has advantages in the edge preservation and obtains better segmentation results with respect to other methods.
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