Monitoring big river estuaries using SAR images

Since the launch of the ERS-1/2 Satellites in 1991 and 1995 respectively, synthetic aperture radar (SAR) images of coastal regions have been acquired and processed at the receiving station of the German Aerospace Center at Neustrelitz on an operational basis in near real time. These data are used to monitor large river estuaries of the German Bight which are morphodynamically very active, i.e. the bottom topography underlies a continuous change due to sediment transport, with strong impact on the main waterways of the river. Because of their all weather, day and night capability radar images are ideally suited to investigate these morphodynamics by monitoring the land-water boundary of the mud flats. Edge detection is a demanding task for radar images as they are contaminated by speckle noise. The water-line is extracted using edge detection methods based on a combination of blocktracing, wavelet-edge detection, and a snake algorithm resulting in the final coastline. The detected shorelines are transformed into isolines of bottom topography by combining them with available tide gauge information. Longer time series of such water lines are used for monitoring changes of topography over the years by comparing images taken at a similar tidal situation. The examples given, range from coastline monitoring, bottom topography control to sediment transport measurements. The areas investigated are the large estuaries of the German rivers at the North Sea (i.e. Ems, Weser, Elbe and Eider) and the Canadian Mackenzie delta.