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Journal of Sensors
Volume 2015, Article ID 450857, 6 pages
http://dx.doi.org/10.1155/2015/450857
Research Article

Automated Waterline Detection in the Wadden Sea Using High-Resolution TerraSAR-X Images

DLR Maritime Security Lab, Henrich-Focke-Straße 4, 28199 Bremen, Germany

Received 8 January 2015; Revised 25 March 2015; Accepted 1 April 2015

Academic Editor: Armando Marino

Copyright © 2015 Stefan Wiehle and Susanne Lehner. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We present an algorithm for automatic detection of the land-water-line from TerraSAR-X images acquired over the Wadden Sea. In this coastal region of the southeastern North Sea, a strip of up to 20 km of seabed falls dry during low tide, revealing mudflats and tidal creeks. The tidal currents transport sediments and can change the coastal shape with erosion rates of several meters per month. This rate can be strongly increased by storm surges which also cause flooding of usually dry areas. Due to the high number of ships traveling through the Wadden Sea to the largest ports of Germany, frequent monitoring of the bathymetry is also an important task for maritime security. For such an extended area and the required short intervals of a few months, only remote sensing methods can perform this task efficiently. Automating the waterline detection in weather-independent radar images provides a fast and reliable way to spot changes in the coastal topography. The presented algorithm first performs smoothing, brightness thresholding, and edge detection. In the second step, edge drawing and flood filling are iteratively performed to determine optimal thresholds for the edge drawing. In the last step, small misdetections are removed.