A Study of Decadal Coastal Changes on Western Taiwan Using a Time Series of ERS Satellite SAR Images

In this paper, coastal line changes were monitored and analyzed from a sequence of ERS-1/2 SAR images covering the years 1996 to 2005, totaling 44 images for each year. Waterlines were extracted using a multi-scale edge detection algorithm, and further refined by means of morphology. Substantial analysis was carried out in conjunction with ground survey and sonar bathymetric mapping. In addition, tidal records were used to ensure all the shore lines been calibrated to the same tidal level. Results showed that Waisanting Sandbar, a north-southward sandbar, experienced significant accretion and erosion, moving southward about 700 meters during a 10-year period, and shrinking to just one third of its 1996 size. The surrounding coastal waters and the estuary of the Peikang River receded substantially, moving inward toward the coastal flat. The water channel became even more heavily deposited as a result. Finally, Haifengdao Sandbar, another sandbar, moved southward about 1.5 km, although its size remained the same from 1996 to 2005. It also showed a clear tendency to receding inward. We conclude that satellite remote sensing by SAR, aided by ground tidal data, bathymetric maps, and optical images, provides an effective and efficient tool for understanding coastal processes over large areas of coverage and long time spans.