Quantitative Analysis of Shoreline Changes in Western Taiwan Coast Using Time-Series SAR Images

Abstract

In this study, satellite synthetic aperture radar (SAR) image dataset spanning 15 years was acquired for temporal analysis of the shorelines changes. Focus is placed on how the natural forces impact on the coastline and sandbank changes. The waterlines were extracted from SAR images based on a wavelet correlator. Tidal and bathymetric data were used to validate the waterline extraction and were subsequently integrated for analysis. Since waterlines depend on the tide, detection of inter-tidal zones and sandbanks over long periods of time is necessary. Rapid changes of the central coast of western Taiwan are observed via spatial-temporal analysis of physical mechanisms of coastal changes within sandbanks, which have experienced an extent of size variations. These variations depict the interchanges of deposition and depletion from sand supply and the changes of waves–currents–coast interactions due to the presence of natural forces and human settlements. Human-made structures impact the current field (velocity and direction) by diverting the direction of the current from northward to southward along the coast. As a result, they indirectly affect the course of sandbank displacement. Sediment transport plays a vital role in shifting sandbars off the coast. Winter monsoons and tidal currents together have constantly exerted influence on moving barrier sandbanks southwardly and have distorted their shape.