| dc.description.abstract | The aim of this study was to construct the coastal near shore topography of Taiwan island by using image processing techniques with optical satellite images. This research included three main components. The first was to extract the entire waterline of Taiwan island, the second was to construct the regional tidal flat digital elevation model (DEM), and the last was to generate onland information from ASTER stereo-imaging.
In this study, we investigated the potential for waterline extraction from multiple images acquired by the optical/near infrared sensor of the SPOT5 satellites. SPOT images were acquired by optical sensors, which often showed coastal waters in a range of different reflectance. In general, NIR（near infrared light）is commonly used to delineate the waterline. Because its high absorption in the water, the reflectance of NIR from the exposed terrain to sea area declines rapidly. Due to this property, the difference in the NIR reflectance can be used to determine the position of waterline. By using image-processing techniques, the waterline of all Taiwan island were extracted.
The DEM of the inter-tidal areas near the Xianshan Wetland could also be constructed from the “waterline method”. The concept of waterline method is to find the georegistered positions of the boundary between a water body and an exposed land mass from a remotely sensed image using image processing techniques, then superimposing the heights of the waterline relative to tidal level on the corresponding positions. From multiple images obtained under different tidal conditions, it was possible to build up a set of heighted waterlines within the inter-tidal zone. Gridded DEM was then generated by interpotation.
From the above-mentioned method, I constructed two tidal flat DEMs during 1994~1997 and 2004~2006. Comparing the changes between these two DEMs I found that：outer skirt of the Xianshan Wetland and Gangnan coastal scenic area were under erosion, other regions such as south and west of Keya rivermouth, west of Haishan fishing port were under deposition. The reduction of sediment transport from the Fongshan river and the Toucian river, along with strong southward winter monsoon and the construction of Hsinchu harbor could be the main reasons for Xianshan Wetland changes in the past ten years. | en_US |