利用衛星影像萃取近岸地形-以台灣北部為例

Application of satellite remote sensing to coastal topography generation – A case study in Northern Taiwan

楊勤儀(Chin-Yi Yang)

指導教授 ： 張中白 ； 馬國鳳

國立中央大學/地球科學學院/地球物理研究所/碩士(2007年)

摘要

本研究利用光學衛星影像以影像處理技術建立全台水線與台灣北部的近岸地形。研究內容總共分為三部分：首先為萃取台灣全島水線，其次為建立潮間帶地形，最後則是以ASTER衛星感測器之立體影像對製作近岸陸地地形資訊。
利用SPOT-5衛星中之近紅外光波段影像萃取水線為研究首要目標。水線之定義為水陸交界處，光學影像部分波段在遇有水體的狀況下，會有逐漸衰減的趨勢，其中近紅外光波段在光學影像中具有高辨識水線位置之特性，通常運用於水線萃取。因此藉由近紅外光波段遇水體的高反射率加上影像處理技術應用可萃取出台灣全島水線。
潮間帶地形高程模型（香山溼地）的建立使用「水線萃取」法。「水線萃取」的概念是利用衛星影像萃取出水線位置，並附予其相對座標資訊，再將一系列水線配合影像拍攝時間，以潮位資料作為其高程，進行水線套疊並作內插，如此便能建立潮間帶之DEM。利用以上敘述方法，建立1994-1997年間與2004-2006年間兩個時期之潮間帶DEM。經由前後期地形比較，新竹香山溼地的外側、港南濱海區域均處於侵蝕階段；而在客雅溪出口以西與南邊，還有海山漁港以西均有淤積之現象。整個香山溼地於近十年間的改變，應主要與頭前溪、鳳山溪歷年輸砂量逐漸減少、由北往南吹送之強烈冬季季風、新竹漁港的興建等原因相關。
在近岸陸地地形建立部分，則是使用同軌成像之ASTER立體影像對。ASTER感測器之第三光譜波段（0.78 ~ 0.86 μm）具有垂直向地底方向和向後傾斜的影像對，藉由此一特殊成像系統，以獲得30 m解析度之DEM。
本研究中嘗試用許多影像處理相關技術建立近岸地型資訊，以適當的光學衛星影像配合影像處理技術，是一個用於建立完整近岸地形有效率的工具。

關鍵字

遙測 ； 水線 ； 近岸地形 ； 台灣

並列摘要

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.

並列關鍵字

none

參考文獻

施介嵐、史天元，2006，以ASTER立體影像對產製數值覆蓋模型之精度研究，航測及遙測學刊，第11券，第1期，第59-68頁。

陳良健、徐啟崇，1990，多光譜影像特徵分析於灘線萃取之研究，航測及遙測學刊，第四券，第三期，第17-30頁。

劉彥秀，2002，最小二乘模型與影像套合之後續探討，國立成功大學測量工程學系碩士論文。

陳建文，2002，彩色影像邊緣線萃取之研究，國立成功大學測量工程學系碩士論文。

吳秋慧，2005，淡水河口海岸帶及濁水溪口海岸帶地質特徵之比較，國立台灣大學海洋研究所碩士論文，共72頁。