衛星影像的灘線辨識及其應用至灘線變遷之研究

Abstract

本研究主要提出灘線平移修正法(one-line shifting method, OSM)配合往昔研究的波浪變形經驗公式，將不同時間衛星影像所擷取出來的灘線位置平移至平均潮位的位置，使各灘線位於同一基準上以便進行比較分析。另外並透過潮位資料融合法，修正臺灣西海岸的潮汐能量消散，使Nao.99b潮位模式的均方根誤差在10cm以下，其誤差改善率在西部海岸為64%，西南海岸為73%，東部海岸為17%。在已知近岸底床坡度的情況下測試出Mase(1989)所提出的R2%為最合適的溯升經驗公式。本研究建立一完整的流程在底床坡度未知的情況下，亦可由結合OSM與潮位、波浪溯升及平均水位抬升三影響修正的最佳疊代方法決定之。 本文應用所提衛星影像擷取灘線方法來分析外傘頂洲、臺南安平養灘區域及臺中港北側淤沙區三處灘線的變化。由結果發現自1999年以來外傘頂洲面積逐漸變小，並漸漸向東邊的臺灣本島靠近，呈現一陸化的現象。臺南安平養灘區域在馬刺型突堤興建後有中央侵蝕，北側淤積的現象，並約於2005年年底開始趨於穩定。臺中港北淤沙區的灘線分析結果顯示臺中港北堤至北攔沙堤間的沙灘段自1993年開始由於臺中港北堤的擴建工程而持續有淤積的現象直至2004年趨於穩定。在無實測海岸地形資料下，本研究方法可提供大區域海岸規畫利用及環境評估所需海灘變遷評估工作之參考。

The one-line shift method (OSM) is proposed to determine MWL-datum-based shoreline positions of three sequential satellite images considering tidal variations, wave run-up and wave set-up in the thesis. Accurate calculation of tidal levels at research site where tidal observation is unavailable is also developed through spatial data interpolation based on originally simulated tidal level by the NAO.99b model. The corrected tidal calculation was examined valid by a root mean squared error less than 10 cm for all examined places around Taiwan and by modification on relative error up to 64% for western waters, to 73% for south-western waters and to 17% for eastern waters. When the beach slope is known, empirical expression of R2% proposed by Mase(1989) is examined best for modification on shoreline detection considering wave’s runup among all existed formula of runup. When the beach slope is unknown, an applicable procedure is also proposed to correct shoreline detection through optimization of shoreline original obtained by the proposed OSM method and correction for wave’s runup and setup. The proposed method was applied to investigate the shoreline revolution at the Waisanding Sandbar, Anping beach and north beach of Taichung Harbor. The result indicates that the Waisanding Sandbar is migrating landward to the west of Taiwan since 1999 and its whole area is decreasing by a fast rate. The Anping beach between two breakwaters acts with beach receding at the central part and proceeding at the northern beach. The northern beach of Taichung Harbor has a continuous shoreline accretion after the extension of northern breakwater in 1993 until 2004 and keeps beach stable since 2004. The proposed method of shoreline detection of some satellite images can be applicable for an evaluation on beach evolution in coastal engineering planning and environmental assessment when topographical data is unavailable.