利用衛星影像劃設金門海岸潮間帶與監測時序變化

Using Satellite Imageries to Delineate Intertidal Zone and Monitor Coastline Changes in Kinmen

在氣候變遷與人為影響的陰影籠罩下，國人對於海岸地區的保護以及潮間帶等生物棲地的保育觀念逐漸增強。內政部於105年公布之國土計畫法與104年公布之海岸管理法中皆明確針對海岸地區增加保、防護機制，確保自然海岸零損失以促進永續發展。然而在實務上仍缺乏一套大尺度的測量方法提供海岸地區的範圍劃設以及變遷偵測。本研究主要利用衛星觀測結合潮汐模型的方式建置海岸地形，提供劃設參考潮位線的依據以利後續制定潮間帶的範圍，研究區域以國內岸際變遷較為顯著的金門縣為標的。金門海岸線近期疑因人為超抽海砂導致過去一、二十年產生顯著變化，平均潮位線除人造設施外，多呈現退縮態勢，尤以金寧鄉西側水頭港口週邊以及金沙鎮北側的蘭洋段較為嚴重。本研究首先製作海岸地形模型並以無人駕駛航空器系統所製作之地表模型進行相對高程檢核，兩者之差值均方根（root-mean-square of the difference, RMSD）在慈湖南側灘地為53公分。後續依據歷史影像所劃設的動態海岸地形分析，金門西側水頭碼頭旁於2006–2017的平均潮位線較1996–2006的平均潮位線退縮81.21±8.56公尺，北側蘭洋段為77.10±8.21公尺，南側機場段為16.09±3.92公尺，若以長期平均來看，整體退縮速率介於每年0.64–8.12公尺，如此脆弱的地區亟待政府建立一套健全海岸保防護機制。 Under the looming of climate change crisis and threats by rapid urban expansion, coastal area has become a fragile zone that urgently needs a long-term management plan for a sustainable future. The Ministry of the Interior of Taiwan has promulgated Spatial Planning Act in 2016 and Coastal Zone Management Act in 2015, which aim to ensure zero loss of the natural coast and to prevent natural hazards damaging the environment. However, a practical solution applicable to delineate intertidal zone and to timely update tidal lines on a large scale has been poorly investigated. This study intends to utilize satellite remote sensing imageries and DTU10 tide model to first reconstruct a satellite-based coastal digital elevation model (DEMSat), and then delineate intertidal zones for protective purposes. We chose Kinmen island of Taiwan as an example to demonstrate a significant retreat of coastline at mean water owing to sea sand over-dredging in the strait. The coastal DEMSat is firstly validated by an independent DEM stereo-paired from unmanned aerial vehicle (UAV) images, with an accuracy of 53 cm. The temporal DEMs made in two epochs, 1996–2006 and 2006–2017, are compared to obtain retreating distances at 81.21±8.56 m for west shore, 77.10±8.21 m for north shore, and 16.09±3.92 m for south shore. The general retreating rate is ranging between 0.64 and 8.12 m per year in this area.

Under the looming of climate change crisis and threats by rapid urban expansion, coastal area has become a fragile zone that urgently needs a long-term management plan for a sustainable future. The Ministry of the Interior of Taiwan has promulgated Spatial Planning Act in 2016 and Coastal Zone Management Act in 2015, which aim to ensure zero loss of the natural coast and to prevent natural hazards damaging the environment. However, a practical solution applicable to delineate intertidal zone and to timely update tidal lines on a large scale has been poorly investigated. This study intends to utilize satellite remote sensing imageries and DTU10 tide model to first reconstruct a satellite-based coastal digital elevation model (DEMSat), and then delineate intertidal zones for protective purposes. We chose Kinmen island of Taiwan as an example to demonstrate a significant retreat of coastline at mean water owing to sea sand over-dredging in the strait. The coastal DEMSat is firstly validated by an independent DEM stereo-paired from unmanned aerial vehicle (UAV) images, with an accuracy of 53 cm. The temporal DEMs made in two epochs, 1996–2006 and 2006–2017, are compared to obtain retreating distances at 81.21±8.56 m for west shore, 77.10±8.21 m for north shore, and 16.09±3.92 m for south shore. The general retreating rate is ranging between 0.64 and 8.12 m per year in this area.