台灣四面環海，海岸線長達一千五百多公里，海洋資源豐富，但也與鄰近國家產生利益衝突，為掌握東海與南海島礁之國土資訊，對於重要島礁自然與人為活動進行監測，以維護我國海域島礁主權及海洋權益，特別近岸水深及棲地底質資料，對航行、海洋資源及生態系研究都相當重要，而遙測影像可以經濟有效率的觀測並分析地表特徵，進而萃取出各類地表資訊。傳統現地調查耗時費力，只能針對小部分樣區調查，然而上述不利的特性卻正好非常適合使用衛星影像來進行大範圍及大尺度的調查。本研究針對東沙環礁海洋國家公園進行研究，使用多光譜光學衛星影像配合現地地真資料，進行近岸的水深估計及棲地分類並分析誤差。加上無人飛行載具空拍影像，同時俱有高機動性及解析度，可針對有興趣的測試區，進行小範圍高時間密度的監測，連結實地調查的資料與大範圍的衛星影像。另外配合熱紅外之衛星影像可用於反演海水表面溫度，分析海水暖化現象對珊瑚及海草的影響。最後將研究成果套用至其他島礁。本計劃將發展近岸水深估計及棲地底質分類演算法，於東沙環礁海洋國家公園進行驗證，並測試套用至太平島及其他島礁。本計畫將分三年進行研究，利用衛星影像對東沙環礁所選測試區進行監測，配合歷史資料及現地調查，將成果套用到太平島及其他島礁。第一年對珊瑚及海草棲地監測，比較多時期影像偵測變遷，特別針對20多年來只在2014年及2015年發生的大面積海草消失分析，並監測發展及恢復情形。配合無人飛行載具空拍影像作為橋樑，連結實地調查的資料與大範圍的衛星影像，分析監測點的珊瑚、海草、海藻等隨時間的消長變化。第二年利用底質分類成果加入物理模型與經驗模型，提升衛星影像對近岸水深進行估計。第三年則加入熱紅外衛星影像，分析海水表面溫度，配合現地調查水質、鹽度、水溫等環境因子的相關性，並建立珊瑚、海草、海藻等隨時間的消長變化之原因。此研究成果將對航行、海洋資源及生態環境監測有所幫助，且應用至南海島礁將有助於維護我國海域島礁主權及海洋權益。 ;Because of the wide area and sailing inconvenience caused by reef patches in lagoon, the Dongsha Atoll have not complete surveyed for a long time. The investigation is not conducive to the traditional characteristics but just suitable for satellite images of large scale investigation. This study focuses on the ecological environment of Dongsha ocean national park, investigates the influence of natural and artificial disturbances on coral habitats and the recovery and the ability to adapt. This subproject used multi-spectral optical satellite images cooperated with in situ ground truth data, to investigate the habitat distribution of sea grass and live coral, and estimate the area. The accuracy evaluation of the habitats survey with ground truthing can reach 80% accuracy. The satellite images from different seasons indicate seasonal changes of the sea grass and algae. Furthermore, thermal images from satellite can also provide information to estimate sea surface temperature and observe global warming phenomenon. Recently developed Unmanned Aerial Vehicle (UAV) will be adopted to take aerial images with high resolution. It can monitor test areas with high temporal density and bridge the satellite images and ground surveys.In this 3-year subproject, the selected test sites in Dongsha Atoll are monitored by satellite images. Combine the ground truth data collected with other subprojects, the result will be applied to the whole atoll. In the first year, satellite images with visible bands are used to monitor the coral reef and sea grass habitat, and the changes in area. Especially the recovery of the sea grass which disappear for 30 Km2 in north crest around July in 2014 and 2015. In the second year, UAV will be the bridge between the satellite images and ground surveys test sites for the changes of coral, sea grass and algae. The classification results will also be applied to water depth estimation with physical and empirical models. Finally in the third year, thermal band of satellite image will be adopted for sea surface temperature estimation. Combine with the water quality, salinity and temperature measured on site, it may provide reason for the sea grass disappearance the Dongsha Atoll. The approach can further be applied to the South China Sea.
