以衛星影像的擷取水線及平移灘線探討黃金海岸的冬夏季及長期的灘線變遷

Abstract

本文提出平移不同時間衛星影像的水線至平均灘線的方法，並探討台南黃金海岸的灘線變遷。本文透過一系列的影像處理可獲得正確的水線，使用的影像處理技巧除了一般的IHS轉換、影像強化、形態學及Canny法，並特別提出碎波帶的白泡沫雜訊的消除，以避免將碎波位置誤辨為水線的邊界偵測。本文再以影像拍攝時間的潮位及前灘坡度，計算平移的水平距離，得到灘線位置。由兩個時期的實測灘線為基準與擷取影像的水線及平移灘線比較，二者的RMSE分別從5.9及11.06 m，下降至5.25及8.26 m，Bias分別從-2.68及-8.14 m，下降至0.27及-2.82 m，證實本方法的可行性。 分析黃金海岸自2003年至2014年間灘線及零米線上海灘面積的結果發現，在夏季時灘線往陸側後退，而冬季時往海側前進，有季節性灘線變遷的現象。以波浪及底質的粒徑代入Sunamura與Horikawa(1974)的海灘剖面的判別分類，獲得一致的侵淤結論。黃金海岸的灘線變化特性，在2003年至2005年間，二仁溪河口沙洲及灣裡的段海灘有嚴重的侵蝕。2011年至2014間，長突堤南側區內的沙灘淤積，有舒緩此區域的原侵蝕程度;但是，卻在長突堤北側的海灘侵蝕更加的嚴重。2003年至2014間的灘線長期變遷趨勢呈現南侵北淤，因受長突堤的影響，造成侵淤變化點往北移700 m。

An applicable method of shifting detected waterlines from satellite images for different times of year to the corresponding shorelines was proposed and its application to the shoreline evolution of the Gold coast at Tainan was investigated in this thesis. Some techniques of image processing were used to detect the waterlines, including the HIS image fusion, image enhancement, morphological image processing and Canny methods. The RMSEs between measured in-site shorelines and the detected waterlines from satellite images for two cases are 5.9 m and 11.06 m. The corresponding biases are -2.68 m and -8.14 m. If the shifted shorelines are compared with the measured ones, RMSEs are 5.25 m and 8.26 m and biases are 0.27 m and -2.82 m, respectively. The reduction in RMSEs and biases proves the proposed method suitable for the shoreline change. An analysis on the calculated shorelines and land areas above the mean water level during 2003 to 2014 shows that the shoreline moves landwards during the summer but seawards during the winter to have a seasonal change. The results was verified by the index of beach profile type introduced by Sunamura and Horikawa(1974). The Gold coast suffers from severe beach erosion at the Wan-Li beach and northern estuary of the Erren river during 2003 and 2005. The construction of a series of short and long groins during 2010 and 2013 retards the beach erosion but induces another point of beach erosion at the northern part of the end of long groins. The trend of long-term beach evolution at the Gold coast shows beach erosion at the southern part and accretion at the northern part during 2003 to 2014. The invariant point of different shorelines moves north by 700 m after the construction of groins.