| 摘要: | 海岸地區為大氣、海洋、陸地的交界，受到人為經濟活動與自然活動之交互作用相當密集而複雜，加上氣候變遷引致海水位上升及極端氣候事件增加所導致的海岸侵蝕、淤積、溢淹等海岸災害可能對沿岸居民安全產生嚴重且立即性的威脅，因此為了能提升海岸安全及保護，對於海岸災害、海岸狀況的了解便顯得重要。 參考CoastView Project中建立的許多海岸狀況監測指標(Coast State Indicators，簡稱CSIs)，透過指標中適當的參數可以描述海岸狀況及變化的趨勢，其中沉積物體積為描述海岸狀況的一項重要指標，此項指標中的參數包括沙灘寬度、高度、坡度等等，這些參數都可透過灘線之量測而取得，因此灘線位置的量測便顯得重要。 本論文建立了一套可利用微波雷達量測灘線之方法。首先說明雷達回波的原理與機制，並根據微波雷達對海面及陸地之不同的回波特性以標準偏差區分出來，透過雷達影像之決定盲區、雷達強度校正、轉速校正、座標轉換及標準偏差計算得到雷達標準偏差影像，再經過高反差處理、過濾雜訊、邊緣化處理等過程取得由雷達影像量測出之灘線位置。 本研究為證明雷達量測灘線之可行性，利用影像觀測及DGPS-RTK方法量測灘線結果與之比較，首先說明CCD影像正射化的過程，其過程經過鏡頭扭曲的校正、影像正射化、參考點之空間校正，再將正射化後之CCD影像量測出灘線之位置與雷達量測之位置進行比較，其結果相近。DGPS-RTK對灘線進行量測，並將其量測結果與雷達量測之結果進行比較與討論，其結果比雷達與影像的比較結果更為良好。 確認雷達量測灘線的可行性後，將灘線位置結合水位資料取得垂直剖面之潮間帶地形變化。其方法流程為將雷達的標準偏差影像先取垂直沿岸之切線，將此切線上的標準偏差值隨時間排列紀錄，並經過高反差處理、過濾雜訊、Canny邊緣化等過程取得時間上灘線位置變化，代入灘線之水位資料後，做時間的平均得到潮間帶垂直剖面地形變化。 本研究以東北季風及西南季風為例，透過灘線位置的變化討論不同季風情況下永安漁港南方沙灘受到突堤效應之影響結果，並根據結果討論岸線侵蝕或淤積的狀況。透過垂直剖面潮間帶地形的變化情況可以估算潮間帶地形之砂的變化量，將估算之砂的變化量與輸砂通量公式比較，結果位於同一值級。Coastal zone is the intersection among atmosphere, sea and land, where the processes involved are complex and intense owing to the interactions of human activities and nature. Due to the global climate change and sea level rise, and the occurrence frequency of extreme weather events exhibits an increasing trend, and therefore enhance the coastal hazard such as coastline erosion, coastal inundation and coastal ecosystem degradation. These hazards bring direct impacts to the coastal residents. In order to increase coastal safety, it is important to realize coastal situation.According to the CoastView Project, the coastal situation can be represented by the coast state indicators (CSIs) which are a reduced set of parameters that can simply, adequately and quantitatively describe the dynamic-state and evolutionary trends of a coastal system. For example, the beach volume, which is one of the CSIs, can be described by the variables of beach width, beach height, beach slope etc., and these variables can be obtained by estimating the waterline position. The detecting of the waterline position is of an important task regarding to the coastal management.In this study, we proposed a new method to detect the waterline position using microwave radar. According to the principle and mechanism of the radar backscattering mechanisms, we distinguished the area of beaches and seas according to the corresponding temporal variation of the radar backscatter strength. After the processes of radar signals through radar intensity correction, spatial geometric correction, coordinate transformation and the standard deviation of radar backscatter intensity, we can obtain the waterline position by image processing methods, i.e. the high-contrast-edge method and the filter noise process.In order to assess the feasibility of present method, we compare the results of waterline position with CCD image method and the actual DGPS-RTK survey. After the process of lens distortion correction and orthographic projection, the waterline estimation results of the CCD orthoimages agree with the results of radar method. The comparison of waterline estimation using DGPS-RTK survey shows good consistency with our method.Furthermore, the topographic vertical profiles of the intertidal flat are obtained by combining the waterline position and the water level information. Using the chronological record by high-contrast-edge treatment, filtering noise process, we can obtain the change of waterline position with time, and obtain the time averaged topographic vertical profile of the intertidal flat by combining with water level information. Finally we use DGPS RTK to measure the topography of intertidal flat to confirm the accuracy that the radar estimated.In this study during the strong winter northeast monsoon and summer southwest monsoon events, we estimate the change of topography at the south intertidal flat of Yong-An fishery port, and discuss the coastal erosion under the groin effect. |
