應用福衛二號影像測繪海灘潮間帶地形之嘗試

Abstract

海灘地形具動態、敏感之特性，容易受到波、流、潮汐和風等外營力作用的影響而產生變化。傳統上各國政府為了管理、保護海岸，都會以海灘剖面的定期測量方式來監測海灘地形，掌握其侵淤變化情形。但傳統的海灘剖面測量作業相當費時費力，尤其像是台灣全島大範圍的調查。我國擁有的福爾摩沙二號衛星，其所拍攝影像因具有高造訪率及高解析度的特色，一般認為具有大地環境監測的功能，因此我們嘗試利用其對同一地區海岸所拍攝之系列衛星影像資料，建構一套結合蒐集實測潮位資料，判識影像濱線和應用地理資訊系統等技術的調查模式，期望能夠用於大區域的海灘潮間帶地形測繪，以節省地面調查工作所需耗費的人力、物力和時間。研究結果顯示，由於衛星影像產出不夠穩定，可用影像的頻率未如預期，因此原先構想的測繪技術並無法真正產出良好品質的海灘潮間帶地形圖，更無法取代傳統的地形剖面測繪。但在混合使用了不同季節的影像資料後，部分沙岸地區可以繪製出代表那段特定期間的一種海灘地形平均狀態，如能用於長時距的海灘地形變化趨勢比較，仍有其應用價值。

Beaches are dynamic systems sensitive towards the effects of external forces, such as waves, currents, tides, and winds. Beach morphology provides essential information for hazard mitigation and coastal management, which is why many countries in the world have the beach surveillance programs to monitor the morphological changes. On the other hand, traditional methods of beach profile measurements are extremely time- and energy-consuming, especially for an island-wide investigation that is required for the likes of Taiwan. With the advantages of daily revisits and high image resolution provided by the FORMOSAT-2, we have the opportunity to use its images for monitoring the morphological changes along the sandy beach reaches in Taiwan. Waterline, one of the distinguished shoreline indicators, is collected from series of FORMOSAT-2 images and combined with tidal records to establish 3-D databases that can be used to make morphological maps of the intertidal beach. Due to the instability of the satellite image production, however, this practice did not bring us a more convenient, time-efficient, inexpensive, and reliable surveillance method for monitoring the beach morphology changes as we had expected. Nonetheless, in some shore reaches, when the seasonal change is not obvious, a morphological map produced from images of different seasons is still valuable. It could be used to identify the trends of morphological changes on a long term basis.