海岸環境中，河口是最富生產力同時也是最易受人為活動影響之區域，當河川夾帶的陸源物質經由河口流入近岸海域時，受到河口環境的動力過程對物質傳輸、分佈的影響，因此，若能了解河口沖淡水舌的特性及控制其分佈型態的主要因子，對了解沿海地區的生地化循環及生態特性有所幫助。本研究以蘭陽溪口為研究場址，收集了河川流量、衛星遙測近海面二維風場等觀測資料，配合模式河口水位及近岸潮流場的結果，來分析SPOT衛星觀測到的蘭陽溪口水舌擺盪的情形。本研究是國內首次，以遙測影像，有系統的探討河口淡水舌的時空分佈及其與環境因子的關係。
本研究的首要之務在使用光譜影像分類法，萃取蘭陽溪口水舌的分佈範圍。影像分類技術一般是用於陸地為基礎的數據，較少應用在海洋的研究上。本研究透過監督式最大似然分類原理，得到蘭陽溪口水舌在影像中分佈的情形及範圍，可供給進一步探討淡水舌動力之研究。研究結果顯示，影響蘭陽溪口水舌南北向擺盪的因子不止一項。潮汐作用是一重要因子，當受到退潮流影響時，潮流將水舌往河口北方推移；漲潮時，潮流將水舌向河口南方推移；在潮流較弱時，則風的影響就較為明顯；沿岸之平均流與外海之流場也可能對水舌有重要的影響，值得進一步探討。由衛星影像得到的河口水舌分佈的面積，與蘭陽大橋流量站前一日的流量大小，有很好的相關性。河川流量的大小，會影響水舌向外海擴散的距離。

Estuaries are the most productive areas in the coastal environment and also most susceptible to human disturbances. When a river runs into the coastal zone, it is affected by the adjacent ocean circulation that influences the dynamic process of the suspended material dispersion. Therefore, to understand the characteristics of a river plume and the major factors controlling its distribution patterns is helpful to delineate the biogeochemical pathways and ecological feature in the coastal areas. For this study, we derived the distribution patterns of the Lanyang River plume from SPOT satellite images; we also collected data on the river discharge, satellite-observed two-dimensional sea surface wind field, and model results of the tidal motion. Using these data, we tried to understand the size and variation of the Lanyang River plume. This study is the first to use remote sensing images to investigate spatial and temporal distribution of river plume and its relationship to environmental factors.
The foremost task of this study is to use spectral image classification to objectively generate the Lanyang River plume distribution. Image classification techniques are typically applied to land-based data sets, but rarely used for oceanographic application. In this study, we applied supervised maximum likelihood classification, to classify surface water off the Lanyang River mouth using SPOT data from the following three bands: XS1(545 nm), XS2(645 nm), and XS3(840 nm). The retrieved images were used to investigate river plume behaviors. The results show that Lanyang River plume distribution patterns were influenced by more than one factor. The tidal effect could be important. In 8 out of 14 cases, the plume distribution was consistent with the tidal current, namely: the plume to the north of the river mouth during ebbing tides, and to the south during flood tides. The wind effect would be more obvious if the tidal current was weak. However, other factors, such as the mean coastal current and the offshore flow field, could also play important role in controlling the river plume distribution and warrant further study. Satellite-measured river plume area was correlated well with the river discharge rate with a 1-day time lag, i.e., the plume size is well correlated with the discharge on the previous day. The correlation would be even better, if the cumulative discharge of the previous 3 days are used. The offshore distance of the river plume appears to be affected by the magnitude of river discharge, and also by wind direction.

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