碩士 / 國立臺灣大學 / 海洋研究所 / 98 / This thesis addresses on methodologies of how to estimate the sea surface current field by using time series of marine Radar imageries; the skills developed are then applied to analyze the tidal-flow patterns associated with the tongue-like plume of Danshuei River estuary. The kernel of the methodology contains respectively the segmenting sub-areas from qualified raw Radar data, calculating corresponded 3-dimensional spectrum of Radar echo intensity, setting criteria for eliminating noises and interferences in the spectral domain, and finally transforming the higher harmonic components and least square fitting the spectral components to obtain the current components. In a situation with higher radio interferences (such as that from a nearby Radar), the method of standing-wave removal, has been used tentatively for reducing the interferences, shows delighted results for pre-processing the spectral components.
For validation purpose, currents estimated from Radar imageries by using the developed methodology have been compared with the synchronous measurements of water flows by virtue of a S4 current meter, which is 5m below water surface and was mounted on an observation pile (the latter is located about 3.284 km west of the Radar). Comparison results show reliable relationship between the estimations and the measurements.
The Danshuei River estuary is influenced mainly by semi-diurnal tidal currents. A clear tongue-like bright zone (implying flow convergence and energetic scatters) has been observed occurring frequently in the Radar imageries. The tongue-like pattern, moves outward and inward of the estuary with the alternation of tidal flows, has close correlation to the behavior of the river plume. Due to wave-current interactions, the arrival of tongue-like pattern implies a higher intensity of horizontal convergence of surface flow, which then favors the intensification of surface scatters and therefore beneficial to the accuracy of current estimation by using Radar imageries. The flow patterns around the river plume of Danshuei River estuary, as well as some of behaviors of the latter have been reported in the context too.
| Identifer | oai:union.ndltd.org:TW/098NTU05279023 |
| Date | January 2010 |
| Creators | Jing-Ying Hsieh, 謝佳穎 |
| Contributors | 王冑 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 49 |
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