碩士 / 臺灣大學 / 海洋研究所 / 98 / When non-linear internal wave (NLIW) propagates, its associated current will generate convergence and divergence on sea surface. The convergence will concentrate short surface waves and make sea surface rougher. This roughness is related to the bright patches on satellite radar images, therefore, radar images may be used to study the location, wavelength and propagation of NLIW. But the relation between rough surface on radar images, the location of NLIW peak, and the visual image of surface roughness is still to be verified. One sees roughness by the wave height that is mostly determined by waves longer than 1m, while radar sees mostly the surface wave about 0.04~0.1 meter long. Therefore, sea surface roughness means differently to human eyes and to satellite radars, because they look at different bands of wavelength. Their quantitative relation depends on the viewing angle and height, illuminating direction of the sun, and the direction and wavelength of surface waves.
The objective of this study is to resolve the response of surface waves to the bathymetry-induced convergence/divergence, and to differentiate the sea surface roughness viewed by human eyes, by optical sensors, and by satellite radars. As gravity waves propagate upstream across Keelung Sill, they are slowed down by the current, their wavelengths are shortened by the convergence effect, and their wave heights increase. Waves less than 1.2 meters long can not pass over the sill due to the current on the sill. But one sees largest wave height over the sill, there are few short gravity waves and the sea surface is smoother. Satellite radar observes short waves, its image shows dark band over the sill, representing low backscattering cross-section, low surface roughness, and smoother surface. The largest roughness to satellite radar is 200 m downstream from the boundary between dark and bright bands on radar image, where convergence is the strongest. Visually rough surface is in the region where the current speed reaches maximum, or from the sill top to 16 m down stream of above boundary. This dissimilarity on surface roughness raises caution on interpreting satellite radar images with visual experience on ocean phenomena.
| Identifer | oai:union.ndltd.org:TW/098NTU05279006 |
| Date | January 2010 |
| Creators | Chih-Jung Chang, 張志榮 |
| Contributors | Cho-Teng Liu, 劉倬騰 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 75 |
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