碩士 / 國立成功大學 / 水利及海洋工程學系 / 88 / The Synthetic Aperture Radar (SAR) that mounts on the ERS satellite has been applied to oceanic researches for many years and proven a useful tool of physical oceanographers studying the ocean, but there remain aspects of performance and accuracy at the nearshore wave analysis that require investigation. The main theme of this paper is to discuss the feasibility of applying numerical tools to analyzing the nearshore SAR images.
Two-dimensional Fourier transform method was chosen to process SAR images for determining wave directional spectra in this study. To justify the accuracy and precision of our numerical program, we compared the analyzed results of simulated images with input conditions. Also, the case study results of a previous research were adopted to contrast to our estimation of wave parameters. It was shown that our program is good enough to catch wave information from SAR images. However, some of images can’t reach for satisfied results. One is because the gray value distributions of images are broadened, i.e. the gray values are too scattered. The other case is when the angle between wave propagation direction and satellite track is too narrow, the estimated result will be far from the ground truth measured in-situ observation.
The well-developed program was then applied to wave analysis of nearshore SAR images and the estimated results were compared with measured data of data buoys which are deployed in the locations covered by SAR images. In the process we have to decide the sub-image size for 2D Fourier transform. It was shown that an image of 128×128 pixels is least uncertain. However, a moving average technique of all sub-images, often used in SAR image analysis for reducing variance, may not be appropriate and necessary in analyzing nearshore SAR images. The reason is obvious that wave direction and wavelength are not ergodic and keeping changes in shallow water. Hence, the wave information derived from a sub-image should not be averaged with results from other nearby sub-images. Several case studies also shown that the wave direction and wavelength estimated from a sub-image are quite different from the field data measured on data buoys in the steep-down shallow water. It may suggest that some of wave information derived from SAR images can not appropriately represent wave characteristics in nearshore wave field.
Key Words : SAR、Wavenumber Spectrum、Wave Direction Spectrum
| Identifer | oai:union.ndltd.org:TW/088NCKU0083012 |
| Date | January 2000 |
| Creators | Hong Peng Lin, 林鴻鵬 |
| Contributors | Chia Chuen Kao, Laurence Z. H. Chuang, 高家俊, 莊士賢 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 58 |
Page generated in 0.1252 seconds