Accuracy promotion of determining wave rays and bathymetric estimation from satellite images using bi-dimensional empirical mode decomposition.

• Main Authors: Hsiao, An-Yu, 蕭安佑
• Other Authors: Chang, Hsien-Kuo
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/72755819034670349114

碩士 === 國立交通大學 === 土木工程系所 === 102 === Bathymetric estimation was commonly obtained using single/multi-beam echo sounder on boats. The marine surveying needs high cost, much time and possible risk of staff security. For solving the disadvantage, the method of estimating bathymetry from wave lengths between two crest lines of satellite images using image processing and bi-dimensional empirical mode decomposition (BEMD). Some techniques of image processing include: (1) determining extremals of reflectivity of satellite images regarded as possible crest lines; (2) Using the Otsu algorithm for the threshold of reflectivity and BEMD for reasonable crest lines; (3) determining wave rays normal to smoothed crest lines and calculated wavelength between two adjacent crest lines along a wave ray; (4) calculating the water depth through dispersion relation of the Airy wave theory when the wave period and wave length are obtained in the previous steps. The Fangliao coast of Pingtung county and the north Toucheng coast of Ilan county are chosen for examining the accuracy of the proposed method by the root mean squared error between the measured and calculated water depths. Six selected beach profiles are evaluated to have RMSE of 0.90m and 1.00m, respectively, for the Fangliao coast and the Toucheng coast using corrected wavelengths. The RMSEs are much less than those of 1.42 m and 2.54 m for the Fangliao coast and the Toucheng coast using originally obtained wavelengths. The proposed method is examined applicable for providing estimated bathymetry for coastal planning when measured bathymetry is unavailable.