Accuracy evaluation of extracting shorelines of satellite images

• Main Authors: Wu, Cheng-Chieh, 吳政杰
• Other Authors: Chang, Hsien-Kuo
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/84787667467090230556

碩士 === 國立交通大學 === 土木工程學系 === 98 === A method for accurately extracting shorelines of satellite images is investigated in this study. Above all the pixel resolution of a satellite image is doubled using fused HIS (Hue, Saturation, Intensity). The shoreline of a satellite image is detected by supervised classification on fused HIS associated with a newly-defined NDWI using maximum likelihood method. The detected shoreline of a chosen satellite image is compared with the measured shoreline in site to have a RMSE (root mean squared error) of about 7 m. Due to different tidal levels of different satellite images the detected shorelines are not based on the same datum. The originally detected shorelines can be shifted to the mean water level using tidal deviation from the mean water level associated with measured or computed bottom slopes. The corrected shoreline is closer to the measured shorelines than the original one by a RMSE of about 6 m. The computed bottom slope from an empirical formula including wave height and period and sand diameter is applicable for shifting the detected shoreline to the mean water level when the measured bottom slope is unavailable. The examined shoreline detection of a satellite image is applied to investigate the shoreline revolution of Gold beach in Tainan from 2004 to 2008. The change of detected shorelines at the same datum shows that the beach erodes in the summer and deposits in the winter. An average of shoreline retreat about in the south part from 2004 to 2005 is demonstrated to be about 100 m but the beach in the north part is in an equilibrium state. The result is different from the previous work indicating erosion happens in the south part but deposits in the north part. The reason for the beach sediment is explained using the computed sediment on the beach by SMC (coastal model system developed by Ocean and coastal research group of university of Cantabria). Offshore sediment is dominant so that the beach is eroded by large waves in the summer. The small waves in the winter have little impact on beach change. On-offshore sediment is proved to erode the Gold beach by the present study.