| The Yangtze River Estuary is located in the Chinese eastern coast, since the following Xuliujing, the estuary is divided into the south branch and north branch by Chongming island, then south branch is divided into south port and north port by Changxing island near Wusong Estuary, the south port is divided into the south passage and the north passage by Jiuduansha. So there formed "three forks, four estuary ". The Yangtze River estuary, with its own rich natural resources and key location ,turned into an important region of international competition and economic development.Tidal flat is a kind of silty coastal wetlands between the high waterside line at spring tide and the low water line neap tide which is effected regularly by tidal action. It is a dynamic and unstable land and water resources, it is also an important object of resources and environment in the coastal zone. It has unique ecological value and great resources potential. So the study on the character and distribution of tidal flat is very useful for rational exploitation of resources in tidal flat. But as a sensitive area of land-ocean interactions, the temporal and spatial variation of profile shapes of tidal flat is very complex, because of the influences of waves, sediment, offshore currents, geology and storm surges. Waterside line is one of important characteristic parameters of silty tidal flat and it's the instant border line between land and ocean. Tidal channel is a typical geomorphic type of silty tidal flat. It links salt marsh and mudflat. During flood and ebb, these channels act as channels of sea water. Tidal channels control the sedimentation of salt marsh and mudflat and the flux of nutrients. It is the main aisle of mass and energy exchanges between tidal flat and ocean.By using wavelet analysis and image segmentation technique to extract the waterside line information of Jiuduansha; By region growing method and mathematical morphology to extract the tidal channel information of Jiuduansha, then study the fractal dimension.In the course of the study, we got the following results:(1)Jiuduansha was selected as a study area in the Yangtze River estuary. First, we pretreated the image by the mathematical morphology method in order to eliminate the fracture zone formed by inlets. Then, we extracted the waterside line information and removed the high suspended sediment information and other high frequency information by the wavelet multi-resolution analysis method. At last, we evaluated the effect of the waterside line information extraction by the edge connectivity evaluation method. The results show the wavelet multi-resolution analysis method is one of the effective methods to extract waterside line information in the silty tidal flat.(2)Through the application of image segmentation techniques: Compared with the traditional Hough-like method, the paper proposed a new identification method which is suitable for the ring waterside line detection.Firstly, authors detected edges from the image segmentation achieved by the waterside line gray gradient information. Then, dilated and filled the interior by mathematical morphology to connect edges. Finally, authors constructed segment-shaped structural elements to achieve continuous, smooth waterside line. Experimental results show: This method is not only simple, but also the extracted waterside line is good.(3)The panchromatic band remote sensing data received by SPOT5 on May 7, 2005 was used. The tidal channels information was extracted by the region growing method from the selection of the appropriate seed points and gray level threshold. It provided reference for the development and utilization of Jiuduansha tidal resources rationally.(4)The paper applied grayscale morphology to extract tidal channels information of Jiuduansha wetland and calculated the fractal dimensions of different regions by grid method. And, the fractal dimensions were compared and analyzed. The results showed that the fractal dimensions of different regions of Jiuduansha were different, the Shangsha was the largest, the Xiasha second, and the Zhongsha was the last. In the different shores of various regions, fractal dimension of the north of Shangsha was larger than other regions of Shangsha; Fractal dimensions of the northwest - southeast shores of Zhongsha and Xiasha were larger than other regions of Zhongsha and Xiasha. It was mainly related to their geographical locations and different hydrodynamic conditions. Besides, the fractal dimensions of south shore and north shore were also calculated. The results showed that the fractal dimension of south shore was larger than north shore. |
PDF Full Text Request