Tidal Channel Information Extraction And Swing Ratio Analysis Of Jiuduansha In The Yangtze River Estuary Using Remote Sensing

Tidal channel is a typical geomorphic unit developed in the intertidal zone.And it is wely distributed in the estuarine delta,plain coast,gulf,lagoon a nd shallow shoal around the world,and exhibits spatial forms of dendritic,rectangular,parallel or feather.Jiuduansha is located in the middle between south channel and north channel of the Yangtze river estuary.A diversity of tidal channels have been formed due to constantly eroded,migrated,swinging and circuitous in Jiuduansha.It is important to study channel swing ratio further to learn about dynamic landforms change and dynamic deposition rules of Jiuduansha.The dissertation detected the tidal channels graded by Horton-Strahler method in Jiuduansha in 2013-2016 a using remote sensing data.Then the dissertation counted the number,length,density,branch ratio,curvature ratio,swing ratio,and analyzed the relation among the tidal swing ratio and curvature ratio,branch ratio,density.The main results are as follows:The dissertation adopted a fusion of Wavelet transform,Otsu method and mathematical morphology method to detect edge information of tidal channels.In the process of Wavelet transform,reducing the high level detail coefficients was to weaken the tidal flat information and increasing the lower layer detail coefficients was to enhanced tidal channel information;On the basis of Ousu,it could not only maintain the accuracy but also co nnect the breakpoint of tidal channels through the dilation operation of mathematical morphology and the geometric operation of the image.In the process of image geometric operation,we first multiply the dilated image with the low threshold image to get the speckle free image.Compared with the image obtained by Ousu,the channel wth was slightly larger.The better extraction effect could be obtained through the image obtained by Ousu added pixes of breakpoint in the speckle free image.Based on automatic extraction method and ArcGIS manual extraction method,the dissertation extracted the tidal channels in Jiuduansha,then calculated and analyzed swing ratio,curvature ratio,density,branch ratio of tidal channels.The results showed that the swing ratio of tidal channels in the north bank was greater than the south,and with the increase of curvature,swing ratio decreased.When the swing ratio was less than 20m/a,the swing ratio increased slightly with the increase of density.While the swing ratio of tidal channels increased fast with the increase of density when the swing ratio of tidal creek was greater than 20m/a.The tidal channel branch radio presented decreasing trend among Xiasha,Zhongsha and Shangsha,and the statistical result was similar to the tidal channel density.