A Study On DEM Construction And Dynamic Change Of Jiuduansha Wetland Based On 3S Technology

Jiuduansha Wetland is located between the south and north troughs of Sand Bars in the Yangtze River estuary. It is one of national nature reserve and important land resource of Shanghai. However, because of the influence of the Three Gorges dam and other water conservancy projects and the accelerated sea level rise, it is likely the riverine sediment transport rate and the sediment concentration of the Yangtze River will decrease to less than the critical values in the coming decades to result in the tidal bank erosion in the Yangtze River estuary Foreland. So, the dynamic change of Jiuduansha wetland has attracted much attention.The dissertation has studied the dynamic erosion/sedimentation change of Jiuduansha wetland in the recent 20 years by 3S technology, i.e. remote sensing, global positioning system and geographic information system technology. The main contents and results as below:1. In order to obtain the reliable elevation data from the in situ measurement data by RTK-GPS in Jiuduansha wetland for DEM construction, the conversion relationship between geographic coordinate system and Shanghai local projected coordinate system is created, the elevation datum is converted to the theoretical depth datum, and the data quality is validated.2. To counter the problem of very irregular distribution of the in situ measurement data by RTK-GPS, the grid-DEM is generated by ordinary Kriging interpolation, and the TIN is generated by Delaunay triangulation with the boundary condition constraints. The results show that the two DEM precision are close, but ordinary Kriging interpolation is better than Delaunay triangulation in surface smoothing.3. By studying the relationship between the best band for waterline extraction and the tide condition, the conclusion is drawn that short wavelength infrared is the best band for waterline extraction in the middle of flood tide, and red band is the best band in the other tide condition.4. Aiming at Jiuduansha intertidal mudflat is so wide that the waterline is not horizontal completely and shouldn't be simply assumed as a contour, the dissertation develops an elevation acquisition method by waterpoints, which is more reasonable than by waterline. 5. Aiming at the condition that the data source includes contours, waterpoints and scattered points, and the data distribution is very uneven, the Delaunay triangulation with several condition constraints is used to generate TINs, and multi-temporal DEMs are obtained.6. According to the multi-temporal DEMs, the dynamic change rules of Jiuduansha wetland are discussed in area change, horizontal erosion/sedimentation change and vertical sedimentation speed.7. A new parameter of annual erosion/sedimentation activity is defined in the dissertation to reasonably estimate the stability of Jiuduansha wetland.