Retrieval And Analysis Of Elevation At Mudflat Using Remote Sensing

As a sensitive belt of sea and land interaction, silt tidal flat is characterized as muddy surfaces, densely covered and frequently varied tidal creeks. Therefore, the traditional field observation has been restricted by the difficulty of access. Remote sensing, combined with in situ surveying, is an effective tool for monitoring the tidal flats which can be detected by visible and near infrared sensors.On the basis of field survey, multi-temporal remote sensing data and navigational maps were used to interpret wetland in Shanghai, which provide timely data (i.e. amounts and changes of wetland resource) for scientific management on coastal regions.Waterline method and hydrodynamic model were investigated to construct Digital Elevation Model (DEM). According to spectral characteristics of tidal flat and nearshore water body, a decision tree model and region growing method were applied in detecting waterline with improved accuracy. A series of waterlines were extracted from multi-temporal remotely sensing images by above approach. The assignment of an elevation to the waterline was performed according to hydrodynamic model(Delft3D) at the satellite overpass. The waterlines labeled elevation were used to construct DEMs (Digital Elevation Model). This initial DEM was then used to refine the topography in the intertidal zone, and the model was re-run to produce improved water levels and a new DEM. This procedure was iterated by comparing modeled and actual waterlines until no further improvement occurred. Jiuduansha Island with rapid evolution was selected as study area, and multi-temporal remote sensing images ware divided into different groups which spanned a short period to eliminate the error of the dynamics of mudflat. Then the generated DEMs, built by above method, were compared to evaluate the effects of the construction of Deep Water Channel Project (DWCP) at the north of Jiuduansha shoals.Based on the dynamic nature and spectral information of tidal flat, tidal creeks were extracted from high resolution aerial images, on which whether Horton law has general applicability was analyzed. Then Horton law and fractal dimension were applied in quantifying geomorphic changes. The topography of tidal creeks was also acquired using remote sensing waterline method and measured width-depth ratios.Paired measurements of saltmarsh community and spectral characteristics were carried out and were then ordinated using Principal Component Analysis (PCA). According to the relationship between vegetation spectrum and environmental factors, vegetation cover, elevation of tidal flat and tidal creeks were selected as additional information for vegetation classification. With the fuzzy matrix and previous classification, the second classification was made on the error pixels in terms of fuzzy membership function of different vegetation and additional information. The results indicated this approach obviously improved the accuracy of vegetation classification.Heighted waterlines and corresponding field measurements were employed to acquire the mean annual accretion/erosion rate between satellite and survey time. We also studied the accretion/erosion pattern and factors which influenced the evolution of tidal flat. The interactions of between vegetation and tidal elevation were also investigated according to the extracted vegetation and inversed DEM at Dongtan. To analyze the impacts of vegetation on hydrodynamics, tidal current and suspended sediment concentration were measured and compared at vegetation and unvegetation fields respectively. The interaction of the accretion/erosion rate and extracted vegetation using remote sensing method showed the same conclusion with which was made by field survey.At last, 3D visualization of tidal flat, tidal level and nearshore flow field were implemented by the field visualization technique of GIS, which made marine scientist more intuitionistic understanding the hydrodynamic process at coastal region.