Topographic Mapping Of Chongming Dongtan Tidal Flat With A Terrestrial Laser Scanner

Tidal flat topographic data are vital in the morphology changing study.The conventional survey methods cannot meet the requirement for large area coverage and high accuracy.With the rapid development of laser technology,3D laser scanning technology applied to object measurement has become a new technology to obtain spatial data after the GPS technology.So the application of laser scanning technology provides a favorable opportunity for the establishment of the high accuracy digital terrain model and terrain information acquisition.In order to monitor the wetland vegetation cover,elevation changes and 3D geometry information of tidal flat on Chingming Dongtan,a tidal flat at the Eastern headland of Chongming Island in Yangtze estuary,this study described a method to measure the spatial geometry using a terrestrial laser scanner and GPS-RTK technology.Through this study,this paper mainly obtained following results:1)The paper introduced the principle of terrestrial laser scanner and its working process.With the use of GPS-RTK technology the merge of multi-station data on Chongming Dongtan were implemented based on multi-station scanning and fixed location reflectors realized.2)Multi-scale-point-cloud filtering algorithm was designed to filter the vegetation and retrieve the terrain elevation.The scale effects were important factors to influence the optimal size of the window,so the results of different windows were tested and compared with the RTK data to determine the best terrain resolution.Finally two phases of DEMs and vegetation heights in September,2013 and October,2014 were produced.The result shows that Terrestrial Laser Scanner is able to filter the short vegetation with height less than 0.5m and sparse vegetation with density less than 90 plants unit/m2.3)Creating digital terrain model Chongming Dongtan by Interpolation of Inverse Distance Weighted with the high density point cloud data as the source data.Extracting tidal creek shape data two phases of September,2013 and October,2014,fractal dimension were applied in quantifying geomorphic changes of tidal creek;To analyze how ecological engineering affect the erosion and deposition tidal flat of Chongming Dongtan with the two phase digital terrain model,the tidal without vegetation were divided into the south parts,middle parts and north parts.The result shows that ecological engineering break tidal creak in north and middle parts and little affect the south part,silting intensity of tidal flat is decreased from north to south.