The Watershed Terrain Extraction Technology Based On Unmanned Aerial Vehicle

The study of water and sediment movement in basin is an important branch and research hotspot of river dynamics at present.Whether physical model experiment or numerical simulation,the key basic problem to solve first is obtaining and extracting the high-precision three-dimensional terrain of the studied sub-basin,and on this basis to reconstruct the basic unit of water and sediment movement(slope,gully slope and channel).Due to the large varitation of the topographic and the veritical and horizontal topography of the sub basin,many problems have been brought to the extraction of high precision 3D Terrain.With the arrival of the era of big data and the acceleration of the digital integration process,this contradiction is more prominent,It has become an indispensable part of the watershed research to obtain the real-time and high-precision image of the underlying surface of the river basin,and reconstruct the 3D terrain of the corresponding region.Although the traditional aviation and aerospace remote sensing technology can provide the data basis for the watershed research in a certain degree,it is difficult in real-time,accuracy,economy and other aspects and obtain the optimal solution.In recent years,UAV remote sensing technology with its fast and convenient,simple operation,strong flexibility and low cost advantages,obtained in the emergency disaster emergency data and small fast mapping shows the unique advantage and application areas are more extensive.This paper first discusses the relevant methods of watershed terrain extraction,summarizes the advantages and disadvantages of each method,summarizes the application status of UAV remote sensing technology and the system composition of UAV.Analysis of the reasons for the camera distortion and the influence on the accuracy of reconstruction of 3D model,a two-dimensional control field on the UAV is equipped with digital camera calibration,through the experimental analysis of the error of image distortion and image distortion correction.This study is based on photogrammetry theory,using the method of SfM to reconstruct the regional images obtained by the UAVs,and the reconstruction of terrain under different altitude three-dimensional point cloud precision are analyzed and evaluation.And provides the basis for the accuracy control of the actual 3D Terrain Reconstruction process.Based on the two different geomorphic features of the micro topography,which are respectively of the steep slope of the river basin and the river channel(or channel),respectively was carried out based on the uav image photography and 3 d terrain.In the study of the steep slope micro-terrain,the images of the steep slope were extracted from the images with different flight heights.The D8 method was used to extract the trench channel formed by rainfall.In the course of river terrain extraction,the accuracy of single and double route is evaluated,and the river terrain and steep terrain are compared.The applicability of SfM method in extracting different terrain is analyzed.At the same time,the terrain extracted from UAVs is compared with the traditional large cross-section method,which shows the advantages of real-time,fast and high precision of UAV in the process of terrain extraction.