Offset Measurement Along Active Fault Based On Portable UAV And Structure From Motion

Earthquake is one of the most destructive natural disasters,and its formation mechanism has always been the focus of earth science research.Active tectonic is closely related to the formation of earthquake,studying the basic characteristics of which is of great significance for study of the earthquake formation mechanism and fault activity trend prediction.In order to obtain the characteristic parameters of active tectonic quantitatively,it is necessary to acquire high-precision and high-resolution terrain data.Traditional data acquisition methods mainly use total station and GPS measurements,which have high data acquisition accuracy,but low efficiency and small range.Airborne LiDAR technology can efficiently collect large-scale and high-quality terrain data,and has a certain penetration of surface vegetation,but its high technical cost and complex data processing limit its applications in the study of active tectonic.In recent years,a photogrammetric technique based on SfM method has provided a new choice of terrain data acquisition.The SfM method can extract and match the corresponding feature points from multi-view optical images,and then automatically solve the camera’s position and orientation as well as the 3D coordinates of the object point.The data collection of SfM method is most based on the Unmanned Aerial Vehicle(UAV),which is characterized by simple and flexible operation,high data acquisition efficiency,and low technical cost,and can be used to obtain high-quality 3D terrain data.This dissertation focuses on the typical tectonic geomorphology in the central section of the Altyn Tagh fault as a case study,discussing the application of the SfM method in the study of offset measurement.The main contents include:(1)Sort out the basic principle,technical process and data processing methods of the existing UAV SfM technology,and summarize the measurement method of active tectonic geomorphology based on high-precision terrain data.(2)Evaluate the measurement accuracy of portable UAV.This dissertation summarizes the principles and methods of nonmetric camera calibration.Based on indoor and outdoor UAV camera calibration yards,camera calibration experiments are performed to solve the camera’s internal orientation elements and distortion parameters.Meanwhile,the measurement accuracy evaluation experiment is carried out to evaluate the measurement accuracy of portable UAV images without control points and discuss its applicable conditions in fault offset measurement.(3)Taking two typical geomorphologic points in the Gebiling area and the Wuzunxiaoer area in the middle section of the Altyn Tagh fault as research areas,the surface 3D model isreconstructed using UAV SfM technology to extract the topographic features of typical faulted landforms,and measure offset distances and analysis ancient earthquakes.The results indicate that the offset distances obtained based on portable UAV and SfM method without control points,and the frequency of paleoearthquakes are consistent with the paleoearthquake events revealed by geological trench.