Research On Accuracy Analysis Of UAV Oblique Photogrammetry And Extraction Of Individual Elements In Debris Flow And Evaluation Of Susceptibility

The fragile geological environment in the loess area is vulnerable to the influence of externally induced factors,which provides favorable conditions for geology disasters such as debris flow,landslides and collapses,and makes frequent geological disasters.In the investigation of geological disasters in the loess area,traditional artificial ground survey methods are of great danger and cannot be effectively implemented.The use of photogrammetry and remote sensing non-contact measurement techniques,realizing efficient and accurate access to information related to hazards is an urgent task faced in the current geological disaster investigation and evaluation and a technical problem that must be solved.This paper firstly introduces the principle and technical process of oblique photogrammetry of UAV and analyzes its absolute and relative accuracy in depth.It verifies that under the condition that there is no field ground control point,the oblique photography of UAV can meet the geometric accuracy requirements of geological disaster investigation.Then,taking the debris flow in Zhaojiagou area of loess area as the research object,15 qualitative and quantitative hazard information were extracted based on the analysis of the 3D model,DOM and DEM of debris flow obtained through oblique photography and image processing of drones and related geological data.Finally,a semi-qualitative and semi-quantitative scoring model based on the analytic hierarchy process was studied and constructed to evaluate the vulnerability of debris flow in Zhaojiagou,and the reliability was compared with the evaluation results of field survey data.The specific work and conclusions are as follows:(1)Through the field investigation of the Zhaojiagou debris flow on the artificial ground,the comparative experimental data were collected and acquired.Through the collection of the data of the geological map,the topographic map and the rainfall contour map and so on,the related data were completed and analyzed.Flight and measurement acquired experimental oblique images and data.(2)The accuracy analysis of UAV oblique photogrammetry shows that the absolute measurement accuracy based on the POS data is two orders of magnitude lower than that of POS + GCP data,and the relative measurement accuracy is only 0.5 order of magnitude.In geological disaster survey,most of the data are relative data(such as height difference,slope,etc.).Under the non-mapping accuracy requirements,the accuracy of photogrammetric measurement supported by POS data can meet the geological disaster investigation needs.(3)Based on the real-world 3D model,DOM,DEM and other results,a comprehensive qualitative analysis and quantitative information calculation of the debris flow in Zhaojiagou was conducted.The SVM classification method was used to extract the vegetation cover information based on the debris flow catchment area,and two slope acquisition methods were studied,one more crude but efficient and the other more cumbersome but accurate.(4)The semi-quantitative and semi-quantitative score model based on Analytic Hierarchy Process(AHP)was researched and constructed.Applying this model to the results of oblique photogrammetry survey,the total score of debris flow in Zhaojiagou was 86 and the degree of susceptibility was moderate.The total score of artificial ground survey was 96 points,and the degree of susceptibility was moderate.Finally,the comparison of the two results shows that based on oblique photography measures,the resulting element information is faster,more scientific and reasonable.