Research On The Applicability Of Extracting Gully Parameters And Topographic Factors With UAV Photogrammetry In The Loess Plateau

The Loess Plateau has high gully density,fragmented terrain,and severe gully erosion.The accurate expression of topography and landform is of great significance in watershed erosion assessment,ecological management and vegetation restoration.In recent years,unmanned aerial vehicle photogrammetry technology has been widely used in agronomy,forestry,geology and other research fields,but the research on the accuracy evaluation and applicability analysis of terrain parameter extraction in the Loess Plateau is lacking.In this paper,the small watersheds of Qiaogou in Suide County and Hegou in Wuqi County are selected as the study area,with the help of geographic information system technology and the application of mathematical statistics,explore the accuracy of unmanned aerial vehicle photogrammetry technology for extracting gully parameters and topographic factors in the hilly area of the Loess Plateau,as well as the causes of errors,provide a reference for its further application in the Loess Plateau.The specific conclusions are as follows:(1)Compared with 3D laser scanning,UAV photogrammetry has higher accuracy in extracting the twodimensional morphological parameters of the groove,and the percentage error is mainly distributed within10%.The measurement error of the extracted three-dimensional morphological parameters is within 20%,large-scale trenches with steep ditch walls and more vegetation have large measurement errors,the measurement error of small trench with gentle slope and less vegetation is small.It is difficult to capture the cliffs of the trench by the way of vertical photography by drones,thereby reducing the accuracy of trenching parameters extraction.Consumer-grade cameras cannot effectively filter vegetation.The digital surface model(DSM)data obtained by drone photogrammetry contains certain vegetation information,which affects the extraction accuracy of trench parameters to a certain extent.Compared with 3D laser scanning,the accuracy of UAV vertical photogrammetry for grooving geomorphological parameters is slightly lower,and there are certain limitations in monitoring the short-term dynamic changes of grooving.(2)Extract the characteristic parameters of three different scale plots,research shows,under the 3×3analysis window,the DSM?0.15 m slope extraction results show the characteristics of "gentle slope and steep slope",and the measurement accuracy is low.But compared to DEM?5m,when the analysis window is the same,the results extracted by DSM?0.15 m can describe the surface undulation and the degree of fragmentation better.The main trunks and tributaries of the watershed extracted by the two data sources are similar,but the shape of the river network extracted by DSM?0.15 m is more natural,sample B(19.21hm~2),the difference in gully density extracted by the two data sources does not exceed 0.5km/km~2,when the catchment area increases(C sample 204.78 hm~2),the resolution affects the extraction of river networks in the basin,and the high-resolution UAV photogrammetric data can be extracted to small tributaries.Compared with the 1:10,000 topographic map,the shape of the river network measured by drones is more in line with reality.By appropriately reducing the resolution of UAV photogrammetry data through resampling,errors can be reduced.Compared with DSM?0.15 m and DEM?5m,DSM?1m not only contains surface details,and the extracted results can reflect the actual situation.(3)Analyze the slope extraction under special terrain conditions,under simply changing surface conditions,the slope results extracted from different data sources are similar,for uniformly changing slopes,the slopes extracted from different data sources differ by about 5%,when the local surface changes gently,the slopes extracted from different data sources differ within 3%;under compound terrain conditions where the terrain suddenly changes,the extraction of slope is greatly affected by topographical changes,ridges and caverns,the slope measurement results vary greatly,this is because the sudden change of the slope affects the result of the overall slope extraction.The slope of the slope extracted by the slope is compared with the slope extracted by drone photogrammetry,it can reduce the influence of the sudden change of the slope value on the overall slope slope extraction,thereby reducing the error.This method can be used as a reference when extracting the overall slope slope.