Accuracy Assessment For Construction Methods Of Terrace Digital Elevation Model

Loess Plateau is key research area because of its serious soil erosion.Soil erosion is affected by a variety of factors,and terrain factors(slope,slope length,etc.)are primary elements of soil erosion,which are usually extracted on the basis of Digital Elevation Model(DEM).However,current DEMs are limited to represent natural landform,and usually unable to show the information of artificial landform like terraces.In the Loess Plateau,in order to prevent soil erosion and improve people’s living conditions,large areas of terraces have been built after several years’ management.However,the terraces could affect surface micro-morphology drastically and make a great influence on the slope,slope length and soil erosion process.Therefore,it is essential to provide some methods of constructing DEMs with terraces,information(T-DEM).In the meantime,the precision of DEM has increasingly become critical issue.This study concentrates on analyzing terrain characteristics and evaluating the precision of different methods of constructing T-DEM.It aims to provide support to relevant studies and it is also meaningful for improving the methods of constructing T-DEM.The study chooses terraces in Huaishuwozi basin as case study area.5m resolution DEM,WorldView3 image with a resolution of 0.3m and the point cloud data gathered by 3D scanner were employed.Then elevation,slope,slope length and LS factor extracted from different types of T-DEMs constructed by different methods were selected to analyze the terrain characteristics.Besides,from the perspective of terrain factors and DEM terrain representation error,this study intensively assesses the precision of two construction methods.The results revealed:(1)Actual terrace types are not exact the same with all kinds of theoretical models.T-DEM should be built according to the reality or experiences,instead of an absolute bench terraces.(2)Rapid modeling method should be adopted in large study area considering the efficiency and feasibility.For a certain area and a single factor,the actual ridge-based method is much better for describing elevation,slope and LS factor,while the rapid modeling method has smaller gap with reality in terms of slope length.The actual ridge-based method is better for describing overall terrain characteristics in a comprehensive study.(3)The DEM terrain representation error calculated from sloping terrace by actual ridge-based method is more suitable to the actual landform.However,unlike other terrain factors,the result of DEM terrain representation error calculated from bench terrace by the same method is the worst.The bench terrace and sloping terrace constructed by rapid modeling method have close accuracy.