梯田区侵蚀地形因子随DEM分辨率变化的特征分析

摘要

通过无人机航空摄影测量,获取高精度DEM,分析提取的坡度、坡长和LS因子,同时通过分辨率的变化,计算并分析了这些参数的变化情况.研究表明:基于无人机获取的DEM能够较好地表达梯田地形特征,梯田地形因子分布特征与地形特征吻合,大值集中于梯田过渡的陡坡处,小值集中于田面.随着分辨率的降低,非梯田区坡度整体呈现衰减趋势,坡长呈现增长趋势,LS先小幅增加,后由于坡度衰减明显,LS呈现衰减趋势,但变化幅度不大;而梯田区随着分辨率的降低,小坡度和超大坡度所占比例均减小,平均坡度降低,但坡长增加显著,因此导致LS增长较显著,在20m分辨率下,LS因子被高估约1/3.梯田通常作为水保措施因子单独来考虑,由于分辨率对地形因子影响较大,因此梯田区的地形因子估算需要考虑分辨率的影响.%Terrain is a main environmental factor which affects the surface hydrology and soil erosion.Slope steepness,slope length and LS factor are important parameters in soil erosion.model.As a water conservation measure,terraced field changes the surface morphology and affects slope steepness,slope length and LS factor.Terrain features of the terraced area based on low resolution DEM are fuzzy and difficult to be reasonably estimated due to the lacking of high precision.High resolution DEM,which was accessed by UAV aerial photogrammetry technology,was used to analyze slope steepness,slope length and LS factor under different resolutions.Meanwhile,the changes of these parameters were calculated and analyzed in a none terraced area with the same resolution changes as comparison.The result showed that the DEMs which were accessed by UAV can express the terrace terrain features in details.Distribution of terraced terrain factors coincided with topographic features.These features showed high values distributed in the ridge area and small values distributed in terrace surface.With the decrease of DEM resolutions,the slope steepness of none terraced areas was decreased while the slope length was increased,and LS value was increased firstly and then decreased because of the fast decrease of the slope stcepness,but the variation range was relatively small.For terraced areas,the portion of both small and large part of the slope steepness was decreased,average slope steepness was also decreased.Slope length had a clear increasing trend,so as the LS factor.Under the resolution of 20 m,LS factor was overestimated for about 33％.Terracing is usually considered as a project factor in soil erosion models of soil and water conservation measures.Due to the large influence of resolution on LS factors,the estimation of erosion in terraced field needs to consider the effect of resolution changes.