基于汇流累积计算的沟壑密度分析方法

沟壑密度是评价地表侵蚀影响,水土流失情况,进行地貌类型分析等的重要指标。文章基于研究区填洼后的DEM,利用地表汇流累积分析原理和栅格重分类方法,通过研究沟道覆盖区栅格数与汇流累积栅格二值化阈值间的关系,选择合适的阈值用于提取地表沟道。然后结合自然地表高程,分析合理的高程和相对高程栅格重分类阈值并进行高程栅格二值化,将二值化结果作为乘积模板并配合栅格细化算法优化沟道提取结果。最终利用1km~2单位面积规则格网对沟道提取结果进行目标栅格数统计计算,得到地表沟壑密度值。结果显示,该方法基于30 m分辨率DEM提取的西安市地表沟壑密度均值为1.29km/km~2。除雁塔区,其余各行政区统计均值与前人研究结果基本吻合。试验结果证明,基于本方法可以高效较精确地计算该市地表沟壑密度,分析结果可以量化研究区沟壑密度特征值以及通过栅格像元灰度变化体现沟壑密度变化趋势。

Gully Density Analysis Based on Flow Accumulation Method

Gully density is an important indicator to assess the impact of surface erosion,soil erosion,landform analysis etc.Based on DEM filling,using surface flow accumulation and raster reclassification analysis principles,we researched the relationship between the number of grids in the channel coverage area and the binarization threshold of the accumulation grids,and selected an appropriate threshold to extract the surface channel.According to the natural surface elevation,the reasonable thresholds were analyzed.Reclasscifying the elevation and relative elevation rasters and thining,we used the binarization results as the product template to optimize the channel extraction results.Finally,we calculated the number of target grids in each 1-km2 unit area to qualify the grid raster density of research zone.The results showed that the mean value of surface gully density in Xi'an City is 1.29 km/km2 based on DEM with 30 m resolution.In addition to the Yanta District,the results were consistent with previous studies in average gully density of the remaining administrative regions.It certificated that this analytical method can be used to calculate the density of the urban gully effectively and accurately.The results can be used to quantify the characteristic values of the gully density in the study area and reflect the variation trend of the gully density through the gray-scale variation of the grid pixels.