基于ROC曲线的山区沟道提取最佳汇流量阈值分析

Analysis of optimal runoff accumulation threshold for mountain gully extraction based on ROC curve

沟道是影响坡面单元提取及水土保持图斑构建的重要基础,确定最佳汇流量阈值是提取流域沟道的关键。文中以大别山区金寨县铁冲乡小流域为研究区,结合野外调查,采用ROC曲线法定量确定大别山区小流域沟道提取的最佳汇流量阈值,并将该方法提取的结果与实际沟道网络进行精度评价。研究结果表明:1)采用不同汇流量阈值对沟道提取特征有明显影响,随着汇流量阈值的增加,沟道等级减少,沟道密度与数量呈指数趋势减少。2)不同地貌类型的沟道起点汇流量阈值有一定差异,低丘陵、高丘陵、低山分别为1.57hm^(2)、2.18hm^(2)、2.30hm^(2)。利用汇流量阈值抽取一级沟道样本点,得到ROC曲线下面积AUC=0.702,约登指数最大值2.21hm^(2)为最佳汇流量阈值,最佳阈值提取的沟道RMSE为29.76m,沟道套合差1.74%,沟道提取效果理想。3)基于ROC曲线的最佳阈值提取沟道结果符合研究区地貌特征,与实际沟道网络一致,表明利用ROC曲线可定量化确定最佳汇流量阈值,在大别山区适用性良好。

Gully is an important basis for slope unit extraction and soil and water conservation pattern construction.Determining the optimal runoff accumulation threshold is the key to extract gully.In this paper,a small watershed in Tiechong Township,Jinzhai County,Dabie Mountain area was taken as the research area.Combined with field investigation,the ROC curve was used to quantitatively determine the optimal runoff accumulation threshold for gully extraction in Dabie Mountain small watershed,and the accuracy of the results extracted by this method was evaluated with the actual gully network.The result shows that:1)Different runoff accumulation thresholds significantly influence the characteristics of gully extraction.With the increase of runoff accumulation threshold,gully grade decreases,and gully density and number decrease exponentially.2)There are certain differences in the runoff accumulation threshold at gully starting point in different geomorphic types,which are 1.57hm^(2),2.18hm^(2)and 2.30hm^(2)in low hill,high hill and low mount,respectively.The first level gully sample points were extracted using the runoff accumulation threshold,and the area under ROC curve(AUC)is 0.702,the maximum Youden index 2.21hm^(2)is the optimal runoff accumulation threshold,the RMSE of the gully extracted with the optimal threshold is 29.76m,and the difference area of the gully overlay is 1.74%.The gully extraction effect is ideal.3)The gully extraction results based on the optimal threshold of the ROC curve are consistent with the geomorphic features of the study area and the actual channel network,which indicates that the optimal runoff accumulation threshold can be determined quantitatively by the ROC curve and is suitable for Dabie mountain area.