基于DEM的黄土崾岘提取及其地形特征分析

崾岘是将要被切穿的鞍部,是正负地形矛盾斗争的结果,也是重要的地形控制点。典型的崾岘多位于黄土高原黄土地貌区,又称黄土崾岘,其对识别沟间地与沟谷的斗争程度有一定的指示作用。本文以黄土高原样区为例,基于1:1万DEM（5 m分辨率）和影像分辨率为0.95 m的遥感影像,利用流域边界算法和缓冲区标定,分析窗口选择5×5,实现了崾岘点位的半自动化提取。并对各崾岘点位求取坡度等地形因子,总结崾岘的空间格局和地形特征。结果显示,崾岘多分布在主流域边界和垂直于主沟道的最宽部分,地形控制作用明显。崾岘的坡度、起伏度、切割深度等值均大于鞍部值,同时,高级流域区的崾岘值大于低级流域区的崾岘值,反映出崾岘具有侵蚀程度强、表层完整性低、地表破碎度高的特点。总体而言,崾岘受沟道蚕食度高,从侧面反映了黄土地貌的发育阶段,是黄土地貌发育到中期的标志性产物。

Extraction of Loess Dissected Saddle and Its Terrain Analysis by Using Digital Elevation Models

Dissected saddle, as an important terrain control point, is the result of the struggle statue between positive and negative terrains. The width of the dissected saddle ranges from only a few meters to about twenty meters, which represents the critical stage of gully capture. That is, the headward erosion of gullies on both sides of watersheds are going to erode and dissect the boundary of the watershed. Thus, the division of positive terrains and the connection of negative terrains are achieved. The typical dissected saddle is located in the loess landform in the Loess Plateau, also known as the loess dissected saddle. This dissected saddle could act as an important indicator for distinguishing the extent between loess interfluve area and loess gully area during the landform evolution process. In this paper, taking the typical loess landform as an example, and on a basis of DEM data and remote sensing images, the semi-automatic extraction of dissected saddles is conducted. The terrain characteristics of these extracted dissected saddles, i.e., slope, relief, depth of cut, were then calculated based on the DEM data. Moreover, the spatial pattern of the dissected saddle was summarized. The experimental results show that the dissected saddles are distributed at the boundary of the main stream and perpendicular to the widest part of the main channel, indicating an obvious terrain controlling effect. The quantity and distribution of dissected saddles determine the development and the shape of the watershed to some extent. The results of slope, relief, and depth of cut for dissected saddles are all larger than that for the normal saddles. At the same time, the value of the high-hierarchical watershed is greater than the value of the lower-hierarchical watershed, which reflects that the dissected saddle has characteristics of strong erosion and high surface fragmentation. In summary, the dissected saddle is highly eroded by the channel, which could help to demonstrate the development stage of the loess landform. Along with the development of the landform, the dissected saddle could be regarded as a symbol, indicating the development of the loess landform has reached the metaphase of the landform evolution process.