As one of most active gully types in the Chinese Loess Plateau,bank gullies generally indicate soil loss and land degradation.This study addressed the lack of detailed,large scale monitoring of bank gullies and proposed a semi-automatic method for extracting bank gullies,given typical topographic features based on 5 m resolution DEMs.First,channel networks,including bank gullies,are extracted through an iterative channel bum-in algorithm.Second,gully heads are correctly positioned based on the spatial relationship between gully heads and their corresponding gully shoulder lines.Third,bank gullies are distinguished from other gullies using the newly proposed topographic measurement of "relative gully depth (RGD)."The experimental results from the loess hilly area of the Linjiajian watershed in the Chinese Loess Plateau show that the producer accuracy reaches 87.5%. The accuracy is affected by the DEM resolution and RGD parameters,as well as the accuracy of the gully shoulder line.The application in the Madigou watershed with a high DEM resolution validated the duplicability of this method in other areas.The overall performance shows that bank gullies can be extracted with acceptable accuracy over a large area,which provides essential information for research on soil erosion,geomorphology,and environmental ecology.
在黄土材料和消除适当地代表真黄土表面的地方，一个模仿的黄土分水岭被采用与黄土分水岭进化在斜坡光谱调查变化。模仿的黄土分水岭的进化被人工的降雨的 exogenetic 力量驾驶。为三个月的一个时期，有不同紧张和持续时间的二十个人工的降雨事件被执行。在这个过程，九个 DEM 数据设定，有 10 公里格子分辨率的各个，被靠近范围的摄影测量学的方法建立。斜坡系列然后从这些 DEM 被提取。小心地设计的量的分析的随后的系列显示了在斜坡光谱和模仿的黄土分水岭的进化之间的一种强壮的关系。斜坡光谱的量的索引变化了定期跟随模仿的黄土分水岭的进化。吝啬的斜坡，斜坡光谱信息熵(H)，地面驱动力( T d ),平均数补丁区域( AREA_MN )，传染索引( CONTAG )，和补丁结合索引(结合)不停地增加跟随模仿的分水岭的进化，当时偏斜度(S)，周界区域分数维的尺寸( PAFRAC )，和散布和并排索引( IJI )代表了一个相反的趋势。所有这些索引在早、活跃的发展时期活跃地变化了，但是慢慢地在稳定的发展时期。这些试验性的结果显示斜坡系列的时间系列能有效地描绘模仿的黄土分水岭的斜坡分发，因此为为黄土地形建模介绍一个潜在的方法。
Gully feature mapping is an indispensable prerequisite for the motioning and control of gully erosion which is a widespread natural hazard. The increasing availability of high-resolution Digital Elevation Model(DEM) and remote sensing imagery, combined with developed object-based methods enables automatic gully feature mapping. But still few studies have specifically focused on gully feature mapping on different scales. In this study, an object-based approach to two-level gully feature mapping, including gully-affected areas and bank gullies, was developed and tested on 1-m DEM and Worldview-3 imagery of a catchment in the Chinese Loess Plateau. The methodology includes a sequence of data preparation, image segmentation, metric calculation, and random forest based classification. The results of the two-level mapping were based on a random forest model after investigating the effects of feature selection and class-imbalance problem. Results show that the segmentation strategy adopted in this paper which considers the topographic information and optimal parameter combination can improve the segmentation results. The distribution of the gully-affected area is closely related to topographic information, however, the spectral features are more dominant for bank gully mapping. The highest overall accuracy of the gully-affected area mapping was 93.06% with four topographic features. The highest overall accuracy of bank gully mapping is 78.5% when all features are adopted. The proposed approach is a creditable option for hierarchical mapping of gully feature information, which is suitable for the application in hily Loess Plateau region.
LIU KaiDING HuTANG GuoanZHU A-XingYANG XinJIANG ShengCAO Jianjun
