Gully Features Extraction And The Regional Difference Analysis In The Severe Soil Erosion Region Of Loessplateau Of China Based On Multisource Data

Gullies caused by the water erosion are widespread in the Loess Plateau region of China. This landform is characterized by the frequent material exchange and strong morphological changes. The morphology of gully developed in different regions owns obvious regional difference, which not only shapes different kinds of landform but also affect the soil and water conservation and agricultural production. The study on regional differences of gully is needed for investigating the laws of development and distribution,meanwhile it can be regarded as a starting point for the research in geomorphology, soil erosion, ecology and so on. A few of studies have forced on the regional difference of gully in Chinese Loess Plateau, however, due to the limitations of study data and methods, many core issues are needed to be addressed including the effective method for gully feature extraction, the index system for gully feature quantitative analysis, and the investigation of influence mechanisms. Further exploration of these scientific issues is expected to provide a breakthrough for the study of loess gully.In this study, firstly, the methodology for gully feature extraction has been proposed based on multi-source data which make it possible for extracting gully features covering the severe soil erosion area of the Loess Plateau. And then, the quantitative indexes for gully feature are designed for investigating the spatial distribution rules on different scales. Furthermore, the gully regionalization map has been created based on group analysis method. Finally, the influence mechanism is analyzed according to the correlation analysis between gully features and multiple geographical elements. The main research contents and conclusions of this study are listed as following:(1) The study systematic elaborate the basic concepts, developmental processes and characteristics of loess gully. Further, the type division system for loess gully has been proposed from the perspective of erosion age, morphological characteristics,erosion characteristics, and gully extent. In addition, after pointing out the disadvantages of the existing methods including based on stream network analysis and positive and negative terrain analysis, an object-oriented research perspective for loess gully is proposed which has been applied in the further study.(2) A two-level gully feature extraction method has been designed based on high-resolution DEM and imagery. The experimental results in three typical catchments(Yaojiawan in Suide, Zhifanggou in Ansai, Xialiugou in Changwu) prove the effectiveness of such method.(3) Based on the medium resolution DEM and image, a regional-scale gully feature extraction method is proposed,which integrates terrain skeleton information and image features. In this method, the extracted stream network from DEM is used for revising the predicted results using objected-based image analysis. The experiment results show that, the terrain skeleton information play an important roles in gully feature extraction which can overcome the limitations in gully feature description due to the low resolution.(4) Quantitative analysis indexes of loess gullyare defined and calculated based on four different watershed units, so that spatial distribution of gully feature are discussed.The created gully regionalization map using group analysis can provide an important reference for the study of loess landform and soil and water conservation.(5) The coloration analysis is conducted between gully features and topographic features, soil, vegetation cover, land use, and soil erosion intensity. The results show that,there are good correlations between soil erosion rate and gully density and gully division degree, and the latter is more relevant which can be applied for regional-scale soil erosion evaluation. Yellow soil, cinnamon soil, chestnut soil and gray cinnamon soil are more risky for gully development which should be paid more attention. In the field of land use, woodland, grass and shrub own higher gully division degree, however,cultivated land and artificial land own relative lower gully division degree.The research contents in this paper including feature extraction,pattern analysis and mechanism investigation which are in accord to research paradigm of geography.The external manifestation and intrinsic mechanism of regional difference of loess gully have been revealed in this study, which can bring innovative understandings for digital terrain analysis and loess landform.