DEM Based Research On Positive-Negetive Terrains And Their Spatial Variation On Loess Plateau

Loess Positive and Negative Terrains are the most macroscopic dualistic components of the earth's surface. The Loess Positive and Negative Terrains (P-N terrains), which are widely distributed on the Loess Plateau, are discussed in this paper by introducing its characteristic, demarcation, distribution rules as well as extraction method. Using 5 m-resolution DEMs (scale is 1:10000) as original test data, P-N terrains of 86 geomorphological units in different parts of west Shanxi, north Shaanxi and east Gansu Loess Plateau are extracted accurately by using of an improved Snake model method. Then ten indicators (Nibble Degree, Proximity Distance, Mean-slope Difference, Inciensiveness, Mean-Roughness-Ratio, Shape Index, Moran's Index, Evenness Index, Fragmentation, Fractal Dimension) for depicting the landform evolution, spatial configuration and geomorphologic landscape characteristics of P-N terrains are proposed, and the correlation between the indicators are discussed also. Ten thematic maps which describing the spatial variation of P-N terrains are made by using of the GIS spatial interpolation method. The spatial distribution rules of these indicators and the relationship between the P-N terrains and Loess relief are discussed for further understanding of Loess landform. Finally, with the integration of P-N terrains indices, a series of multi-scale segmentation classification methods are applied to make a proper classification which reflecting the features of positive and negative terrain well in the study area. Zonal statistics showed that nibble degree is 0.423 in loess tableland and tableland ridge area,0.826 in loess ridge area and 1.041 in area of loess hill and hill-ridge area. Results show that P-N terrains are an effect clue to reveal energy and substance distribution rules on the Loess Plateau. A continuous change of P-N terrains from south to north in Shaanxi Loess Plateau shows an obvious spatial difference of Loess landforms. This research is significant on the study of Loess land forms with the Digital Terrains Analysis methods, and is an important reference for the development of water conservation measures in the Loess Plateau.