Investigation Of Loess Positive And Negative Terrain Based On DEMs

China loess plateau is world-wide famous for its peculiar and unique landforms. Distributing staggered spatially and zigzaggedly, the loess positive and negative terrain (hereafter called P-N terrain for short) are mainly separated by the loess shouderlines which is a key terrain structure line in the loess area. The study on the characteristics of P-N terrain and their interaction could be an effective clue for making a deeper investigation of loess landforms, e.g. loess terrain development, surface erosion at both local and regional scales.The study firstly expatiate the conceptual model of P-N terrain. Then a DEM based positive and negative terrain automatic extraction methods called "neighborhood judgment method of slope deformation" is developed. Then the extraction accuracy as well as the application suitability of this method are explored.The methodology of landscape ecology is employed to study loess landscape features constructed by P-N terrain. A series of quantitative indicators are proposed. They are two dimensional landscape indicators (including: shape index, boundary density, fragmentation degree, symmetrical index and fractal value), three dimensional shape indicators (including: mean-slope-difference, mean-elevation-difference and mean-roughness-worse) and terrain development indicators (including: nibble degree and approximation degree).A series of thematic maps was produced to investigate the spatial distribution of P-N terrain based on the DEMs from 48 test areas of typical loess landform areas in northern Shaanxi. According to the spatial distribution pattern and the development trend, the paper discussed the external manifestation and geographical meaning of P-N terrain. in Loess Plateau.Positive terrain covers 60.5% of the total loess area in northern Shaanxi, The extracted P-N terrain indexes could be found to possess of a rather strong relation with their landform characteristics. Index of nibbled degrees and approximation degrees shows the landform development and the developmental stages of drainage system within a watershed area. The study is hopeful to make a deeper understanding of loess erosion landforms and their development rules, as well as to play a great role in the reconstruction of ecological environment in Loess Plateau.