Separation Of DEMs Into Terrain Slope Types For Slope Statistical Distribution Model

Slope is an important index of surface morphology analysis,and the statistical distribution of slope is often presented by histogram.The theoretical distribution model of slope is a general mathematical model describing the probability distribution of slope,which promotes the theoretical research of slope.However,the model is not suitable for the area with multiple topographic types.The purpose of this study is to propose a complete and practical method for the separation of the terrain slope types to extend the applicable scope of the model.The proposed method was applied to the research sites with different topographic complexity and the applicability of the method in each site was evaluated through analysis.The main conclusions of the thesis are as follows:(1)The method proposed in this study includes five main steps: low-pass filtering of percent slope,determination of the optimal neighborhood windows,threshold determination of histogram segmentation,terrain slope types extraction and theoretical frequency calculation.The method can divide complex terrains into single terrain slope types and can be used to expand the applicable scope of the theoretical distribution model of grand slope from a single terrain sample area to a multi-terrain type sample area.(2)Based on the high-frequency information lost in the low-pass filtering process,using the mean change point analysis method to calculate the optimum neighborhood window can effectively avoid the error caused by traditional manual reading method.The optimal slope filtering results retained the necessary macroscopic topographic features and provided a basis for the histogram segmentation.(3)The valley floor method and OTSU method were used to determine the histogram segmentation threshold.The results showed that the two methods can divide multi-peak slope histograms into several simple single-peak histograms effectively.After comparison,the applicability of these two methods is different,so it is necessary to choose according to the specific situation of the research sites.(4)The research sites are divided by the terrain slope type's separation method,and the results are satisfactory.The four sites of Loess Plateau can be divided into two terrain slope types and the more complex QinBa site can be divided into four types.The slope frequency curve of each terrain slope type showed unimodal distribution.The histograms similarity between the combined slope theoretical frequency curves of each types and the actual slope frequency curves of the research sites were higher than 0.8,indicating that the theoretical frequency curves can simulate the actual slope's statistical distribution well.