|Thesis Advisor||李锐 杨勤科
|Place of Conferral||北京
（2）通过独立结构变异函数理论模型（Independent Structures Model, ISM）拟合得出坡度各空间频率组分随分辨率降低的变化特征以及不同地形类型区各组分的差异性。随分辨率降低坡度整体变异性减小，相关距离增大；随分辨率降低受影响最大的为空间高频组分，而空间低频组分随分辨率变化较小；在6个分析样区的模拟结果表明，NE样区和NS样区坡度信息在空间低频组分占的比重较大；LP样区和SE样区在空间高频组分占的比重较大；SC样区在空间中频组分占的比重较大；SD样区在各个空间频率组分所占比重居中。以上结论较好地解释了分辨率降低过程中不同地形类型区坡度变化的差异性。
（5）以土壤侵蚀分类分级标准（SL 190-2007）所规定的水蚀面蚀评价方法为土壤侵蚀强度评价依据，以安塞县为研究区，基于90m SRTM计算的坡度（以下简称SRTM坡度）、降尺度变换后90m SRTM坡度（以下简称降尺度变换坡度）和25m分辨率坡度分别进行土壤侵蚀强度评价，探讨坡度降尺度变换对区域土壤侵蚀评价的影响，并对比基于三种坡度数据的土壤侵蚀强度评价结果。从图面效果和统计信息来看，基于降尺度变换坡度和基于25m分辨率坡度进行的土壤侵蚀强度评价结果相似，而基于SRTM坡度的土壤侵蚀强度评价结果与前两者有较大差别，其土壤侵蚀强度评价结果偏弱。坡度降尺度变换对区域土壤侵蚀评价是必要的。
Slope gradient is one of the main factors in soil erosion. In the research of regional soil erosion accessment, slope gradient is generally calculated from lower resolution DEM. However, slope gradient becomes smaller with resolution becomes coarser, thus makes it difficult to show the relationship between slope gradient and soil erosion and makes the modeling result of regional soil erosion poor. In this research, the digital image process, digital terrain analysis and geostatistical analysis were mixed together. We studied the relationship between slope gradient and resolution, explained the reason of slope reduction with resolution, build a theoretical slope distribution model, got a mathmetial slope down-scaling model and the key parameter in the model over China(downscale from 90m SRTM to 25m) and evaluated the change of regional soil erosion accessment result because of slope down-scaling.
There are 60 research sites in this paper. Six of them are called analyse-samples which ared used in study of slope reduction with resolution, validation of theoretical slope distribution model and mathmetial slope down-scaling model. Fifty three of them are called downscaling validation-samples which are used in validation of parameters of mathmetial slope down-scaling model over China. One of them are called soil erosion accessment-samples which is used in comparation of soil erosion accessment based on coarser and down-scaling slope. The results of this research are as follows.
（1）There are some differences between varied terrain types in the change of basic slope statistics with resolution. Mean slope and slope standard deviation (STD) reduce with resolution becomes coarser. However in different terrin types the change is different. In Loess Hilly area (LP sample) and Red Soil Hilly areas (SE sample) the change is most intensive. In Rocky Area of Shandong province (SD sample) the change is moderate. In Northeast Gentle Hilly Black Soil area (NE sample) and Wind Drift Sand area in North Shannxi Province (NS sample) the change is most gentle. In Purple Soil Hilly area in Sichuan province the change is gentle when resolution is finer and is more intensive when resolution is coarser. Frequency and Cumulate Frequency curves moves to gentle slope with resolution become coarser. The change in different terrain types is similar as the change of mean slope and STD of slope.
(2) Semi-variogram is a useful tool in analyse of terrain structures. Change of slope information in different scale components with resolution and terrain types can be detected. The overall variance of slope reduces and correlation distance becomes larger with resolution becomes coaser. The result of ISM model shows that with resolution becomes coarser the change of high frequency component of slope is most significant and that of low frequency component is small. In NE and NS sample low frequency component of slope is more important than in other samples. However in LP and SE sample high frequency component of slope is more important than in other samples. In SC sample moderate frequency component of slope is more important than in other samples. In SD sample the proportion of high, low and moderate frequency component in overall variance is moderate in the six samples. The result well explained the reason for the difference in slope scale effect with resolution in different terrain types.
(3) This paper got a theoretical slope distribution model based on slope gradient of DEM surface and The chi-square distribution. The main parameter in this model is std of slope gradient p and q. The model efficiency is dependent on whether the terrain type is single in the study area that is whether p and q is normally and independent with zero mean and eaqual variance. The model has been used in the six analyse-samples at series of resolutions. The result shows that the model used in this paper can model slope frequency and cumulate frequency curves, mean and std of slope. The model efficiency is high in the six analyse-samples.
(4)Slope down-scaling mathematical model was got based on theoretical slope distribution model and histogram matching method and applied in the six analyse-samples. The most important parameter in the slope down-scaling mathematical model in this paper is the std of p and q at high resolution. The paper offers the std of p and q at resolution of 25m based on 25m Hc-DEM all over China and the parameter was validated at the 53 downscaling validation-samples.
(5) In this paper the method showed in Standards for classification and gradation of soil erosion (SL-190-2007) was used as the method of soil erosion assessment. The study area is the county of Ansai. In order to know the influence of slope-downing to soil erosion assessment, the slope based on 90m SRTM (SRTM slope for short) was downscaled through the slope down-scaling mathematical model to 25m. Then soil erosion grade was calculated based on SRTM slope, 25m slope and the downscaled slope. The result shows that the erosion grade result is similar based on 25m slope and the downscaled slope. However there is difference between erosion grade result based on SRTM slope and the other two slope surfaces, the erosion grade result based on SRTM is relatively gentle. The slope downscaling process in regional soil erosion assessment is essential.
Key words: slope scaling effect; soil erosion; semivariogram; slope down-scaling
王春梅. 坡度尺度效应与转换及其对土壤侵蚀评价影响研究[D]. 北京. 中国科学院研究生院,2012.
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