地形信息对确定DEM适宜分辨率的影响

Effects of different topographic attributes on determining appropriate DEM resolution

分辨率会直接影响基于栅格数字高程模型(DEM)的数字地形分析结果,因此在实际应用中,需要选择适宜的DEM分辨率。目前采取的基本方法,基于某种地形信息定量刻画尺度效应曲线,从而确定DEM适宜分辨率,但对于采用不同地形信息时所产生的影响尚缺乏研究。本文针对该方法中通常采用的坡度、剖面曲率、水平曲率等3种地形信息,每种地形信息提取时,分别使用两种不同的常用算法,在3个不同地形特征的研究区中,逐一计算其在不同分辨率下的局部方差均值,以刻画尺度效应曲线,确定相应的DEM适宜分辨率,并进行对比分析。结果表明:①采用剖面曲率或水平曲率所得适宜分辨率结果基本相同,但采用坡度所得出的适宜分辨率结果则有明显差别,后者所得的适宜分辨率更粗;②采用不同地形信息时,越是在平缓地形为主的研究区,所得的适宜分辨率结果越相近,在复合地形特征的研究区所得到的适宜分辨率区间均明显较宽;③地形属性计算时所用的算法对适宜分辨率结果的影响不明显。

Due to the scale effect of changing resolution for grid-based digital terrain analysis, it is important to determine an appropriate resolution （or a range of appropriate resolutions） for gridded digital elevation model （DEM） in practice. The commonly-used approach to determining appropriate resolutions is based on a scale ef- fect curve characterized by certain types of statistics （the mean of local variance is commonly used）, which is calculated on the multi-resolution dataset of a specific topographic attribute derived from the gridded DEMs with a series of spatial resolutions. The resolution with the highest value of the mean of local variance is consid- ered to be an appropriate DEM resolution. Although several topographic attributes （such as slope gradient and curvature） have been used in this approach, there are few researches on the effects of different topographic attri- butes on the results from this approach. In this paper, we used an experiment to compare the effects of three types of topographic attributes （i.e., slope gradient, profile curvature, and horizontal curvature） applied to deter- mining appropriate DEM resolutions. The experiment was conducted in three study areas with different terrain conditions, i.e. Xuancheng area with low relief, Coweeta area with high relief, and Kaixian area with more com- plex terrain conditions. The tested topographic attributes were calculated from the DEMs with a series of spatial resolutions （i.e., 5, 10, 15, 20, 25, 30, 50, 100, 150, 200, 300 m）. For each topographic attribute, two wide- ly-used algorithms were tested. One is proposed by Wood （1996）, and the other is the one implemented in Arc- GIS software. The appropriate DEM resolution for a study area had the highest value of the mean of local vari- ance derived from each tested topographic attribute, respectively. Experimental results showed that the effects of slope gradient and curvature are different on the results of the appropriate DEM resolution, while there is little difference between the results from profile curvature and horizontal curvature. The appropriate resolutions based on slope gradient information （i.e., 15, 50, and 100 m for Xuancheng area, Kaixian area, and Coweeta area, re- spectively） are coarser than those based on curvature information （i.e., 5, 10-15, and 5 m for Xuancheng area, Kaixian area, and Coweeta area, respectively）, while the difference between them is less for the study areas with low relief. When slope gradient information was used, the appropriate resolution results for the study area with high relief are coarser than those for the area with low relief. When curvature information was used, the appropri- ate resolution results for the study areas with simple terrain conditions （such as Xuancheng area with low relief, and Coweeta area with high relief） are finer than those for the study area with complex terrain conditions. The range of appropriate resolutions from each topographic attribute for the study areas with simple terrain condi- tions is much wider than that for the study areas with complex terrain conditions. For each specific topographic attribute there is no difference between the effects of the tested algorithms of topographic attribute on the results of appropriate resolutions.