基于球体网格与DEM的流域地形特征尺度效应分析——以长江流域为例

Scale Effect Analysis of Basin Topographic Features Based on Spherical Grid and DEM:Taking the Yangtze River Basin as An Example

基于球体大圆弧八叉树剖分网格和全球共享DEM(Digital Elevation Model)数据分别构建长江流域多层次三维地理场景,提取流域相关地形参数,分析流域地形特征随度量尺度变化的趋势与规律.结果显示,同尺度下球体网格模型的上下表面积、起伏度均小于DEM模型对应的特征值,而地形粗糙度、二维和三维分形维数以及广义分形维数和多重分形谱值的范围等均大于DEM对应的特征值.所有尺度下,球体网格模型表面的二维分形维数均大于2,而对应DEM的二维分形维数均小于2,但两种模型的三维分形维数均小于3.研究表明,DEM与球体网格模型在计算地形参数时均具有尺度效应,所有参数值随着剖分层次/数据分辨率的提高而增加,但增加的趋势不尽相同;两种模型在表达地形多尺度特征时具有良好的一致性;球体网格在大区域地形无缝可视化和地形参数提取精度方面具有一定优势.该研究可为流域生态环境监测以及流域分布式水文模型构建等提供科学参考.

In order to extract watershed-related topographic parameters and analyze the tendency and regularity of watershed topographical features with metric scales,a method for constructing multi-level three dimensional geographical scenes of the Yangtze River Basin is introduced by using spherical geodesic octree grid(SGOG)and global shared DEM,respectively.The experiments show that the upper and lower surface areas and topographic relief of the spherical grid model at the same scale are smaller than the corresponding eigenvalues of DEM.And the surface roughness,2 D and 3 D fractal dimensions,and the ranges of general fractal dimensions and multifractal spectral values are larger than the corresponding eigenvalues of DEM.The 2 D fractal dimension of the sphere mesh model is greater than 2 at all scales,while the fractal dimension of the corresponding DEM model is less than 2,but the 3 D fractal dimension of both models is less than 3.Results prove that both DEM and spherical mesh models have scale effects in calculating terrain parameters,and all parameter values increase with the increasing level of profile or data resolution,but the increasing trend is different.Both models have good consistency in expressing the multi-scale features of terrain.They also prove the satisfactory for seamless visualization of large-area terrain by using the sphere grid model,and it has certain advantages in accuracy of terrain parameter extraction.The proposed method in this research can provide scientific reference for watershed ecological and environmental monitoring and the construction of distributed hydrological models in the basin.