利用分形参数进行地貌定量分区研究——以鄂尔多斯块体及周边为例

STUDY ON THE GEOMORHOLOGIC ZONATION BY FRACTAL PARAMETERS——A CASE STUDY OF ORDOS BLOCK AND ITS SURROUNDING AREAS

地貌分区是地学研究的基础内容之一。传统的地貌分区大多是定性的划分,随着数字地形技术以及分形分析方法的成熟,利用分形参数进行定量化的地貌分区成为可能。本文利用水平分辨率为90m的SRTM数据,采用元分维模型,通过变差函数法计算了鄂尔多斯块体及周边地形的分形参数。在65×65,129×129以及257×257等3种尺度滑动窗口中得到的分形参数的特征表明了研究区地形分形特征的尺度不变性至少在2.97km到11.61 km范围内是存在的,而且分形参数分布具有明显的区域差异。结合地表分维值和截距值用K-Means非监督分类法进行综合地貌定量分区,所得结果与地貌类型有很好的吻合关系,每一地貌分区都具有特征的分形值组合。河套盆地和银川盆地是地表分维值高值区和截距值低值区,分维值主要为2.8～3.0,截距值主要为0～1;鄂尔多斯块体南部陕北黄土高原区地表分维值主要为2.5～2.7,截距值主要为2.5～3.5;吕梁山、贺兰山、乌拉山等山区也是截距值高值区,主要为2.5～3.5,但地表分维值较低,主要为2.4～2.6。鄂尔多斯块体北部库布齐、毛乌素等沙漠区与渭河、山西盆地带都是地表分维值低值区,地表分维值大部分低于2.5,但两区域的截距值差异明显。沙漠区地形起伏较缓,截距值主要为0～1.5,而渭河盆地和山西盆地带的截距值没有明显的优势范围。分形值组合所显示的分形特征与地质构造、地貌类型等具有明显的相关性。因此,利用分形参数进行地貌分区是一种可行的定量方法。

Geomorphologic zonation is one of the fundamental works in Geoscience, but it was mostly qualitative in the past. Several studies on the quantitative geomorphologic zonation have been done based on the terrain factors such as slope, aspect and relief in recent years, however, many problems are still unresolved. As the digital terrain technology and the fractal theory become more mature, it is possible to classify quantitatively landforms by such fractal parameters as the surface fractal dimension（D） and the ordinate-intercept（γ）. In this paper Ordos Block and its surrounding areas were chosen, and, based on the 90-m-resolution SRTM data, the variogram method and the cellular fractal model were adopted to calculate their fractal parameters in such three sizes of the moving windows as 65×65, 129×129 and 257×257. The results in these moving windows indicate together that the scale-invariance of the landforms of Ordos Block and its surrounding areas hold over at least from 2.97km to 11.61km, and the distributions of the fractal parameters are region-dependent apparently. The quantitative geomorphologic zonation by the fractal dimension and the ordinate-intercept comprehensively is achieved with the K-Means unsupervised classification. The resultant regions are consistent with the geomorphologic types and each zone has the characteristic fractal values. Hetao Basin and Yinchuan Basin are characterized by high surface fractal dimensions and low ordinate-intercepts（ D--2.8 -3.0 ,T = 0 - 1 ）in contrast to the mountainous areas including Luliang Mountain, Helan Mountains and Wulaer Mountains where low surface fractal dimensions and high ordinate-intercepts（ D = 2.4 - 2.6, T = 2.5 -3.5）are found. The other regions are defined by the following fractal parameters respectively： North Shaanxi Loess Plateau in the southern part of Ordos Block, D = 2.5 - 2.7 and T = 2.5 - 3.5 ; Kubuqi Desert and Mu Us Desert in the northern part of Ordos Block, D = 2.2 - 2.4 and T = 0 - 1 ; Shanxi Basin Belt and Weihe Basin, D = 2.2 - 2.4 and no predominant ordinate-intercept values. The comprehensive zonation result shows that the fractal feature is related with the geological structures and the geomorphologic types closely in each zone, it is therefore feasible to classify landforms quantitatively by fractal parameters.