三峡蓄水后典型河段分形维数的变化分析

针对三峡工程蓄水后下游河道河床表面形态的变化,采用分形维数对河床表面形态进行量化,并分析河道冲淤调整特点,对河床表面分形维数(BSD)的变化特点及物理意义进行探讨。结果表明,BSD与河床各个剖面形态之间的关系是整体与部分的关系,BSD能全面地反映床面形态的复杂程度。三峡蓄水后,宜昌-虎牙滩和宜都河段BSD明显增大,关洲河段增大幅度较小,而芦家河河段BSD值略有减小,同时,各河段BSD的变化可在一定程度上表征三峡蓄水后下游河道河床综合阻力的调整结果。可通过对各河段演变趋势的分析,来预测其BSD的变化,进而为分析其阻力和水位的变化趋势提供依据。     

河川径流遥感监测研究进展

河川径流参数是用于地表水资源评估、全球变化监测和生态环境保护的基础数据.现有的河川径流监测数据基于水文监测站点获取.近年来,受经济和政治原因的影响,全球水文监测站点在逐渐减少.随着全球变化研究对区域乃至全球水文监测数据需求的增加,监测站点有限及监测数据格式多样等问题逐渐凸显.过去15年,卫星遥感技术在河川径流监测领域的研究和应用实践,使上述问题的解决成为了可能.总结了河川径流遥感监测方法和技术研究进展,包括地基高低频雷达、航空航天雷达和多光谱卫星遥感监测3个方面;介绍了全球大型河川径流与湖泊水体动态监测重大应用成果及未来研究计划.指出在未来具有全天时、全天候,高时空分辨率,以及多水文要素探测能力遥感卫星发射之前,应充分利用遥感野外观测实验,完善河川径流监测技术方法,并综合应用已有高时空分辨率的多光谱和微波遥感数据,开展径流监测应用研究.     

矿床空间分布的分形研究及其找矿意义——以三江南段银铅锌矿床分布为例

矿床的空间分布规律对地质勘查和找矿工作具有指导作用,三江南段地区是我国重要的多金属成矿区带,因此在该地区使用现代数学理论来研究矿床的空间分布规律具有重要意义。本文在深入研究三江南段地区银铅锌成矿机理、成矿地质背景以及数盒子法(Box-counting method)的基础上采用近年来广泛使用的关联维数来研究该地区银铅锌矿床的空间分布规律。首先借助G IS技术量测了13个银铅锌矿床之间的距离,用不同的标度r及其对应的关联函数C(r)得到一点对序列(r,C(r)),然后通过在平面坐标下作出(lnr,lnC(r))的散点图,使用最小二乘法拟合直线来估算关联维数,整体拟合得到的关联维数D=0.875;分段拟合得到的关联维数D1=0.184、D2=1.00。研究结果表明三江南段地区的银铅锌矿床在空间上具有分形丛集分布的特征。依据本次研究,将该地区划分为三个银铅锌矿密集区,并就该地区找矿工作提出指导意见,同时也探讨了关联维数与盒子维数的差异。     

Spatial and temporal variations of coastlines in northern China (2000-2012)

This study examined the spatial distribution of the continent coastline in northern China using remote sensing and GIS techniques, and calculated the fractal dimension of the coastline by box-counting method, with a time span from 2000 to 2012. Moreover, we analyzed the characteristics of spatial-temporal changes in the coastline's length and fractal dimension, the relationship between the length change and fractal dimension change, and the driving forces of coastline changes in northern China. During the research period, the coastline of the study area increased by 637.95 km, at a rate of 53.16 km per year. On the regional level, the most significant change in coastline length was observed in Tianjin and Hebei. Temporally, the northern China coastline grew faster after 2008. The most dramatic growth was found between 2010 and 2011, with an increasing rate of 2.49% per year. The fractal dimension of the coastline in northern China was increasing during the research period, and the most dramatic increase occurred in Bohai Rim. There is a strong-positive linear relationship between the historical coastline length and fractal dimension (the correlation coefficient was 0.9962). Through statistical analysis of a large number of local coastline changes, it can be found that the increase (or decrease) of local coastline length will, in most cases, lead to the increase (or decrease) of the whole coastline fractal dimension. Civil-coastal engineering construction was the most important factor driving the coastline change in northern China. Port construction, fisheries facilities and salt factories were the top three construction activities. Compared to human activities, the influence of natural processes such as estuarine deposit and erosion were relatively small.     

Spatial structure of central places in Jilin Central Urban Agglomeration,Jilin Province,China

Using the radius of gyration from fractal theory, this paper describes the calculation of fractal dimensions for the four tiers of central places in the Jilin Central Urban Agglomeration(JCUA), Jilin Province, China and the structural characteristics of each tier: 1) the 1st tier central place, Changchun Proper(not including Shuangyang District), provides the most service functions and has the most stable primate position; 2) the 2nd tier central places, Jilin Proper, Siping Proper, Liaoyuan Proper and Songyuan Proper have unclear statuses and do not provide certain functions; 3) the 3rd tier central places comprise 23 county-level cities, counties and urban districts(including Shuangyang District of Changchun), exhibiting a dense spatial structure that agrees with theory; 4) the 4th tier contains the largest number of central places(248 designated towns), but they are loosely distributed. In this study, a spatial image of the JCUA was created, based on vectorized data of the urban settlement distribution, which was then modified and abstracted to create a hexagonal network covering the JCUA. Compared to the traditional central place model, the modified spatial image conforms to the K = 3 principle. In reality, however, the growth of some 3rd tier central places should be increased with the cities being upgraded to the 2nd tier so as to overcome that tier′s functional deficiency. The loose distribution in the 4th tier should also be changed. This apparent anomaly can be explained by the fact that the classic hexagon model used to describe the way market areas layout does not exist in the real world. However, this should not be viewed as an obstacle to using central place theory. If its assumptions are properly applied, it can still assist research into the spatial structure of regions.     

基于特征选取及广义傅立叶分形的SAR图像海洋溢油检测算法

针对海上溢油SAR图像中油膜与类油膜的识别问题,提出了一种结合傅立叶分形与特征提取的检测算法。由于分形特征可以具有无穷多的细节,并在不同的研究尺度存在自仿射特性。这与油膜及类油膜表面的几何形貌特征非常吻合。该算法通过计算样本的傅立叶分形特征,组成油膜与类油膜的特征空间。然后,应用基于差分进化的特征选取方法将利于分类的重要特征值筛选出来。再利用重要特征值对原有样本进行分类。实验表明,经特征选取的分形特征向量能够以100%的准确率将两类样本区分开。该算法在选取重要特征的同时实现了对高维特征空间降维的目的,该思想可以应用于其他的基于高维特征的识别系统中,具有普遍的适用性。     

Selection of Less Biased Threshold Angles for SAM Classification Using the Real Value–Area Fractal Technique

The accuracy of classification of the Spectral Angle Mapping (SAM) is warranted by choosing the appropriate threshold angles, which are normally defined by the user. Trial‐and‐error and statistical methods are commonly applied to determine threshold angles. In this paper, we discuss a real value–area (RV–A) technique based on the established concentration–area (C–A) fractal model to determine less biased threshold angles for SAM classification of multispectral images. Short wave infrared (SWIR) bands of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images were used over and around the Sar Cheshmeh porphyry Cu deposit and Seridune porphyry Cu prospect. Reference spectra from the known hydrothermal alteration zones in each study area were chosen for producing respective rule images. Segmentation of each rule image resulted in a RV–A curve. Hydrothermal alteration mapping based on threshold values of each RV–A curve showed that the first break in each curve is practical for selection of optimum threshold angles. The hydrothermal alteration maps of the study areas were evaluated by field and laboratory studies including X–ray diffraction analysis, spectral analysis, and thin section study of rock samples. The accuracy of the SAM classification was evaluated by using an error matrix. Overall accuracies of 80.62% and 75.45% were acquired in the Sar Cheshmeh and Seridune areas, respectively. We also used different threshold angles obtained by some statistical techniques to evaluate the efficiency of the proposed RV–A technique. Threshold angles provided by statistical techniques could not enhance the hydrothermal alteration zones around the known deposits, as good as threshold angles obtained by the RV–A technique. Since no arbitrary parameter is defined by the user in the application of the RV‐A technique, its application prevents introduction of human bias to the selection of optimum threshold angle for SAM classification.     

基于Budyko假设和分形理论的水沙变化归因识别——以北洛河流域为例

全球气候变化及人类活动深刻影响了区域水文过程,进行水沙变化归因识别对流域生态保护和高质量发展尤为重要。基于Budyko假设和分形理论,采用弹性系数法,对北洛河流域上（丘陵沟壑区）、中（土石山林—高塬沟壑区）、下游（渭北旱塬农区）3种不同地貌和植被类型区1959—2019年的水、沙通量变化进行归因分析。结果表明,北洛河上、中、下游径流量均显著减少,由20世纪60年代的35 mm、32 mm、34 mm,减少到21世纪10年代的19 mm、24 mm、6 mm,60 a减少率分别为0.3 mm a^-1、0.2 mm a^-1、0.4 mm a^-1。上游输沙量极显著减少,中游降低趋势不显著,下游显著减少,由20世纪60年代的99×10⁶ t、8×10⁶ t、3×10⁶ t,减少到21世纪10年代的10×10⁶ t、3×10⁶ t、0.3×10⁶ t,60 a减少率分别为1.5×10⁶ t a^-1、0.04×10⁶ t a^-1、0.1×10⁶ t a^-1。20世纪70年代以来,上游径流变化逐渐受人类活动影响,且影响程度逐渐增强,21世纪10年代人类活动贡献率达66.3%;气候变化是中游径流变化的主控因子,21世纪10年代降雨和潜在蒸散发的贡献率分别为77.0%和20.2%;下游径流减少主要为人类活动影响,21世纪10年代其贡献率为64.3%。对比20世纪60年代流域输沙量变化始终受人类活动主导,21世纪10年代人类活动对上、中、下游输沙量减少的贡献率分别为80.7%、59.2%和92.7%。上游人类活动对输沙量减少的贡献中,退耕还林等沟坡措施和沟道工程措施分别为39.0%、42.7%,中、下游人类活动贡献的估算结果反映出高植被覆盖区和农区汲水灌溉对区域水、沙的影响特征。     

线状空间数据传输的几何相似性度量算法与实验分析

 同一地物在不同比例尺或者不同来源的地图上通常存在着相似性,对于图形几何形似性度量方法的研究有利于地图编制、查询、匹配、更新。线状地物要素在地图中占有很大的比例,因此,本文以线状空间目标为例,在前人的基础上给出了线状空间数据的几何图形相似性度量模型:(1)以差异距离作为相似性特征的位置相似度;(2)以分形维数作为相似性特征的形状相似度;(3)以长度或者周长作为相似性特征的大小相似度。相对于(3)大小相似度而言,(1)位置相似度、(2)形状相似度综合考虑了几何图形整体统计的方法和局部几何特征结构。完成多尺度传输的线状空间数据几何相似性度量实验,并对数据传输量与几何相似性度量方法进行比较,实验结果表明:基于广义Hausdorff距离模型的中位数Hausdorff距离的位置相似性对于空间数据渐进性传输具有稳定性和可行性。最后,总结了本文的研究成果,并展望了该方向进一步研究的若干问题。     

The method of a two-point conditional column density for estimating the fractal dimension of the distribution of galaxies

We suggest a new method for estimating the fractal dimension of the spatial distribution of galaxies: the method of selected cylinders. We show the capabilities of this method by constructing a two-point conditional column density for galaxies with known redshifts from the LEDA database. The fractal dimension of a sample of LEDA and EDR SDSS galaxies has been estimated to be 2.1±0.1 for cylinder lengths of 200 Mpc. A major advantage of the suggested method is that it allows scales comparable to the catalog depth to be analyzed for galaxy surveys in the form of conical sectors and small fields in the sky.