玛纳斯河流域土壤斑块标度频度分形关系初探     

禹朴家  徐海量  乔木  安红燕  刘世薇 《中国沙漠》2011,30(3):729-734

 分形理论在研究不规则几何图形方面优越性显著。作者运用分形理论和景观生态学原理,在讨论了玛纳斯河流域土壤类型分布格局的基础上,对土壤图斑面积与斑块形状指数的标度-频度关系进行了定量分析。主要结果是:①玛纳斯河流域土壤类型多样性指数为2.834,最大斑块指数为8.885。两种景观指数值都较大,说明虽然流域内土壤类型的丰富度较高,但其土壤斑块却由少数几种土壤类型所控制。②玛纳斯河流域土壤斑块面积与斑块形状指数标度-频度双对数回归分析的相关系数均大于95%,其相关关系显著。③玛纳斯河流域土壤斑块面积与斑块形状指数的标度-频度分形关系是客观存在的,并不受统计所选的标度影响,具有标度不变性。  相似文献   

基于城市斑块的空间城市人口潜能模拟——以京津冀为例     

董南  王黎明  马明娟 《地球信息科学学报》2014,(3):402-410

城市潜能是城市空间相互作用的一个量化指标,用以表征区域内任一地点所受到的周围所有城市的作用合力。以城市人口规模作为潜能计算指标的城市潜能即为城市人口潜能。由于在地理信息系统中通常以点代表城市的空间位置,以点的属性字段存储城市人口数量,因此,城市人口潜能模拟最便捷的方法是建立基于城市点源数据的空间分析模型,但这种方法存在明显不足:(1)国家基础地理信息数据库中的城市点位经纬度绝大多数与现实中的城市人口质心不吻合;(2)多数城市通常都由空间上相互分离的多个城市用地斑块构成,城市辖区内部的斑块与斑块之间也存在相互作用。本文通过将独立的城市斑块作为基本空间分析单元来设计基于城市人口潜能的模拟技术方案,提出了斑块分层方法,构建了京津冀时间耗费栅格面,通过python建模技术,在ArcGIS平台上实现了对京津冀城市人口潜能的精细化数值模拟。  相似文献   

Quasi-geostrophic shallow-water vortex–patch equilibria and their stability     

Hanna Płotka  David G. Dritschel 《地球物理与天体物理流体动力学》2013,107(6):574-595

We examine the equilibrium form, properties, stability and nonlinear evolution of steadily-rotating simply-connected vortex patches in the single-layer quasi-geostrophic model of geophysical fluid dynamics. This model, valid for rotating shallow-water flow in the limit of small Rossby and Froude numbers, has an intrinsic length scale L _D called the “Rossby deformation length” relating the strength of the stratification to that of the background rotation. Here, we generate steadily-rotating vortex equilibria for a wide range of γ?=?L/L _D , where L is the typical horizontal length scale of the vortex. We vary both γ (over the range 0.02?≤?γ?≤?10) and the vortex aspect ratio λ (over the range 0?<?λ?<?1). We find two modes of instability arising at sufficiently small aspect ratio λ?<?λ _c (γ): an asymmetric (dominantly wave 3) mode at small γ (or large L _D ) and a symmetric (dominantly wave 4) mode at large γ (or small L _D ). At marginal stability, the asymmetric mode dominates for γ???3, while the symmetric mode dominates for γ???3. The nonlinear evolution of weakly-perturbed unstable equilibria results in major structural changes, in most cases producing two dominant vortex patches and thin, quasi-passive filaments. Overall, the nonlinear evolution can be classified into three principal types: (1) vacillations for a limited range of aspect ratios λ when 5?≤?γ?≤?6, (2) filamentation and a single-dominant vortex for γ???1, and (3) vortex splitting – asymmetric for 1???γ???4 and symmetric for γ???4.  相似文献   

Influence of landscape evolution on the distribution of floristic patterns in northern Amazonia revealed by δ13C data     

H. Zani  D. F. Rossetti  M. L. C. Cohen  L. C. R. Pessenda  E. H. Cremon 《第四纪科学杂志》2012,27(8):854-864

The Amazonian lowlands include large patches of open vegetation which contrast sharply with the rainforest, and the origin of these patches has been debated. This study focuses on a large area of open vegetation in northern Brazil, where δ¹³C and, in some instances, C/N analyses of the organic matter preserved in late Quaternary sediments were used to achieve floristic reconstructions over time. The main goal was to determine when the modern open vegetation started to develop in this area. The variability in δ¹³C data derived from nine cores ranges from ?32.2 to ?19.6‰, but with nearly 60% of data above ?26.5‰. The most enriched values were detected only in ecotone and open vegetated areas. The development of open vegetation communities was asynchronous, varying between estimated ages of 6400 and 3000 cal a BP. This suggests that the origin of the studied patches of open vegetation might be linked to sedimentary dynamics of a late Quaternary megafan system. As sedimentation ended, this vegetation type became established over the megafan surface. In addition, the data presented here show that the presence of C₄ plants must be used carefully as a proxy to interpret dry paleoclimatic episodes in Amazonian areas. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Characteristics of freshly deposited sand and finer sediments along an island-braided, gravel-bed river: The roles of water, wind and trees     

Angela M. Gurnell  Trevor D. Blackall  Geoffrey E. Petts 《Geomorphology》2008,99(1-4):254-269

Over the past two decades there has been a growing interest in the geomorphological mosaic along large floodplain rivers where channel dynamics are seen to drive habitat-patch creation and turnover and to contribute to high biological diversity. This has required a new perspective on fluvial geomorphology that focuses on biological scales of space and time. This study examines the spatial pattern of surface fine sediment accumulations along a reach of a large gravel-bed river, the Tagliamento River in NE Italy; an area with a moist Mediterranean climate and seasonal flow regime. The study investigates changes in sediment characteristics during the summer low-flow period between April and September. Focussing on five areas representing a gradient from open, bar-braided to wooded island-braided morphologies, the paper demonstrates the importance of riparian vegetation and aeolian–fluvial interactions.Significant contrasts in particle size distributions and organic content of freshly deposited sand and finer sediments were found between sampling areas, geomorphological settings, and sampling dates. In particular, wooded floodplain and established islands supported consistently finer sediment deposits than both open bar surfaces and the lee of pioneer islands, and in September significantly finer sediments were also found in deposits located in the lee of pioneer islands than on open bar surfaces. Overall, the September samples had a greater variability in particle size characteristics than those obtained from the same sites in April, with a general coarsening of the D₅ (φ) (i.e., the coarse tail of the particle size distribution). Also in September, crusts of fine sediment (30 μm < D₅₀ < 64 μm) had formed on the surface of some of the open bar and pioneer island deposits within the more open sampling areas along the study reach. These crusts possessed similar particle size characteristics to aeolian crusts found in more arid environments. They were significantly finer than April samples and September subcrust samples obtained from the same sites and had similar particle size characteristics to some samples taken from wooded floodplain, established island surfaces and the lee of pioneer islands that were not crusted.Local climatological and river level data confirm significant wind and rainfall events during a period of consistently low river levels between the April and September sampling periods. These support deflation, deposition and rain wash of finer sediment during the summer, with windblown sediments being deposited on bar surfaces and in the lee of pioneer islands where wood and young trees provide foci for accelerated sedimentation and island growth as well as on marginal floodplains and established islands. We conclude that along braided rivers in moist settings but with a distinct dry season, aeolian reworking of sediment deposits may have a more important role in driving habitat dynamics than previously considered.  相似文献   

Radio Tomography: A New Experimental Technique   总被引：2，自引：0，他引：2  

S. E. Pryse 《Surveys in Geophysics》2003,24(1):1-38

The technique of radio tomography has developed during the past fifteen years from a theoretical concept to an established experimental method, used for geophysical investigations ofsolar-terrestrial processes. It also has potential in the mapping and modelling of the ionised atmosphere for application to practical radio systems. The method involves measurement of the electron content of the ionosphere along a large number of intersecting satellite-to-receiver ray paths, with tomographic inversion of the data to give a two-dimensional image of the spatial distribution of plasma density in the region of ray-path intersection. The emphasis in this review is on experimental tomographic observations, which have highlighted the capabilities and potential of the technique. Examples are presented from the equatorial sector where the equatorial anomaly is a significant feature, the mid-latitude sector where radio propagation is often influenced by the presence of the main ionisation trough, and the auroral and polar regions where footprints of solar-terrestrial coupling processes are frequently to be seen.  相似文献   

Influence of livestock soil eutrophication on floral composition in the Pyrenees mountains     

S 《山地科学学报》2008,5(1):63-72

Livestock behaviour in the Pyrenees includes free grazing and a long resting period that provokes the accumulation of dung and urine in some places,so-called camping areas. The aims of this study were （i） to analyze any change in floral composition,and in nutritional and chemical contents of plants in a livestock camping area; and （ii） to relate the floral composition with soil chemical properties. In a linear transect,five sampling zones were established,from the centre of the camping area to the surrounding Nardus stricta-dominant pasture. The above ground plant biomass and the topsoil were sampled in each zone with 6 replicates per zone. Plant species were classified and weighed to calculate above ground biomass,nutritional and chemical contents,and Shannon diversity and evenness indices. Additionally,soils were sampled in two periods,at the beginning and at the end of grazing period. Soil available nutrients （nitrate,ammonium,phosphorus,potassium,calcium and magnesium）,total nitrogen,organic carbon and pH were measured.
Plant chemical contents （protein,lignin and others） were significantly related to the proportions of grasses,legumes and other plants; so,the protein content is positively correlated with legumes plant biomass while lignin content is negatively correlated with grasses. Both plant and soil nutrients increased linearly towards the centre of the camping area. However,the relationship among plant species richness,diversity and evenness relative to its position along the studied transect was bell-shaped. From the outskirts to the centre of the camping area,plants with low nutrient demand were progressively replaced by those with medium and high nutrients demand and by pioneers.
Nardus stricta-dominant pasture has low plant diversity and plant nutrient content as well as a poor soil nutrient availability. The presence of the camping area introduced patches with more soil nutrients and new species in the large spatial scale. However at a small spatial scale,the strong soil nutrien  相似文献   

基于“3S”技术的违法建筑及设施影像监测信息系统设计与实现     

王永乔 《测绘与空间地理信息》2011,34(3):71-73,77,80

随着“3S”技术发展的日臻完善,为城市和农村的违法建筑及设施的监测提供了强大的技术基础和物质保障.文章以”3S”技术为基础,设计了杭州市余杭区建筑及设施的影像监测综合管理信息系统,并阐述了系统设计的基本思路及流程,介绍了系统的功能和关键技术在实施过程中的应用.  相似文献   

利用矢量影像法进行土地利用变化自动检测   总被引：2，自引：0，他引：2  

王刚武 《测绘通报》2017,(7):55-60

为解决土地利用矢量图与遥感影像的变化检测问题,提出了一种基于类别的矢量图与遥感影像变化检测方法。在矢量图约束下,对遥感影像进行影像分割获取像斑;提取像斑在遥感影像上的直方图特征,采用G统计量度量像斑之间的特征距离;利用像斑与其他相同类别像斑之间的特征距离,构建单波段上像斑的类别异质度,自适应加权组合各波段上像斑的类别异质度构建像斑的类别异质度;依据最大熵方法获取各地物类别对应的异质度阈值,以类别为单位对各像斑进行变化判别,获取变化检测结果。在QuickBird遥感影像上的试验验证了本文方法的有效性,实现了矢量图与遥感影像的自动变化检测。  相似文献   

土地利用数据库综合中图斑拓扑关系的创建和一致性维护   总被引：5，自引：0，他引：5  

陈先伟  郭仁忠  闫浩文 《武汉大学学报(信息科学版)》2005,30(4):370-373

以LANDUSE-DAT文件为例，论述了土地利用地图综合中图斑多边形拓扑关系的特点、数据结构定义及生成方法，阐述了土地数据库综合过程中图斑拓扑关系一致性的维护方法。  相似文献