时间序列异常值探测的Bayes方法及其在电离层VTEC数据处理中的应用   总被引：2，自引：0，他引：2  

归庆明  李涛  衡广辉 《武汉大学学报(信息科学版)》2011,(7):802-806

基于Bayes统计推断理论,提出了自回归模型中异常值定位的Bayes方法;在正态-Gamma先验分布下,分别基于均值漂移模型和方差膨胀模型,提出了后验概率的计算方法,并运用Bayes方法估计了异常扰动;最后将该方法应用到电离层VTEC数据处理的建模中,比较模型修正前后预报的结果,验证了新方法的有效性。  相似文献   

960MHz至1610MHz频段全球业务及GNSS频谱兼容分析     

卢鋆  杨强文 《武汉大学学报(信息科学版)》2011,36(10):1172-1176

研究了960 MHZ~1 610 MHz频段内GNSS系统之间以及其他业务和GNSS之间的兼容环境。以北斗卫星导航系统为例,利用抗干扰系数计算了GPS、GALILEO对北斗系统的干扰;其次,依据ITU规定的发射机频率容限和可允许的最大杂散发射或杂散域发射功率电平等约束条件,定义了其他业务对北斗系统的潜在干扰,创新性地利...  相似文献   

基于ADTD系统监测的雷电流幅值累积概率特征分析   总被引：2，自引：0，他引：2  

李家启  王劲松  申双和  李博  陈宏  林涛 《气象》2011,37(2):226-231

雷电流幅值累积概率分布是雷电活动规律的重要指标.通过对ADTD闪电定位系统监测的雷电资料的数理统计分析,采用IEEE工作组和

推荐的公式对比分析了重庆地区的雷电流幅值累积概率的拟合效果.结果表明:雷电流幅值累积概率分布特征随极性存在显著差异,雷击大地密度随雷电流幅值不同而差异较大;同时,采用I...  相似文献   

正确认识和对待天气气候预报的不确定性   总被引：3，自引：2，他引：1  

王东海  杜钧  柳崇健 《气象》2011,37(4):385-391

美国国家科学发展的指导机构同家研究顾问委员会(NRC)不久前发表了一份关于天气、气候和水文预报的不确定性的凋研报告.报告强调了预报不确定性信息在终端用户应用气象预报作决策中的重要性,同时指出一个预报如果没有定量地估计它的不确定性,那么该预报是不完全的.该报告中文版的出版工作正在进行中,现藉此机会向读者综合地介绍一下预报不确定性的问题.文中首先讨论了预报不确定性的缘由以及应该如何来科学地对待它.然后介绍了要应对这一问题所要进行的一些具体措施和策略.最后,简要地介绍了美国气象界为此所做的一些努力和计划以供参考.通过上述讨论和介绍,希望引起更多的人对预报不确定性问题的重视并科学应对以更好地服务社会.  相似文献   

Regionalization of low flows based on Canonical Correlation Analysis   总被引：2，自引：0，他引：2  

George TsakirisIoannis Nalbantis  George Cavadias 《Advances in water resources》2011,34(7):865-872

Regional analysis of low-flow statistics is a critical step in solving water resources management problems related to the requirements of the Water Framework Directive. Important element in this analysis is the determination of homogeneous sub-regions based on physiographic characteristics of the corresponding basin. The purpose of this paper is to investigate the use of the canonical correlation method for partitioning the set of drainage basins of a region into a number of homogeneous sub-regions and determining the relations between the physiographic and low-flow statistics of the basins of each sub-region. The method is also proposed to be used for classifying an ungauged basin in a sub-region of gauged basins.  相似文献   

A multiple-point statistics algorithm for 3D pore space reconstruction from 2D images   总被引：1，自引：0，他引：1  

Alireza HajizadehAliakbar Safekordi  Farhad A. Farhadpour 《Advances in water resources》2011,34(10):1256-1267

Fluid flow behavior in a porous medium is a function of the geometry and topology of its pore space. The construction of a three dimensional pore space model of a porous medium is therefore an important first step in characterizing the medium and predicting its flow properties. A stochastic technique for reconstruction of the 3D pore structure of unstructured random porous media from a 2D thin section training image is presented. The proposed technique relies on successive 2D multiple point statistics simulations coupled to a multi-scale conditioning data extraction procedure. The Single Normal Equation Simulation Algorithm (SNESIM), originally developed as a tool for reproduction of long-range, curvilinear features of geological structures, serves as the simulation engine. Various validating criteria such as marginal distributions of pore and grain, directional variograms, multiple-point connectivity curves, single phase effective permeability and two phase relative permeability calculations are used to analyze the results. The method is tested on a sample of Berea sandstone for which a 3D micro-CT scanning image is available. The results confirm that the equi-probable 3D realizations obtained preserve the typical patterns of the pore space that exist in thin sections, reproduce the long-range connectivities, capture the characteristics of anisotropy in both horizontal and vertical directions and have single and two phase flow characteristics consistent with those of the measured 3D micro-CT image.  相似文献   

Compositional changes in sigmoidal carbonate clinoforms (Late Tithonian,eastern Sardinia,Italy): insights from quantitative microfacies analyses     

ALESSANDRO LANFRANCHI  FABRIZIO BERRA  FLAVIO JADOUL 《Sedimentology》2011,58(7):2039-2060

Quantitative analysis of sediment composition was performed on a kilometre wide section of Upper Tithonian low relief (up to 70 m), gently inclined (3° to 15°), sigmoidal carbonate clinoforms (eastern Sardinia) to identify changes in sediment composition along the slope and across the studied succession. These changes may reflect modifications of the carbonate factory and of processes responsible for sediment transport. Point‐count analysis of carbonate microfacies, Q‐mode/R‐mode cluster analysis and Spearman’s rank provided a composition‐based classification of microfacies and highlighted relationships among sediment components. The studied clinoforms are mainly composed of non‐skeletal grains (70%), such as peloids and lithoclasts, together with micrite and cements and only a limited contribution from coated grains (2%). Among skeletal grains (28%), the greatest contribution derives from a coral–stromatoporoid–encruster reef that provided 15% of the components. Crinoids, brachiopods and other along‐slope thriving biota provided nearly 5% of the allochems, whilst fragments of molluscs (gastropods, bivalves and diceratids) from the backreef sourced another 2%. The contribution of platform interior biota is negligible (1%). The association of composition‐based facies varies along the slope. The upper slope beds consist of coral‐stromatoporoid grainstone to rudstone; the middle slope deposits are dominated by encruster‐lithoclast grainstone and packstone. At the lower slope, peloidal lithoclastic packstone as well as brachiopod–crinoidal wackestone prevail. Also the association of skeletal grains changes along the slope. The encruster–frame builder association typifies the upper slope whilst encrusters characterize the middle slope sediments. In the lower slope encrusters are equally represented as the brachiopod–crinoid association. Along‐slope compositional changes evidence a scarce downslope transport of frame builders and a progressive enrichment in along‐slope thriving biota. Quantitative analysis of microfacies allowed the sigmoidal clinoforms to be grouped into six sets. Each set gathers sigmoids with a similar sediment composition. Coated grains are dominant in the first set whilst they are lacking in the overlying sets reflecting a change in the carbonate factory. Other major compositional changes among the sets concern the relative amounts of peloids, micrite, frame builders (corals and stromatoporoids) and encrusters. The contribution of peloids varies inversely to that of cements and micrite as evidenced in the third and fifth sets which, respectively, record the highest occurrence of peloids or cement and micrite. Variations in the amount of frame builders and encrusters are instead non‐linear. High percentages of both frame builders and encrusters, as recorded in the second and fifth sets, are related to low amounts of peloids and lithoclasts that probably reflect episodes of reduced background sedimentation. This study demonstrates that quantitative analysis of carbonate microfacies represents a powerful tool that can improve the reconstruction of the stacking pattern in carbonate slope successions both in outcrop and in subsurface settings.  相似文献   

基于点估计法的黄土边坡可靠度研究   总被引：1，自引：0，他引：1  

张亚国  张波  李萍  李同录 《工程地质学报》2011,19(4):615-619

在不同的黄土地区选取4个工点的典型路堑高边坡,基于点估计理论和有限元强度折减法计算边坡可靠指标。结果表明:工点2的稳定系数虽达到1.46,却有19.2%的失效概率; 工点1和4的坡型、地层岩性及层厚等工况较接近,失效概率差值达29.8%,参数变异性是造成其差异的主要原因。用点估计法计算边坡可靠度,并采用可靠度理论分析黄土边坡稳定性,能较好的解决土性参数离散性对边坡稳定性评价的影响。  相似文献   

观音岩水电站坝址区右岸岩体溶蚀发育机理研究   总被引：1，自引：0，他引：1  

王锦国  周志芳  陈松峰 《工程地质学报》2011,19(3):409-416

观音岩水电站位于金沙江上游,坝型初拟混凝土重力坝和心墙堆石坝组合坝.坝址区分布有侏罗系中蛇店组(J2s)地层,岩性主要为钙质铁质胶结的砾岩、石英砂岩,其中砾石成分以泥晶灰岩和生物灰岩为主.在地下水作用下砾岩钙质溶蚀形成规模较大的囊状空腔或孔洞,砂岩则表现为钙质胶结物流失溶蚀呈砂土状或砂糖状,对坝基稳定性造成了一定的影响...  相似文献   

非一致性水文频率分析的研究进展   总被引：8，自引：0，他引：8  

梁忠民  胡义明  王军 《水科学进展》2011,22(6):864-871

水文频率分析计算需满足独立随机同分布假设,其中同分布是指水文样本在过去、现在和未来均服从同一总体分布,即样本应具有一致性。然而,由于气候变化及人类活动的影响,使得一致性的假设受到挑战,因此变化环境下传统频率计算方法获得的设计结果,其可靠性受到质疑。为此,探索适应非一致性极值系列的频率分析方法已显得非常重要。总结介绍国内外关于非一致性水文频率分析的一些代表性研究成果,主要集中在以下两方面:一是基于还原/还现途径;二是基于非一致性极值系列直接进行水文频率分析途径。最后对进一步值得研究的问题进行了展望。  相似文献