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Nonstationarity of the Mean and Unbiased Variogram Estimation: Extension of the Weighted Least-Squares Method 总被引：1，自引：0，他引：1
When concerned with spatial data, it is not unusual to observe a nonstationarity of the mean. This nonstationarity may be modeled through linear models and the fitting of variograms or covariance functions performed on residuals. Although it usually is accepted by authors that a bias is present if residuals are used, its importance is rarely assessed. In this paper, an expression of the variogram and the covariance function is developed to determine the expected bias. It is shown that the magnitude of the bias depends on the sampling configuration, the importance of the dependence between observations, the number of parameters used to model the mean, and the number of data. The applications of the expression are twofold. The first one is to evaluate a priori the importance of the bias which is expected when a residuals-based variogram model is used for a given configuration and a hypothetical data dependence. The second one is to extend the weighted least-squares method to fit the variogram and to obtain an unbiased estimate of the variogram. Two case studies show that the bias can be negligible or larger than 20%. The residual-based sample variogram underestimates the total variance of the process but the nugget variance may be overestimated. 相似文献
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影响砂土液化的因素有很多,建立多指标的液化预测模型非常有必要。目前所有的多指标砂土液化预测模型,均默认选取的判别因子之间相互独立,不存在相关性,可能导致各判别因子之间存在信息叠加而发生误判。以唐山地震砂土液化的25个案例为样本,选取8个影响因素作为砂土液化预测的初始判别指标,首先采用主成分分析（PCA）对各判别指标进行分析,对存在相关性比较高的指标进行了降维处理。基于降维后的4个主成分换算得到新的样本数据,以18个案例为学习样本,建立主成分分析与距离判别分析（DDA）相结合的砂土液化预测模型。利用建立的预测模型对18个案例进行回判,结果全部正确。对其他7个案例的液化情况进行了预测,并与规范法、Seed方法、BP法、DDA法的判别结果进行分析比较,结果表明基于主成分分析与距离判别方法的砂土液化判别模型预测准确率为100%。将模型应用于工程实例,判别结果也与实际情况一致,表明该模型具有良好的预测功能,可在实际工程中应用。 相似文献
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介绍了利用隧道施工的位移量测信息来选择计算模型的原理和方法。应用实例表明，本文所提出的方法有较好的应用前景。 相似文献
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建立储层四维地质模型的新尝试——以冀东高尚堡沙三段储层模型的建立为例 总被引：2，自引：0，他引：2
油田注水开发过程中，储层物性、微观孔隙结构和非均质性都会发生动态变化。建立反映储层性质动态变化的四维地质模型对于深化高含水期油田地质特征的认识、预测剩余油的分布规律、提高油田开发效果具有十分重要的地质意义。论文立足于油田开发过程中储层的动态变化，以冀东高尚堡沙三段储层建模为例，综合不同开发阶段的井网及相应的取心、测井和实验测试资料，研究注水过程中储层参数的变化规律，应用随机建模方法建立了不同开发阶段的储层三维地质模型，对储层四维地质模型的建立进行了有益的尝试，并在油田的实际应用中取得了较好的效果。 相似文献
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In petroleum exploration and production, it is essential to have good estimations of the uncertainties on the reserves. Uncertainties
on the velocity model used during the data processing are of major importance in this estimation. The generation of several
velocity fields gives access to a quantified estimation of the uncertainties due to the velocity model inversion. The use
of statistical methods helps in generating several important, equiprobable velocity fields, matching all the available velocity
information. This paper presents an efficient simulation algorithm to generate instantaneous velocity fields, constrained
by the distribution of values measured at the wells, and calibrated by the stacking velocities, taken as root-mean-square
velocities. The simulations also match the covariance model given for the instantaneous velocity fields. The method is developed
in a simple one-layer case with constant velocity, and then extended to more realistic situations. Finally, a real data application
is shown, using data provided by ENI–Agip Division, and the efficiency of the proposed simulation method is discussed. 相似文献
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The simulation of flow in porous and fibrous permeable media is of high importance in many scientific and industrial applications. Although the finite element models at the representative elementary volume scales are used to solve a huge amount of scientific and engineering problems, they are hardly used to efficiently simulate pore-fluid flow problems at the particle scales. This encourages the development of numerical models to match the needs of such studies. In this paper, we propose a new Gray Lattice Boltzmann numerical model for simulating fluid flow in permeable media. Unlike most previous models, our proposed model has the ability to simulate multi-layers and space-variable permeability while preserving the continuity of the macroscopic velocity field. The model is verified with the available analytical solutions and a derived analytical expression for the case of variable porosity. In addition, we examine the importance of introducing a transition layer with a defined porosity function near the boundaries and interfaces. If this layer exists in practice, then the numerical results reveal that it cannot be neglected, and its impact is significant on the obtained velocity distribution. Finally, in the light of the obtained results, we can state that the proposed model has great potential to simulate complex and heterogeneous media with smoothness and accuracy, so that it may enrich the research content of the emerging computational geosciences. 相似文献
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文中介绍了断裂带地球化学深穿透理论与技术方法,并结合钾盐找矿实践,对相关技术方法的应用进行了探讨。断裂带地球化学深穿透技术包括地表测线、稀有气体同位素示踪和钾盐深度预测模型,笔者的主要思路是通过地表元素异常来捕捉可能来自深部的物源信息,预测大概的找钾靶区和深度,降低找矿成本。沿垂直于构造断裂带的方向采集地表沉积物、水样,分析其化学元素含量或比值,可以有效识别地球化学异常点;通过分析沿断裂带上升的卤水中逸出的稀有气体(氦、氩、氖等)同位素组成,可以判别气体的来源和断裂的深度,从而辅助判别卤水来源和深度;通过文章给出的一系列地球化学指标和方法,可以识别异常、综合判别卤水或盐类物质来源和深度,灰色模型和异常判别程序的编制可以大大缩短运算和判别时间。上述方法在实际工作中取得了较好的效果,在今后研究和实践中可以进一步提高和完善。 相似文献
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Frits Agterberg 《Mathematical Geology》2007,39(1):1-25
This paper is concerned with the lognormal, and its logbinomial approximation, in connection with a three-parameter version
of the model of de Wijs. The three parameters are: overall average element concentration value (ξ), dispersion index (d), and apparent number of subdivisions of the environment (N). Multifractal theory produces new methods for estimating the parameters of this model. In practical applications, the frequency
distribution of element concentration values for small rock samples is related to self-similar spatial variability patterns
of the element in large regions or segments of the Earth's crust. The approach is illustrated by application to spatial variability
of gold and arsenic in glacial till samples from southern Saskatchewan. It is shown that for these two elements the model
of de Wijs is satisfied on a regional scale but degree of dispersion decreases rapidly toward the local, sample-size scale.
Thus the apparent number of subdivisions (N) is considerably less than would be expected if degree of dispersion were to extend from regional to local scale. A random-cut
variant of the model of de Wijs produces an empirical frequency distribution of relative element concentration values that
can be related to random dispersion index 相似文献
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珍珠岩为一种酸性火山玻璃熔岩,配用不同胶结剂可制成多种珍珠岩制品,具有重量轻、耐腐蚀、隔音好、不燃烧等性能,广泛应用于建筑、化工及国防等领域。辽西地区珍珠岩是辽宁乃至全国重要产地之一,因此研究该地区珍珠岩矿床成因及成矿模式,具有重要的现实意义。在充分收集该地区珍珠岩矿床地质特征基础上,结合前人的研究成果,总结了矿床的时空分布规律,分析了矿床成因,构建了成矿模式。结果表明,辽西地区具有较好的珍珠岩成矿环境条件,需进一步开展矿产资源评价工作。 相似文献
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基于水平集法的基本思想,讨论了含有不同类型包裹体分布的岩石的二维和三维有限元建模方法。对于二维有限元模型的建立,考虑了以椭圆形为例的规则包裹体的周期分布、位置及包裹体大小均随机变化的多种情况。建议了包裹体和基岩之间界面的材料特性过渡处理方法。同时给出了含有非规则形状包裹体的建模方法。对于三维有限元模型的建立,则考虑了以任意大小椭球体为例的包裹体分布情况。该种建模方法的优点是对于不同的含有任意分布的包裹体的岩石试件,均可以采用相同的有限元网格,即,材料特性的变化不受有限元网格的制约。该法缺点是增加了计算资源。最后结合基于弥散裂缝模型的水力压裂数值计算方法,模拟了含有不同包裹体分布的岩石试件的水力压裂传播特点。 相似文献
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雨量站网布设会影响径流模拟精度,研究不同雨量站密度和空间分布的径流响应规律对提高径流模拟精度和减小不确定性具有重要意义。应用新安江模型和HBV（Hydrologiska Fyrans Vattenbalans）模型,以湘江流域为研究对象,采用贝叶斯方法比较分析在不同雨量站密度及空间分布下径流模拟的不确定性。结果表明:增加雨量站密度可以降低面雨量的估计误差,使模型在不同的雨量站空间分布下具有较高的模拟精度;通过优化雨量站空间分布,可以减小雨量站网布设导致的模型不确定性,从而提高径流模拟精度;在相同的降雨输入和参数采样方法下,新安江模型和HBV模型对降雨输入导致的不确定性响应规律具有相似性,但是本研究结果显示在湘江流域新安江模型的模拟精度更高,而HBV模型的不确定性更大。 相似文献
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In petroleum exploration and production, it is important to have good estimations of the uncertainties on the reserves. Uncertainties
in the velocity model used during the data processing are of major importance in this estimation. The use of geo-statistical
tools can help in dealing with these uncertainties. Up to now, a strong limitation has been the inability to properly merge
velocity functions measured in the wells with seismic velocity data. This was due to the different “supports” among the two,
i.e. the well velocity may be regarded as a direct measurement of the instantaneous velocity field, while the seismic velocities
correspond to an “average along the travelled paths” of this field. The problem is that, apart from the well positions, the
instantaneous velocity field is out of reach. Luckily, for many practical applications, it is enough to know just its covariance
model. However, no algorithmic method is available in the literature to yield the covariance model, and geologists are forced
to use arbitrary distributions. The present paper proposes an original method to obtain a good estimate of this covariance
model, using widely available information, mainly seismic stacking velocities. This method was first developed in a simple
one-layer case with constant velocity, and then extended to more realistic situations. Finally, a real data application is
performed, which highlights the robustness of the resulting estimation. 相似文献
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基于GIS的北京市延庆县地质灾害易发性区域划分 总被引：3，自引：0，他引：3
随着灾害科学研究的深入，区域地质灾害已成为其重要的研究领域。文章利用遥感技术及GPS工具获取地质灾害的特征信息，在对地质灾害的成因背景分析基础上，运用GIS空间分析功能和地质灾害危险性评价、评估理论构建了地质灾害发育度模型。以北京市延庆县为实验区，采用ArcEngine＆．NET进行易发性分区程序的编写，计算研究区域内单元网格的发育度值。为了克服调查数据的局限性和人为因素，在计算发育度时引入修正系数，从延庆县DEM数据中提取单元格网内的地形坡度值，根据坡度值区间确定修正系数。将发育度计算结果按照一定规律、原则聚类。进行地质灾害易发性区域划分，取得了与实际情况较为一致的结果。基于“3S”技术及灾害地质条件，采用地质灾害发育度模型，可以较好地用于区域地质灾害易发性区域的划分，并能为防灾、减灾提供重要信息。 相似文献
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On the modelling of two-dimensional aeolian dunes 总被引：4，自引：0，他引：4
J. M. T. STAM 《Sedimentology》1997,44(1):127-141
In this study the modelling of aeolian dunes is treated from the background of the physical processes that form them. The paper concentrates on two-dimensional modelling, which can be applied to transverse and barchan dunes. The basic assumptions and equations are discussed and three models are presented: (a) a kinematic model which is based on a linear variation of the sediment transport with the topographic height; (b) an analytical model based on a boundary-layer model of the wind velocity and Bagnold's linearized sediment transport formula; (c) a generalization of this analytical model in a computer program which includes a simple routine for simulating the redistribution of sediment through avalanching. The relative importance of the simplifications is considered and indications are given for the practical applications of these three models in field studies. 相似文献
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The continental area of Portugal is now entirely covered by a soil geochemical survey (1 site/135 km2), taking as the sampling media topsoils (upper mineral horizons, A) and organic horizons (humus, O). Standard methods for sampling, sample preparation and analysis were used in order to achieve high quality and consistent data. Each sample was analyzed for 32 chemical elements, pH, electrical conductivity and organic matter content.The main purpose of the survey was to obtain baseline levels for various chemical elements. The compilation of all data (nearly 45,000 individual data) in an organised way, led to the production of the first Soil Geochemical Atlas of Portugal. In this Atlas it is possible to find for each chemical element a set of information statistics (basic statistical parameters, boxplots, cumulative frequency curves, etc.), maps of spatial distribution, among other information of geochemical and environmental interest. This paper gives an overview of the Soil Atlas and examples of application. The data were used to calculate reference values for 9 elements of environmental importance and to obtain empirical formulae allowing the estimation of elements in the coarse fraction of soils (< 2.00 mm) from known concentration in a finer fraction (< 0.18 mm). 相似文献
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This paper aims to investigate the impact of sample size on geotechnical probabilistic model identification. First, the copula approach is presented to model the bivariate distribution of geotechnical parameters. Thereafter, the AIC scores are adopted to identify the best-fit marginal distribution and copula. Second, the variation of AIC scores because of small sample size is investigated using simulated data. Finally, the impact of the variation of AIC scores on identification of the best-fit marginal distribution and copula is examined. The minimum sample sizes for geotechnical data are also suggested to obtain a correct identification of the probabilistic models. The results indicate that the AIC scores estimated from a small sample exhibit large variation. The variation of the AIC scores has a significant impact on probabilistic model identification. The marginal distributions and copulas have a low percentage of correct identification when sample size is small. The percentages of correct identification for the marginal distributions and copulas increase with increasing sample size. The correlation coefficient between geotechnical parameters has a much larger impact on probabilistic model identification than the COV of geotechnical parameters. The suggested minimum sample sizes for geotechnical data are useful for guiding practical geotechnical site investigation. 相似文献
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在基于GIS技术的矿产资源评价工作中,矿产资源潜力评价的自动制图模型通常用来统计综合多源地学信息以便自动圈定成矿远景靶区。在本文中,笔者以人工智能研究领域中的一种不确定推理模型——确定性理论为基础,提出了一种新的矿产资源潜力评价的自动制图模型——合成有矿可信度模型。该模型可以根据研究区各种成矿有利和不利证据的空间分布图,统计生成对应于每一种证据的有矿可信度栅格图,然后,按照特定的有矿可信度合成规则,将所有的有矿可信度栅格图统计综合生成合成有矿可信度栅格图。以该图为依据,可以把研究区内合成有矿可信度相对较高的成矿远景区圈定出来。也可以生成研究区合成有矿可信度等值线图。应用该模型预测了新疆北部多拉纳萨依—阿舍勒地区的多金属成矿远景,并将预测结果与证据加权模型预测结果进行了比较,两种模型的预测结果基本相似,证明了该模型的有效性和实用性。 相似文献