Hierarchical decomposition of variance with applications in environmental mapping based on satellite images     

Ferenc Csillag  Sándor Kabos 《Mathematical Geology》1996,28(4):385-405

A quadtree-based image segmentation procedure (HQ) is presented to map complex environmental conditions. It applies a hierarchical nested analysis of variance within the framework of multiresolution wavelet approximation. The procedure leads to an optimal solution for determining mapping units based on spatial variability with constraints on the arrangement and shape of the units. Linkages to geostatisiics are pointed out, but the HQ decomposition algorithm does not require any homogeneity criteria. The computer implementation can be parameterized by either the number of required mapping units or the maximum within-unit variance, or it can provide a spectrum of significances of nested ANOVA. The detailed mathematical background and methodology is illustrated by a salt-affected grassland mapping study (Hortobágy, Hungary), where heterogeneous environmental characteristics have been sampled and predicted based on remotely sensed images using these principles.  相似文献   

CSU－RAMS模式在区域气侯模拟中的应用   总被引：1，自引：0，他引：1  

万齐林  施永年 《热带气象学报》1996,(2)

将ＣＳＵ－ＲＡＭＳ（中尺度）数值模式改造成“区域气候数值模式”以及进行区域气候数值模拟的试验研究。说明将有限区域中尺度数值模式与ＧＣＭ模式嵌套应用到区域气候数值模拟研究上能够取得有意义的结果。它能在一定程度上改善ＧＣＭ模式的不足。可以更为细致地描述大气环流的变化特征,是了解区域气候变化的有效方法之一。  相似文献   

Weak-contrast approximation of the elastic scattering matrix in anisotropic media     

Bjørn Ursin  Geir U. Haugen 《Pure and Applied Geophysics》1996,148(3-4):685-714

The plane-wave reflection and transmission coefficients at a plane interface between two anisotropic media constitute the elements of the elastic scattering matrix. For a 1-D anisotropic medium the eigenvector decomposition of the system matrix of the transformed elasto-dynamic equations is used to derive a general expression for the scattering matrix. Depending on the normalization of the eigenvectors, the expressions give scattering coefficients for amplitudes or for vertical energy flux.Computing the vertical slownesses and the corresponding polarizations, the eigenvector matrix and its inverse can be found. We give a simple formula for the inverse, regardless of the normalization of the eigenvectors. When the eigenvectors are normalized with respect to amplitudes of displacement (or velocity), the calculation of the scattering matrix for amplitudes is simplified.When the relative changes in all parameters are small, a weak-contrast approximation of the scattering matrix, based on the exactly determined polarization vectors in an average medium, is obtained. The same approximation is also derived directly from the transformed elasto-dynamic equations for a smooth vertically inhomogeneous medium, proving the consistency of the approximation.For monoclinic media, with the mirror symmetry plane parallel to the interface, the approximative scattering matrix is given in terms of analytic expressions for the non-normalized eigenvectors and vertical slownesses. For transversely isotropic media with a vertical axis of symmetry (VTI) and isotropic media, explicit solutions for the weak-contrast approximations of the scattering matrices have been obtained. The scattering matrix for amplitudes for isotropic media is well known. The scattering matrix for vertical energy flux may have applications in AVO analysis and inversion due to the reciprocity of the reflection coefficients for converted waves.Numerical examples for monoclinic and VTI media provide good agreement between the approximative and the exact reflection matrices. It is, however, expected that the approximations cannot be used when the symmetry properties of the two media are very different. This is because the approximation relies on a small relative contrast between the eigenvectors in the two media.Presented at the Workshop Meeting on Seismic Waves in Laterally Inhomogeneous Media, Castle of Trest, Czech Republic, May 22–27, 1995.  相似文献   

地下水非稳定流的LTFAM算法     

王文科  李俊亭 《地球科学与环境学报》1993,(4)

渗流域内应用拉普拉斯变换(LT)建立相应的有限分析(FAM)方程,顾及渗流域内地下水流的初始条件和边界条件,可在LT空间构成一个封闭的以水头像函数为变量的线性方程组。将此方程组所得的解,通过Stehfest数值反演公式,可归化为时间域的解(水头)。由于时间t被隐含在数值方程内,从而克服了传统数值法按时段(△t)逐步迭代的缺陷,提高了计算效率,也为用嵌入法建立地下水流管理模型提供了一条捷径。  相似文献   

含煤层地质环境下地震波场的数值模拟   总被引：3，自引：2，他引：1  

潘冬明  杨顶辉 《地球物理学进展》1997,12(1):74-83

本文对含低速煤层地质环境下弹性波场多波多分量地震资料进行了二维数值模拟研究,对人工边界反射进行了有效处理,频散效应得到了有效的压制,对几种不同激发与观测排列方式下的弹性波资料进行了模型计算与分析。  相似文献   

Engineering geological studies and tunnel support design at Sulakyurt dam site, Turkey   总被引：2，自引：0，他引：2  

H. Basarir 《Engineering Geology》2006,86(4):225-237

This paper presents the results of engineering geological investigations and tunnel support design studies, carried out at the Sulakyurt dam site, northeast of Ankara, Turkey. The Sulakyurt dam will be used for flow control and water storage for irrigation projects. Studies were carried out both in the field and the laboratory. Field studies include engineering geological mapping, intensive discontinuity surveying, core drilling and sampling for laboratory testing. The diversion tunnel will be driven in rock mass, consisting of granite and diorite. Empirical, analytical and numerical methods were combined for safe tunnel design. Rock mass rating (RMR), Rock mass quality (Q) and Geological strength index (GSI) systems were used for empirical rock mass quality determination, site characterization and support design. The convergence–confinement method was used as analytical method and software called Phase², a 2D finite element program, was utilized as numerical method. According to the results acquired from the empirical, analytical and numerical methods, tunnel stability problems were expected in both granite and diorite rock masses. The support system, suggested by empirical methods, was applied and the performance of suggested support system was evaluated by means of numerical modelling. It was concluded that the suggested support systems were adequate, since after applying the suggested support system to granite and diorite, tunnel deformation and the yielded elements around the tunnel decreased significantly. Thus, it is suggested that for more reliable support design empirical, numerical and analytical methods should be combined.  相似文献   

A multi-method approach to study the stability of natural slopes and landslide susceptibility mapping   总被引：8，自引：0，他引：8  

M. Fall  R. Azzam  C. Noubactep 《Engineering Geology》2006,82(4):241-263

In this paper, a multi-method approach for the assessment of the stability of natural slopes and landslide hazard mapping applied to the Dakar coastal region is presented. This approach is based on the effective combination of geotechnical field and laboratory works, of GIS, and of mechanical (deterministic and numerical) stability analysis. By using this approach, valuable results were gained regarding instability factors, landslide kinematics, simulation of slope failure and coastal erosion. This led to a thorough assessment and strong reduction in the subjectivity of the slope stability and hazard assessment and to the development of an objective landslide danger map of the SW coast of Dakar. Analysis of the results shows that the slides were influenced by the geotechnical properties of the soil, the weathering, the hydrogeological situation, and the erosion by waves. The landslide susceptibility assessment based on this methodological approach has allowed for an appropriate and adequate consideration of the multiple factors affecting the stability and the optimization of planning and investment for land development in the city.  相似文献   

The deep-seated slope deformation at Encampadana, Andorra: Representation of morphologic features by numerical modelling     

Marcel Hürlimann  Alberto Ledesma  Jordi Corominas  Pere C. Prat 《Engineering Geology》2006,83(4):343-357

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Natural and man-induced stress evolution of slopes: the Monte Mario hill in Rome     

F. Bozzano  S. Martino  M. Priori 《Environmental Geology》2006,50(4):505-524

The paper deals with stress-release effects induced by man-made cuts or excavations into natural stiff clay slopes that experienced erosion in response to valley deepening. The study was focused on the Monte Mario hill in Rome (Italy), which formed part of an area of recent urban expansion. The methodology of the study relied on a reference engineering-geology model, which was developed on the basis of site and laboratory data and stress–strain analyses. The latter analyses were carried out with the finite-difference code FLAC 4.0. Numerical modelling was based on a sequential approach, taking into account the main evolutionary stages of the Tiber river valley in Romeȁ9s urban area and then making cuts at the bottom of the slope located south of the Monte Mario Astronomical Observatory. The simulation revealed the stress-release effects that fluvial erosion and excavation fronts have caused on the investigated slopes and their consequent gravitational instabilities. These processes appear with metre-scale displacements, followed by stress-release cracks (actually observed on the slopes under review). In quantifying stress-release deformations, the simulation took into account the possible role of creep in the observed retardation of stress-release effects.Research activities were carried on with the co-operation of Dȁ9Arcangelo A. (Consorzio TREESSE, andrea.darcangelo@libero.it) and Moretti S. (IMG S.r.l. Servizi Tecnici per lȁ9Ingegneria e lȁ9Ambiente, moretti@img-srl.it)  相似文献   

Occurrence of salt water above fresh water in dynamic equilibrium in a coastal groundwater flow system near De Panne, Belgium     

A. Vandenbohede  L. Lebbe 《Hydrogeology Journal》2006,14(4):462-472

A salt water lens is found above fresh water under the shore between Dunkerque (France) and Nieuwpoort (Belgium). This inverse density distribution is in a dynamic equilibrium. It develops due to the infiltration of salt water on the back shore during high tide. Under this salt water lens, water infiltrated in the adjacent dune area flows towards the sea and discharges at the seabed. This water quality distribution differs from the classic salt water wedge under fresh water described in the literature. Here, the evolution to this water quality distribution is simulated with a density dependent numerical model. A large tidal range, shore morphology and a permeable groundwater reservoir are the main conditions for the observed water quality distribution. By altering these conditions, intermediate water quality distributions between the classic salt water wedge and the one discussed here develop. Based on these simulations, it is expected that similar kinds of inverse density distribution could be present in a number of coastal areas, which have tides, a gently sloping shore and a permeable substratum.  相似文献