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1.
The inference of ancient environmental conditions from their preserved response in the sedimentary record still remains an outstanding issue in stratigraphy. Since the 1970s, conceptual stratigraphic models (e.g. sequence stratigraphy) based on the underlying assumption that accommodation space is the critical control on stratigraphic architecture have been widely used. Although these methods considered more recently other possible parameters such as sediment supply and transport efficiency, they still lack in taking into account the full range of possible parameters, processes, and their complex interactions that control stratigraphic architecture. In this contribution, we present a new quantitative method for the inference of key environmental parameters (specifically sediment supply and relative sea level) that control stratigraphy. The approach combines a fully non‐linear inversion scheme with a ‘process–response’ forward model of stratigraphy. We formulate the inverse problem using a Bayesian framework in order to sample the full range of possible solutions and explicitly build in prior geological knowledge. Our methodology combines Reversible Jump Markov chain Monte Carlo and Simulated Tempering algorithms which are able to deal with variable‐dimensional inverse problems and multi‐modal posterior probability distributions, respectively. The inverse scheme has been linked to a forward stratigraphic model, BARSIM (developed by Joep Storms, University of Delft), which simulates shallow‐marine wave/storm‐dominated systems over geological timescales. This link requires the construction of a likelihood function to quantify the agreement between simulated and observed data of different types (e.g. sediment age and thickness, grain size distributions). The technique has been tested and validated with synthetic data, in which all the parameters are specified to produce a ‘perfect’ simulation, although we add noise to these synthetic data for subsequent testing of the inverse modelling approach. These tests addressed convergence and computational‐overhead issues, and highlight the robustness of the inverse scheme, which is able to assess the full range of uncertainties on the inferred environmental parameters and facies distributions. 相似文献
2.
A novel inverse modelling method is applied to the problem of constraining the environmental parameters (e.g. relative sea level, sediment supply) that control stratigraphic architecture. This technique links forward modelling of shallow-marine wave/storm-dominated stratigraphy to a combination of inverse methods formulated in a Bayesian framework. We present a number of examples in which relative sea-level and sediment-supply curves were inferred from synthetic vertical successions of grain size (e.g. wells) and synthetic thickness curves (e.g. seismically derived isopachs) extracted from a forward model simulation. These examples represent different scenarios that are designed to test the impact of data distribution, quantity and quality on the uncertainty of the inferred parameters. The inverse modelling approach successfully reproduces the gross stratigraphic architectures and relative sea level and sediment-supply histories of the synthetic forward model simulation, within the constraints of the modelled data quality. The relative importance of the forcing parameters can be evaluated by their sensitivity and impact on the inverted data. Of equal importance, the inverse results allow complete characterisation of the uncertainties inherent to the stratigraphic modelling tool and to the data quality, quantity and distribution. The numerical scheme also successfully deals with the problem of non-uniqueness of the solution of the inverse problem. These preliminary results suggest that the inverse method is a powerful tool in constraining stratigraphic architecture for hydrocarbon reservoir characterisation and modelling, and it may ultimately provide a process-based geological complement to standard geostatistical tools. 相似文献
3.
We have formulated a 3-D inverse solution for the magnetotelluric (MT) problem using the non-linear conjugate gradient method. Finite difference methods are used to compute predicted data efficiently and objective functional gradients. Only six forward modelling applications per frequency are typically required to produce the model update at each iteration. This efficiency is achieved by incorporating a simple line search procedure that calls for a sufficient reduction in the objective functional, instead of an exact determination of its minimum along a given descent direction. Additional efficiencies in the scheme are sought by incorporating preconditioning to accelerate solution convergence. Even with these efficiencies, the solution's realism and complexity are still limited by the speed and memory of serial processors. To overcome this barrier, the scheme has been implemented on a parallel computing platform where tens to thousands of processors operate on the problem simultaneously. The inversion scheme is tested by inverting data produced with a forward modelling code algorithmically different from that employed in the inversion algorithm. This check provides independent verification of the scheme since the two forward modelling algorithms are prone to different types of numerical error. 相似文献
4.
Calculating the two-dimensional magnetotelluric Jacobian in finite elements using reciprocity 总被引：6，自引：0，他引：6
Patricia Pastana de Lugão Philip E. Wannamaker 《Geophysical Journal International》1996,127(3):806-810
To speed up the calculation of the field Jacobian for 2-D magnetoteliuric inversion using finite elements, the principle of electromagnetic reciprocity is applied. The governing relationship for the Jacobian of the field along strike is obtained by differentiating the Helmholtz equation with respect to the resistivity of each region in the finite-element mesh. The result is a similar Helmholtz equation for the Jacobian, with new sources distributed over all nodes within the parameter medium. However, according to the principle of electromagnetic reciprocity, the roles of sources and receivers are interchangeable. Utilizing reciprocity, the field values obtained from the original forward problem and for new unit sources imposed at the receivers are then utilized in the calculation of the Jacobian by simple multiplication and summation with finite-element terms at each rectangle in the mesh. For the auxiliary (across-strike) fields, the Jacobian terms are obtained by solving source vectors loaded with parabola coefficients used in the approximation to Maxwell's equations. Jacobian terms for the apparent resistivity ( p a ), the impedance phase (φ) and the vertical magnetic field ( K zy ) are then calculated utilizing the parallel- and auxiliary-field Jacobians. Comparison of Jacobian values obtained from reciprocity calculations and by differencing two forward solutions show that the reciprocity method is accurate and can be used to decrease the number of calculations required to obtain sensitivities by one to two orders of magnitude. 相似文献
5.
6.
1 IntroductionFlooding simulation and damage evaluation has attracted attention in environmental disaster research fields for many years. Since the 1990s, especially in recent years, using geographic information systems (GIS) technology and its powerful functions of spatial analysis and visualization to simulate and display flooded area and to evaluate disaster damage has become a research hotspot. Most of the papers involved in this field are from hydraulic and hydrologic point of view and b… 相似文献
7.
An iterative solution to the non-linear 3-D electromagnetic inverse problem is obtained by successive linearized model updates using the method of conjugate gradients. Full wave equation modelling for controlled sources is employed to compute model sensitivities and predicted data in the frequency domain with an efficient 3-D finite-difference algorithm. Necessity dictates that the inverse be underdetermined, since realistic reconstructions require the solution for tens of thousands of parameters. In addition, large-scale 3-D forward modelling is required and this can easily involve the solution of over several million electric field unknowns per solve. A massively parallel computing platform has therefore been utilized to obtain reasonable execution times, and results are given for the 1840-node Intel Paragon. The solution is demonstrated with a synthetic example with added Gaussian noise, where the data were produced from an integral equation forward-modelling code, and is different from the finite difference code embedded in the inversion algorithm 相似文献
8.
Results are presented from a numerical simulation of two-dimensional flow patterns in a braided river using a simple cellular routing scheme. The results of the routing scheme are compared with field measurements of discharge per unit width obtained within the study reach at low flow and, for higher flows, with the predictions of a more sophisticated hydraulic model that solves the two-dimensional shallow water form of the Navier–Stokes equations. An assessment is made of the sensitivity of the routing scheme to variations in the values of its main parameters, and appropriate values are determined based on the physical characteristics of the study site and available flow measurements. It is shown that despite the simple approach adopted by the cellular routing scheme to simulate processes of water redistribution, it is able to replicate accurately both the field data and the results of the more sophisticated hydraulic model. These results indicate that the routing scheme outlined here is able to overcome some of the limitations of previous simple cellular automata models and may be suitable for use in modelling bedload transport and channel change in complex fluvial environments. As such this research represents a small and ongoing contribution to the field of numerical simulation of braided river processes. 相似文献
9.
Using geographic information system to study flooded area and damage evaluation has been a hotspot in environmental disaster research for years. In this paper, a model for flooded area calculation and damage evaluation is presented. Flooding is divided into two types: ‘source flood’ and ‘non-source flood’. The source-flood area calculation is based on seed spread algorithm. The flood damage evaluation is calculated by overlaying the flooded area range with thematic maps and relating the result to other social and economic data. To raise the operational efficiency of the model, a skipping approach is used to speed seed spread algorithm and all thematic maps are converted to raster format before overlay analysis. The accuracy of flooded area calculation and damage evaluation is mainly dependent upon the resolution and precision of the digital elevation model (DEM) data, upon the accuracy of registering all raster layers, and upon the quality of economic information. This model has been successfully used in the Zhejiang Province Comprehensive Water Management Information System developed by the authors. The applications show that this model is especially useful for most counties of China and other developing countries. 相似文献
10.
M. Sambridge P. Rickwood N. Rawlinson S. Sommacal 《Geophysical Journal International》2007,170(1):1-8
Automatic differentiation (AD) is the technique whereby output variables of a computer code evaluating any complicated function (e.g. the solution to a differential equation) can be differentiated with respect to the input variables. Often AD tools take the form of source to source translators and produce computer code without the need for deriving and hand coding of explicit mathematical formulae by the user. The power of AD lies in the fact that it combines the generality of finite difference techniques and the accuracy and efficiency of analytical derivatives, while at the same time eliminating 'human' coding errors. It also provides the possibility of accurate, efficient derivative calculation from complex 'forward' codes where no analytical derivatives are possible and finite difference techniques are too cumbersome. AD is already having a major impact in areas such as optimization, meteorology and oceanography. Similarly it has considerable potential for use in non-linear inverse problems in geophysics where linearization is desirable, or for sensitivity analysis of large numerical simulation codes, for example, wave propagation and geodynamic modelling. At present, however, AD tools appear to be little used in the geosciences. Here we report on experiments using a state of the art AD tool to perform source to source code translation in a range of geoscience problems. These include calculating derivatives for Gibbs free energy minimization, seismic receiver function inversion, and seismic ray tracing. Issues of accuracy and efficiency are discussed. 相似文献
11.
区域尺度蒸散发遥感估算——反演与数据同化研究进展 总被引：3，自引：0，他引：3
遥感技术近年来在估算区域尺度蒸散发中应用广泛。不同方法在驱动数据、模型机理和适用范围往往存在很大差别。鉴于此,阐述了基于传统方法空间尺度扩展的遥感模型,经验统计公式,特征空间法,单源、双源垂向能量平衡余项法等几类的遥感蒸散发反演方法,简要介绍了三温模型、非参数化模型、半经验模型、集成模型等常用模型。同时,分析了遥感数据同化实现连续估算区域蒸散发的主要思路,综述了基于能量平衡和基于复杂过程模型的数据同化的原理、方法演进及常用同化算法等。最后,探讨了各类区域蒸散发遥感方法的优劣、展望了模型机理完善、不确定性研究、结果验证等与蒸散发直接反演和数据同化相关的研究方向。 相似文献
12.
基于探索性空间数据分析技术(ESDA)划分出京津冀都市地区的中心区域和外围区域,并在传统经济收敛模型基础上,运用空间俱乐部收敛模型和局部空间回归模型对京津冀都市地区经济收敛情况进行研究。结果表明,首先,京津冀都市地区已形成了以北京、天津和唐山为核心的中心区域和以张家口市、保定市为核心的环绕京津的外围区域,京津冀都市地区整体上存在微弱的经济收敛。其次,京津冀都市地区中心地区由于经济发展水平较高,空间外溢效应较大,加之中心地区接受知识、技术扩散的能力较强,存在经济收敛,并且收敛速度较快,而外围区域则不存在经济收敛。再次,中心地区和外围地区内部存在经济收敛系数结构的不稳定性。 相似文献
13.
J. Gonçalvès S. Violette F. Guillocheau† C. Robin† M. Pagel‡ D. Bruel¶ G. de Marsily E. Ledoux¶ 《Basin Research》2004,16(4):569-586
A basin model was built to simulate in three dimensions the 248 Myr geological history of the Paris basin, France, i.e. sedimentation, erosion, compaction heat and fluid flow. This multidisciplinary study was based on a detailed stratigraphic database of more than 1100 well logs together with a hydrodynamic database of 1000 data (heads and permeabilities). The region covers a maximum surface area of 700 000 km2. The NEWBAS code of the Ecole des Mines de Paris was used in order to simulate compaction and heat and fluid flow. Three examples of the use of this model are given to illustrate different features of the geological functioning of the basin. (i) By modelling processes such as sedimentation, compaction, fluid and heat flow, the model provides estimates of the hydraulic conductivity fields within one order of magnitude from observations at the regional scale. This permeability field can reproduce the present‐day observed pressures and fluxes in the basin. (ii) Observed excess pressures in the main aquitards are considered as possible consequences of the geological history of the basin. The calculated excess pressures are small and stay within the range of the measured values, between 0 and 2.75 MPa, close to the pressures in the aquifers. However, the weak excess pressures measured in the Callovo–Oxfordian sequence in the eastern part of the basin are not reproduced by the model. Mechanisms other than compaction disequilibrium must be invoked. (iii) This model also calculates regional‐scale palaeofluid flow whose value is currently arbitrarily assumed by geochemists when studying diagenetic processes. Hence, it provides a hydrologic background for diagenetic models. The cementation in the western Keuper reservoirs was investigated. Topographically driven flow during tectonic inversion periods, e.g. the Lower Cretaceous and Early Tertiary, is shown to be a plausible cause of brine migrations. This brine displacement would then explain the high salinities recorded in the fluid inclusions trapped in the Keuper cements. The conditions for the migration would have been most favourable at the time of the maximum burial, i.e. the Early Tertiary and not the Early Cretaceous as previously suggested. 相似文献
14.
水文循环模拟中蒸散发估算方法综述(英文) 总被引：1，自引：1，他引：0
Actual evapotranspiration is a key process of hydrological cycle and a sole term that links land surface water balance and land surface energy balance.Evapotranspiration plays a key role in simulating hydrological effect of climate change,and a review of evapotranspiration estimation methods in hydrological models is of vital importance.This paper firstly summarizes the evapotranspiration estimation methods applied in hydrological models and then classifies them into the integrated converting methods and the classification gathering methods by their mechanism.Integrated converting methods are usually used in hydrological models and two differences exist among them:one is in the potential evaporation estimation methods,while the other in the function for defining relationship between potential evaporation and actual evapotranspiration.Due to the higher information requirements of the Penman-Monteith method and the existing data uncertainty,simplified empirical methods for calculating potential and actual evapotranspiration are widely used in hydrological models.Different evapotranspiration calculation methods are used depending on the complexity of the hydrological model,and importance and difficulty in the selection of the most suitable evapotranspiration methods is discussed.Finally,this paper points out the prospective development trends of the evapotranspiration estimating methods in hydrological modeling. 相似文献
15.
河流与含水层水力耦合模型及其应用 总被引：16，自引：0，他引：16
本文在分析河水与地下水相互作用规律的基础上,提出了河流－含水层相互作用水力耦合模型的建模思路、数值解法及应用实例。河流模型采用忽略河槽调蓄作用的圣维南连续方程,含水层模型为潜水二维渗流方程,二者通过动态水量交换机制实现耦合,模型的水量交换机制可以分别模拟含水层顶托排泄、河流压力渗和淋滤渗漏等不同方式的水量转换过程。河水模型和地下不模型分别用欧拉法和三角网格差分法来求解。实际应用表明耦合模型能较准确 相似文献
16.
This study compared three hydrological methods – low flow frequency analysis, flow duration curve (FDC), and concentration-discharge (C-D) modeling – to determine the water requirement of the Gavkhuni wetland located in an arid region of Iran. Due to the effects of water impounding upstream on the hydrological regime of the Gavkhuni's inflow after construction of the Zayandehrud dam, none of the methods produced satisfactory results.Consequent modification of the hydrological regime of the wetland's inflow using a scaling process allowed all the methods except low flow frequency analysis to dependably estimate the base flow for the wetland. The results of the C–D method revealed that this method can provide a minimum health condition from the water quality point of view, while the results of the FDC demonstrated that not only the inflow estimated using this method can supply minimum conditions in terms of water quality parameters, but it also covers most areas of the wetland, based on the results of hydraulic modeling.The results reveal that the hydrological methods implemented in this study can dependably estimate environmental water allocation for wetlands in arid and semi-arid regions when there is no detailed knowledge about the biological requirements of the wetlands' biota. 相似文献
17.
Michael E. Hodgson 《The Professional geographer》1989,41(1):51-61
A widely used method for grid interpretation from a set of discrete sample points is based on the inverse distanceweighted model. This method requires the identification of k-nearest sample points for each grid point, probably the most time-consuming portion of the grid interpolation process. Three searching methods for identifying the k-nearest sample points are discussed and compared. Two of these methods were consistenty faster without sacrificing accuracy than the brute-force searching method, and one method was from one to over 90 times faster than the brute-force searching method. 相似文献
18.
The hydraulic and sedimentary characteristics of the spawning habitat of Atlantic salmon (Salmo salar) in tributary and mainstem locations in a river system in north-east Scotland are described. Salmon used spawning sites with a relatively wide range in sediment characteristics, although measures of central tendency were all in the gravel (2–64 mm) size-class. The dominant factor differentiating the sediment characteristics of study sites was the level of fine sediment, which accounted for significant differences between tributary and mainstem samples. The ranges of depth and velocity in areas used for spawning by salmonids were found to be similar in all tributary study sites. However, due to the interdependence of depth and velocity, major differences were observed between tributary and mainstem study sites in that spawning in larger streams tended to be associated with deeper, faster flowing water. Spawning locations were shown to have similar Froude number, despite different sized streams and species of salmonid. Due to its dimensionless nature and significance in characterising flow hydraulics, the Froude number is proposed as a potentially useful variable for describing the habitat of aquatic organisms. 相似文献
19.
腾格里沙漠西南缘地下水水化学形成特征及演化 总被引：6，自引：2，他引：4
以邓马营湖区为核心,对腾格里沙漠西南缘地下水数据进行水文地球化学特征分析,并运用PHREEQC2.0软件反向模拟沿运移路径地下水的补给机理及演化过程。结果显示:受水文地质条件制约,从山前洪积扇地下水的补给区深入腾格里沙漠过渡带再到邓马营湖区中深层地下水,水化学类型从HCO3-—Ca2+—Mg2+型过渡为Cl-—SO24-—Na+—Mg2+型再过渡到HCO3-—SO42-—Na+型。其影响因素基本包括:溶滤与蒸发浓缩作用、阳离子交换吸附作用、以及微弱的混合作用和地下水补给水源水化学成分控制。矿物饱和指数以及反向水文化学地球化学模拟的结果显示,由西南向东北沿水流方向各物质溶解沉淀情况复杂,除斜长石与方解石外,岩盐、石膏、白云石等浓缩沉淀显著,表明蒸发浓缩作用控制强烈。 相似文献
20.
用地布局一直是城市总体规划中的关键难题,以往的规划方案多凭借规划师的经验判断、简单的图层叠加和有限的公众参与生成。然而新的城乡规划法要求从多角度综合考虑城乡用地布局问题,更加注重规划过程的科学性和准确性,也就特别需要有一种适应多情景分析下的城市用地布局模拟与方案评价方法。文章以江苏省太仓市为例,借助GIS技术的强大空间分析功能,探讨了这种方法的技术流程：① 参考已有的大尺度城市未来模型,结合我国特别是研究区的区域特点,构建一个实用的城市未来模型(Urban Future Model,UFM);② 通过用地评价、战略归纳、情景模拟等步骤,生成若干个可选的用地布局模拟方案;③ 应用多目标达成矩阵法从粮食、生态、灾害等多个角度对这些方案进行综合评价,并根据评价结果选择一个最佳方案作为本轮总规用地布局的规划参考方案。 相似文献