电阻率层析成像数据采集系统

上世纪90年代出现的电阻率层析成像技术是电法勘探的革命性进展．目前已在硬件和软件上取得重大发展．对数据采集系统,本文以MIR／MIS仪器为主从电极转换器、测量主机、控制软件、阵列电极和电缆系统几个方面全面地介绍了该技术的原理与设计。对主要的技术性能进行了讨论,对比和分析了不同设计思路的特点和利弊．简单介绍了国内外同类仪器的发展概况。     

电阻率层析成像非线性反演

本文通过概率成像法、α中心法、遗传算法的有机结合, 实现了2-D电阻率层析成像非线性反演.首先,根据概率成像结果指示出的2-D地质异常体的相对电性和大致分布范围,合理地确定出α中心的位置与强度系数的变化范围.其次,以α中心法作为2-D地电结构的正演手段,采用遗传算法反演出各α中心的强度系数.在此基础上, 应用α中心法重新构建出地下介质电阻率的分布.通过对均匀半空间中赋存2-D地质异常体模型的反演试验, 获得了令人满意的结果.     

Hydraulic tomography for detecting fracture zone connectivity

Fracture zones and their connectivity in geologic media are of great importance to ground water resources management as well as ground water contamination prevention and remediation. In this paper, we applied a recently developed hydraulic tomography (HT) technique and an analysis algorithm (sequential successive linear estimator) to synthetic fractured media. The application aims to explore the potential utility of the technique and the algorithm for characterizing fracture zone distribution and their connectivity. Results of this investigation showed that using HT with a limited number of wells, the fracture zone distribution and its connectivity (general pattern) can be mapped satisfactorily although estimated hydraulic property fields are smooth. As the number of wells and monitoring ports increases, the fracture zone distribution and connectivity become vivid and the estimated hydraulic properties approach true values. We hope that the success of this application may promote the development and application of the new generations of technology (i.e., hydraulic, tracer, pneumatic tomographic surveys) for mapping fractures and other features in geologic media.     

Radar tomography for NDT: comparison of techniques

Feasibility and potential of tomography by Ground Penetrating Radar are investigated through experiments on laboratory models. The aim is the development of radar tomography procedures for inspection of structures like walls or pillars in historical buildings. Two different approaches are explored to satisfy high-resolution requirements. The first approach improves the results of classical traveltime (TT) and amplitude tomography (AT) on thin straight or curved rays through a progressive reduction of the null space of the problem. TT is a quantitative tool based on the thin ray assumption that allows a good tradeoff between robustness and resolution. AT is as robust as TT, but its results have only qualitative contents, since the energy transferred to the medium is basically unknown and the scattering effects are not taken into account. In the second approach, GPR is considered as a diffracting source, so that migration (MIG) and diffraction tomography (DT) are applied to overcome the geometrical optic approximations. While DT is in principle the best tool to invert the scattered field and to achieve the maximum resolution, MIG can be a more robust solution that requires less preprocessing of the data. All these advantages and drawbacks of the different approaches are discussed with some examples on synthetic and real data.     

岫岩陨石坑三维Q值层析成像

到2009年为止,世界上已发现176个陨石撞击坑.从20世纪80年代起,中国学者从地质、地球化学和地质钻探角度推断并证实辽宁省岫岩县的一个环形构造为陨石撞击而成,但该坑的深部构造及整体特征仍有待地球物理方法来确认.本文从地震勘探角度利用三维Q值层析成像方法首次对岫岩坑的地震波衰减结构进行了研究,以便对该撞击构造有个整体认识.Q值结构对了解地壳的非弹性性质、地壳介质非均匀性有着重要意义.利用基于吸收特征时间t*的三维Q值层析成像方法,计算了岫岩坑地震折射方阵的观测数据的振幅谱,并通过拟合振幅谱得到了反映地震波衰减的t*.利用t*通过三维Q值层析成像方法获得了该坑的三维Q值结构.结果表明:该陨石坑内从地表到深度100 m的Q值层对应坑内上部107 m厚的湖泊相沉积物,深度100~300 m的Q值层对应坑内下部厚度为188 m的角砾岩堆积透镜体.深度300~700 m的Q值层对应角砾岩堆积透镜体下面的下元古界变质岩系程度较低的撞击破碎层.大约250 m深处的波阻抗界面与地质钻孔的260 m深处的陨石冲击分界面相对应.     

浅谈反射地震走时层析中的正则化

反射地震走时层析本质上是一个病态问题,而正则化是改善问题病态程度的有效手段.反射地震走时层析最终可归结为线性方程组的求解,本文讨论了在线性方程组求解过程中正则化的作用和方式.正则化的作用有:(1)用超定分量约束欠定分量和零空间分量;(2)用先验信息约束欠定分量和零空间分量;(3)对射线的不均匀覆盖进行阻尼;(4)对数据的不准确性进行阻尼.正则化的加入方式有:(1)加法型(将正则化矩阵补在层析矩阵后面,包括导数型正则化和零阶正则化,一阶导数型正则化对应最平坦解,二阶导数型正则化对应最光滑解,零阶正则化对应紧约束解);(2)乘法型(将正则化矩阵与层析矩阵相乘,主要包括阻尼型正则化).并利用简单的模型对正则化的效果进行了试验,发现经各种正则化约束后,与未加任何正则化约束得到的速度模型比较,尽管恢复的异常体的幅度不如后者大,但得到的速度剖面要平滑得多,更利于后续的射线追踪正演和层析反演.     

A hybrid fast algorithm for first arrivals tomography

A hybrid algorithm, combining Monte-Carlo optimization with simultaneous iterative reconstructive technique (SIRT) tomography, is used to invert first arrival traveltimes from seismic data for building a velocity model. Stochastic algorithms may localize a point around the global minimum of the misfit function but are not suitable for identifying the precise solution. On the other hand, a tomographic model reconstruction, based on a local linearization, will only be successful if an initial model already close to the best solution is available. To overcome these problems, in the method proposed here, a first model obtained using a classical Monte Carlo-based optimization is used as a good initial guess for starting the local search with the SIRT tomographic reconstruction. In the forward problem, the first-break times are calculated by solving the eikonal equation through a velocity model with a fast finite-difference method instead of the traditional slow ray-tracing technique. In addition, for the SIRT tomography the seismic energy from sources to receivers is propagated by applying a fast Fresnel volume approach which when combined with turning rays can handle models with both positive and negative velocity gradients. The performance of this two-step optimization scheme has been tested on synthetic and field data for building a geologically plausible velocity model.This is an efficient and fast search mechanism, which permits insertion of geophysical, geological and geodynamic a priori constraints into the grid model and ray path is completed avoided. Extension of the technique to 3D data and also to the solution of 'static correction' problems is easily feasible.     

Image-domain wavefield tomography for tilted transversely isotropic media

Transversely isotropic models with a tilted symmetry axis have become standard for imaging beneath dipping shale formations and in active tectonic areas. Here, we develop a methodology of wave-equation-based image-domain tomography for acoustic tilted transversely isotropic media. We obtain the gradients of the objective function using an integral wave-equation operator based on a separable dispersion relation that takes the symmetry-axis tilt into account. In contrast to the more conventional differential solutions, the integral operator produces only the P-wavefield without shear-wave artefacts, which facilitates both imaging and velocity analysis. The model is parameterized by the P-wave zero-dip normal-moveout velocity, the Thomsen parameter δ, anellipticity coefficient η and the symmetry-axis tilt θ. Assuming that the symmetry axis is orthogonal to reflectors, we study the influence of parameter errors on energy focusing in extended (space-lag) common-image gathers. Distortions in the anellipticity coefficient η introduce weak linear defocusing regardless of reflector dip, whereas δ influences both the energy focusing and depth scale of the migrated section. These results, which are consistent with the properties of the P-wave time-domain reflection moveout in tilted transversely isotropic media, provide important insights for implementation of velocity model-building in the image-domain. Then the algorithm is tested on a modified anticline section of the BP 2007 benchmark model.     

Adjoint method for the optimum planning of industrial pollutant sources

The deterioration of air quality is threatening the life and health of people. Scientists in China and other countries have done a great deal of research work on the details of air pollution and the methods of preven-tion and control during the past decades. Up to now, most of the achievements are concentrated on the techniques of controlling pollutant sources and the programs of reduction, which focus on the improve-ment of air quality and the restoration of environment. The techniques of con…     

电磁成像正演仿真与传感器参数优化设计

应用有限元方法对电磁层析成像测量进行正演模拟,计算不同测量组合下各种典型流型的电势实部和虚部分布,考察电极个数、电极张角以及电极厚度对模拟测量响应的影响,并采用神经网络方法对传感器各结构参数进行优化设计.研究结果表明,介质分布对电势影响起主要作用,其中虚部分布特征更加明显;传感器各参数中电极数目对测量值影响较大,电极张角和电极厚度有一定影响.     

面向电离层反演的参数平滑迭代层析方法

层析是电离层三维结构反演的重要技术.增加约束可缓解层析模型的病态问题.然而, 迭代层析中, 大量无射线穿过的网格易对施加的约束产生与真实意图相违背的约束结果(称负面约束).针对该问题, 提出了一种参数平滑的迭代层析方法(iterative tomography method via parameters smoothing, ITPS).每次迭代中, 先用Chapman函数及最小二乘法拟合及改正每一垂直剖面, 获取关于Chapman函数参数的二维图像, 然后用移动窗口法平滑各参数图像并以此改正各网格的电子密度.实验表明: ITPS方法可一定程度上减少负面约束并抑制层像的扰动.相对于MART和CMART算法, ITPS方法在垂直剖面、F2层临界频率(f_oF₂)、F2层峰值高度(h_mF₂)、斜电子总含量(Slant Total Electron Content, STEC)及h_mF₂以上电子密度等方面均具有更佳的表现.相对于精度较高的CMART算法, ITPS方法在f_oF₂与h_mF₂的平均优化率分别为7.49%及6.60%, STEC的平均优化率为5.19%, h_mF₂以上电子密度的平均优化率为11.41%.

     

瞬变电磁快速成像解释系统研究

为了提高瞬变电磁测深法对地探测的垂向分辨能力,文中研究了磁偶源瞬变电磁法快速成像的方法.详细讨论了电磁波与地震波在介质中的传播规律,分析了磁偶源瞬变电磁场在远区的响应特性.根据磁偶源瞬变电磁场与反射地震波的传播规律的相似性,提出了TEM资料拟地震快速成像解释的思路.理论模型正、反演计算结果表明方法理论是可行的,野外实测资料处理结果进一步说明了该方法是有效的.     

广义散射层析成像反演

本文详细地给出了基于非均匀介质的体散射广义散射层析成像反演的基本理论.广义散射层析成像反演可以描述为波场的反向传播和对成像场进行局部波数域滤波的过程.在数值算例中,利用背景速度沿深度方向均匀变化的v（z）介质中的简单的方块作为速度异常体的模型,通过对该模型产生的低频的Born数据和声波的正演数据的测试,在对采集系统进行有限频率带宽和空间孔径的校正来进行局部成像矩阵谱的恢复中,可以看出模型中各点的谱在恢复后的质量无论从覆盖的面积范围还是幅值的均一性上都有着明显的提高;在对速度模型的重建中,广义散射层析成像反演能够很好地恢复速度模型的低频分量,即便是方块速度异常体相对于背景速度的平均速度扰动是23%也能很好地重建模型中的速度,且对于不同的背景速度模型基本上都能很好地恢复Marmousi速度模型的低频分量.所以该方法将基于Born模型的层析成像反演适应范围进行了一定程度的扩展.     

初至波相位走时层析

近地表速度结构通常是利用射线走时层析或菲涅尔体走时层析等反演方法得到的,但它们的目标函数仍利用射线走时残差构建,导致反演精度不高.为此,本文提出了基于散射积分算法的初至波相位走时层析成像方法.该方法的核心是:(1)提出了依赖于频率的相位走时概念;(2)利用依赖于频率的相位走时信息,而非单一的无限频率射线走时;(3)发展了一种改进的相位展开方法,即通过监测相位不连续性和2π周期判定来消除相位折叠现象;(4)考虑了地震波传播的有限频特征,即基于波动理论而非传统的射线路径或有限空间的菲涅尔体构建核函数.通过利用Overthrust模型的数值实验及与传统射线走时层析和菲涅尔体走时层析的对比表明:本文提出的方法是一种有效的初至波走时反演方法.同时,基于Overthrust模型的数值试验还证明了下列结论,即通过挖掘更多的走时信息的确可以获得更高的反演精度和分辨率.     

工业企业震害预测信息系统建设

大型工业企业的地震灾害具有经济损失高、破坏性强、次生灾害突出、受影响范围广等特点。依据大型工业企业的生产特点，结合工业企业防震减灾的需求，分析了工业企业的震害预测信息系统结构和特征，详细阐述了使用地理信息系统应用软件ArcView为开发平台，建立工业企业GIS震害预测信息系统的基本方法和步骤，并阐明了系统的主要功能和特点。     

Iterative geophysical tomography

Summary The algorithm of iterative geophysical tomography is presented. The medium is approximated smoothly by means of B-splines. The tww-point problem of ray computation is solved with the aid of paraxial approximation. The parameters of the medium are obtained from the iterative algorithm of minimizing the quadratic form. Two numerical 2-D examples are given.

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EUREKA industrial R&D projects for an improved environment

International collaboration is increasingly necessary in the field of environmental protection in relation to industrial research and development. The EUREKA initiative, launched in 1985, aims to increase industrial productivity and competitiveness in Europe by encouraging cross-border high technology research and development. The programme encompasses a number of ‘umbrella’ projects—EUROMAR, EUROCARE, EUROENVIRON, EUROTRAC and ENVINET. Each of these is designed to generate and support research and development projects. The paper gives examples of the projects and discusses the value of such large-scale international collaboration.     

有限频与射线层析成像比较研究综述

从正演近似性和反演多解性两方面对有限频与射线理论的争论历史和比较研究进展进行介绍并评述.从早期的衍射层析成像开始,回顾了有限频理论的发展历史.详细介绍了2005至2006年问有限频理论的拥护者与质疑者之间的一场影响深远的争论.这场争论纠正了之前十多年许多地震学家将地震波相关走时与初至走时相混淆的错误认识,使有限频理论得...     

电离层三维层析成像的自适应联合迭代重构算法

在电离层层析成像过程中,联合迭代重构算法是一种常用的反演算法.然而,该算法迭代收敛较慢,反演结果精度不高.为此,本文发展了一种自适应的联合迭代重构算法,该算法利用上一轮的电离层电子密度反演结果,自适应地调整松弛因子和加权参数.通过模拟数据和实测数据对该算法的反演结果进行了验证,并将得到的反演结果与电离层测高仪数据进行了比较,结果表明,该算法能够有效地反演电离层电子密度,且反演结果精度优于常用的联合迭代重构算法.