跨孔电磁波层析处理中阻尼系数的确定与应用     

罗德建  高文利 《物探化探计算技术》2007,(Z1)

代数重建技术ART(Algebra Reconstruction Technology)是一种层析处理数学方法,具有计算速度快、图形简洁直观等优点,被应用于电磁波CT方法的数据处理中。但该处理方法易发散,结果难以控制,因此它的敛散性成为提高其应用的主要问题。这里通过在ART算法中加入阻尼系数的做法保证了迭代的收敛,并对阻尼系数的取值范围进行了探讨,成功地用于电磁波数据处理中。  相似文献   

基于电偶源的体积分方程法三维电磁反演   总被引：5，自引：0，他引：5  

张辉  李桐林  董瑞霞 《吉林大学学报(地球科学版)》2006,36(2):284-288

利用体积分方程对电偶源激发时均匀导电半空间频率域三维电磁场进行正反演计算。计算中参考Eaton等提出的方法将雅可比矩阵分为线性和非线性偏微分项求解,然后利用阻尼最小二乘技术进行最优化迭代拟合。这种反演方法具有更广的适用范围和更高的计算精度,能够准确、稳定地得到较高分辨率的地下三维异常体电阻率分布图像。  相似文献   

Solutions of the inherent problem of the equivalence in direct current resistivity and electromagnetic methods through global optimization and joint inversion by successive refinement of model space     

S.P. Sharma  S.K. Verma 《Geophysical Prospecting》2011,59(4):760-776

The problem of equivalence in direct current (DC) resistivity and electromagnetic methods for a thin resistive and conducting layer is well‐known. Attempts have been made in the past to resolve this problem through joint inversion. However, equivalence still remains an unresolved problem. In the present study, an effort is made to reduce non‐uniqueness due to equivalence using global optimization and joint inversion by successive refinement of the model space. A number of solutions derived for DC resistivity data using very fast simulated annealing global inversion that fits the observations equally well, follow the equivalence principle and show a definite trend. For a thin conductive layer, the quotient between resistivity and thickness is constant, while for a resistive one, the product between these magnitudes is constant. Three approaches to obtain very fast simulated annealing solutions are tested. In the first one, layer resistivities and thicknesses are optimized in a linear domain. In the second, layer resistivities are optimized in the logarithmic domain and thicknesses in the linear domain. Lastly, both layer resistivities and thicknesses are optimized in the logarithmic domain. Only model data from the mean models, corresponding to very fast simulated annealing solutions obtained for approach three, always fit the observations. The mean model defined by multiple very fast simulated annealing solutions shows extremely large uncertainty (almost 100%) in the final solution after inversion of individual DC resistivity or electromagnetic (EM) data sets. Uncertainty associated with the intermediate resistive and conducting layers after global optimization and joint inversion is still large. In order to reduce the large uncertainty associated with the intermediate layer, global optimization is performed over several iterations by reducing and redefining the search limits of model parameters according to the uncertainty in the solution. The new minimum and maximum limits are obtained from the uncertainty in the previous iteration. Though the misfit error reduces in the solution after successive refinement of the model space in individual inversion, it is observed that the mean model drifts away from the actual model. However, successive refinement of the model space using global optimization and joint inversion reduces uncertainty to a very low level in 4–5 iterations. This approach works very well in resolving the problem of equivalence for resistive as well as for conducting layers. The efficacy of the approach has been demonstrated using DC resistivity and EM data, however, it can be applied to any geophysical data to solve the inherent ambiguities in the interpretations.  相似文献   

Transient electromagnetic field in magneto-viscous medium     

Felix M. Kamenetsky  George M. Trigubovich 《Journal of Applied Geophysics》2011,75(2):373-378

When using Transient Geo-Electromagnetics (TEM) unusually slow decaying transients are sometimes observed in the absence of well-conductive objects. Many researchers explain this phenomenon by presence of material with magneto-viscous or superparamagnetic (SPM) properties. The analysis of electromagnetic (EM) field equations in conductive SPM medium is suggested in the present paper. It is shown that in a simplest case of small size single-domain magnetic particles with relative higher potential barrier energy, the SPM-medium is characterized by a very slow decaying exponential transient magnetic field, the level of which is much more as compared to that of due to non-magnetic medium of the same conductivity. This situation is traced up to the late transient time like 0.1 s and more. SPM and Induction fields are in the near zone additive. They depend in a different way on the superparamagnetic and electric properties of the SPM-medium. They also depend in different ways on the transient time and on the size of the transmitter–receiver configuration. These characteristics make it possible to recognize the presence of SPM-effect and to separate these fields.  相似文献   

海洋拖曳式水平电偶源数值模拟与电场接收机研制   总被引：6，自引：6，他引：0       下载免费PDF全文

陈凯  景建恩  魏文博  盛堰  罗贤虎  陈光源  史心语 《地球物理学报》2013,56(11):3718-3727

海洋天然气水合物资源调查中,电磁法已成为地震勘探最有效的补充手段之一,而我国海洋水合物电磁探测中的拖曳式电场接收机此前是空白.本文从方法原理、仪器设备和海洋试验等方面,对海洋拖曳式水平电偶极-偶极方法进行研讨.建立三维电阻率模型,进行数值模拟,讨论收发距、发射频率、拖曳装置离海底高度等参数与电场异常响应的关系,针对特定模型给出了最佳观测参数以指导仪器硬件设计与海洋测试.在此基础上,采用高级嵌入式计算机的智能化控制、前端低噪声斩波放大、高精度同步采集等技术,研制了由拖体、承压舱、采集电路、低噪声电场传感器等组成的海洋拖曳式水平轴向电场接收机,其系统噪声达到2 nV/√HZ @(1~100Hz).将自主研制的电场接收机用于国内首次拖曳式电偶极-偶极方法的海洋试验与评估,并对海试资料进行了处理与分析.研究结果表明,所研发的仪器达到了设计指标,能够用于海洋天然气水合物调查.  相似文献   

EH-4连续电导率仪在西南岩溶地区找水中的应用   总被引：1，自引：0，他引：1  

谢兰芳  廖圣柱  周传公 《安徽地质》2011,21(1):63-65,76

针对西南岩溶地区水文地质构造及富水性特征,利用EH-4电磁测深剖面的电阻率差异确定在缺水区域的井孔位置;并对典型案例进行介绍;最后对在工作过程中的经验认识进行总结概括,希望对今后类似地区进行找水起到一定的指导作用。  相似文献   

Unsupervised change detection in multitemporal SAR images using MRF models     

Liming Jiang  Mingsheng Liao  Lu Zhang  Hui Lin 《地球空间信息科学学报》2013,16(2):111-116

An unsupervised change-detection method that considers the spatial contextual information in a log-ratio difference image generated from multitemporal SAR images is proposed. A Markov random filed (MRF) model is particularly employed to exploit statistical spatial correlation of intensity levels among neighboring pixels. Under the assumption of the independency of pixels and mixed Gaussian distribution in the log-ratio difference image, a stochastic and iterative EM-MPM change-detection algorithm based on an MRF model is developed. The EM-MPM algorithm is based on a maximiser of posterior marginals (MPM) algorithm for image segmentation and an expectation-maximum (EM) algorithm for parameter estimation in a completely automatic way. The experiment results obtained on multitemporal ERS-2 SAR images show the effectiveness of the proposed method.  相似文献   

三套国外TEM软件正反演结果对比     

王兴春  武军杰  邓晓红  张杰  杨毅 《物探与化探》2012,36(3):507-510

在对三套国外瞬变电磁软件Maxwell、EM vision和Emigma研究分析的基础上,设计均匀半空间、层状介质和均匀半空间加载板状体及棱柱体的模型,逐一比较分析三套软件的异同,并进行了均匀半空间和层状介质的1D反演,通过模拟计算和结果分析,比较不同条件下各软件的特点和结算结果的准确性。结果表明,在均匀半空间和层状介质条件下,三套软件的正演计算结果能完全吻合,但瞬变电磁3D正演问题还未从根本上得以解决。  相似文献   

多波束测深系统内部参数的设定与校准          下载免费PDF全文

白大鹏  梅赛  于得水  陆凯 《海洋测绘》2012,32(5):19-21

以EM710RD多波束测深系统为例,通过高精度测量获得的系统参数,对该系统内部参数的设定与校准过程进行详细分析,从而为多波束测量外业工作提供参考依据。  相似文献   

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韩晶  邓喀中  李北城 《大地测量与地球动力学》2012,32(4):94-98

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