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通过时间-频率转换关系,TEM数据可以转换成平面波场测深数据,从而可以对TEM资料进行拟平面波场处理解释.在对瞬变电磁视电阻率数据向平面波场测深视电阻率数据转换时,发现由于瞬变电磁使用晚期计算公式及装置问题,使测深曲线早期数据发生畸变.文中建立了视电阻率曲线进入晚期所满足的关系式,从理论上给出不同情况下瞬变电磁测深视电阻率曲线进入晚期的临界点.以瞬变电磁、大地电磁、CSAMT为例,对大量的模型进行正演计算,对计算结果进行对比分析,建立不同地表电性结构、不同时间延迟情况下,瞬变电磁早期数据误差的校正量板. 相似文献
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对于接地源时间域瞬变电磁法,当选取适当的激励波形后,可将辐射场与自有场分离开来, 实现频率域电磁法无法实现的近源深部勘探;水平分层大地的解析分析表明,随着偏移距的缩短,接地导线源的场对地层的反映变得更为灵敏;时间域瞬变电磁法的探测深度主要由观测时长决定.基于接地源近场测深的优越性,作者提出短偏移瞬变电磁探测技术并首次命名为SOTEM, 采用了1000 m的偏移距对埋深为1400 m的某盐矿溶腔进行探测, 在全期视电阻率-深度剖面上圈定的溶腔分布被钻孔所揭露, 验证了SOTEM方法的探测能力.该方法为大深度、高分辨探测地下矿产资源提供了新的技术手段. 相似文献
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由于人工源电磁探测效果与收发距离有一定关系，本文首先分析了收发距离为零的中心回线源瞬变电磁法（Transient Electromagnetic Method，TEM）视电阻率定义和算法特点，回溯了从圆形回线到矩形的修正式中心回线装置的发展过程；概述了从中心回线发展到接地导线源短偏移瞬变电磁（Short-Offset TEM，SOTEM）理论上的可行性；列举了将LOTEM（Long-Offset TEM）从数倍于探测深度的观测区推进到近源区后的探测实例.对于频率域人工源电磁法，介绍了起源于MT（Magneto-Telluric）的CSAMT（Controlled Source Audio-frequency Magneto-Telluric）与电磁频率测深法不同发展道路.电磁频率测深将观测区从远区推进到了中区；广域电磁法通过全区视电阻率新定义不仅提高了解释精度，而且将传统CSAMT远场观测模式推进到中区探测模式；最后指出，如能采用新的点微元假设计算方法，可有望分离自有场和辐射场，实现频域电磁近源探测. 相似文献
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在地球物理电(磁)法正演计算中常涉及贝塞尔函数积分,快速汉克尔数字滤波是最常用的计算方法之一.然而不同的汉克尔滤波系数,计算结果的精度也有所差异.本文对比了五组高精度快速汉克尔长滤波系数的计算精度,分析了不同核函数对计算精度的影响;同时将五种滤波系数应用于电阻率测深法、频域电磁测深法、瞬变电磁测深法的正演计算中,比较了不同滤波系数对响应和视电阻率模拟时精度的变化关系.经过大量的模型计算表明:滤波的精度并不单纯的只与滤波系数个数有关,而是多种因素综合作用的结果.本文的研究对于电(磁)法正演计算汉克尔滤波系数的选择具有指导作用,有利于节省计算机资源,提高计算效率. 相似文献
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电性源地空瞬变电磁法具有工作效率高、勘探深度大、采集信号信噪比高、适用于地形地质条件复杂地区等优点.但是,到目前为止,由于尚未建立起该方法的解释系统,大大制约了该方法的发展.本文旨在建立起完整的地空电磁探测系统,丰富整个探测系统的理论.本文围绕地空瞬变电磁法全域视电阻率定义、瞬变电磁虚拟波场的克希霍夫偏移成像、逆合成孔径成像方法三个科学问题进行了系统研究.提出了用磁场强度定义全域视电阻率的迭代算法,理论模型试验结果表明计算出的视电阻率曲线首支趋于第一层电阻率,尾支趋于最后一层电阻率,实现了全空域、全时域视电阻率的计算;在先前研究的基础上,实现了适合电性源地空装置的瞬变电磁虚拟波场的克希霍夫偏移成像;采用相关迭加技术,实现孔径内多测点数据合成,将传统的单点处理方式发展成为逐点推移多次覆盖的逆合成孔径处理方法.层状模型试验表明:(1)全域视电阻率能够光滑、完整、渐变地反映出模型的电性信息变化;(2)当改变三层模型中间层电阻率时,全域视电阻率曲线随着参数的改变分异明显,对电性层的识别容易且直观;(3)由于在电阻率计算中同时考虑了接收机高度、偏移距、时间等各参数的影响,全域视电阻率可实现全空域、全时域的视电阻率计算.含水采空区的复杂模型算例表明:(1)根据不同测线的全域视电阻率结果可以看出,在靠近采空区的位置,全域视电阻率断面可以清晰地反映出采空区的空间位置,随着测线离采空区越来越远,采空区异常越来越弱直至消失;(2)波场变换和偏移成像的结果显示存在两个电性差异较大的界面,上界面指示地表,由于空气和大地之间的电性差异较大,故该界面波场信号反映强烈,遍布整个区域,下界面异常信号则主要集中在中部,向外逐渐减弱,指示采空区;(3)逆合成孔径成像结果表明地表界面在合成前后没有变化,而采空区异常合成后范围明显变小,且异常边界清晰,指示的采空区位置与模型吻合很好.本文借助于逆合成孔径雷达成像的基本思想,建立了一套电性源瞬变电磁地空逆合成孔径成像方法.基于反函数思想结合迭代算法提出的电性源地空瞬变电磁法的全域视电阻率定义方法,实现了全空域、全时域的视电阻率计算;借鉴瞬变电磁拟地震偏移成像算法,实现了瞬变场的三维成像;借鉴逆合成孔径雷达的思想,提出电性源瞬变电磁地空逆合成孔径算法,进一步提高了成像的分辨率.采空区模型算例表明相关叠加合成确实具有增强有用信号、提高信噪比、提高分辨率的诸多优点,证实了瞬变电磁地空逆合成孔径成像方法的有效性. 相似文献
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S-s方式瞬变电磁测深资料处理方法研究 总被引：5，自引：0，他引：5
根据半无限均匀介质空间中电磁场的表达式,本文分析了S-s方式瞬变电磁测深法的全区视电阻率定义的基本性质并讨论了求解方法.在此基础上,引入了基于感应电动势的"虚拟全区视电阻率"概念,从而解决了全区视电阻率的解的唯一性和存在性等问题.理论算例表明,"虚拟全区视电阻率"能较好的反映地下一维电性层电性垂向变化特征,故对瞬变电磁测深资料的定性解释有一定的实际应用价值,同时对一维反演(构制初始模型和确立目标函数)也有重要意义. 相似文献
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《地球物理学进展》2015,(1)
电性源瞬变电磁法的基本理论是建立在水平电偶极子的基础之上的,但是实际生产中发射源常为接地长导线,随着短偏移距观测方式的实现,一方面发射源的尺寸不能忽略,偶极子条件不再成立,需要新的方式计算电磁场响应;另一方面,受制于场地条件,发射源可能无法水平、笔直地铺设,这种源形态上的改变必然会对接收点处的响应带来影响,并最终影响到数据解释.本文从电性源一维正演理论出发,研究了发射源发生偏移和弯曲给电磁响应和视电阻率带来的影响,并以某金矿探测为实例做出了验证和说明.研究认为源形态的改变对电磁响应和视电阻率造成的影响随着偏移距的改变而改变,对于电磁响应,偏移距越大影响越小,而对于视电阻率,偏移距越大影响越大.因此在实际生产中应尽量保证源的正规铺设,详细记录实际源的坐标位置与形状,并尽量在偏移距较小的区域内观测. 相似文献
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D. PATELLA 《Geophysical Prospecting》1980,28(6):956-960
In this paper a theorem is demonstrated which allows—after the introduction of a suitable dipole kernel function or dipole resistivity transform function—to write the apparent resistivity function as an Hankel transformable integral expression. As a practical application of the theorem a procedure of quantitative interpretation of dipole soundings is suggested in which the dipole resistivity transform function obtained after inversion of the original dipole apparent resistivity data is used to control the goodness of the set of layering parameters which have been derived with our previous method of transformation of dipole sounding curves into equivalent Schlumberger diagrams. 相似文献
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The analytical solution and algorithm for simulating the electric potential in an arbitrarily anisotropic multilayered medium produced by a point DC source is here proposed. The solution is presented as a combination of Hankel transforms of integer order and Fourier transforms based on the analytical recurrent equations obtained for the potential spectrum. For the conversion of the potential spectrum into the space domain, we have applied the algorithm of the Fast Fourier Transform for logarithmically spaced points. A comparison of the modelling results with the power‐series solution for two‐layered anisotropic structures demonstrated the high accuracy and computing‐time efficiency of the method proposed. The results of the apparent‐resistivity calculation for both traditional pole‐pole and tensor arrays above three‐layered sequence with an azimuthally anisotropic second layer are presented. The numerical simulations show that both arrays have the same sensitivity to the anisotropy parameters. This sensitivity depends significantly on the resistivity ratio between anisotropic and adjacent layers and increases for the models with a conductive second layer. 相似文献
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Ahmet T. Baokur 《Geophysical Prospecting》1999,47(2):149-177
Noise contamination of measured data greatly affects the final results of inversion. Three types of noise source — random and systematic errors and the uncertainties due to the inadequacy of the mathematical model in representing the actual physical conditions — are discussed in the framework of resistivity sounding data. Two methods are proposed for describing these uncertainties. The first possibility is to smooth the measured data by a combination of simple fitting functions that satisfies the ‘1D smoothness’ criteria and consequently simulates the behaviour of a 1D Schlumberger apparent resistivity curve. The second method is to derive weight coefficients from the differences between the measured and the smoothed data sets. Both methods are carried out under the control of the interpreter. The relative merits and drawbacks of the direct and iterative interpretation methods used for the estimation of the parameters of the layered earth model are summarized. Two variants of the combination of these methods are presented to obtain more powerful and automatic interpretation schemes. In the sequential interpretation, an initial guess supplied by the direct method is improved by the iterative method to obtain a reasonable fit between the measured data and the model response. In the simultaneous interpretation, the successive application of the direct and iterative methods is carried out, starting from the first branch of the apparent resistivity curve. The operation is then shifted to subsequent branches that represent the deeper parts of the geoelectric section. This is similar to the data acquisition applied in direct current sounding in which the depth penetration is increased by expanding the current electrode spacings. The proposed sequential and simultaneous interpretation algorithms require minimum aids and efforts of the interpreter. 相似文献
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DEEP TECTONIC STRESS CHANGE BASED ON LONG-TERM APPARENT RESISTIVITY TIME SERIES: A CASE STUDY FROM NORTH SECTION OF YISHU FAULT ZONE 
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下载免费PDF全文 Almost all the destructive earthquakes, so called tectonic earthquake, are produced by tectonic movement. The tectonic movement will cause resistivity changes in the earth. It's valuable for strong earthquake forecast to study the relationship between the resistivity change and tectonic movement. According to magnetotelluric sounding method, we establish a robust estimate method to calculate the long-term apparent resistivity from seismic station monitoring data. We first use 1D layered earth models to test the sensitivity of this method. Then we process the continually observed long term electromagnetic data in 4 years (from 2011 to 2014) from Anqiu seismic station which is very close to the north section of Yishu fault zone. The apparent resistivity curves and the apparent resistivity time series for different frequencies are obtained. The time series show the resistivity increase in the selected 4 years, which is in good agreement with the GPS baseline data. This also satisfies the results from rock mechanics experiments on deep rocks (upper mantle) that the resistivity will increase with improved stress in a high temperature and pressure environment. The method is valuable for studying electromagnetic precursor of strong earthquakes and strong earthquake prediction. 相似文献
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Matrix equations are derived to transform the resistivity sounding data obtained in one type of a four-electrode array to the corresponding resistivity sounding data that would be obtained using a different four-electrode array. These expressions are based primarily on recent work in which we have established a linear relation between the apparent resistivity and the kernel function by using a powerful exponential approximation for the kernel function. It is shown that the resistivity sounding data of two different four-electrode arrays have a linear relation through an essentially non-singular matrix operator and, as such, one is derivable from the other for a one-dimensional model and it can also be extended to two-dimensions. Some numerical examples considering synthetic data are presented which demonstrates the efficiency of the method in such transformations. Two published field examples are also considered for transformation giving a reliable interpretation. 相似文献
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A. T. BAOKUR 《Geophysical Prospecting》1984,32(1):132-138
Different sets of filter coefficients for the linear filter technique for the computations of resistivity and EM sounding curves are evaluated for several electrode and coil configurations. Instead of this procedure, the two-electrode filter can be used for computations of Wenner, Schlumberger, and dipole—dipole apparent resistivity model curves by defining convolutional expressions which contain the new input functions in terms of the resistivity transform function. Similarly, the Schlumberger filter performs the computations of dipole—dipole apparent resistivity model curves. The Wenner, Schlumberger, and dipole—dipole filter functions are defined in terms of the two-electrode filter using the new convolutional expressions. A relationship between the Schlumberger and dipole—dipole filter functions is given. The above arguments are adopted for the computations of EM sounding curves. It is shown that the EM filter for the horizontal coplanar loop system (which is identical to the two-electrode filter) performs the computations of the mutual coupling ratios for perpendicular, vertical coplanar, and vertical coaxial loop systems. In the same way, the Schlumberger filter can be used to compute vertical coaxial sounding curves. The corresponding input functions are defined in terms of the EM kernel for all convolutional expressions presented. After these considerations, integral expressions of the mutual coupling ratios involving zero-order Bessel function are derived. The mutual coupling ratio for the vertical coaxial loop system is given in the same form as the mutual coupling ratio for the vertical coplanar loop system. 相似文献
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频率域可控源电磁是在大地电磁测深的基础上发展起来的一种人工源电磁测深法,其二维电磁响应的计算须采用数值模拟方法.本文以Matlab为程序编译工具,采用双二次插值的有限单元法,推导出相应的计算公式.为了模拟无穷远边界及满足计算机的内存需求,在保证计算精度的情况下设计了非均匀网格剖分.在程序编制中,只存储有限元系数矩阵的非零元素,大大减少了正演计算的时间.针对频率域可控源电磁法中卡尼亚电阻率在过渡区和近区畸变的问题,给出了全区视电阻率的迭代公式,并对典型的一维层状模型以及简单二维模型进行了计算.过渡区和近区数据经过校正后,可以正确反映出模型的地电特征,证明了线源下近区勘探的可能性. 相似文献
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利用逆重复M序列伪随机信号良好的自相关特性,提出相关检测地电传输特性的编码电磁勘探法.分析了编码电磁测深原理及参数提取方法.同时记录发送电流信号和多收发距电磁场响应,对源信号和场信号进行相关运算,解卷积分离接收系统响应后可得到大地的频率特性或时间特性,以此实现地电断面的精细探测.在时间域,大地冲激响应和阶跃响应含有丰富的地电信息.通过冲激响应的峰值时间或阶跃响应的晚期渐近值可估计地电阻率分布.基于层状模型的大地冲激响应和阶跃响应正演计算结果表明,编码电磁测深法对大埋深薄层目标体有精细的分辨能力.可应用于能源、矿产资源、水资源、环境地质及工程地质勘察,有良好的应用前景. 相似文献