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A numerical experiment has been applied to explore the potentialities and the limitations of the inversion of IP-affected TEM responses of a two-layer earth with a polarizable layer above (Model 1) or below (Model 2) a nonpolarizable layer. The IP effects have been incorporated into the models via a Cole–Cole complex frequency-dependent conductivity. One of us computed synthetic in-loop and coincident-loop transient responses with added Gaussian noise, and the other performed single and joint inversion of the two sets of pseudo-experimental data. Model 1 turns out to be advantageous over Model 2 in TEM applications and gives a good fit of the Cole–Cole parameters (chargeability, IP time constant, and exponent) even in the absence of a priori information. In the case of Model 2, the lack of a priori information causes problems as to recognize which layer is polarizable, and the fit of the Cole–Cole parameters is generally worse. The layer thicknesses and resistivities are rather accurate in both groups of models, irrespective of whether a priori information is available. As the upper layer increases in thickness (H1), the fit of its parameters ever improves in both models while the parameters of the lower layer, on the contrary, contain a greater error. Joint inversion of in-loop and coincident-loop transients improves the fit in most cases.Relative rms error (σrel) does not depend on the upper layer thickness for Model 1 but decreases as H1 increases in the case of Model 2. The error in joint inversion is times that in single inversion, which means that additional criteria other than σrel may be useful to estimate the inversion quality. 相似文献
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去除水平均匀大地和二层大地视复电阻率谱中感应耦合效应的谱激电反演 总被引：1，自引：0，他引：1
在频率未达相位峰值频率时,不极化水平均匀大地和二层大地的感应耦合谱的每个频段都可近似地用一个Cole-Cole谱拟合。极化水平均匀大地和底层极化的二层大地的总视复电阻率谱的每个频段都可用乘法或加法组合的两个Cole-Cole谱很好拟合,反演得到的激电谱都近似等于激电效应的贡献,但只有乘法组合反演得到的感应耦合才能代表感应耦合的贡献。 相似文献
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在地球物理勘探过程中,观测数据有限且存在误差,导致反演结果存在非唯一解。为了解决非唯一性问题,笔者研究了交叉梯度数学理论,实现了用交叉梯度约束2D 大地电磁和地震初至波走时的联合反演,并建立了2个模型。通过各自模型实验和不同模型间的对比,证明了交叉梯度联合反演比单独反演修复几何形态和物性参数的效果好,且交叉梯度与岩石物性无关;利用得到的交叉梯度图进一步证明了联合反演模型相似度高,也从交叉绘图中得到联合反演的物性关系更好的结论,反向证明了联合反演的正确性。 相似文献
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《Russian Geology and Geophysics》2014,55(12):1452-1460
Lenses of water-saturated unfrozen rocks (taliks) in permafrost are important sources of freshwater in high-latitude regions. Taliks stand out against the host frozen rocks in much lower resistivity and thus are detectable by resistivity surveys. TEM soundings are especially efficient in this application as they can go without galvanic grounding, have small offsets, and are sensitive to buried conductors. Early-time TEM data in the Taz area of the Yamal-Nenets district bear strong effects of fast-decaying inductively induced polarization (IIP), which rules out the use of nonpolarizable earth assumption for their interpretation. The TEM responses are inverted by means of the TEM-IP software using the model of a polarizable earth with Cole-Cole complex frequency-dependent conductivity. The resulting earth model mainly includes three layers, with a 100 to 250 m thick highly resistive polarizable upper layer. The polarization parameters of the layer (chargeability, time constant and exponent) are typical of frozen sedimentary rocks, while the presence of a talik reduces notably the effective resistivity and chargeability. This feature can be used as a guide to taliks, as it was confirmed by TEM surveys and subsequent drilling.© 2014, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. 相似文献
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We have simulated ungrounded horizontal loop transient responses of a two-layer earth consisting of a magnetically viscous layer above (model 1) or below (model 2) a nonmagnetic layer. The transient responses of a two-layer magnetically viscous earth can be computed using the superposition principle because magnetic relaxation and eddy current responses are independent at electrical conductivities typical of the real subsurface. The transients are presented and analyzed in the form of Y = f(h1) functions, where h1 is the upper layer thickness and Y is the response (at some fixed time) of a two-layer ground normalized to that of a uniform ground with its magnetic viscosity as in the upper (model 1) or lower (model 2) layer. In model 1, the Y function increases as magnetic viscosity grows in the upper layer while the latter is thinner than the loop size, but the magnetic relaxation responses of a thicker upper layer are almost identical to that of a uniform magnetically viscous ground. In model 2, the Y responses are likewise almost identical to that of a uniform magnetically viscous ground (h1 = 0) as far as the thickness of the upper layer remains small, but they decrease, first slowly and then ever more rapidly, after the layer becomes 15–20% thicker than the transmitter size. The effective sounditng depth in a magnetically viscous ground being controlled by the size of the transmitter, it is reasonable to use geometrical sounding to resolve the vertical distribution of magnetic viscosity. 相似文献
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视复电阻率频谱的一种近似反演方法 总被引：5，自引：0，他引：5
Luo Yanzhong Fang Sheng 《地球科学》1986,(1)
基于稀释系数不随频率变化的假设,导出了复电阻率视频谱与真频谱及柯尔-柯尔频散视参数与真参数之间的近似关系式。通过对理论视频谱进行的反演和计算证明,即使在稀释系数幅值随频率的相对变化达100%的情况下,选用特征频率的稀释系数值,所导出的视参数与真参数的近似关系式仍有实用价值。从而为频谱激电法资料的反演,计算极化体真参数提供了一种简便而有效的近似方法。 相似文献
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Hou Weisheng Cui Chanjie Yang Liang Yang Qiaochu Clarke Keith 《Mathematical Geosciences》2019,51(1):29-51
In each step of geological modeling, errors have an impact on measurements and workflow processes and, so, have consequences that challenge accurate three-dimensional geological modeling. In the context of classical error theory, for now, only spatial positional error is considered, acknowledging that temporal, attribute, and ontological errors—and many others—are part of the complete error budget. Existing methods usually assumed that a single error distribution (Gaussian) exists across all kinds of spatial data. Yet, across, and even within, different kinds of raw data (such as borehole logs, user-defined geological sections, and geological maps), different types of positional error distributions may exist. Most statistical methods make a priori assumptions about error distributions that impact their explanatory power. Consequently, analyzing errors in multi-source and conflated data for geological modeling remains a grand challenge in geological modeling. In this study, a novel approach is presented regarding the analysis of one-dimensional multiple errors in the raw data used for model geological structures. The analysis is based on the relationship between spatial error distributions and different geological attributes. By assuming that the contact points of a geological subsurface are decided by the geological attributes related to both sides of the subsurface, this assumption means that the spatial error of geological contacts can be transferred into specific probabilities of all the related geological attributes at each three-dimensional point, which is termed the “geological attribute probability”. Both a normal distribution and a continuous uniform distribution were transferred into geological attribute probabilities, allowing different kinds of spatial error distributions to be summed directly after the transformation. On cross-points with multiple raw data with errors that follow different kinds of distributions, an entropy-based weight was given to each type of data to calculate the final probabilities. The weighting value at each point in space is decided by the related geological attribute probabilities. In a test application that accounted for the best estimates of geological contacts, the experimental results showed the following: (1) for line segments, the band shape of geological attribute probabilities matched that of existing error models; and (2) the geological attribute probabilities directly show the error distribution and are an effective way of describing multiple error distributions among the input data.
相似文献11.
为提高饶河流域洪水预报精度,将全过程联合校正(EPJC)方法与三水源新安江(XAJ)模型结合,按一定比例划分洪水预报总误差为各过程误差,基于系统响应理论反演得到面雨量计算误差和模型参数误差,重新输入流域水文模型正演得出校正后的洪水过程。选取洪峰流量相对误差、峰现时间绝对误差、径流深相对误差和确定性系数作为模型评价指标,量化XAJ预报与EPJC校正结果,并与传统的动态系统响应曲线(DSRC)方法进行对比。结果表明,EPJC能够考虑全过程误差,与实际误差分布情况更相符,可提升饶河流域的洪水作业预报精度,值得进一步研究与推广。 相似文献
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In the differentially normalized method of electromagnetic sounding (DNME), the transmitter and receiver are grounded electrical circuits. The conduction and polarization properties of a section are studied by measuring the electrical potential difference (ΔU(t)) and the second potential difference (Δ2U(t)); the latter characterizes the spatial inhomogeneity of the electromagnetic field. Measurements of Δ2U(t) are strongly influenced by three-dimensional inhomogeneities within the receiver spread. To reduce this effect, measurements are made in two positions (left and right) of the transmitter circuit relative to receiver with subsequent averaging of the measured data. Often in field studies, the transmitter and receiver circuits are at an angle to each other, and the use of two transmitters in measurements leads to the need to determine a generalized transmitter for one-dimensional forward numerical modeling of field data.The effect of the off-axis (diagonal) position of the transmitter and receiver circuits on the data of electromagnetic pulse sounding and their inversion for a one-dimensional polarizable conducting medium have been studied in real and numerical experiments. In modeling, the effect of induced polarization (IP) is taken into account by introducing the resistivity frequency dispersion (Cole-Cole equation). Validity of the calculation of the generalized transmitter is estimated for the solution of the one-dimensional forward problem with the inversion of field diagonal measurements. The effect of three-dimensional objects on the results of measurements using the above observation system is estimated by solving the 3D forward problem for a polarizable conducting medium. 相似文献
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We apply the representer method, a data assimilation algorithm, to single-phase Darcy flow in porous media. The measurement
array that yields the assimilated data can be expressed as a vector of linear functionals of pressure. The a priori discretization
errors in the representer method are analyzed in terms of the convergence properties of the underlying numerical schemes used
in each part of the algorithm. We formulate some proof-of-concept numerical experiments that illustrate the error analysis. 相似文献
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S. R. Joshi 《Environmental Geology》1989,14(3):203-207
Four possible sources of analytical error in the measurement of unsupported210Pb and/or nuclear fallout radionuclide (such as137Cs) profiles in sediment cores are pointed out. Each of these errors, if present, can significantly alter the true profile of the radionuclide under consideration. It is shown that simple procedural modifications can substantially improve the quality of analytical data that are subsequently used to develop intricate mathematical models to aid the interpretation of observed radionuclide profiles. 相似文献
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大地的感应激发极化效应有时会在瞬变电磁晚期响应上产生负值变号现象。常规实电阻率瞬变电磁反演由于没有考虑激发极化效应,对于观测数据负值部分的解释一直存在问题,这影响了反演解释的真实性和可信度。对此,本文首先将Cole-Cole复电阻率模型加入正演计算,并验证了计算的准确性。然后在阻尼最小二乘法的基础上加入Occam平滑约束来构建反演方程,能够同时反演出零频电阻率、充电率、时间常数以及频率相关系数,实现了一维瞬变电磁复电阻率反演算法。最后,建立具有不同程度激发极化效应的典型层状理论模型进行反演试算与结果分析,结果表明,在激发极化效果明显的低阻高极化地层中,复电阻率反演效果更好。与实电阻率反演结果的对比说明,瞬变电磁复电阻率反演既可以达到实电阻率的常规反演效果,也能解决实电阻率无法实现的负值拟合问题。 相似文献
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This paper reviews the validity of earlier models obtained after quantitative interpretation of GDS data and presents a fresh
model using the inversion scheme EM2INV. The 2-D inversion of data is more objective than the earlier interpretation performed
by using trial and error method. The inversion results indicate that the present model differs from the earlier ones. The
reason could be that available GDS data are sufficient only for deriving the horizontal variation of subsurface resistivity.
In order to study the vertical resistivity variation additional MT sounding data would be required. It would therefore be
desirable to carry out MT survey in the specified area. A more comprehensive/appropriate model could be derived from joint
inversion of GDS and MT data. 相似文献
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时移地球物理监测是观测地下物性参数随时间动态变化的有效方法。地球物理反演结果会受到测量误差、测量环境的噪声污染以及地球物理反演多解性等系统性因素的影响。如果对时移地球物理数据进行不同时刻数据的单独反演,可能会导致不同时刻的反演结果可对比性差,从而影响时移地球物理的监测效果。针对可控源音频大地电磁法在监测领域的实际需求,将不同时刻的观测数据放在一起反演,不同时刻的电阻率模型相互约束,实现了时移可控源音频大地电磁法三维反演。设计三种类型模型进行合成数据的单独反演和时移反演对比试算,验证了时移反演算法的有效性。反演结果表明：通过加入相邻时刻模型约束,时移反演可以更好地聚焦异常体的位置,降低噪声以及测量环境变化对反演结果的影响,防止反演伪影掩盖真实的地下变化。研究成果为时移可控源音频大地电磁法的实际应用奠定了良好基础。 相似文献
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Norman Fry 《Journal of Structural Geology》1979,1(3):221-229
For a homogeneously deformed rock composed initially of an isotropic distribution of object shapes, finite strain may be determined from the correlation between the orientations of either two-dimensional or one-dimensional sample cuts and the frequencies with which they intersect marker objects. Mimran previously published an incorrect method for planar samples under the heading ‘density distribution technique’. Methods are described by which the three-dimensional strain may be directly determined from six general samples, either linear or planar. Construction of two-dimensional ellipses as an intermediate step is unnecessary and enforces practical difficulties.These methods may be simplified by use of samples parallel to known principal axes or planes of the finite strain. In this case the same large errors may arise from slight misorientation of samples as with other methods of strain measurement. A new quick method is proposed, combining linear and planar measurements of frequencies of intersected objects, which is thought to be the first method to circumvent a large part of the error from this error source. For example, if true X:Z ratio is 9 : 1, and orientations in the XZ plane are misjudged by 8°, normal methods give 38% error where the new method gives, with care, an error of 1.9%. For methods of strain measurement such as are described here the concept of strain ellipsoid is unnecessarily limiting, and should be abandoned. 相似文献