Transient Electromagnetic Method Research Articles

Borehole transient electromagnetic stereo imaging method based on horizontal component anomaly feature clustering

In the present study, according to the borehole transient electromagnetic method, the transceiver is placed into the borehole in front of the heading face for the purpose of detection. This can not only avoid the interference of metal support in the roadway, but also detect the hidden disaster-causing water body within a short distance. However, there is an issue of abnormal location in borehole transient electromagnetic method. In order to determine the location of transient electromagnetic anomalies in the borehole, the transient electromagnetic three-dimensional forward modeling is used to analyze the response characteristics of three components. According to the response characteristics of the horizontal component of the abnormal body in different quadrants, a method for calculating the rotation angle of the XOY plane of the abnormal center is proposed, based on the amplitude of the horizontal component and the abnormal quadrant. The resistivity of each depth calculated by the vertical component is regarded as an independent abnormal body, and the depths' mapping relationship with the sampling time is established. Next, based on K-means clustering, the corresponding characteristic value of horizontal component anomaly curve are binary classified, and the resistivity distribution quadrant of the entire data set is automatically divided. Finally, the borehole transient electromagnetic inversion resistivity stereo imaging method is obtained. The algorithm of this paper is used to calculate the stereo imaging of the three-dimensional numerical model, and the results show that the algorithm achieves good results for the small-scale and low resistivity abnormal body in the radial direction of the borehole. In summary, the method of borehole transient electromagnetic stereo imaging based on clustering is an organic combination of geophysics and machine learning, which can provide technical support for advanced detection and fine interpretation of hidden water damage in underground heading faces.

Three‐dimensional inversion of semi‐airborne transient electromagnetic data based on finite element method

ABSTRACTThe semi‐airborne transient electromagnetic method is characterized by a large detection depth, high signal‐to‐noise ratio, fast acquisition rate, low cost, and ability to be used for exploration in scenarios with complex geological conditions. As a result, the semi‐airborne transient electromagnetic method has a great potential in the fields of mineral exploration, hydrological study and geohazard detection. However, most of the existing semi‐airborne transient electromagnetic data interpretation methods still rely on one‐dimensional forward modelling and inversion, which could lead to an incorrect geological interpretation. In this paper, we develop a three‐dimensional inversion for semi‐airborne transient electromagnetic data to recover a reliable subsurface conductivity distribution. The forward modelling is based on the effective vector finite element method with an unstructured tetrahedral mesh, which is capable of simulating complex geo‐electric structures and the topography. Through the numerical experiments of several three‐dimensional synthetic models, we study the influence of the number of excitation sources, flight mode and complex topography on the inversion results. The synthetic model studies reveal that: (1) by increasing the number of excitation sources, we can obtain a higher resolution conductivity image with less artefacts; (2) the detectability can be increased by flying along the terrain when the topography is complex; (3) the topography should be considered in the forward modelling and inversion to obtain a reasonable conductivity model using the semi‐airborne transient electromagnetic method; and (4) the three‐dimensional inversion still works when the inhomogeneity is present nearby the transmitter.

Innovative Surface-Borehole Transient Electromagnetic Method for Sensing the Coal Seam Roof Grouting Effect

With the purpose of monitoring coal seam roof grouting, an innovative surface–borehole transient electromagnetic (TEM) method to compare the Earth resistivity distribution of the coal seam roof before grouting and after grouting is proposed. The TEM secondary field time–decay curve of the proposed surface–borehole TEM method is compared with that of the traditional surface TEM method. It is found that the time–decay curve of the former is very different from that of the latter. For the first time, forward modeling algorithm has been proposed to evaluate the TEM response characteristics of Earth, with an inversion algorithm developed to invert the measured data into resistivity distribution. A field work has been implemented with the customized equipment to evaluate the surface–borehole TEM method. In the field work, the proposed surface–borehole TEM measurement is performed twice, i.e., before and after the coal seam roof grouting. The analysis results demonstrated that the resistivity distribution had a distinct change near the depth of grouting with low resistivity distribution replaced by high resistivity distribution, which validates the effectiveness of the proposed surface–borehole TEM method.

Hybrid Memetic Pretrained Factor Analysis-Based Deep Belief Networks for Transient Electromagnetic Inversion

As a trenchless detection approach, the transient electromagnetic method (TEM) can effectively detect well-conducted geoelectric structures, such as groundwater structures. The nonlinear TEM inversion process represented by neural network (NN) inversion does not rely on the initial model, which helps it efficiently and accurately obtain geoelectric structures. In this article, a factor analysis (FA)-based deep belief network (DBN) inversion framework built on hybrid memetic pretrained (HMP), HMP-FADBN, is proposed. We construct a DBN with restricted Boltzmann machines (RBMs) and backpropagation NNs (BPNNs) as the base fitting skeleton. FA is used to reduce the dimensionality of the feature space of the DBN. The hybrid memetic (HM) whale optimization algorithm (WOA) pretrains the network parameters and uses the memetic strategy to adjust the coordinated development system of social and individual cognition to enhance the network training effect. Numerical examples show that the prediction accuracy of the proposed HMP-FADBN for TEM geoelectric models is improved from more than 10% to approximately 2%. Moreover, 5%, 10%, and 15% noise tests show that the trained NN has good generalization and denoising abilities, and the prediction accuracy is less than 3% (affected by the maximum noise). Finally, the developed method is successfully applied to a landslide TEM survey, and the predicted quasi-2D geoelectric structure is consistent with the original geological structure.

Using Wavelet Packet Denoising and a Regularized ELM Algorithm Based on the LOO Approach for Transient Electromagnetic Inversion

Transient electromagnetic method (TEM) inversion is a complex nonlinear problem with high dimensionality and ill-posedness. Using traditional neural networks based on a gradient algorithm to solve the TEM inversion problem might result in a slow convergence where the model falls easily into local minima. To solve these problems, a wavelet packet denoising (WPD) technology and a regularized extreme learning machine (ELM) algorithm based on the leave-one-out cross-validation (LOO) approach are proposed in this article. First, the WPD method is based on the hard threshold, the Shannon entropy with a Sym15 wavelet, which is provided to suppress the noise from the TEM data. Moreover, the learning process of the ELM model is optimized by randomly setting the hidden layer parameters instead of updating based on the gradient algorithm, which accelerates the learning speed. Finally, the LOO methodology is introduced to optimize the regularization factor of the ELM to improve the prediction accuracy and generalization ability of the approach. The inversion results of two typical TEM layered geoelectric models, two anomalous body models, and one field example are provided to prove the validity and feasibility of the proposed approach. In addition, compared with other traditional methods [ELM, backpropagation (BP), radial basis function (RBF), and linear support vector machine (LSVM)], the introduced method achieves higher inversion accuracy, better stability, and stronger forward data fitting ability, enabling it to effectively solve the TEM inversion problem.

Transient Electromagnetic Inversion: An ICDE-Trained Kernel Principal Component OSELM Approach

The traditional extreme learning machine (ELM) inversion of transient electromagnetic method (TEM) based on random initial weights is known to be inept for its low-computational efficiency and poor generalization performance. To solve these problems, a kernel principal component online sequential extreme learning machine (KPCOSELM) trained by an improved chaotic differential evolution (ICDE) method is proposed. An additional kernel principal component (KPC) layer is used, which reduces the dimension of TEM data and enhances the computational efficiency of online sequential extreme learning machine (OSELM). Moreover, a novel ICDE algorithm is presented for improving the learning ability and generalization performance of OSELM inversion. In the proposed ICDE, the tent chaotic sequence is adopted to enhance the global exploitation ability, and a constraint factor is added to ensure better convergence. The feasibility and effectiveness of the proposed inversion method are evaluated via four groups of experiments. The inversion results of the synthetic and field examples show that the proposed approach outperformed other methods in terms of computational efficiency and prediction accuracy, and realized satisfactory performance in TEM inversion, which provides a new strategy for the application of neural networks in TEM inversion.

Application Analysis of Various Geophysical Methods in Volume Calculation of Different Landfills

Garbage disposal has gradually become a key issue faced by environmental governance. What must be controlled in garbage disposal is the calculation of garbage volume. In this paper, according to the different landfill conditions of a landfill in Anhui, including: covering soil, overlying HDPE membrane, overlying concrete, etc., combined with the physical differences between the rock mass and the garbage at the bottom of the landfill. The landfill covered with HDPE membrane adopts the transient electromagnetic method, the landfill covered with soil layer adopts the high-density electrical method, and the landfill covered with concrete adopts the combination of transient electromagnetic method and ground penetrating radar. At the same time, Combines the borehole data to determine that the resistivity value of the interface between the garbage and the soil was 29 Ω⋅m. Finally, the sections of multiple survey lines can accomplish three-dimensional stereoscopic that calculate the distribution and actual volume of the garbage. This method is used to determine the final investment cost.

3-D Large-Scale TEM Modeling Using Restarting Polynomial Krylov Method

The transient electromagnetic (TEM) method is widely used in near-surface geophysical prospecting. The high-precision forward and inversion of large-scale complex models is a challenging problem. It is difficult to solve the large-scale problems using the direct solvers due to the large memory requirements. In this article, we present a restarting polynomial Krylov method for modeling 3-D large-scale TEM responses. The mimetic finite volume method is carried out for spatial discretization. The step-off TEM response then can be expressed as a matrix exponential function. The restarting polynomial Krylov method is used to solve the matrix exponential function. For a given restart subspace dimension, the residual is used to obtain the forward response at any time that meets the given accuracy. This method does not need to solve large-scale linear equations. Furthermore, the memory usage is mainly determined by the number of spatial discrete grids and the restart subspace order. The numerical experiments of large-scale model demonstrated that the method is accurate and uses limited memory.

Quasi-2-D Robust Inversion of Semi-Airborne Transient Electromagnetic Data With IP Effects

Semi-airborne transient electromagnetic (SATEM) method has been efficiently used recently in geophysical exploration due to its relatively portability compared to the standard airborne surveys. However, the SATEM data are often complicated by induced polarization (IP) effects manifesting as abnormal decay and sign reversal in the responses. The IP information can be extracted from SATEM data by joint inversion of the electromagnetic data into the electrical resistivity and IP parameters described in Cole-Cole model. In this paper, we introduce a quasi-two-dimensional inversion scheme to recover the resistivity and IP parameters from SATEM responses by (1) a fast semi-analytical method for Jacobian matrix calculation; and (2) a staged inversion strategy with lateral constraints. The methodology is examined on two synthetic polarized models. Our study indicates that the proposed scheme can improve inversion stability and recover the underground resistivity and IP property distributions.

TEM-NLnet: A Deep Denoising Network for Transient Electromagnetic Signal With Noise Learning

Transient electromagnetic (TEM) method is a widely adopted technology in geophysics. TEM signals received by coils will be disturbed by complex noises. Compared with traditional filtering-based methods, deep-learning-based TEM signal denoising methods achieved impressive denoising performance. However, the existing deep-learning-based methods rely heavily on simulated noise with a certain distribution to construct paired datasets for supervised learning. In real scenarios, if the noise distribution of acquired TEM signals has a huge difference (e.g., the type of noise distribution, the level of noise) with that of the simulated datasets, the trained model may not always be valid. To address this issue, a novel noise-learning-inspired deep denoising network (namely, TEM-NLnet) is proposed for TEM signal denoising. Specifically, instead of inserting the simulated noise, we first learn the noise appeared in real-world signals through generative adversarial networks (GANs), such that the generator can produce the learned noise to construct paired datasets for training. Then, a deep-neural-network-based denoiser is imposed to learn mapping from the noise TEM signal to the corresponding noise-free one. Extensive experiments on the simulated and actual geological datasets show that compared with other state-of-the-art TEM denoising methods, our proposed method achieves better performance in terms of quantitative and visual results. Models and code are available at <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://github.com/wmyCDUT/TEM-NLnet_demo</uri> .

Transient Electromagnetic 1‐Dimensional Inversion Based on the Quantum Particle Swarms Optimization‐Smooth Constrained Least Squares Joint Algorithm and Its Application in Karst Exploration

Before the construction of the bridge bored pile in the karst area, geological conditions of the excavation area should be investigated. In order to avoid the karst caves in underground space making adverse impacts on the construction, bearing capacity, and stability of pile foundation, in this paper, we use the transient electromagnetic method to detect the karst development in the bearing layer of the pile foundation, which is different from the traditional karst survey method. To improve the interpretation accuracy of transient electromagnetic detection for karst caves, the quantum particle swarm optimization (QPSO) algorithm was combined with the smooth constrained least squares (CLS) algorithm, and the transient electromagnetic inversion based on the QPSO‐CLS joint algorithm was generated. Better inversion results were achieved by the proposed method in this study. Based on the inversion calculation results of simulation data and field test data, it is further demonstrated that the QPSO‐CLS joint algorithm has high optimization efficiency without manually setting the initial model. The interpretation results are consistent with the theoretical model and drilling logging results, which proves the adaptability of the proposed algorithm.

Aftereffects in the Transient Electromagnetic Method: Inductively Induced Polarization

Abstract —Inductively induced electric polarization (IIP) is one of the aftereffects inherent in the geologic materials and affecting results of the transient electromagnetic method. Its effect on the inductive transient response manifests itself as a nonmonotonic EMF decay, including the polarity reversal. The dependence of IIP on many conditions makes it difficult to study the basic regularities in its manifestation. One of the ways to address this problem is to present the simulation results as a normalized transient response. From the most general point of view, the intensity and time range of the IIP manifestation are controlled by the competition between induction and induced polarization phenomena. Induced polarization manifests itself differently, depending on the transmitter used for the excitation of the ground response. Therefore, when studying polarizable ground, the results of the conventional IP method and those of the TEM method do not always correlate.

Influences of the Earth’s Magnetic Field on the Transient Electromagnetic Process in the Geoelectric Field: an Experimental Study

Abstract —A mathematical model of the influence of the Earth’s magnetic field (the Hall effect) on results of the controlled source transient electromagnetic (TEM) method has been elaborated. For identification of this effect, we propose a schematic layout of the experimental grounded system with a pulsed loop source and signals recording by radial receive lines equally spaced relative to the loop. The 2018–2019 special field experiments were conducted in the Tatar region of the West Siberian Lowland with an aim to estimate the Hall effect contributions to the TEM method. To detect the Hall effect, transient electromagnetic responses were measured mainly by four receive lines radiating from a 500×500 m square loop. Analysis of the TEM results processing aimed at improving the signal quality and reducing the interference revealed a great similarity in signals from the radial lines, which is theoretically possible only under the Hall effect. Comparison of the field signals with the theoretical ones enabled estimation of the components caused by the Hall effect, in particular, conductivity at ~0.002 S/m.

Orientation Detection of Unequally Spaced Complexed Grounding Grids using Transient Electromagnetic Method

Configuration of Grounding Grid is required for all currently proposed Fault Diagnosing methods of Grounding Grid if the configuration is unknown then Grounding Grid Configuration detection techniques are applied and all of these latest techniques further requires the oriented angle at which the grid is laid and if the orientation of the grid is unknown or incorrect then the calculated configuration will be misleading and incorrect and we will fail to diagnose the Grounding Grid Fault. In this paper Transient Electromagnetic Method approach is used for orientation detection of Unequally Spaced Grounding Grids which are categorized as complexed grids further classified as Unequally spaced grounding grids with a diagonal element at larger mesh, smaller mesh, or in both of these meshes. In TEM method Equivalent Resistivities and Magnetic Field Intensities are found at eight different points in a circular path of constant radius r to determine the size of meshes and the presence of conductors whether diagonal or not diagonal. Model Designing and Simulations are performed using COMSOL Multiphysics 5.4 software, values of Magnetic Field Intensities and EMF are derived from COMSOL Multiphysics 5.4 software and the EMF values are further called in a MATLAB code to run through a number of mathematical formulations and Equivalent Resistivity is obtained for all desired points. Obtained values of Equivalent Resistivity and Magnetic Field Intensities verifies the effectiveness of the proposed approach for orientation detection of complexed grounding grid.

Three-dimensional transient electromagnetic response of multiple grounded-wire sources

Multiple grounded-wire sources combination are proposed to improve the signal strength and resolution of the transient electromagnetic method. Multi-source excitation from the different direction was executed to identify the conductive body in the subsurface and achieve refined detection of the target body. The vector finite element method based on the rational Krylov subspace projection algorithm was used to calculate transient response of the target bodies. The voltage response calculated by our algorithm was compared with that calculated by the integral equation method and the results agreed well with them. We designed different grounded-wire combinations, including a single source, pairs of sources, and groups of three and four sources, and analyzed induced EMF and the secondary field response of one conductive body. It indicates that multi-source transient method can obtain stronger signals, which is beneficial to the discovery of deep weak anomalies. Finally, we established two adjacent conductive block bodies and compared their electromagnetic response for the different source combination. The results showed that multiple-source transient electromagnetic response anomaly amplitude and lateral resolution are superior to those of a single source. Multi-channel diagram for multiple sources have two obvious peaks, especially for three sources and four sources, but the induced EMF from a single source does not differentiate between the two conductive bodies in the horizontal direction. Multiple grounded-wire source combinations are used not only for the surface transient electromagnetic method but can also be extended to the grounded electrical-source airborne transient electromagnetic survey.

A new transient electromagnetic prospecting method in TBM tunnel environment

Tunnel boring machine (TBM) construction is a safe and efficient tunnel construction method at this stage, which contributes to the essential role of ahead prospecting methods, an essential prerequisite for ensuring the safety of TBM construction. Due to the high interference in the TBM tunnel environment, it is difficult to effectively apply multiple ahead prospecting methods. The existing geophysical methods are restricted because of the extremely small prospecting space in the TBM tunnel environment. Also, the TBM tunnel environment is required to introduce high-resolution detection methods. This paper proposes an ahead prospecting method suitable for TBM tunnel, using the simulation of three-dimensional vector finite element. Specifically, this prospecting method uses transient electromagnetic electrical radiation sources to emit and receives the Ex. Besides, the full field apparent resistivity imaging method is used to perform imaging interpretation of the adverse geological structures in front of the tunnel face in a semi-quantitative manner, to obtain the prospecting results required for the ahead prospecting in TBM tunnel.

Research on Airborne Electromagnetic Whole-area Apparent Resistivity Imaging Algorithm in the Detection of Goaf in Rail Transit

Depth apparent resistivity imaging is an important process of data processing and analysis in the aviation transient electromagnetic method. It can provide reference value of conductor depth, vertical extension, and other information, and can accurately provide the measurement of each aviation transient electromagnetic measurement system. The structural section of the apparent conductivity of the one-dimensional layered medium on the line. As an advanced geophysical exploration technology, the aerial transient electromagnetic method has been applied significantly in the exploration of polymetallic minerals abroad in recent years. In this paper, based on the theory of ground-to-air transient electromagnetic method with multiple radiation sources, a corresponding multi-component global apparent resistivity definition method is established. The advantages of using the magnetic field strength to define the global apparent resistivity of the multi-radiation field source ground-air system are analysed. For each component of the magnetic field strength, respective global apparent resistivity algorithms are proposed to realize the multi-component, full-time, and full-space visual resistivity. The resistivity is calculated, and the influence of the offset on the global apparent resistivity is analysed. By adjusting the relative position of the source and the current direction and other parameters, the multi-radiation source transient electromagnetic ground-air system can not only strengthen the signal strength of different components, weaken random interference, but also better distinguish the location of underground anomalies

Research on application of mine transient electromagnetic method in detecting collapse column

The transient electromagnetic detection has been widely applied to mine roadway excavation engineering. In order to figure out the front geological conditions of roadway excavation, the application of mine transient electromagnetic method (TEM) in detecting collapse column was conducted in this paper by taking the TEM-based advanced detection of 53152 working face in a mine located in Jincheng, Shanxi Province as an example. The results showed that if TEM is applied, geological structures like water-free collapse column could be largely delineated. Besides, by combining the interference source of detection environment and related geological data nearby the detection site, ‘false abnormalities’ could be effectively eliminated, thus providing the reference basis for the water prevention and control work of mines.

Analysis of response characteristics of comprehensive geophysical prospecting technology in concealed water-bearing structures

The mine transient electromagnetic method and the mine direct current method were used to detect the abundant water at 1,144 m ahead of the track roadway on the 9101 working face in the Chaoyang Coal Mine. Low-resistance abnormal areas indicated by both methods were analyzed comprehensively for early warning of water hazards. The results showed that two low-resistance abnormal areas were indicated by the mine transient electromagnetic method and the existence of a low-resistance abnormal area was indicated by the direct current method. Both methods showed the existence of a low-resistance abnormal area ahead, delineating possible illegal mining areas of old kilns ahead, which were verified by drilling. The methods can indicate the direction for drilling. The case shows that the combination of different geophysical prospecting methods can eliminate their limitations and that comprehensive detection can reduce omissions, which has a good guiding significance for safe mine excavation.

Numerical Modelling of TEM Fields by the Edge-Based Finite Element Method Using Tetrahedral Element for Central Rectangular Loops

In this study, we have implemented an edge-based finite element method for the numerical modeling of the transient electromagnetic method. We took the Helmholtz equation of the electric field as the governing equation for the edge-based finite element analysis. The modeling domain was discretized using linear tetrahedral mesh supported by Whitney-type vector basis functions. We inferred the equations by applying the Galerkin method. The system of equation was solved using a corrected version of the Bi Conjugate Gradient Stabilized Method (BiCGStab) algorithm to reduce the computational time. We obtained numerical solution for electric field in the Laplace domain; then the field was transformed into the time domain using the Gaver-Stehfest algorithm. Following this, the impulse response of the magnetic field was obtained through the Faraday law of electromagnetic induction as it is considerably more stable and computationally more efficient than inversion using the Fourier Transform. 3D geoelectric models were used to investigate the convergence of the edge-based finite element method with the analytic solution. The results are in good agreement with the analytical solution value for two resistivity contrasts in the 3D geoelectric brick model. We also compared the results of tetrahedral elements with the brick element in the 3D horizontal sheet and 3D conductive brick model. The results indicated that these two elements show very similar errors, but tetrahedral reflects fewer relative errors. For the low resistivity geoelectric model, numerical checks against the analytical solution, integral-equation method, and finite-difference time-domain solutions showed that the solutions would provide accurate results.