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In transient electromagnetic surveys, the collected data inevitably contain noise originating from both natural and cultural sources. This noise has the potential to mask transient electromagnetic responses linked to geological features, thereby posing challenges in accurately interpreting subsurface structures. Hence, the implementation of effective noise reduction techniques is crucial in ensuring the accuracy and reliability of inversion outcomes in transient electromagnetic surveys. This study introduces a novel approach that merges k‐means clustering with locally weighted linear regression to denoise transient electromagnetic data. The results from synthetic examples illustrate that the k‐means locally weighted linear regression method can predict transient electromagnetic data closely resembling true values, similar to the long short‐term memory autoencoder. Occam's inversion results derived from denoised data using both the k‐means locally weighted linear regression and long short‐term memory–autoencoder methods can well reflect the true model. Notably, a key advantage of the k‐means locally weighted linear regression method is its independence from labelled data as the sample set. The k‐means locally weighted linear regression method was applied to field data collected at the Narenbaolige coalfield in Inner Mongolia, China. Occam's inversion models generated from the denoised field data delineate the boundary between the basaltic body and sedimentary rocks, aligning with drilling data. The inversion models derived from the noisy field data also can capture this boundary, but deep section views reveal the presence of numerous intricate high‐resistivity anomalous bodies. These observations highlight the effectiveness of the k‐means locally weighted linear regression method in denoising transient electromagnetic data. [ABSTRACT FROM AUTHOR]

Inverse problems are typically tackled using deterministic optimization methods that may become trapped in a local minimum or probabilistic methods that can be computationally demanding. In this study, we explore the potential of the back propagation neural network (BPNN) optimized by the genetic algorithm (GA) for onshore transient electromagnetic (TEM) inversion. The GA is employed to optimize the initial parameters of the BPNN, enhancing its global optimization ability. Once the BPNN optimized by GA (GA-BPNN) is properly trained, it can provide the distribution of subsurface electrical conductivity (σ) in 0.1 s. We train the GA-BPNN using synthetic datasets generated by TEM forward modeling and assess its reliability using both synthetic and field data. Theoretical simulations demonstrate that compared with BPNN, the error of GA-BPNN on the inversion results of six samples is reduced by 23.2%. Furthermore, this method can provide reliable results even in the presence of noise in the TEM response. Finally, applying this inversion method to karst exploration with measured data proves the reliability and robustness of the proposed method. The proposed method can support quasi-real-time imaging of subsurface structures and provides a powerful tool for the interpretation of field TEM data. [ABSTRACT FROM AUTHOR]

The Meijiayan landslide in Pengshui County within Chongqing City is a medium-scale soil landslide triggered by the excavation of roadbeds. To delve into the influencing factors and assess the stability of this landslide, it is crucial to meticulously map the subterranean geological framework of the area. Such an analysis lays the groundwork for evaluating and mitigating the risks of future landslide instabilities. In this context, the semi-airborne transient electromagnetic method (SATEM), which is complemented by a receiving system mounted on an aerial platform, stands out as an innovative geophysical exploration technique. This method is adept at conducting swift measurements across complex terrains, making it particularly valuable for areas prone to such geological events. This paper presents the utilization of a cutting-edge loop source SATEM system, which was operationalized via a rotor-based unmanned aerial vehicle (UAV). The system was employed to conduct shallow geological structure detection experiments on the Meijiayan landslide. The SATEM detection outcomes have unveiled fluctuations in the electrical distribution across the upper strata, which are indicative of the subsurface geological boundaries, faults, and areas potentially rich in water within the landslide region. These discoveries affirm the viability of utilizing loop source SATEM for the identification of shallow geological structures in regions susceptible to landslides. The findings indicate that while the landslide is currently in a stable condition, it poses a significant risk of movement, especially during the rainy season, with the potential for landslides to be exacerbated by extreme or sustained rainfall events. [ABSTRACT FROM AUTHOR]

Data processing techniques in transient electromagnetic (TEM) methods face numerous challenges, such as the problem of 3-D imaging and the demand for new data processing techniques arising from the development of small-loop TEM devices. We have developed an imaging algorithm based on gradient features derived from TEM data to address these challenges. We found that normalising the gradient field of TEM responses under appropriate background conditions enables imaging of the target. Numerical experiments conducted under theoretical models have validated the feasibility of this approach and highlighted the significance of background fields. We further designed more complex models and achieved 3-D imaging of synthetic data within seconds, demonstrating the method's high efficiency and applicability to high-dimensional data. Subsequently, we applied the algorithm to challenging small-loop TEM data and demonstrated its superior performance compared to the inversion method, which presents a novel approach for processing data from small-loop TEM devices. This study demonstrates that the algorithm possesses characteristics of high efficiency and wide applicability, suitable for TEM data from various dimensions and types of devices. Furthermore, it holds promising potential in assisting the enhancement of the efficiency of the three-dimensional inversion of TEM data. [ABSTRACT FROM AUTHOR]

The probing depth of the transient electromagnetic method (TEM) refers to the depth range at which the underground conductivity changes can be effectively detected. It typically ranges from tens of meters to several kilometers and is influenced by factors such as instrument parameters and the conductivity of the subsurface structure. Rapid and accurate probing depth is useful for the selection of appropriate inversion parameters and improving survey accuracy. However, mainstream methods suffer from issues such as low computational precision, large uncertainties, or high computational requirements, making them unsuitable for processing massive airborne electromagnetic data. In this study, we propose a prediction model based on deep learning that can directly compute the probing depth from the TEM responses, and its effectiveness and accuracy are validated through synthetic models and field measurements. We compared the performance of classic deep learning models, including CNN, RESNET, and RNN, and found that RNN performed the best overall on both synthetic and field data. Furthermore, we apply this algorithm to deep learning-based ATEM inversion by constraining the one-dimensional resistivity model depths in the training set, to reduce the non-uniqueness of the inversion, accelerate the convergence, and improve its prediction accuracy. [ABSTRACT FROM AUTHOR]

In this study, a recently developed time-domain electromagnetic method called the short-offset grounded-wire transient electromagnetic (SOTEM) method, which is a near-source observation method, was adopted to obtain strong signals and great detection depths. The responses of the SOTEM and long-offset transient electromagnetic (LOTEM) methods were compared to further guide and promote the SOTEM method. Currently, the comparison between SOTEM and LOTEM methods is primarily based on one-dimensional (1D) models. However, most geological bodies are three-dimensional (3D) structures. We investigated the responses of a grounded-wire transient electromagnetic method based on 3D models using the 3D finite-difference time-domain method. In addition, the signal strengths, detection sensitivities and detection depths of the SOTEM and LOTEM methods were compared. The results revealed that the field amplitudes of Ex (electrical component parallel to the transmitting source) and ∂By/∂t (magnetic component perpendicular to the transmitting source horizontally) were higher at the short offsets than at the long offsets. For the ∂Bx/∂t (magnetic component parallel to the transmitting source) and the vertical magnetic component ∂Bz/∂t, at initial times, the responses received would be stronger when closer to the transmitting source, whereas at later times, the responses would be stronger when farther from the source. Ex detection sensitivity increased with an increase in the offset at initial times, and increased with a decrease in the offset at later times. The detection sensitivities of the three magnetic field components at short offsets were higher than those at long offsets. The ∂By/∂t effective detection depth was the greatest. Generally, the effective detection depths of the three magnetic field components increased with decreasing offset. The range of the ratio of the horizontal distance, r, between the transmitting source and the target body to the effective detection depth H was 0.5-1.1. [ABSTRACT FROM AUTHOR]

The CUGTEMGK II transient electromagnetic instrument is used for real-time geophysical exploration of mine roadways, generating 3D model imaging results, and providing forecasting and warning data for water inflow in underground rock layers, displacement of roadway roof and walls, etc. Machine learning algorithms integrated deep convolutional neural networks, multilayer neural networks, data binary output, fuzzy decision matrix warning, etc., to provide rough warning results with wide coverage and precise warning results with narrower coverage. Through simulation analysis, both rough warning results and precise warning results show certain data sensitivity, with the precise warning results able to provide high sensitivity warning results 24 h before encountering problematic rock layers during roadway excavation. [ABSTRACT FROM AUTHOR]

The resolution ability of the transient electromagnetic method (TEM) for double-layer water-filled goaf is affected by the low resistance shielding effect of the overlying strata. Currently, there is a lack of quantitative research on how the parameter changes of the upper water-filled goaf affect its resolution capability. In this study, through numerical and physical simulations, the relative error of the TEM response between single- and double-layer water-filled goafs was regarded as the evaluation index to analyse and summarize the resolution capability of the TEM for double-layer water-filled goaf under different burial depths, thicknesses, and areas of the upper water-filled goaf. The results are summarized as follows. (ⅰ) The resolution capability of the TEM for double-layer water-filled goaf decreased with the increasing burial depth, thickness, or area of the upper water-filled goaf. (ⅱ) The rate of decrease in resolution gradually accelerated as the burial depth increased. Conversely, as the thickness increased, the decrease rate in resolution gradually reduced. Furthermore, the resolution decreased rapidly and then tended towards a fixed value as the area increased. (ⅲ) The maximum value of the relative error curve moved towards the early stage with the increasing burial depth, resulting in a detection depth of the target body smaller than the actual value. Moreover, it moved towards the later stage with the increasing thickness or area, resulting in a detection depth of the target body greater than the actual value. [ABSTRACT FROM AUTHOR]

The development of coal seam wind oxidation zone has a huge impact on the production organization and safe mining of coal mines. This paper focuses on the technical difficulties in delineating the coal seam wind oxidation zone in the eastern uplift zone of Junggar Coalfield, and studies the feasibility of using transient electromagnetic method to explore the coal seam wind oxidation zone. Firstly, the electrical resistivity logging curves of normal strata and coal seam wind oxidation areas in the research area were analyzed, and the differences in electrical properties between normal areas and coal seam wind oxidation areas were summarized. A geoelectric model of coal seam wind oxidation areas was constructed based on the electrical resistivity logging curves; then, MAXWELL software was used to numerically simulate the transient electromagnetic response of the theoretical model. It was found that the resistivity cross-section of the transient electromagnetic inversion in the coal seam wind oxidation zone exhibited abnormal characteristics of shallow low resistance layer thickening and reduced low resistance anomaly amplitude, which can be used to delineate the distribution range of the coal seam wind oxidation zone; finally, based on numerical simulation, on-site experiments were conducted in the Chuancao Gedan Coal Mine. Combined with drilling conditions, the experimental data were analyzed from the perspectives of transient electromagnetic inversion resistivity cross-section and plane. The results showed that the transient electromagnetic method is feasible for detecting and dividing wind oxidation zones.

The geological section of Eastern and Western Siberia is a complex object for a seismic exploration. The reason for this is the extremely high variability of the upper part of the section lithology, rough terrain, and permafrost rocks. This paper delivers an alternative approach to predicting the velocity model of the upper part of the section. The approach based on the original method of restoring the elastic-velocity characteristics from the data of transient electromagnetic method (TEM) in the near field zone.Research devoted to test the methodology of the shallow section velocity model calculation based on TEM data in a number of fields in Eastern and Western Siberia. Derived results aimed to improve the accuracy of the geological model building and the reliability of the hydrocarbon plays prediction.Synthetic modeling and field data confirm the high level of the proposed methodology effectiveness. It was shown that for the Eastern Siberia settings, an improvement in the quality of processing of seismic data consists in a significant increase in the dynamics and coherence of seismic recordings. In Western Siberia, it is possible to take into account the velocity anomalies associated with the permafrost rocks and zones of transit from the onshore part of the survey area to the sea.

The field data acquisition of transient electromagnetic method is prone to jump due to various random disturbances. Wavelet denoising realizes data denoising by multi-scale decomposition, threshold setting and reconstruction of signal. In order to improve the data quality of TEM after wavelet denoising, a new wavelet denoising method based on the optimal threshold reference is proposed to improve the threshold selection method. Combined with the application of transient electromagnetic method in water-rich engineering, the noise reduction results of data under different threshold conditions are compared and analyzed, and the practical application effect of the proposed algorithm is discussed. The results show that the proposed method can further reduce the value of the induced electromotive force curve in the range of 1-4 ms, and make the whole period attenuation characteristics of the data more obvious. The smoke ring inversion results of the denoised data were analyzed, and three locations with relatively large electrical differences were explained, and the inversion results of the denoised data based on the optimal threshold reference were verified to be more accurate.

At present 1D inversion is commonly used for data processing and interpretation of transient electromagnetic (TEM) method. It is important to study the resolution-capability for the thin layer to take better advantage of ground-based loop-source TEM method. In this study, we employ 1D Occam's inversion method to qualitatively and quantitatively study the resolution capability for a thin layer. The thin layer has low resistivity, and its thickness is 10 m. The buried depth ranges from 10 to 100 m with 10 m intervals. The numerical modeling results show that the inverted resistivity and thickness will more coincide with the true values of the thin layer if the differences of resistivity between the thin layer and background medium increase. The depth of the inverted minimum resistivity agrees with the position of the low-resistivity thin layer. For background resistivity less than 100 Ω·m, the maximum depths are 40, 50 and 80 m for ratios of 1:5, 1:10 and 1:20 between the resistivities of the thin layer and the background medium, respectively. The maximum depth indicates the one within which the thin layer can be well detected by TEM methods. For the background resistivity of 200 Ω·m, the corresponding maximum depths are 30, 30 and 60 m. This study will help to optimize the field-work parameter designing and to improve the accuracy of data processing and interpretation.

In practical exploration, the complex and diverse topographic effects are important for the processing and interpretation of EM exploration data. The interpretation of the electromagnetic data results in large errors when the influence of topographical factors is simply ignored. At present, the study of TEM is mainly based on the ideal situation of flat terrain, and the study of topographic effect is less. However, topographic relief is inevitable in practical exploration. In this article, the correctness of the time-domain 3-D forward evolution based on the finite-element method (FEM) is verified by comparing the numerical results with those of the homogeneous full-space and half-space analytical solutions and the lumped high conductor model. In this article, 3-D numerical simulations of time-domain transient electromagnetic methods are calculated based on the FEM. Several exploration scenarios for complex terrain were constructed under the transmitting loop source, and the effect of terrain size and filling medium changes on the electromagnetic response was analyzed. The parameters of the topographic effect, earth resistivity, surface resistivity, and target conductivity are analyzed from the z-component of the magnetic field, apparent resistivity, and time-domain numerical solution, and the relative error distribution results in the whole observation period are shown. The results show that the influence of topographic effects on the electromagnetic response is concentrated in the early part of the time domain, with puddles of the same size having a higher influence on the electromagnetic response than raised soils and hollows. In practical exploration, puddles should be avoided where possible, whereas small-sized topographic reliefs and hollows have a negligible effect on the electromagnetic response.

The initial inversion model is typically established in a transient electromagnetic nonlinear inversion, assuming the accurate capture of the number of layers in the geoelectric model; however, this assumption leads to significantly poorer inversion results for complex models when obtaining the exact number of layers from available a priori information, which is challenging. This study proposes a segmented regularized inversion method to enhance inversion accuracy and stability under varying conditions. The process involves two key steps: Firstly, a segmented initial model is established based on preliminary information. The layering criteria and layer thickness threshold for each segment are set during inversion to reduce dependence on the accuracy of the preliminary information. Secondly, a segmented regularization constraint is added to the objective function to improve the efficiency and stability of the inversion, as numerous parameters can exacerbate the problem of inversion ambiguity. Subsequently, an improved sparrow search algorithm (ISSA) is utilized to optimize the inversion objective function. This enhances the efficiency of searching for the objective function and the algorithm's ability to escape local optimal solutions. The proposed method is evaluated using one-dimensional and two-dimensional models with different initial models and inversion algorithms and applied to the inversion of on-site exploration data in a coal mining area in Chongqing. Comparative results demonstrate that the proposed segmented regularization method, based on the improved sparrow search algorithm, exhibits superior practicality and a higher fitting accuracy. [ABSTRACT FROM AUTHOR]

The transient electromagnetic method (TEM) is widely used in the exploration of mineral, petroleum, and geothermal resources due to its sensitivity to low-resistivity bodies, limited site constraints, and strong resistance to interference. In practical applications, the TEM often uses a long wire source instead of an idealized horizontal electric dipole (HED) source as the excitation source. This is due to the complex external conditions and the relatively large distance between the receiving zone and the transmitter source. Compared to the HED, the long wire source can provide a larger excitation current, generating stronger signals to meet the requirements of a higher signal-to-noise ratio or deeper exploration. It also produces longer-duration signals, thereby providing better resolution. Additionally, for the interpretation of TEM data, three-dimensional forward modeling plays a crucial role. However, the mature traditional TEM forward method is based on a simple, sometimes inappropriate model, as it is well established that the induced polarization (IP) effect is widely present in the deep earth, especially in oil and gas reservoirs. The presence of the IP effect results in negative responses in field data that do not conform to the traditional theoretical decay law of TEM, which can significantly impact data processing and inversion results. To address this issue, a TEM forward modeling method considering the IP effect based on the spectral element method (SEM) has been developed in this study. Firstly, starting from the Helmholtz equation satisfied by the time domain electric field, we introduce the Debye model with polarization information into the forward modeling by utilizing the differential form of Ohm's law. As a result, we derive the boundary value problem for the time domain electric field that considers the induced polarization effect. Using Gauss–Lobatto–Legendre (GLL) polynomials as the basis functions, the SEM is employed to discretize the governing equations at each time step and obtain spectral element discretization equations. Then, temporal discretization equations are derived using the second-order backward Euler formula, and the linear system of equations is solved using the Pardiso direct solver. Finally, the electromagnetic responses at any time channel are obtained via SEM interpolation and numerical integration, thereby achieving three-dimensional TEM forward modeling considering the IP effect. The results indicate that this method can effectively reflect the spatial distribution of polarizable subsurface media. It provides valuable references for studying the polarization parameters of subsurface media and performing a three-dimensional inversion of TEM data considering the induced polarization effect. [ABSTRACT FROM AUTHOR]

Transient electromagnetic method (TEM) is an effective tool to map the groundwater distribution in tunnel construction. To highlight the structural information of the water-bearing zones, inverse wavefield transform is used to extract pseudo-wavefield from TEM data. To provide accurate and reliable pseudo-wavefield, pseudo-wavefield extraction should tackle the large dynamic range of the kernel function, ill-posed inverse transform function, and self-adaptive solving. In this paper, a series of works had been done to solve the above problems. Based on the property of the wavefield transform and its kernel function, we provided an empirical formula to shorten the integral interval of the inverse wavefield transform. A self-adaptive method combined with the precise integral method (PIM) was conducted to provide accurate equation solving. The data misfit between the modeling data and the fitted data is less than 2.5% in our numerical models. The traces of the pseudo-wavefield highlight the boundary of the low-resistivity layers of different depths and thicknesses. For the field data measured in a constructing tunnel, the reflection in our pseudo-wavefield traces provided massive subsurface electrical interfaces with a data misfit of less than 5%. Combined with the low-resistivity zones in the apparent resistivity results, three water-bearing zones were highlighted and then verified by a drilling test, which confirms the reliability and practicality of our method. [ABSTRACT FROM AUTHOR]

The integrated engineering geological investigation in shallow waters has disadvantages such as low exploration precision and resolution. Therefore, the transient electromagnetic method is introduced into the engineering geological investigation in shallow waters. The research results of existing achievements of the transient electromagnetic method are analyzed. Based on the Maxwell equations, a high-precision transient electromagnetic field response formula based on multi-turn rectangular and small frame current source in shallow water is derived, and the induced voltage expression is obtained. The simulation model of shallow water layer and water bottom half space is designed to calculate the transient electromagnetic response of shallow water layer. The optimal inversion technique of high-precision transient electromagnetic in shallow waters is studied, and the feasibility and effectiveness of the forward inversion method are verified by practical projects. Through the comparison and analysis of simulation model calculation and measured data, it is proved that the forward and inversion method is fast and accurate, which can effectively solve the geological problems such as soil and water boundary, soil and rock boundary, karst and fracture in engineering investigation. [ABSTRACT FROM AUTHOR]

Due to the large terrain fluctuation and drop in Qianshuta well field, the layout of the ground large loop transient electromagnetic method detection device is limited. In order to find out the distribution range of goaf under the second Shanjing line of oil and gas pipeline in this area, numerical simulation and field test of small loop transient electromagnetic method were carried out to analyze the feasibility of ground detection, and optimized parameters were applied to the field. The results show that the numerical simulation confirms that the 3 m×3 m small loop transient electromagnetic method can effectively detect the goaf with a depth of more than 200 m and a mining height of more than 1 m, and has a more obvious effect on the water-filled goaf with low resistance; the field test adopts the small loop transient electromagnetic method with optimized parameters such as the length of the transmitting wire frame 3 m×3 m, the number of stacking times of 15, the transmitting frequency of 16 Hz, and more than 8 A transmitting current, which can achieve the purpose of effective detection and verify the correctness of the numerical simulation; a total of 5 abnormal areas were delineated and explained in the No.3 coal seam, which were inferred to be gobs or burned rock voids. The reliability of the small loop transient electromagnetic detection method is fully verified.

The Meijiayan landslide in Pengshui County within Chongqing City is a medium-scale soil landslide triggered by the excavation of roadbeds. To delve into the influencing factors and assess the stability of this landslide, it is crucial to meticulously map the subterranean geological framework of the area. Such an analysis lays the groundwork for evaluating and mitigating the risks of future landslide instabilities. In this context, the semi-airborne transient electromagnetic method (SATEM), which is complemented by a receiving system mounted on an aerial platform, stands out as an innovative geophysical exploration technique. This method is adept at conducting swift measurements across complex terrains, making it particularly valuable for areas prone to such geological events. This paper presents the utilization of a cutting-edge loop source SATEM system, which was operationalized via a rotor-based unmanned aerial vehicle (UAV). The system was employed to conduct shallow geological structure detection experiments on the Meijiayan landslide. The SATEM detection outcomes have unveiled fluctuations in the electrical distribution across the upper strata, which are indicative of the subsurface geological boundaries, faults, and areas potentially rich in water within the landslide region. These discoveries affirm the viability of utilizing loop source SATEM for the identification of shallow geological structures in regions susceptible to landslides. The findings indicate that while the landslide is currently in a stable condition, it poses a significant risk of movement, especially during the rainy season, with the potential for landslides to be exacerbated by extreme or sustained rainfall events.

The probing depth of the transient electromagnetic method (TEM) refers to the depth range at which the underground conductivity changes can be effectively detected. It typically ranges from tens of meters to several kilometers and is influenced by factors such as instrument parameters and the conductivity of the subsurface structure. Rapid and accurate probing depth is useful for the selection of appropriate inversion parameters and improving survey accuracy. However, mainstream methods suffer from issues such as low computational precision, large uncertainties, or high computational requirements, making them unsuitable for processing massive airborne electromagnetic data. In this study, we propose a prediction model based on deep learning that can directly compute the probing depth from the TEM responses, and its effectiveness and accuracy are validated through synthetic models and field measurements. We compared the performance of classic deep learning models, including CNN, RESNET, and RNN, and found that RNN performed the best overall on both synthetic and field data. Furthermore, we apply this algorithm to deep learning-based ATEM inversion by constraining the one-dimensional resistivity model depths in the training set, to reduce the non-uniqueness of the inversion, accelerate the convergence, and improve its prediction accuracy.

The main factors restricting the mining speed of the working face in Yuenan Coal Mine are the water-rich area of limestone above the coal seam and the internal geological concealed structure. The transparent detection of the working face is carried out by using transient electromagnetic method, radio wave perspective and slot wave seismic geophysical methods. In the process of detection, it is found that the induced voltage received by the secondary wave field of transient electromagnetic method is more sensitive to the area of rich water and low resistance, and the lateral situation of coal seam can be identified by observing the energy attenuation emitted and received by radio wave perspective. The integrated analysis of envelope amplitude, spectrum and dispersion curve of in-seam wave seismic imaging has good effect on identifying fault strike. Through the identification of the comprehensive response characteristics of the abnormal region by the induction factor in the multi-wave field, the plane map is superimposed according to the abnormal area delineated by the multi-source wave field, and a variety of abnormal characteristics are shown synthetically, which can effectively identify the correlation between the water-rich area of the roof of the working face and the internal structural area of the coal seam, and clearly judge the existence of the water channel. The test results show that the geophysical method can find out the internal abnormal area of the mining face and predict in advance, and the combined detection of various geophysical methods can provide a reference basis for similar geological conditions in the future.

In tunnel construction, hazardous water structures pose significant risks. The transient electromagnetic method (TEM) is widely used for advanced geological prediction due to its sensitivity to conductive targets. Currently, loop sources are generally used to detect these structures, but the space in the tunnel limits the magnetic moment and detection distance. This article proposes using an electric wire source TEM configuration on the tunnel sidewall for lateral exploration. The feasibility of this configuration is preliminarily analyzed using 3D numerical simulations based on tensor grids. The simulations include the six electromagnetic components under the axial electric source and the effects of offset, tunnel spatial conductivity, and tunnel size on the response. The results show that the inline electric field component and the vertical-induced electromotive force component are more sensitive to the target body in this configuration. We also found that when there is a small difference in resistivity between the target body and the surrounding rock, the sensitivity of the induced electromotive force z-component to the abnormal body will be reduced. When the distance between the source and the receiver is large, the broadside-induced electromotive force component can also be used to identify anomalous body electrical properties. Moreover, the conductivity and size of the tunnel have a certain impact on the detection results. In the next research, it is necessary to select more suitable model parameters for numerical simulations based on the actual conditions. [ABSTRACT FROM AUTHOR]

The transient electromagnetic (TEM) method is a non-contact technique used to identify underground structures, commonly used in mineral resource exploration. However, the induced polarization (IP) will increase the nonlinearity of TEM inversion, and it is difficult to predict the geoelectric structure from TEM response signals in conventional gradient inversion. We select a heuristic algorithm suitable for nonlinear inversion—a whale optimization algorithm to perform TEM inversion with an IP effect. The inverse framework is optimized by opposition-based learning (OBL) and an adaptive weighted factor (AWF). OBL improves initial population distribution for better global search, while the AWF replaces random operators to balance global and local search, enhancing solution accuracy and ensuring stable convergence. Tests on layered geoelectric models demonstrate that our improved WOA effectively reconstructs geoelectric structures, extracts IP information, and performs robustly in noisy environments. Compared to other nonlinear inversion methods, our proposed approach shows superior convergence and accuracy, effectively extracting IP information from TEM signals, with an error of less than 8%. [ABSTRACT FROM AUTHOR]

We propose a 3-D transient electromagnetic inversion method based on explicit finite-difference forward modeling. For forward modeling, we calculate the whole-space initial field excited by magnetic dipole sources at an initial time after the current is switched off and apply Maxwell's equations on time using the modified DuFort–Frankel method and staggered grids. For inversion, we use the least squares optimization method. We test the inversion method using synthetic and field data. The conductivity brick is recovered well in synthetic. The inversion results of field data are consistent with the known geological conditions. The synthetic and field examples show that the inversion method based on explicit finite-difference forward modeling is effective. [ABSTRACT FROM AUTHOR]

Geothermal resource is a kind of crucial clean, renewable energy with high potential development and application. However, it involves great exploiting risks since it buried deep beneath the crust of the Earth. The location and depth of geothermal resources can be determined using the geophysical methods. Controlled source audio-frequency magnetotellurics (CSAMT) and transient electromagnetic method (TEM) have relatively high efficiency and robustness. In this paper, a simplified geothermal system resistivity model was established, which allowed TEM and CSAMT to differentiate target faults with various characteristics (resistivity, dip angle and width). Through a comprehensive electromagnetic exploration in Huairen County, Shanxi Province, China as an example, the performance of TEM and CSAMT in determining geothermal resources was evaluated. The results showed that both methods could examine the geoelectrical structures from various perspectives, and the effectiveness of comprehensive electromagnetic method for geothermal resources was presented. [ABSTRACT FROM AUTHOR]

Understanding the response of the transient electromagnetic method (TEM) to bad geological bodies is essential to improve the accuracy of tunnel forward geological prediction. Based on considering the similarity criterion, four groups of model tests were established to study the response law of small fixed-loop and central-loop TEM to water-bearing structures in tunnels. In the model tests, the non-central point field correction method was used to correct observation data of small fixed-loop TEM. Subsequently, the response and imaging results of central-loop and small fixed-loop TEM were compared and analyzed. The results show that the response of small fixed-loop TEM is more sensitive to water-bearing structures compared with central-loop TEM. Moreover, the three-dimensional imaging results obtained from the small fixed-loop TEM more accurately depict the spatial location and morphological characteristics of water-bearing structures. Finally, the engineering application demonstrates that the small fixed-loop TEM is effective and successful in detecting water-bearing structures, which can provide practical guidance for tunnel construction and disaster management. [ABSTRACT FROM AUTHOR]

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The main factors restricting the mining speed of the working face in Yuenan Coal Mine are the water-rich area of limestone above the coal seam and the internal geological concealed structure. The transparent detection of the working face is carried out by using transient electromagnetic method, radio wave perspective and slot wave seismic geophysical methods. In the process of detection, it is found that the induced voltage received by the secondary wave field of transient electromagnetic method is more sensitive to the area of rich water and low resistance, and the lateral situation of coal seam can be identified by observing the energy attenuation emitted and received by radio wave perspective. The integrated analysis of envelope amplitude, spectrum and dispersion curve of in-seam wave seismic imaging has good effect on identifying fault strike. Through the identification of the comprehensive response characteristics of the abnormal region by the induction factor in the multi-wave field, the plane map is superimposed according to the abnormal area delineated by the multi-source wave field, and a variety of abnormal characteristics are shown synthetically, which can effectively identify the correlation between the water-rich area of the roof of the working face and the internal structural area of the coal seam, and clearly judge the existence of the water channel. The test results show that the geophysical method can find out the internal abnormal area of the mining face and predict in advance, and the combined detection of various geophysical methods can provide a reference basis for similar geological conditions in the future. [ABSTRACT FROM AUTHOR]

The transient electromagnetic method (TEM) is a geophysical exploration method that can efficiently acquire subsurface electrical parameters. For airborne, towed and other mobile platforms, TEM systems, large data volumes and the traditional one-dimensional denoising method with low efficiency and low signal-to-noise ratio (SNR) of late-time are the main bottlenecks limiting its reliable application. To address this problem, this paper proposes a neural network structure suitable for two-dimensional (2D) TEM data processing. The proposed structure combines a classical convolutional neural network denoising autoencoder with a gated recurrent neural network autoencoder, called the CNN-GRU dual autoencoder (CG-DAE). This method can directly input 2D TEM response data as images into the network for processing, which greatly improves data processing efficiency compared to single-time-channel processing. The simulation experiments verified the effectiveness of CG-DAE. After using CG-DAE denoising, the SNR of late-time (0.2–1 ms) signals is improved to nearly 29 dB, the 2D anomaly layer position is clear and the relative error (RE) between the denoised data and the corresponding clean data is <1.41%, while the RE of the late-time signals can be reduced to 3.68%. The proposed method can lay the foundation for fast processing of TEM data based on mobile platforms such as those that are airborne and/or towed. [ABSTRACT FROM AUTHOR]

This study probed the existence of groundwater in a mineral concentration area, using high-density electrical and transient electromagnetic methods. Our objective was to understand the dynamic changes in groundwater resources accurately and support the development of a sustainable ecological environment in the Gobi Desert area. The study demonstrates that the combination of the high-density electrical and transient electromagnetic methods guides the hydrological drilling construction in this area effectively. It also provides a reference for the selection and application of geophysical exploration methods under similar geological conditions for future studies.

The transient electromagnetic inversion of detection signals mainly depends on fast inversion in the half-space state. However, the interpretation results have a certain degree of uncertainty and blindness, so the accuracy and applicability of the three-dimensional full-space inversion need to be investigated. Two different three-dimensional full-space inversions were carried out. First, the numerical characteristic parameters of the response signals were extracted. Then, the correlations between the numerical characteristic parameters and physical parameters of the water-bearing abnormal bodies were judged, and the judgment criterion of the iterative direction was proposed. Finally, the inversion methods of the iterative algorithm and the BP neural network were utilized based on the virtual example samples. The results illustrate that the proposed numerical characteristic parameters can accurately reflect the response curve of the full-space surrounding rock. The difference in the numerical characteristic parameters was used to determine the update direction and correction value. Both inversion methods have their advantages and disadvantages. A single inversion method cannot realize the three-dimensional inversion of the physical parameters of water-bearing abnormal bodies quickly, effectively and intelligently. Therefore, the benefits of different inversion methods need to be considered to comprehensively select a reasonable inversion method. The results can provide essential ideas for the subsequent interpretation of the three-dimensional spatial response signals of water-bearing abnormal bodies.

It urgently demands wellside remote and well advance detection technique in petroleum exploration and metallic minerals prospecting, as well as underground space detection. Combining the theory of three-component induction logging and transient electromagnetic field, a time domain electromagnetic tensor logging method was proposed. Based on the solution of the 9 components of alternating magnetic field in 3D induction logging, a transmission line algorithm was adopted to fastly solve Dyadic Green’s function. Hence, the theoretical formula was obtained for time domain electromagnetic tensor field by converting magnetic tensors into time domain. The attenuation versus time for all of the induced voltage components was analyzed by making use of a three-layered medium with a deviated well, and the tensor electromagnetic response characteristics of the target layer was obtained. Eventually, the effect of time domain electromagnetic tensor measurement was testified on the basis of downhole transient electromagnetic data. The results show that the attenuation curves for xz, yz, zx and zy components of induced voltage tensor have an electromagnetic feature excited by a vertical magnetic dipole, while the rest of components meet with the feature excited by a horizontal magnetic dipole; the voltage components related to z component can be used as preferred parameters for their significant resolution to the electrical interface of strata, while the others can be considered as auxiliary parameters; the low resistivity target layer can be clearly identified in the multi-channel curves and induced voltage tensor time sections, which provide an effective tool for the measured data processing and interpretation. [ABSTRACT FROM AUTHOR]

We used transient electromagnetic (TEM) to map the hydrogeological structures in the Choushui River Alluvial Fan in Yunlin County of central Taiwan. A total of 63 TEM measurements were collected using the FASTSNAP system with 50 × 50 m in-loop configurations in the middle and distal fan. The 1D model, based on prior information, was constructed from the inverted soundings. Results showed a thin, resistive shallow layer and a 40 m low-resistive (6–42 ohm-m) zone beneath it. High-resistive zones (50–170 ohm-m) were found from 50–120 m depth, and low-resistive zones were revealed below 120 m in some areas. Results were consistent with resistivity and lithology logs from nearby wells. The inverted TEM models provide reliable subsurface information when prior informations of vertical electrical sounding and TEM were considered. We interpolated resistivity at 10 m, 50 m, 100 m, and 160 m depth from the 1D model results to produce a slice map of the area, which indicated variations, trends, and depths of the sediment deposits. The TEM method successfully identified the hydrogeological structures, showing that the upper 40 m of sediment acts as a confining layer for the aquifer structure from 50 m to 120 m depth. [ABSTRACT FROM AUTHOR]

Featured Application: Assessment of environmental risks in connection with the technogenic thawing of permafrost soils in the places of waste storage of mining enterprises in the Far North. The relevance of the work is due to the risks of an uncontrolled increase in circulating water leaks through sides and bed of the dam, caused by thawing of permafrost soils in the Far North. The main aim of the work is to scientifically substantiate a set of engineering measures to reduce filtration consumption and restore and maintain the waterproofing of the tailing dump. The object of the study was the tailing dump of the concentration plant, with adjoining filter walls. The tailing dump has been exploited since 1996; for the last 20 years, circulating water leaks into the shunting tank located below were recorded. Within the water area of the tailing dump and at the landfalls, geophysical surveys were carried out from ice by the TEM (transient electromagnetic) method. The obtained geoelectric sections made it possible to form a holistic view of the structure of the filtration zones in the right and left bank junctions. The data obtained will be used for planning anti-filtration arrangement. [ABSTRACT FROM AUTHOR]

The initial inversion model is typically established in a transient electromagnetic nonlinear inversion, assuming the accurate capture of the number of layers in the geoelectric model; however, this assumption leads to significantly poorer inversion results for complex models when obtaining the exact number of layers from available a priori information, which is challenging. This study proposes a segmented regularized inversion method to enhance inversion accuracy and stability under varying conditions. The process involves two key steps: Firstly, a segmented initial model is established based on preliminary information. The layering criteria and layer thickness threshold for each segment are set during inversion to reduce dependence on the accuracy of the preliminary information. Secondly, a segmented regularization constraint is added to the objective function to improve the efficiency and stability of the inversion, as numerous parameters can exacerbate the problem of inversion ambiguity. Subsequently, an improved sparrow search algorithm (ISSA) is utilized to optimize the inversion objective function. This enhances the efficiency of searching for the objective function and the algorithm’s ability to escape local optimal solutions. The proposed method is evaluated using one-dimensional and two-dimensional models with different initial models and inversion algorithms and applied to the inversion of on-site exploration data in a coal mining area in Chongqing. Comparative results demonstrate that the proposed segmented regularization method, based on the improved sparrow search algorithm, exhibits superior practicality and a higher fitting accuracy.

The transient electromagnetic method (TEM) is widely used in the exploration of mineral, petroleum, and geothermal resources due to its sensitivity to low-resistivity bodies, limited site constraints, and strong resistance to interference. In practical applications, the TEM often uses a long wire source instead of an idealized horizontal electric dipole (HED) source as the excitation source. This is due to the complex external conditions and the relatively large distance between the receiving zone and the transmitter source. Compared to the HED, the long wire source can provide a larger excitation current, generating stronger signals to meet the requirements of a higher signal-to-noise ratio or deeper exploration. It also produces longer-duration signals, thereby providing better resolution. Additionally, for the interpretation of TEM data, three-dimensional forward modeling plays a crucial role. However, the mature traditional TEM forward method is based on a simple, sometimes inappropriate model, as it is well established that the induced polarization (IP) effect is widely present in the deep earth, especially in oil and gas reservoirs. The presence of the IP effect results in negative responses in field data that do not conform to the traditional theoretical decay law of TEM, which can significantly impact data processing and inversion results. To address this issue, a TEM forward modeling method considering the IP effect based on the spectral element method (SEM) has been developed in this study. Firstly, starting from the Helmholtz equation satisfied by the time domain electric field, we introduce the Debye model with polarization information into the forward modeling by utilizing the differential form of Ohm’s law. As a result, we derive the boundary value problem for the time domain electric field that considers the induced polarization effect. Using Gauss–Lobatto–Legendre (GLL) polynomials as the basis functions, the SEM is employed to discretize the governing equations at each time step and obtain spectral element discretization equations. Then, temporal discretization equations are derived using the second-order backward Euler formula, and the linear system of equations is solved using the Pardiso direct solver. Finally, the electromagnetic responses at any time channel are obtained via SEM interpolation and numerical integration, thereby achieving three-dimensional TEM forward modeling considering the IP effect. The results indicate that this method can effectively reflect the spatial distribution of polarizable subsurface media. It provides valuable references for studying the polarization parameters of subsurface media and performing a three-dimensional inversion of TEM data considering the induced polarization effect.

Groundwater environment is closely related to the protection and restoration of surface ecological environment, and the detection of groundwater resources is an important content to master the characteristics of groundwater environment. In the setting of the ecological restoration of Hongshaquan Open-pit Mining Area, four different geoelectric models are constructed on the basis of geological column and its resistivity logging curves obtained by a borehole. Based on one-dimensional forward theory, the transient electromagnetic induced voltage and its apparent resistivity response curves with a small coil device are obtained. Comparative analysis for these curves shows that induced voltage and its apparent resistivity under different aquifer geoelectric model conditions are sensitive to aquifer water-bearing response, and there are obvious differences between them in 0.01-50 ms, which reflects the feasibility of using small coil transient electromagnetic method to detect groundwater resources in the study area in theory. Combined with the field detection test data and drilling exposure, the effectiveness and reliability of small coil transient electromagnetic technology in the detection of groundwater resources are verified.

Geothermal resources are a type of important renewable clean energy with high development and usage potential. However, at the same time, geothermal resources are buried deep below the Earth's surface, they involve significant exploiting hazards. Geophysical methods are frequently required to determine the depth and location of geothermal resources. Among geophysical methods, transient electromagnetic method (TEM) and controlled source audio-frequency magnetotellurics (CSAMT) have comparably high effectiveness and accuracy. This article first introduces the algorithm theory of the finite volume method, then establishes a simplified geothermal system resistivity model. Next, based on this model, simulation analyses of the abilities of CSAMT and TEM were performed to distinguish target faults with different resistivities, dip angles and widths. Finally, combined with theoretical analysis, taking a comprehensive electromagnetic exploration of CSAMT and TEM in Huairen County, Shanxi Province, China as an example, the effectiveness of these two methods in exploring typical geothermal resources is verified. It is shown that both methods can reflect the geoelectric structure from different perspectives, and the efficacy in geothermal exploration using comprehensive electromagnetic method is demonstrated. [ABSTRACT FROM AUTHOR]

Heicigou gold mine is a gold polymetallic mine controlled by a northwest trending fault. The magnetic method and induced polarization results show that the gold-bearing alteration zone is distributed discontinuously in a northwest direction, but the spatial distribution characteristics of the alteration zone have not been effectively identified. Although some drilling work has been carried out in the latter, the number and the depths of the drillings have been insufficient to control the distribution of the alteration zone. According to the measured three-component transient electromagnetic anomaly characteristics, we designed corresponding models and carried out three-component forward simulation on the platform of EMIT Maxwell. We summarized the corresponding relationship between the three-component plane change characteristics and the orientation and occurrence of the low-resistivity medium subsurface. We applied this method to the Heicigou gold deposit and found that the occurrence of the ore-bearing alteration zone is northeast. This discovery solved the problem that the previous magnetic method and induced polarization method failed to solve. It corrected the geologists' incorrect understanding of the spatial distribution of the alteration zone. [ABSTRACT FROM AUTHOR]

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Subsea geological exploration is the primary link to ensure the quality and safety of underwater engineering, and appropriate geophysical exploration means are the key to marine geological exploration. Based on the construction project of Dalian Bay Subsea Tunnel, in view of the possible karst caves below the foundation trench for the immersed tubes, which may endanger the construction safety, the single-channel seismic exploration method and the transient electromagnetic method were first used to carry out overall geophysical exploration for the planned alignment of the project and then boreholing was made to verify the results in selected localities. While determining the location, scale and depth of the karst caves, the seabed geological exploration method was explored to provide a reference for underwater engineering and construction. The results of geophisical exploration show that: 1) there are 49 anomalies in the exploration area, mainly reflections of dolomite dissolution fissures or karst development, but no large karst caves, which do not pose a threat to construction safety; 2) the integrated physical and boreholing exploration method can effectively improve the reliability and scientificity of the exploration results, and provide an accurate basis and strong support for underwater engineering in the design and exploration stage. [ABSTRACT FROM AUTHOR]

The observed data of transient electromagnetic (TEM) systems is often contaminated by various noises. Even after stacking averages or applying various denoising algorithms, the interference of the system noise floor cannot be eliminated fundamentally, which limits the survey capability and detection efficiency of TEM. To improve the noise performance of the TEM receiver, we have designed a low-noise amplifier using the current source long-tail differential structure and JFET IF3602 through analyzing the power spectrum characteristics of the TEM forward response. By the designed circuit structure, the JFET operating point is easy to set up. The adverse effect on the JFET differential structure by JFET performance differences is also weakened. After establishing the noise model and optimizing the parameters, the designed low-noise differential amplifier has a noise level of 0.60 nV / Hz , which increases the number of effective data 2.6 times compared with the LT1028 amplifier. [ABSTRACT FROM AUTHOR]

Aiming at the safety and stability issues of the proposed substation in Pingdingshan City, Henan Province, the substation was taken as the research object. Based on the basic geological conditions and mining conditions of the substation, the goaf was detected comprehensively the transient electromagnetic method and drilling detection. By analyzing the longitudinal profile of apparent resistivity obtained by transient electromagnetic detection and the relationship curve between formation depth and apparent resistivity, it could be seen that there are low resistance anomalies in some depths. The horizontal range of the low-resistance anomaly area was further determined by analyzing the horizontal profile of apparent resistivity. The relationship between the drilling depth and the core rate obtained by drilling detection could accurately determine the depth range where the rock formation is relatively broken and has a small amount of water leakage. It could be determined that the abnormal area of the mined-out area is located in the west of the proposed area according to the comprehensive analysis of the two detection results, and there are uncertain factors in the safety and stability of the mined-out area underlying the substation, and effective mined-out area governance measures must be taken to ensure the safe and stable operation of the substation.

Abstract Water inrush disasters poses a great threat to the safe exploitation of coal resources. To solve this problem, the transient electromagnetic method (TEM) was proposed to accurately detect the water accumulation in the goaf. The electromagnetic response characteristics of different water-filled goaves were studied by electromagnetic field theory, numerical simulation and field verification. Through the models of 100% water accumulation, 50% water accumulation, 0% water accumulation, 100% water accumulation with collapsed rock, 50% water accumulation with collapsed rock and 0% water accumulation with collapsed rock goaf, the characteristics of induced voltage attenuation curves were studied. Meanwhile, the relationship between the attenuation voltage value and area of the transmitting coil, the depth of the goaf, the background resistivity, and the delay time were also simulated. The results illustrate that the attenuation curve of induced voltage presented a regular exponential decay form in the 0% water accumulation model but existed abnormal exaltation for voltage in water-filled model. Through the linear fitting curve, it can be seen that the abnormal intensity of the induced voltage becomes stronger as the distance between the measuring point and the center of the target decrement. Moreover, the abnormal amplitude of the induced voltage increases with the rise of the water accumulation and collapsed rock will weakly reduce the low-resistivity anomalous effect on the water-accumulated goaf. In addition, the response value of the attenuation voltage increased as the area of the transmitting coil increases, but decreased with increasing delay time and increasing background resistivity and depth of the target body. The field detection results of the Majiliang coal mine also confirmed the theoretical analysis and the numerical simulation.

Opposing coils transient electromagnetic method (OCTEM) adopts small and weak-coupling transmitting-receiving coils configuration, which helps to reduce side effect and improve the detection resolution. With such advantages, it has been widely used for shallow sub-surface target detection. However, when the method is used in urban area, measured data may be distorted by electromagnetic (EM) interference from nearby metal objects. In practical application, it is necessary to perform modelling to provide guidance for measuring data analysis. Two OCTEM application cases in detecting shallow sub-surface karst caves in urban area with metal objects nearby are presented in this paper. Corresponding modelling are carried out to study the interference effect of the nearby metal objects. The first application case is about the EM interference of a vertical steel tower, of which the influence distance reaches up to 9 m by modelling. The second application case is about the EM interference of a thin aluminum fence, of which the influence distance reaches up to 6 m by modelling. Only when the observation is outside the influence zone, the metal influence can be ignored. When the measurement is inside the influence zone, the metal influence cannot be ignored. However, as the nearby metal objects mainly affects the early data, the subsurface target may also be detected in condition that the target response is stronger than the metal interference, or the target response time window is wider than that of the metal interference. • EM interference from steel tower and metal fence to OCTEM have been simulated. • The nearby metal objects mainly affects the early OCTEM data. • OCTEM can be used in detecting shallow subsurface target. [ABSTRACT FROM AUTHOR]

The transient electromagnetic (TEM) method is a non-contact technique used to identify underground structures, commonly used in mineral resource exploration. However, the induced polarization (IP) will increase the nonlinearity of TEM inversion, and it is difficult to predict the geoelectric structure from TEM response signals in conventional gradient inversion. We select a heuristic algorithm suitable for nonlinear inversion—a whale optimization algorithm to perform TEM inversion with an IP effect. The inverse framework is optimized by opposition-based learning (OBL) and an adaptive weighted factor (AWF). OBL improves initial population distribution for better global search, while the AWF replaces random operators to balance global and local search, enhancing solution accuracy and ensuring stable convergence. Tests on layered geoelectric models demonstrate that our improved WOA effectively reconstructs geoelectric structures, extracts IP information, and performs robustly in noisy environments. Compared to other nonlinear inversion methods, our proposed approach shows superior convergence and accuracy, effectively extracting IP information from TEM signals, with an error of less than 8%.

Highlights: The full-space TEM responses of different water columns were studied. The concept of "geometric gravity center" effect is proposed. This research has been proven in the field. Mine floods caused by water-bearing collapse columns are one of the most significant types of coal mine disasters in advanced detection. The transient electromagnetic method (TEM), one of the most effective means, can detect the collapse column in coal mines. However, the research on TEM used on the ground is mainly limited to half-space that does not follow underground mining conditions. This research used the whole-space TEM to detect the water-bearing collapse columns in front of the roadway. Based on the time-domain finite element method (TDFEM) and actual coal-measure strata data, this paper built the whole-space geo-electric models, summarized response characteristics, and proposed "geometric gravity center" effect. The results showed that the simulation based on TDFEM could accurately reflect the TEM response law, and the advanced detection using TEM in a mine environment was consistent with the actual situation. [ABSTRACT FROM AUTHOR]

The issue of water hazards has led to the restriction of safe and efficient coal mine production in China. The transient electromagnetic method (TEM) is one of the most effective means of detecting the hidden dangers of water hazards in coal mines. However, the current understanding of the whole-space transient electromagnetic response of mine water is only on the general law due to the late start of the forward research. Therefore, this paper established multiple sets of simulation models in the whole area in order to study the rules and factors of transient electromagnetic responses. Subsequently, these laws are used to explain the detection data of TEM in the field. According to the simulation results, the electric properties, distance, and size had the greatest influence on the transient electromagnetic response of regular anomalous geological bodies, while the electromagnetic field projection area also had an impact on irregular ones. Furthermore, field application demonstrated that the response law and TEM's affecting factors are acceptable for directing the detection of transient electromagnetic in coal mines. This research can advance the TEM's data processing and interpretation technology and offer a theoretical basis for detailed investigation. [ABSTRACT FROM AUTHOR]