An Array Source TEM Apparent Resistivity Conversion and Differential Conductivity Imaging Method and its Potential Applications

2019 ◽  
Vol 24 (4) ◽  
pp. 579-592
Author(s):  
Zhipeng Qi ◽  
Xiu Li ◽  
Yingying Zhang ◽  
He Li ◽  
Naiquan Sun
Keyword(s):  
Apparent Resistivity ◽  
Fdtd Method ◽  
Inverse Function ◽  
Imaging Method ◽  
Inversion Algorithm ◽  
Electromagnetic Device ◽  
Transient Electromagnetic ◽  
Potential Applications ◽  
Anomalous Bodies ◽  
Differential Imaging

In this study, for the purpose of accurately detecting fissured disaster sources and diversion channels during tunnel construction, an array source transient electromagnetic device is proposed. Then, an apparent resistance conversion method and an approximate inversion algorithm for the proposed transient electromagnetic device are presented. First, a finite-difference time-domain (FDTD) method is used for the forward modeling of the proposed array source transient electromagnetic device, and the electromagnetic responses of the cracks and water-conducting channels are obtained. When compared with the transient electromagnetic square responses of the traditional loop sources, it is found that the data confirmed that the responses to the anomalies of the proposed array source transient electromagnetic device are more apparent. Then, the transformation from the array source transient electromagnetic field to the apparent resistivity is realized according to the principle of inverse function. In order to clearly identify the boundaries of the targeted anomalous bodies, a multi-source S-inversion algorithm is used to realize the array source transient electromagnetic differential imaging. The method is validated using a theoretical model. It was determined that the results of the differential imaging had effectively identified the boundaries of the anomalous bodies, and the apparent resistivity imaging had successfully determined the resistivity distributions of the anomalous bodies. Furthermore, a combination of the aforementioned methods is used to effectively identify the faults and water-flowing fractures in the model. This study's proposed algorithm was applied to the actually measured data, and the interpretation results were found to be consistent with the excavation results, which fully demonstrated the feasibility of the proposed method.

A generic 1-D imaging method for transient electromagnetic data

Geophysics ◽  
2002 ◽  
Vol 67 (2) ◽  
pp. 438-447 ◽  
Author(s):  
Niels Bøie Christensen
Keyword(s):  
Time Derivative ◽  
Step Response ◽  
Imaging Method ◽  
Nonlinear Inversion ◽  
Inversion Algorithm ◽  
Electromagnetic Data ◽  
Transient Electromagnetic ◽  
Dependent Part ◽  
Space Step ◽  
Forward Mapping

This paper presents a fast approximate 1-D inversion algorithm for transient electromagnetic (EM) data that can be applied for all measuring configurationsand transmitter waveforms and for all field components. The inversion is based on an approximate forward mapping in the adaptive Born approximation. The generality is obtained through a separation of the forward problem into a configuration-independent part, mapping layer conductivities into apparent conductivity, and a configuration-dependent part, the half-space step response. The EM response from any waveform can then be found by a convolution with the time derivative of the waveform. The approach does not involve inherently unstable deconvolution computations or nonunique transformations, and it is about 100 times faster than ordinary nonlinear inversion. Nonlinear model responses of the models obtained through the approximate inversion fit the data typically within 5%.

scholarly journals Global apparent resistivity definition for a high-performance TEM excitation source

2020 ◽  
Author(s):  
He Li ◽  
Wenhan Li ◽  
Zhipeng Qi ◽  
Xiu Li ◽  
Kailiang Lu
Keyword(s):  
High Resolution ◽  
High Performance ◽  
Apparent Resistivity ◽  
Inverse Function ◽  
Excitation Source ◽  
Underground Space ◽  
Electromagnetic Excitation ◽  
Transient Electromagnetic ◽  
Time Period ◽  
Calculation Results

Abstract The high-performance transient electromagnetic method (TEM) excitation source is a new type of source that has been proposed for urban underground space exploration. This source is composed of two trapezoid plates. To ensure that the radiation field was focused in a certain direction, the two trapezoid plate-shaped antennas were arranged into a horn shape. This new source is characterised by high power, directional excitation and high resolution. The corresponding multi-component global apparent resistivity definition method is established for a high-performance transient electromagnetic excitation source. This method is studied using the inverse function theorem. Then, the monotonic relationship between components of the electromagnetic field and resistivity is analysed. For the fields that satisfy the monotonic relationship with half-space resistivity, the apparent resistivity can be calculated correctly to ignore the time period and location in the space. This means that this definition method can eliminate the limitation of early and late times, and the near and far zones. The apparent resistivity calculation results of the theoretical layered model reveal that global apparent resistivity curves show a regular change, which smoothly and comprehensively reflects the change of electrical information in the model. The experimental results of the 3D model show that the five-layer low-resistivity anomaly contained in the urban underground space designed in this paper exhibits an obvious response in the global apparent resistivity profile. It is concluded that a high-performance TEM excitation source possesses a high resolution, clearly reflecting all of the anomalies of a complex urban underground space model.

2-D electromagnetic modeling by finite‐element method with a dipole source and topography

Geophysics ◽  
2000 ◽  
Vol 65 (2) ◽  
pp. 465-475 ◽  
Author(s):  
Yuji Mitsuhata
Keyword(s):  
Finite Element ◽  
Delta Function ◽  
Dipole Source ◽  
Electromagnetic Modeling ◽  
Secondary Field ◽  
Controlled Source ◽  
Transient Electromagnetic ◽  
Isoparametric Finite Element ◽  
Anomalous Bodies ◽  
Element Technique

I present a method for calculating frequency‐domain electromagnetic responses caused by a dipole source over a 2-D structure. In modeling controlled‐source electromagnetic data, it is usual to separate the electromagnetic field into a primary (background) and a secondary (scattered) field to avoid a source singularity, and only the secondary field caused by anomalous bodies is computed numerically. However, this conventional scheme is not effective for complex structures lacking a simple background structure. The present modeling method uses a pseudo‐delta function to distribute the dipole source current, and does not need the separation of the primary and the secondary field. In addition, the method employs an isoparametric finite‐element technique to represent realistic topography. Numerical experiments are used to validate the code. Finally, a simulation of a source overprint effect and the response of topography for the long‐offset transient electromagnetic and the controlled‐source magnetotelluric measurements is presented.

Computer Application in Geosciences: Imaging of the Subsurface by Structural Coupled Inversion of Potential Field Data

2014 ◽  
Vol 644-650 ◽  
pp. 2670-2673
Author(s):  
Jun Wang ◽  
Xiao Hong Meng ◽  
Fang Li ◽  
Jun Jie Zhou
Keyword(s):  
Potential Field ◽  
Field Data ◽  
Gravity Data ◽  
Computer Application ◽  
Magnetic Data ◽  
Imaging Method ◽  
Inversion Algorithm ◽  
Constant Property ◽  
Near Surface ◽  
Potential Field Data

With the continuing growth in influence of near surface geophysics, the research of the subsurface structure is of great significance. Geophysical imaging is one of the efficient computer tools that can be applied. This paper utilize the inversion of potential field data to do the subsurface imaging. Here, gravity data and magnetic data are inverted together with structural coupled inversion algorithm. The subspace (model space) is divided into a set of rectangular cells by an orthogonal 2D mesh and assume a constant property (density and magnetic susceptibility) value within each cell. The inversion matrix equation is solved as an unconstrained optimization problem with conjugate gradient method (CG). This imaging method is applied to synthetic data for typical models of gravity and magnetic anomalies and is tested on field data.

The use and misuse of apparent resistivity in electromagnetic methods

Geophysics ◽  
1986 ◽  
Vol 51 (7) ◽  
pp. 1462-1471 ◽  
Author(s):  
Brian R. Spies ◽  
Dwight E. Eggers
Keyword(s):  
Apparent Resistivity ◽  
Early Time ◽  
Asymptotic Formulas ◽  
Voltage Response ◽  
Late Time ◽  
Induced Voltage ◽  
Resistivity Curve ◽  
Transient Electromagnetic ◽  
Electromagnetic Methods ◽  
Tem Method

Problems and misunderstandings arise with the concept of apparent resistivity when the analogy between an apparent resistivity computed from geophysical observations and the true resistivity structure of the subsurface is drawn too tightly. Several definitions of apparent resistivity are available for use in electromagnetic methods; however, those most commonly used do not always exhibit the best behavior. Many of the features of the apparent resistivity curve which have been interpreted as physically significant with one definition disappear when alternative definitions are used. It is misleading to compare the detection or resolution capabilities of different field systems or configurations solely on the basis of the apparent resistivity curve. For the in‐loop transient electromagnetic (TEM) method, apparent resistivity computed from the magnetic field response displays much better behavior than that computed from the induced voltage response. A comparison of “exact” and “asymptotic” formulas for the TEM method reveals that automated schemes for distinguishing early‐time and late‐time branches are at best tenuous, and those schemes are doomed to failure for a certain class of resistivity structures (e.g., the loop size is large compared to the layer thickness). For the magnetotelluric (MT) method, apparent resistivity curves defined from the real part of the impedance exhibit much better behavior than curves based on the conventional definition that uses the magnitude of the impedance. Results of using this new definition have characteristics similar to apparent resistivity obtained from time‐domain processing.

Measurement and analysis of species distribution in laser-induced ablation plasma of an aluminum-magnesium alloy

2021 ◽  
Author(s):  
Junxiao Wang ◽  
Shuqing Wang ◽  
Lei Zhang ◽  
Maogen Su ◽  
Duixiong Sun ◽  
...  
Keyword(s):  
Species Distribution ◽  
Laser Energy ◽  
Integral Intensity ◽  
Spectral Lines ◽  
Imaging Method ◽  
Measurement And Analysis ◽  
Ablation Plasma ◽  
Spatio Temporal ◽  
Differential Imaging

Abstract We proposed a theoretical spatio-temporal imaging method, which was based on the thermal model of laser ablation and the two-dimensional axisymmetric multi-species hydrodynamics model. By using the intensity formula, the integral intensity of spectral lines could be calculated and the corresponding images of intensity distribution could be drawn. Through further image processing such as normalization, determination of minimum intensity, combination and color filtering, a relatively clear species distribution image in the plasma could be obtained. Using the above method, we simulated the plasma ablated from Al-Mg alloy by different laser energies under 1 atm argon, and obtained the theoretical spatio-temporal distributions of Mg I, Mg II, Al I, Al II and Ar I species, which are almost consistent with the experimental results by differential imaging. Compared with the experimental decay time constants, the consistency is higher at low laser energy, indicating that our theoretical model is more suitable for the plasma dominated by laser-supported combustion wave.

scholarly journals Current and Potential Applications of Artificial Intelligence in Gastrointestinal Stromal Tumor Imaging

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Cai-Wei Yang ◽  
Xi-Jiao Liu ◽  
Si-Yun Liu ◽  
Shang Wan ◽  
Zheng Ye ◽  
...  
Keyword(s):  
Artificial Intelligence ◽  
Tumor Imaging ◽  
Therapy Response ◽  
Imaging Method ◽  
Mesenchymal Tumors ◽  
Potential Applications ◽  
Intellectual Capacity ◽  
Prediction Of Prognosis ◽  
Current Guidelines

The most common mesenchymal tumors are gastrointestinal stromal tumors (GISTs), which have malignant potential and can occur anywhere along the gastrointestinal system. Imaging methods are important and indispensable of GISTs in diagnosis, risk staging, therapy, and follow-up. The recommended imaging method for staging and follow-up is computed tomography (CT) according to current guidelines. Artificial intelligence (AI) applies and elaborates theses, procedures, modes, and utilization systems for simulating, enlarging, and stretching the intellectual capacity of humans. Recently, researchers have done a few studies to explore AI applications in GIST imaging. This article reviews the present AI studies in GISTs imaging, including preoperative diagnosis, risk stratification and prediction of prognosis, gene mutation, and targeted therapy response.

The Research on Development Status and Key Technology of Elastic Wave CT

2013 ◽  
Vol 457-458 ◽  
pp. 1348-1351
Author(s):  
Lei Yang
Keyword(s):  
Elastic Wave ◽  
Error Control ◽  
Research Direction ◽  
Observation System ◽  
Imaging Method ◽  
Inversion Algorithm ◽  
Technical Problems ◽  
Ct Technology ◽  
Development Tendency ◽  
Current Inversion

After introducing the basic definition, technical principle and applied scope of elastic wave CT technology, the paper makes a detailed introduction of the development process of elastic wave CT technology domestic and overseas and main technical problems it faces and believes that the imagining precision of elastic wave CT is often influenced by various factors such as the observation system, test precision, imaging method and error control. Thereinto, the hot issue in the research is put onto the study about inversion algorithm and the paper also elaborates the research direction and development tendency of current inversion algorithm at home and abroad.

The Application of TEM on Detecting Mine Goaf

2014 ◽  
Vol 1073-1076 ◽  
pp. 2153-2157
Author(s):  
Yong Jun Li ◽  
Xiao Ming Li ◽  
Ting Chen
Keyword(s):  
Water Content ◽  
Apparent Resistivity ◽  
Electromagnetic Method ◽  
Transient Electromagnetic Method ◽  
Electrical Characteristics ◽  
Geophysical Prospecting ◽  
Secondary Field ◽  
Low Resistivity ◽  
Transient Electromagnetic

Transient electromagnetic method is one of the geophysical prospecting methods to detect mine goaf. The paper analyzes the unique electrical characteristics of the stratum containing goaf. TEM inverts the apparent resistivity and delineates the mine goaf and determines water content by observing the pure secondary field. The method is sensitive to geologic bodies of low resistivity and has higher resolution. The paper takes some one mine in Shanxi as example to prove the practicability and effectiveness of TEM in production. It has certain reference significance in detecting mine goaf.

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