Direct inversion of time‐domain electromagnetic data

Geophysics ◽  
1987 ◽  
Vol 52 (10) ◽  
pp. 1431-1435 ◽  
Author(s):  
A. G. Nekut
Keyword(s):  
Least Squares ◽  
Time Domain ◽  
Time Derivative ◽  
Image Method ◽  
Simple Method ◽  
Geoelectric Section ◽  
Direct Inversion ◽  
Transient Electromagnetic ◽  
Time Domain Electromagnetic ◽  
Central Loop

This note describes a simple method for converting transient electromagnetic (EM) sounding data into profiles of conductivity versus depth, based on an approximate image representation for the decaying induced ground currents. The method can provide one‐dimensional (1-D) inversion for any kind of time‐domain EM sounding data; the discussion here is limited to the case of central‐loop sounding. In particular, I apply the inversion to some time‐derivative central‐loop sounding data and demonstrate that essentially the same interpretation of the geoelectric section is obtained with the simple image method as is obtained using traditional iterative least‐squares fitting to layered models. This simple inverse can be computed much more quickly than an iterative least‐squares inverse, making it possible to estimate the geoelectric section concomitant with data acquisition.

A simple method of transient electromagnetic data analysis

Geophysics ◽  
1998 ◽  
Vol 63 (2) ◽  
pp. 405-410 ◽  
Author(s):  
Maxwell A. Meju
Keyword(s):  
Data Analysis ◽  
Time Domain ◽  
Mineral Resources ◽  
Ease Of Use ◽  
Simple Method ◽  
Diagnostic Data ◽  
Electromagnetic Data ◽  
Transient Electromagnetic ◽  
Interpretive Model

Time-domain or transient electromagnetic (TEM) methods are used routinely in environmental, hydrogeological, energy, and mineral resources investigations owing to their ease of use and ability to generate diagnostic data. In some typical field situations, the gross structure of the subsurface may be approximately 1-D, so 1-D interpretation schemes can be used to retrieve an interpretive model for the depth soundings.

Three-dimensional transient electromagnetic inversion with optimal transport

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Xiaomeng Sun ◽  
Yanfei Wang ◽  
Xiao Yang ◽  
Yibo Wang
Keyword(s):  
Time Domain ◽  
3D Model ◽  
Optimal Transport ◽  
Three Dimensional ◽  
Experimental Tests ◽  
Transient Electromagnetic Method ◽  
Inversion Problem ◽  
Wasserstein Metric ◽  
Transient Electromagnetic ◽  
Time Domain Electromagnetic

Abstract Transient electromagnetic method (TEM), as one of the essential time-domain electromagnetic prospecting approaches, has the advantage of expedition, efficiency and convenience. In this paper, we study the transient electromagnetic inversion problem of different geological anomalies. First, Maxwell’s differential equations are discretized by the staggered finite-difference (FD) method; then we propose to solve the TEM inversion problem by minimizing the Wasserstein metric, which is related to the optimal transport (OT). Experimental tests based on the layered model and a 3D model are performed to demonstrate the feasibility of our proposed method.

QUASI‐STATIC TIME‐DOMAIN ELECTROMAGNETIC RESPONSE OF A HOMOGENEOUS CONDUCTING INFINITE CYLINDER

Geophysics ◽  
1972 ◽  
Vol 37 (1) ◽  
pp. 92-97 ◽  
Author(s):  
Saurabh K. Verma
Keyword(s):  
Time Domain ◽  
Decay Constant ◽  
Step Function ◽  
Ore Deposits ◽  
Electromagnetic Response ◽  
Infinite Cylinder ◽  
Transient Electromagnetic ◽  
Simplifying Assumptions ◽  
Time Domain Electromagnetic ◽  
Theoretical Results

Under some simplifying assumptions, the transient electromagnetic response of a homogeneous conducting infinite cylinder is derived. Two types of primary disturbances, represented by step‐function and ramp‐function pulses, are considered. Based on the theoretical results, response and decay constant curves are plotted and their utility in time‐domain electromagnetic surveys for conductive elongated ore deposits is described.

Time‐domain electromagnetic detection of a hidden target

Geophysics ◽  
1988 ◽  
Vol 53 (4) ◽  
pp. 537-545 ◽  
Author(s):  
David C. Bartel ◽  
A. Becker
Keyword(s):  
Magnetic Field ◽  
Time Domain ◽  
Time Window ◽  
Time Derivative ◽  
Step Response ◽  
Time Range ◽  
Geometrical Parameters ◽  
Target Signal ◽  
Time Domain Electromagnetic ◽  
The Time Domain

Numerical modeling of the time‐domain electromagnetic (EM) step response of a vertical tabular target hidden beneath a thin conductive overburden reveals that the target’s presence may be detected only during a well‐defined time window. In a situation where the secondary magnetic field is sensed by an airborne system equipped with horizontal coaxial dipoles, a conductance contrast of about ten between the target and the overburden is needed to ensure target detection. This value will, of course, vary with the size and depth of the target and, to a lesser extent, with the geometry of the system. In general, the time at which the window opens is a function of the geometrical parameters of the target, the height of the system, and the conductance of the overburden. For a given target, its width (defined as the ratio of the time of closure to the time of opening) is only a function of the conductance contrast between the target and the overburden. While the target signal is visible, one observes a maximum value of the target‐to‐overburden response ratio. The time at which this occurs is mainly controlled by the conductance of the target. The presence of the overburden causes the target signal to build up gradually before decaying toward zero. However, once the target signal dominates the overburden response, the signal can be approximated by a simple exponential decay over the time range of interest. The time constant of this decay is determined by the size and conductance of the target. Using this model, it is easy to relate the magnetic field step response calculated here to the response observable with a conventional EM system that transmits a primary field pulse of finite duration and detects the time derivative of the secondary magnetic field.

A comparison of loop time-domain electromagnetic and short-offset transient electromagnetic methods for mapping water-enriched zones — A case history in Shaanxi, China

Geophysics ◽  
2017 ◽  
Vol 82 (6) ◽  
pp. B201-B208 ◽  
Author(s):  
Weiying Chen ◽  
Guoqiang Xue ◽  
Afolagboye Lekan Olatayo ◽  
Kang Chen ◽  
Muhammad Younis Khan ◽  
...  
Keyword(s):  
Time Domain ◽  
Mining Depth ◽  
Transient Electromagnetic ◽  
Resolution Capability ◽  
Electromagnetic Methods ◽  
Detection Depth ◽  
Reliable Detection ◽  
Time Domain Electromagnetic ◽  
Tem Method ◽  
And Inversion

Increases in the mining depth of coal pose a significant challenge to the conventional loop source time-domain electromagnetic (TEM) method that requires significant enlargement of the loop size and transmitting current to realize the deeper sounding results required. As an alternative, TEM devices based on a grounded wire source are generally used to solve detections deeper than several hundred meters. To map the water-enriched zones buried underneath approximately 1000 m at a coal mine in Shaanxi, China, loop TEM and short-offset transient electromagnetic (SOTEM) measurements were conducted. We carried out 1D forward modeling and inversion constrained by drilling informa-tion, and the results reveal that the resolution capability of loop TEM and SOTEM is almost the same in detecting a conductive layer in the absence of any noise. However, for a given noise level and decay time, the SOTEM method provides a deeper investigation than loop TEM without compromising sensitivity. The field examples validated the synthetic results. The loop TEM with dimensions of [Formula: see text] realized a maximum depth of 1000 m, whereas the reliable detection depth of 1500 m was achieved by using a 723 m long grounded wire source using the SOTEM method. Moreover, the labor required is significantly reduced, and the efficiency is dramatically raised using the SOTEM method. Our results predict that the SOTEM method should play a more important role in deep hydrogeophysical investigations.

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