Electrical and magnetometric fields in a layered earth containing buried electrodes

Geophysics ◽  
1990 ◽  
Vol 55 (12) ◽  
pp. 1605-1612 ◽  
Author(s):  
D. Veitch ◽  
M. W. Asten ◽  
E. H. van Leeuwen
Keyword(s):  
Half Space ◽  
Field Data ◽  
Massive Sulfide ◽  
Magnetic Field Measurement ◽  
Layered Earth ◽  
Homogeneous Half Space ◽  
Electric And Magnetic Fields ◽  
Borehole Logs ◽  
Two Layer Model ◽  
The Magnetic Field

The number of analytical magnetometric resistivity (MMR) results available for basic earth geometries is limited compared to that of electrical resistivity methods, which is unfortunate since MMR has advantages for certain classes of problems. This paper extends the list of MMR results by deriving the response for the homogeneous half‐space and the multilayered earth. Both are calculated for arbitrary source and receiver positions. We show how the result for the layered earth reduces to that of the half‐space when there is only one layer. Necessary procedures for successful numerical evaluation of results for the layered case are given. Sample borehole logs of electric and magnetic fields for an example of a two‐layer model illustrate an advantage of the magnetic‐field measurement; namely, that it is sensitive to the position of layer boundaries rather than to the position of transmitter electrodes. The algorithm is also applied to interpretation of MMR field data from two boreholes drilled near massive sulfide conductors. The magnetometric influence (or background) due to borehole geometry in an electrically layered earth may be computed and subtracted from the field data, after which it is possible to perform quantitative modeling of the residual MMR anomaly to define the location of ore‐related conductors.

Broadband electromagnetic measurements over a massive sulfide prospect

Geophysics ◽  
1979 ◽  
Vol 44 (10) ◽  
pp. 1677-1699 ◽  
Author(s):  
D. F. Pridmore ◽  
S. H. Ward ◽  
J. W. Motter
Keyword(s):  
Tilt Angle ◽  
Host Rock ◽  
Massive Sulfide ◽  
Massive Sulfides ◽  
Homogeneous Half Space ◽  
Electromagnetic Measurements ◽  
Electric And Magnetic Fields ◽  
Dipole Sources ◽  
The Magnetic Field ◽  
Frequency Distance

This paper presents the results of measurements of the tilt angle and ellipticity of the polarization ellipse of the magnetic field, made at 14 frequencies in the range 10.5 Hz to 86 kHz, over a massive sulfide prospect in the foothills copper belt of California. As is typical of this class of deposit, the massive sulfides grade laterally into the disseminated sulfides of a tuff unit. The host rock resistivities are in the range 80 to 500 ο-m. The interpretation of the results is carried out using crude dike models in free space, although an attempt is made to account for the conductive host rock by examining the electric and magnetic fields generated by magnetic dipole sources over a homogeneous half‐space. The utility of broadband multifrequency electromagnetic (EM) measurements over a complex earth is shown clearly by the results over the prospect. The response of the massive sulfides, disseminated sulfides, and the host rock can all be distinguished when the tilt angle and ellipticity values are contoured in frequency‐distance space. A comparison is made of the results obtained using vertical‐loop, rotating vertical‐loop, and horizontal‐loop transmitter configurations. It is found at this mineral prospect that (1) the results from the vertical‐loop transmitter are easier to interpret, in terms of simple models, than those produced by the horizontal‐loop transmitter, (2) although the rotating vertical‐loop transmitter gives a larger response from the massive sulfides, the results show no more fine structure in the massive sulfides than that shown by the response from the vertical‐loop transmitter; and (3) moving the vertical‐loop transmitter does not give significantly more information about the geology.

Time‐domain solution for horizontal coaxial dipoles on a half‐space

Geophysics ◽  
1986 ◽  
Vol 51 (9) ◽  
pp. 1850-1852 ◽  
Author(s):  
David C. Bartel
Keyword(s):  
Frequency Domain ◽  
Half Space ◽  
Time Domain ◽  
Inverse Laplace Transform ◽  
Direct Solution ◽  
Current Waveform ◽  
Laplace Domain ◽  
Homogeneous Half Space ◽  
The Time Domain ◽  
The Magnetic Field

The practice of transforming frequency‐domain results into the time domain is fairly common in electromagnetics. For certain classes of problems, it is possible to obtain a direct solution in the time domain. A summary of these solutions is given in Hohmann and Ward (1986). Presented here is another problem which can be solved directly in the time domain—the magnetic field of horizontal coaxial dipoles on the surface of a homogeneous half‐space. Solutions are presented for both an impulse transmitter current and a step turnon in the transmitter current. The solution in the time domain is obtained by taking the inverse Laplace transform of the product of the frequency‐domain solution and the Laplace‐domain representation of the current waveform.

Doubling the effective skin depth with a local source

Geophysics ◽  
1999 ◽  
Vol 64 (3) ◽  
pp. 732-738 ◽  
Author(s):  
James E. Reid ◽  
James C. Macnae
Keyword(s):  
Plane Wave ◽  
Half Space ◽  
Survey Design ◽  
Data Interpretation ◽  
Skin Depth ◽  
Local Source ◽  
Electromagnetic Sounding ◽  
Homogeneous Half Space ◽  
Electric And Magnetic Fields ◽  
Thick Overburden

The depth at which the amplitude of the frequency‐domain electromagnetic fields due to dipole and square loop sources over a homogeneous half‐space fall to 1/e of their value at the surface is compared to the conventional plane‐wave skin depth. The skin depth due to a local source depends on the transmitter frequency, half‐space conductivity, transmitter altitude, and transmitter‐receiver offset, and may range from a fraction of to more than twice the plane‐wave skin depth. Unlike the plane‐wave skin depth, the “local‐source skin depth” is different for electric and magnetic fields, and may be nonunique for some transmitter geometries and field components. For all transmitter geometries, however, the local‐source skin depth approaches the plane‐wave skin depth as the transmitter altitude and/or receiver offset increase. The concept of the local‐source skin depth has direct application to survey design and data interpretation. A theoretical example demonstrates that it is possible to predict, for a given survey geometry and frequency range, whether or not an electromagnetic sounding can detect a conductive basement below a thick overburden layer.

INDUCTIVE SOUNDING OF A LAYERED EARTH WITH A HORIZONTAL MAGNETIC DIPOLE

Geophysics ◽  
1970 ◽  
Vol 35 (4) ◽  
pp. 660-703 ◽  
Author(s):  
Abhijit Dey ◽  
Stanley H. Ward
Keyword(s):  
Magnetic Field ◽  
Magnetic Dipole ◽  
Complete Solution ◽  
Vertical Component ◽  
Static Approximation ◽  
Phase Measurements ◽  
Layered Earth ◽  
Electric And Magnetic Fields ◽  
Earth Structures ◽  
The Magnetic Field

A complete solution of the boundary value problem of a horizontal magnetic dipole over homogeneous and n‐layered half‐spaces is outlined. Quasi‐static expressions for the electric and magnetic fields have been obtained and a comparison of the complete solution with the quasi‐static approximation in practical frequency ranges is made. An analysis of the phases and amplitudes of the magnetic field components and of the polarization parameters of the magnetic field reveals that the phase of the vertical component of the magnetic field and the ellipticity of the magnetic field polarization ellipse are the most sensitive indicators of layering. Amplitude measurements are, in general, less effective than phase measurements for resolution of layered earth structures. Results from both parametric and geometric modes of sounding have been studied in detail for a number of two‐ and three‐layered models of varying thicknesses and conductivity contrasts. Deduction of layering for different thicknesses of the top layer from the measurements of [Formula: see text] and polarization parameters, seems relatively easier when the underlying layer is more conductive than the top layer. For models in which the underlying layer is less conductive than the top layer, the phases of both [Formula: see text] and wave tilt are more diagnostic of changes in layer parameters.

Orthogonality in CSAMT and MT measurements

Geophysics ◽  
1993 ◽  
Vol 58 (7) ◽  
pp. 924-934 ◽  
Author(s):  
David E. Boerner ◽  
Ron D. Kurtz ◽  
Alan G. Jones
Keyword(s):  
Magnetic Fields ◽  
Plane Wave ◽  
Field Data ◽  
Necessary Condition ◽  
Far Field ◽  
Single Plane ◽  
Wave Source ◽  
Near Surface ◽  
Layered Earth ◽  
Electric And Magnetic Fields

The electric and magnetic fields from a single plane‐wave source on a one dimensional (1-D) earth, or a plane‐wave source polarized parallel or perpendicular to strike on a two-dimensional (2-D) earth, are orthogonal. On a layered earth and in the far‐field of a controlled source, the electric and magnetic fields are also orthogonal. Therefore, orthogonality of E and H data is a necessary condition to justify the application of 1-D or 2-D modeling algorithms having a plane wave source. A strict criterion to prove orthogonality, and thus provide a rationale for the choice of interpretation methods, can be defined directly in terms of field data. However, field data acquired in the intermediate and near‐field of any electromagnetic (EM) source are generally not orthogonal, even on a plane‐layered earth. Representing these nonorthogonal data in an orthogonal coordinate system can be misleading, particularly for the minor axis components of the polarization ellipses. Nonorthogonality also arises because of 3-D scattering, with one common example being the electric field response of near surface structure. An example of field data illustrates the nonorthogonality in CSAMT measurements caused by the response of surficial geology. In these EM data, the angle between E and H is a sensitive indicator of geological contacts and faults. Quantitative analysis of these data can be performed with the assumptions of a “bulk” 1-D earth (i.e., orthogonal E and H in the far‐field) and purely galvanic scattering of the EM fields.

Transmission line sanitary protective zones. Electromagnetic safety problems

2020 ◽  
pp. 736-736
Author(s):  
N. B. Rubtsova ◽  
A. Y. Tokarskiy
Keyword(s):  
Magnetic Field ◽  
Risk Factor ◽  
Transmission Lines ◽  
General Public ◽  
Field Component ◽  
Regulatory Requirements ◽  
Protection Zones ◽  
Electric And Magnetic Fields ◽  
Health Risk Factor ◽  
The Magnetic Field

The main problems of overhead and cable transmission lines with voltage >=110 kV electric and magnetic fields general public protection are presented. It is shown that it is necessary to develop regulatory requirements for these lines’ sanitary protection zones organization, taking into account the magnetic field component, because its possible health risk factor, up to carcinogenic.

scholarly journals First in-orbit results of the vector magnetic field measurement of the High Precision Magnetometer onboard the China Seismo-Electromagnetic Satellite

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Bin Zhou ◽  
Bingjun Cheng ◽  
Xiaochen Gou ◽  
Lei Li ◽  
Yiteng Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Precision ◽  
Magnetic Field Measurement ◽  
Vector Data ◽  
Magnetic Field Data ◽  
Night Side ◽  
The Difference ◽  
The Magnetic Field ◽  
Ground Calibration ◽  
Data Calibration

Abstract The High Precision Magnetometer (HPM) is one of the main payloads onboard the China Seismo-Electromagnetic Satellite (CSES). The HPM consists of two Fluxgate Magnetometers (FGM) and the Coupled Dark State Magnetometer (CDSM), and measures the magnetic field from DC to 15 Hz. The FGMs measure the vector components of the magnetic field; while the CDSM detects the magnitude of the magnetic field with higher accuracy, which can be used to calibrate the linear parameters of the FGM. In this paper, brief descriptions of measurement principles and performances of the HPM, ground, and in-orbit calibration results of the FGMs are presented, including the thermal drift and magnetic interferences from the satellite. The HPM in-orbit vector data calibration includes two steps: sensor non-linearity corrections based on on-ground calibration and fluxgate linear parameter calibration based on the CDSM measurements. The calibration results show a reasonably good stability of the linear parameters over time. The difference between the field magnitude calculated from the calibrated FGM components and the magnitude directly measured by the CDSM is just 0.5 nT (1σ) when the linear parameters are fitted separately for the day- and the night-side. Satellite disturbances have been analyzed including soft and hard remanence as well as magnetization of the magnetic torquer, radiation from the Tri-Band Beacon, and interferences from the rotation of the solar wing. A comparison shows consistency between the HPM and SWARM magnetic field data. Observation examples are introduced in the paper, which show that HPM data can be used to survey the global geomagnetic field and monitor the magnetic field disturbances in the ionosphere.

Inversion of slingram electromagnetic induction data using a Born approximation

Geophysics ◽  
2013 ◽  
Vol 78 (4) ◽  
pp. E201-E212 ◽  
Author(s):  
Jochen Kamm ◽  
Michael Becken ◽  
Laust B. Pedersen
Keyword(s):  
Half Space ◽  
Born Approximation ◽  
High Efficiency ◽  
Three Dimensions ◽  
Background Model ◽  
Desktop Computer ◽  
Near Surface ◽  
Homogeneous Half Space ◽  
Integral Equation Formulation ◽  
Forward Operator

We present an efficient approximate inversion scheme for near-surface loop-loop EM induction data (slingram) that can be applied to obtain 2D or 3D models on a normal desktop computer. Our approach is derived from a volume integral equation formulation with an arbitrarily conductive homogeneous half-space as a background model. The measurements are not required to fulfill the low induction number condition (low frequency and conductivity). The high efficiency of the method is achieved by invoking the Born approximation around a half-space background. The Born approximation renders the forward operator linear. The choice of a homogeneous half-space yields closed form expressions for the required electromagnetic normal fields. It also yields a translationally invariant forward operator, i.e., a highly redundant Jacobian. In connection with the application of a matrix-free conjugate gradient method, this allows for very low memory requirements during the inversion, even in three dimensions. As a consequence of the Born approximation, strong conductive deviations from the background model are underestimated. Highly resistive anomalies are in principle overestimated, but at the same time difficult to resolve with induction methods. In the case of extreme contrasts, our forward model may fail in simultaneously explaining all the data collected. We applied the method to EM34 data from a profile that has been extensively studied with other electromagnetic methods and compare the results. Then, we invert three conductivity maps from the same area in a 3D inversion.

Numerical seismograms obtained using ω-κ integrals, for a point P source in a vertically inhomogeneous anelastic model

1996 ◽  
Vol 86 (3) ◽  
pp. 750-760
Author(s):  
F. Abramovici ◽  
L. H. T. Le ◽  
E. R. Kanasewich
Keyword(s):  
Half Space ◽  
Homogeneous Layer ◽  
Variable Step Size ◽  
Step Size ◽  
Adaptive Process ◽  
Cpu Time ◽  
Homogeneous Half Space ◽  
Linear Layer ◽  
Variable Step ◽  
Viscoelastic Layers

Abstract This article presents some numerical experiments in using a computer program for calculating the displacements due to a P source in a vertically inhomogeneous structure, based on the Fourier-Bessel representation. The structure may contain homogeneous, inhomogeneous, elastic, or viscoelastic layers. The source may act in any type of sublayer or in the half-space. Synthetic results for the simple case of a homogeneous layer overlaying a homogeneous half-space compare favorably with computations based on the Cagniard method. Numerical seismograms for an elastic layer having velocities and density varying linearly with depth were computed by integrating numerically the governing differential systems and compared with results based on the Haskell model of splitting the linear layer in homogeneous sublayers. Even an adaptive process with a variable step size based on the Haskell model has a poorer performance on the accuracy-cpu time scale than numerical integration.

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