Simultaneous inversion of airborne electromagnetic data for resistivity and magnetic permeability

Les P. Beard; Jonathan E. Nyquist

doi:10.1190/1.1444452

Simultaneous inversion of airborne electromagnetic data for resistivity and magnetic permeability

Geophysics ◽

10.1190/1.1444452 ◽

1998 ◽

Vol 63 (5) ◽

pp. 1556-1564 ◽

Cited By ~ 40

Author(s):

Les P. Beard ◽

Jonathan E. Nyquist

Keyword(s):

Magnetic Permeability ◽

Phase Response ◽

Low Frequencies ◽

Phase Measurements ◽

Oak Ridge ◽

Simultaneous Inversion ◽

Relative Magnetic Permeability ◽

Frequency Independent ◽

Airborne Electromagnetic ◽

Using Data

Where the magnetic permeability of rock or soil exceeds that of free space, the effect on airborne electromagnetic systems is to produce a frequency‐independent shift in the in‐phase response of the system while altering the quadrature response only slightly. The magnitude of the in‐phase shift increases as (1) the relative magnetic permeability is increased, (2) the amount of magnetic material is increased, and (3) the airborne sensor gets nearer the earth’s surface. Over resistive, magnetic ground, the shift may be evinced by negative in‐phase measurements at low frequencies; but over more conductive ground, the same shift may go unnoticed because of the large positive in‐phase response. If the airborne sensor is flown at low levels, the magnitude of the shift may be large enough to affect automatic inversion routines that do not take this shift into account, producing inaccurate estimated resistivities, usually overestimates. However, layered‐earth inversion algorithms that incorporate magnetic permeability as an additional inversion parameter may improve the resistivity estimates. We demonstrate this improvement using data collected over hazardous waste sites near Oak Ridge, Tennessee, USA. Using resistivity inversion without magnetic permeability, the waste sites are almost invisible to the sensors. When magnetic permeability is included as an inversion parameter, the sites are detected, both by improved resistivity estimates and by estimated magnetic permeability.

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Methods for determination of relative magnetic permeability of feebly magnetic materials

10.3403/00172070 ◽

1987 ◽

Keyword(s):

Magnetic Materials ◽

Magnetic Permeability ◽

Relative Magnetic Permeability

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MINIMIZING THE EFFECTIVE AREA OF SCATTERING BY MEANS OF CHANGING THE RELATIVE MAGNETIC PERMEABILITY

ВЕСТНИК ВОРОНЕЖСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА ◽

10.36622/vstu.2021.17.1.013 ◽

2021 ◽

pp. 85-88

Author(s):

А.В. Володько ◽

С.М. Фёдоров ◽

Е.А. Ищенко ◽

М.А. Сиваш ◽

Л.В. Сопина ◽

...

Keyword(s):

Magnetic Permeability ◽

Dielectric Material ◽

Threshold Value ◽

Effective Area ◽

Large Object ◽

Frequency Dependent ◽

Relative Magnetic Permeability ◽

Effective Scattering Area ◽

Maximum Value ◽

Simulation Results

Исследуется зависимость эффективной площади рассеяния (ЭПР) от относительной магнитной проницаемости материала, из которого изготавливается структура. В качестве тела моделирования был выбран шар, который изготовлен из диэлектрического материала, у которого возможно выполнять изменение относительной магнитной проницаемости. По полученным результатам моделирования построены графики зависимости максимального значения моностатической ЭПР от частоты, а также от относительной магнитной проницаемости среды. Было показано, что с увеличением относительной магнитной проницаемости материала изготовления происходит увеличение значения ЭПР объекта, а также обнаружена зависимость эффективной площади рассеяния от соотношения размеров шара и длиной волны, так при превышении порогового значения, после которого шар становится крупным объектом, ЭПР резко возрастает. По результатам исследования был построен график зависимости эффективной площади рассеяния шара от относительной магнитной проницаемости материала изготовления. Доказана возможность применения материала с частотозависимой относительной магнитной проницаемостью в качестве стелс-покрытия. В статье содержится исследуемая модель, графики полученных результатов, по которым можно легко определить зависимость ЭПР от частоты и от относительной магнитной проницаемости материала изготовления The article investigates the dependence of the effective scattering area (ESA) on the relative magnetic permeability of the material from which the structure is made. We chose a sphere as the modeling body, which is made of a dielectric material, in which it is possible to change the relative magnetic permeability. Based on the obtained simulation results, graphs of the dependence of the maximum value of monostatic ESA on frequency, as well as on the relative magnetic permeability of the medium, were constructed. It was shown that with an increase in the relative magnetic permeability of the material of manufacture, an increase in the value of the ESA of the object occurs, and the dependence of the effective scattering area on the ratio of the size of the ball and the wavelength was found, so when the threshold value is exceeded, after which the ball becomes a large object, ESA rises sharply. Based on the results of the study, a graph of the dependence of the effective scattering area of the sphere on the relative magnetic permeability of the material of manufacture was built. The possibility of using a material with a frequency-dependent relative magnetic permeability as a stealth coating was proven. The article contains the investigated model, graphs of the results obtained, by which it is easy to determine the dependence of the ESA on the frequency and on the relative magnetic permeability of the material of manufacture

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Inversion of helicopter electromagnetic data to a magnetic conductive layered earth

Geophysics ◽

10.1190/1.1598113 ◽

2003 ◽

Vol 68 (4) ◽

pp. 1211-1223 ◽

Cited By ~ 50

Author(s):

Haoping Huang ◽

Douglas C. Fraser

Keyword(s):

Magnetic Permeability ◽

Field Data ◽

Model Parameters ◽

Relative Importance ◽

Magnetic Polarization ◽

Inversion Algorithm ◽

Layered Earth ◽

Electromagnetic Data ◽

Airborne Electromagnetic ◽

True Values

Inversion of airborne electromagnetic (EM) data for a layered earth has been commonly performed under the assumption that the magnetic permeability of the layers is the same as that of free space. The resistivity inverted from helicopter EM data in this way is not reliable in highly magnetic areas because magnetic polarization currents occur in addition to conduction currents, causing the inverted resistivity to be erroneously high. A new algorithm for inverting for the resistivity, magnetic permeability, and thickness of a layered model has been developed for a magnetic conductive layered earth. It is based on traditional inversion methodologies for solving nonlinear inverse problems and minimizes an objective function subject to fitting the data in a least‐squares sense. Studies using synthetic helicopter EM data indicate that the inversion technique is reasonably dependable and provides fast convergence. When six synthetic in‐phase and quadrature data from three frequencies are used, the model parameters for two‐ and three‐layer models are estimated to within a few percent of their true values after several iterations. The analysis of partial derivatives with respect to the model parameters contributes to a better understanding of the relative importance of the model parameters and the reliability of their determination. The inversion algorithm is tested on field data obtained with a Dighem helicopter EM system at Mt. Milligan, British Columbia, Canada. The output magnetic susceptibility‐depth section compares favorably with that of Zhang and Oldenburg who inverted for the susceptibility on the assumption that the resistivity distribution was known.

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A Method For Determination Of Specific Electrical Resistance Of Steel And Nano-Coating Sputtered On It

Environment Technology Resources Proceedings of the International Scientific and Practical Conference ◽

10.17770/etr2011vol2.989 ◽

2015 ◽

Vol 2 ◽

pp. 118 ◽

Cited By ~ 1

Author(s):

Andris Martinovs ◽

Josef Timmerberg ◽

Konstantins Savkovs ◽

Aleksandrs Urbahs ◽

Paul Beckmann

Keyword(s):

Electrical Conductivity ◽

Magnetic Permeability ◽

Electrical Resistance ◽

Skin Effect ◽

Specific Electrical Resistance ◽

Specific Electrical Conductivity ◽

Relative Magnetic Permeability ◽

Nano Coating ◽

Cylindrical Steel

The paper describes methods developed to determine specific electrical conductivity and relative magnetic permeability of cylindrical steel items and nano-coatings deposited on them by sputtering. Research enables development of a new method for determination of thickness of vacuum deposited nano- coating that is based on application of skin effect.

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3-D imaging of subsurface magnetic permeability/susceptibility with portable frequency domain electromagnetic sensors for near surface exploration

Geophysical Journal International ◽

10.1093/gji/ggz382 ◽

2019 ◽

Vol 219 (3) ◽

pp. 1773-1785 ◽

Cited By ~ 2

Author(s):

Julien Guillemoteau ◽

François-Xavier Simon ◽

Guillaume Hulin ◽

Bertrand Dousteyssier ◽

Marion Dacko ◽

...

Keyword(s):

Magnetic Permeability ◽

Field Data ◽

Large Data ◽

Archaeological Site ◽

Phase Response ◽

Magnetic Method ◽

Data Sets ◽

Near Surface ◽

Inversion Procedure ◽

Multichannel Deconvolution

SUMMARY The in-phase response collected by portable loop–loop electromagnetic induction (EMI) sensors operating at low and moderate induction numbers (≤1) is typically used for sensing the magnetic permeability (or susceptibility) of the subsurface. This is due to the fact that the in-phase response contains a small induction fraction and a preponderant induced magnetization fraction. The magnetization fraction follows the magneto-static equations similarly to the magnetic method but with an active magnetic source. The use of an active source offers the possibility to collect data with several loop–loop configurations, which illuminate the subsurface with different sensitivity patterns. Such multiconfiguration soundings thereby allows the imaging of subsurface magnetic permeability/susceptibility variations through an inversion procedure. This method is not affected by the remnant magnetization and theoretically overcomes the classical depth ambiguity generally encountered with passive geomagnetic data. To invert multiconfiguration in-phase data sets, we propose a novel methodology based on a full-grid 3-D multichannel deconvolution (MCD) procedure. This method allows us to invert large data sets (e.g. consisting of more than a hundred thousand of data points) for a dense voxel-based 3-D model of magnetic susceptibility subject to smoothness constraints. In this study, we first present and discuss synthetic examples of our imaging procedure, which aim at simulating realistic conditions. Finally, we demonstrate the applicability of our method to field data collected across an archaeological site in Auvergne (France) to image the foundations of a Gallo-Roman villa built with basalt rock material. Our synthetic and field data examples demonstrate the potential of the proposed inversion procedure offering new and complementary ways to interpret data sets collected with modern EMI instruments.

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DESMEX: A novel system development for semi-airborne electromagnetic exploration

Geophysics ◽

10.1190/geo2019-0336.1 ◽

2020 ◽

Vol 85 (6) ◽

pp. E253-E267 ◽

Cited By ~ 1

Author(s):

M. Becken ◽

C. G. Nittinger ◽

M. Smirnova ◽

A. Steuer ◽

T. Martin ◽

...

Keyword(s):

Magnetic Field ◽

Transfer Functions ◽

System Development ◽

Low Noise ◽

Raw Material ◽

Measurement Unit ◽

Fluxgate Magnetometer ◽

Low Frequencies ◽

Airborne Electromagnetic ◽

Fixed Reference

There is a clear demand to increase detection depths in the context of raw material exploration programs. Semi-airborne electromagnetic (semi-AEM) methods can address these demands by combining the advantages of powerful transmitters deployed on the ground with efficient helicopter-borne mapping of the magnetic field response in the air. The penetration depth can exceed those of classic airborne EM systems because low frequencies and large transmitter-receiver offsets can be realized in practice. A novel system has been developed that combines high-moment horizontal electric bipole transmitters on the ground with low-noise three-axis induction coil magnetometers, a three-axis fluxgate magnetometer, and a laser gyro inertial measurement unit integrated within a helicopter-towed airborne platform. The attitude data are used to correct the time series for motional noise and subsequently to rotate into an earth-fixed reference frame. In a second processing step, and as opposed to existing semi-AEM systems, we transform the data into the frequency domain and estimate the complex-valued transfer functions between the received magnetic field components and the synchronously recorded injection current by regression analysis. This approach is similar to the procedure used in controlled-source EM. For typical source bipole moments of 20–40 kAm and for rectangular current waveforms with a fundamental frequency of approximately 10 Hz, we can estimate reliable three-component (3C) transfer functions in the frequency range from 10 to 5000 Hz over a measurement area of [Formula: see text] for a single source installation. The system has the potential to be used for focused exploration of deep targets.

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Estimation and geologic interpretation of regolith chargeability and superparamagnetic susceptibility in airborne electromagnetic data

Geophysics ◽

10.1190/geo2019-0395.1 ◽

2020 ◽

Vol 85 (5) ◽

pp. E153-E162 ◽

Cited By ~ 1

Author(s):

James Macnae ◽

Tim Munday ◽

Camilla Soerensen

Keyword(s):

Magnetic Permeability ◽

Thin Sheet ◽

Secondary Field ◽

Conductivity Model ◽

Electromagnetic Data ◽

Delay Times ◽

Airborne Electromagnetic ◽

Geologic Interpretation ◽

Airborne Electromagnetic Data ◽

Dispersive Models

All available inversion software for airborne electromagnetic (AEM) data can at a minimum fit a nondispersive conductivity model to the observed inductive secondary field responses, whether operating in the time or frequency domain. Quasistatic inductive responses are essentially controlled by the induction number, the product of frequency with conductivity and magnetic permeability. Recent research has permitted the conductivity model to be dispersive, commonly using a single Cole-Cole parameterization of the induced polarization (IP) effect; but this parameterization slows down and destabilizes any inversion, and it does not account for the need for dual or multiple Cole-Cole responses. Little has been published on inverting AEM data affected by frequency-dependent magnetic permeability, or superparamagnetism (SPM), usually characterized by a Chikazumi model. Because the IP and SPM effects are small and are usually only obvious at late delay times, the aim of our research is to determine if these IP and SPM effects can be fitted and stripped from the AEM data after being approximated with simple dispersive models. We are able to successfully automate a thin-sheet model to do this stripping. Stripped data then can be inverted using a nondispersive conductivity model. The IP and SPM parameters fitted independently to each independent measured decay to provide stripping are proven to be spatially coherent, and they are geologically sensible. The results are found to enhance interpretation of the regolith geology, particularly the nature and distribution of transported materials that are not afforded by mapping conductivity/conductance alone.

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