The Finite-Conducting Ground’s Effect on the Inductance of a Rectangular Loop

In an airborne electromagnetic system, which transmits time-domain half-sine current waves generated by a resonance circuit, the inductance of the transmitting loop is of great significance and directly related to parameters of the half-sine current waveform. However, in general, the effect of a finite-conducting ground on the inductance of the transmitting loop was neglected, or the ground was handled as a perfect conductor. In other words, there was no accurate method to evaluate ground’s effect on the inductance of the transmitting loop. Therefore, a new and convenient algorithm, calculating ground’s effect on the inductance of a rectangular loop, is proposed in this paper. An experiment was constructed afield, showing that the inductance increased gradually when the loop was lifted up from 0 m to 30 m, which supported the algorithm positively.

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THEORETICAL RESPONSE OF A TIME‐DOMAIN, AIRBORNE, ELECTROMAGNETIC SYSTEM

Geophysics ◽

10.1190/1.1440043 ◽

1969 ◽

Vol 34 (5) ◽

pp. 729-738 ◽

Cited By ~ 9

Author(s):

P. H. Nelson ◽

D. B. Morris

Keyword(s):

Time Domain ◽

Computational Procedure ◽

Response Curves ◽

Electromagnetic System ◽

Magnetic Dipoles ◽

System Calibration ◽

Input System ◽

Airborne Electromagnetic ◽

Airborne Em ◽

Thickness Parameter

The secondary magnetic field induced by a time‐domain, airborne EM system is calculated by transforming the tabulated mutual impedances of two magnetic dipoles above an earth of homogeneous or layered resistivity structure. The computational procedure is extended to produce response curves useful in interpreting data from a particular system, the Barringer Input system. It is demonstrated that the apparent resistivity can be estimated through use of the receiver channel ratios, a method which is independent of absolute system calibration. Layered earth calculations indicate to what extent conductive overburden cases can be readily distinguished, in terms of the conductivity‐thickness parameter, but separate interpretation of layer resistivity and thickness will require an amplitude‐calibrated flight system.

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Airborne Electromagnetic System Equator. the Comparison of Geological Information in Electromagnetic Soundings in Time Domain and Frequency Domain

10.3997/2214-4609.201901783 ◽

2019 ◽

Author(s):

A.K. Volkovitsky ◽

V.M. Kertsman ◽

J. Moilanen ◽

Y.G. Podmogov

Keyword(s):

Frequency Domain ◽

Time Domain ◽

Electromagnetic System ◽

Electromagnetic Soundings ◽

Geological Information ◽

Airborne Electromagnetic

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Measuring AEM waveforms with a ground loop

Geophysics ◽

10.1190/1.2976791 ◽

2008 ◽

Vol 73 (6) ◽

pp. F213-F222 ◽

Cited By ~ 9

Author(s):

Aaron Davis ◽

James Macnae

Keyword(s):

Electromagnetic Field ◽

High Resistance ◽

Time Domain ◽

Current Waveform ◽

Polarization Effects ◽

Critical Data ◽

Damped Oscillations ◽

Airborne Electromagnetic ◽

Gps Antenna ◽

Ground Loop

Measuring a transmitter-current waveform provides critical data unavailable for some airborne electromagnetic (AEM) systems yet needed to model AEM data quantitatively. We developed a novel experimental method of measuring an airborne transmitter waveform by monitoring the current induced in a closed, multiturn, insulated ground loop of known inductance [Formula: see text] and resistance [Formula: see text]. The transmitter waveform of five different time-domain systems is deconvolved from the measured ground-loop response when excited by the primary electromagnetic field of the AEM system. In general, our measurements agree well with contractor-described transmitter current waveforms, although crucial differences exist between our deconvolved waveforms and those described in the literature. Using the pulse-per-second feature of a GPS antenna, the ground loop can monitor the frequency drift of a frequency-domain system. The ground loop behaves like a lossy electric-field antenna when the resistance closing the ground loop is too large. This leads to negatives in the response of coincident-loop systems without including induced polarization effects. After observing exponentially decaying, oscillating-current responses in high-resistance ground loops, we model the observed current with an LRC circuit whose resistance and capacitance represent generalized effective antenna and free-space values. Our model predicts responses that closely match the damped oscillations seen in the airborne response during flyover; however, it does not work well on conductive ground.

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Detection of a perfect conductor with an airborne electromagnetic system: The Gemini Field Test

Geophysics ◽

10.1190/geo2012-0469.1 ◽

2013 ◽

Vol 78 (5) ◽

pp. E249-E259 ◽

Cited By ~ 6

Author(s):

Adam Smiarowski ◽

James Macnae

Keyword(s):

Field Test ◽

Thin Sheet ◽

Perfect Conductor ◽

Primary Field ◽

Electromagnetic System ◽

Phase Measurements ◽

Electrical Conductivities ◽

Airborne Electromagnetic ◽

Gps System ◽

Geometric Changes

The cores of high-grade nickel and copper sulphides appear as “perfect conductors” to most electromagnetic (EM) and airborne electromagnetic (AEM) systems, because they have bulk electrical conductivities of the order of [Formula: see text]. The EM response of these highly conductive cores is essentially undetectable with off-time measurements or when using nonrigid towed-bird systems. Compact AEM systems with accurate primary field bucking and on-time or in-phase measurements are sensitive to perfect conductors, but are incapable of detecting deep targets. Using a GPS system to define geometry, calculations suggest that it should be easy for an AEM system to detect “perfect conductors” provided the receiver was several hundred meters distant from the transmitter. A twin (Gemini) aircraft test was undertaken to test this concept in 2005. The field test successfully demonstrated detection of very conductive targets. Errors associated with geometric changes were better than 0.5% of the primary field at 400 m separation, allowing detection and characterization of the 30 Hz, in-phase response of small and extended conductors. The test shows that a 200 × 100 m very-strongly conductive thin-sheet target would be detectable to depths of 200 m below surface using off-the-shelf technology. Larger conductors would be detectable at greater depths.

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Development of iFTEM fixed-wing time-domain airborne electromagnetic instrument

10.5194/egusphere-egu2020-7582 ◽

2020 ◽

Author(s):

Fang Ben ◽

Junfeng Li ◽

Wei Huang ◽

Junjie Liu ◽

Shan Wu ◽

...

Keyword(s):

Time Domain ◽

Magnetic Moment ◽

First Generation ◽

Magnetic Moments ◽

Low Frequency ◽

Secondary Response ◽

Electromagnetic System ◽

Software Modules ◽

Airborne Electromagnetic ◽

Deep Depth

&#160; &#160; The fixed-wing time-domain airborne electromagnetic system transmits low-frequency electromagnetic pulse waves with large magnetic moments, receives weak secondary response electromagnetic field signals generated by the underground medium. It can realize deep depth airborne electromagnetic exploration. After 10 years of research and development, the Institute of Geophysical and Geochemical Exploration of the Chinese Academy of Geological Sciences successfully developed the first-generation fixed-wing time-domain airborne electromagnetic system of China in 2016&#8212;&#8212;iFTEM. The peak transmit current is 600A, and the peak magnetic moment is 5.0 &#215; 105Am2. The exploration depth is 350m. Test flights measurement were taken in 2016. Based on the first-generation iFTEM system,&#160;we upgraded the system. The new transmitter has a peak transmit current of more than 1000A and a peak magnetic moment of more than 1,000,000Am2. It has multi-wave transmit capability. The static noise of the three-component induction coil receiving sensor is better than 0.1nT/&#8730;Hz@1kHz. We are developing a time-domain airborne electromagnetic data processing software platform, which includes the data organization, denoising and correction software modules. This paper mainly introduces the development of China's first fixed-wing time-domain airborne electromagnetic instrument. This paper is financially supported by National Key R&D Program of China (2017YFC0601900) and CGS Research Fund (JYYWF20180103).

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3D parametric hybrid inversion of time-domain airborne electromagnetic data

Geophysics ◽

10.1190/geo2015-0141.1 ◽

2015 ◽

Vol 80 (6) ◽

pp. K25-K36 ◽

Cited By ~ 26

Author(s):

Michael S. McMillan ◽

Christoph Schwarzbach ◽

Eldad Haber ◽

Douglas W. Oldenburg

Keyword(s):

Time Domain ◽

Electromagnetic Data ◽

Airborne Electromagnetic ◽

Airborne Electromagnetic Data

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A special circumstance of airborne induced‐polarization measurements

Geophysics ◽

10.1190/1.1443957 ◽

1996 ◽

Vol 61 (1) ◽

pp. 66-73 ◽

Cited By ~ 34

Author(s):

Richard S. Smith ◽

Jan Klein

Keyword(s):

Time Domain ◽

Eddy Currents ◽

High Arctic ◽

Induced Polarization ◽

Laboratory Measurements ◽

Dielectric Polarization ◽

Special Circumstance ◽

Polarization Measurements ◽

Airborne Electromagnetic

Airborne induced‐polarization (IP) measurements can be obtained with standard time‐domain airborne electromagnetic (EM) equipment, but only in the limited circumstances when the ground is sufficiently resistive that the normal EM response is small and when the polarizability of the ground is sufficiently large that the IP response can dominate the EM response. Further, the dispersion in conductivity must be within the bandwidth of the EM system. One example of what is hypothesized to be IP effects are the negative transients observed on a GEOTEM® survey in the high arctic of Canada. The dispersion in conductivity required to explain the data is very large, but is not inconsistent with some laboratory measurements. Whether the dispersion is caused by an electrolytic or dielectric polarization is not clear from the limited ground follow‐up, but in either case the polarization can be considered to be induced by eddy currents associated with the EM response of the ground. If IP effects are the cause of the negative transients in the GEOTEM data, then the data can be used to estimate the polarizabilities in the area.

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Field tests of an experimental helicopter time‐domain electromagnetic system for unexploded ordnance detection

Geophysics ◽

10.1190/1.1759452 ◽

2004 ◽

Vol 69 (3) ◽

pp. 664-673 ◽

Cited By ~ 11

Author(s):

Les P. Beard ◽

William E. Doll ◽

J. Scott Holladay ◽

T. Jeffrey Gamey ◽

James L.C. Lee ◽

...

Keyword(s):

Time Domain ◽

Eddy Currents ◽

Field Tests ◽

Field Trials ◽

Unexploded Ordnance ◽

Signal Attenuation ◽

Signal To Noise ◽

Electromagnetic System ◽

Time Domain Electromagnetic ◽

Unexploded Ordnance Detection

Field trials of a low‐flying time‐domain helicopter electromagnetic system designed for detection of unexploded ordnance have yielded positive and encouraging results. The system is able to detect ordnance as small as 60‐mm rounds at 1‐m sensor height. We examined several transmitter and receiver configurations. Small loop receivers gave superior signal‐to‐noise ratios in comparison to larger receiver loops at low heights. Base frequencies of 90 Hz and 270 Hz were less affected than other base frequencies by noise produced by proximity to the helicopter and by vibration of the support structure. For small ordnance, a two‐lobed, antisymmetric transmitter loop geometry produced a modest signal‐to‐noise enhancement compared with a large single rectangular loop, presumably because the antisymmetric transmitter produces smaller eddy currents in the helicopter body, thereby reducing this source of noise. In most cases, differencing of vertically offset receivers did not substantially improve signal‐to‐noise ratios at very low sensor altitudes. Signal attenuation from transmitter to target and from target to receiver causes signals from smaller ordnance to quickly become indistinguishable from geological background variations, so that above a sensor height of about 3 m only large ordnance items (e.g., bombs and large caliber artillery rounds) were consistently detected.

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