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

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. E249-E259 ◽  
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.

MAPPING EARTH CONDUCTIVITIES USING A MULTIFREQUENCY AIRBORNE ELECTROMAGNETIC SYSTEM

Geophysics ◽  
1978 ◽  
Vol 43 (3) ◽  
pp. 563-575 ◽  
Author(s):  
H. O. Seigel ◽  
D. H. Pitcher
Keyword(s):  
Thin Sheet ◽  
Radar Altimeter ◽  
Electromagnetic System ◽  
Near Surface ◽  
Quantitative Estimates ◽  
Simple Geometry ◽  
Airborne Electromagnetic ◽  
Groundwater Mapping ◽  
Actual Field ◽  
Depth Of Burial

The Tridem vertical coplanar airborne electromagnetic system provides simultaneous in‐phase and quadrature information at frequencies of 500, 2000 and 8000 Hz. The system can map a broad range of earth conductors of simple geometry and provide quantitative estimates of their conductivities and dimensions. Computer programs have been developed to automatically interpret the six channels of Tridem data, plus the output of an accurate radar altimeter, to determine the depth of burial, conductivity and thickness of a near‐surface, flat‐lying conducting horizon. In limiting cases, the interpretation provides the conductance (conductivity‐thickness product) of a thin sheet (ranging from 100 mmhos to 100 mhos) or the conductivity of a homogeneous earth (ranging from 1 mmhos/m to 10 mhos/m). Two actual field examples are presented from Ontario, Canada; one relating to the mapping of overburden conditions (sand, clay and rock, etc) and the other to the mapping of the distribution of a buried lignite deposit. Other areas of potential application of the system to surficial materials would include groundwater mapping, permafrost investigations, and civil engineering studies for roads and pipelines.

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

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Xiao Jia ◽  
Lihua Liu ◽  
Guangyou Fang
Keyword(s):  
Time Domain ◽  
Accurate Method ◽  
Perfect Conductor ◽  
Current Waveform ◽  
Electromagnetic System ◽  
Resonance Circuit ◽  
Airborne Electromagnetic

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.

scholarly journals An airborne electromagnetic system with a three-component transmitter and three-component receiver capable of detecting extremely conductive bodies

Geophysics ◽  
2018 ◽  
Vol 83 (5) ◽  
pp. E347-E356 ◽  
Author(s):  
Richard S. Smith
Keyword(s):  
Secondary Response ◽  
Primary Field ◽  
Linear Combinations ◽  
Phase Component ◽  
Electromagnetic System ◽  
Temporal Shape ◽  
Conductive Body ◽  
Airborne Electromagnetic ◽  
Geometric Relationship ◽  
Relationship Of

Extremely conductive bodies, such as those containing valuable nickel sulfides, have a secondary response that is dominated by an in-phase component, so this secondary response is very difficult to distinguish from the primary field emanating from the transmitter (because by definition they are identical in temporal shape and phase). Hence, an airborne electromagnetic (AEM) system able to identify the response from the extremely conductive bodies in the ground must be able to predict the primary field to identify and measure the secondary response of the extremely conductive body. This is normally done by having a rigid system and bucking out the predicted primary (which will not change significantly due to the rigidity). Unfortunately, these rigid systems must be small and are not capable of detecting extremely conductive bodies buried deeper than approximately 100 m. Another approach is to measure the transmitter current and geometry and subtract the primary mathematically, but these measurements must be extremely accurate and this is difficult or expensive, so it has not been done successfully for an AEM system. I exploit the geometric relationship of the primary fields from a three-component (3C) dipole transmitter. If the transmitter is mathematically rotated so that one axis points to the receiver, then linear combinations of the fields measured by a 3C receiver can be combined in such a way that the primary fields from the transmitter sum to zero and cancel. Alternatively, the measured transmitter current and response could be used to estimate the transmitter-receiver geometry and then to predict and remove the primary field. Any residual must be the secondary coming from a conductive body in the ground. Hence, extremely conductive bodies containing valuable minerals can be found. An AEM system with a 3C transmitter and a 3C receiver should not be too difficult to build.

Development And Evaluation Of A Second-Generation Airborne Electromagnetic System For Detection Of Unexploded Ordnance

2002 ◽  
Author(s):  
William E. Doll ◽  
T. Jeffrey Gamey ◽  
Les P. Beard ◽  
David T. Bell ◽  
J.S. Holladay ◽  
...  
Keyword(s):  
Second Generation ◽  
Unexploded Ordnance ◽  
Electromagnetic System ◽  
Airborne Electromagnetic

An example of 3D conductivity mapping using the TEMPEST airborne electromagnetic system

2000 ◽  
Vol 31 (1-2) ◽  
pp. 162-172 ◽  
Author(s):  
Richard Lane ◽  
Andy Green ◽  
Chris Golding ◽  
Matt Owers ◽  
Phil Pik ◽  
...  
Keyword(s):  
Electromagnetic System ◽  
The Tempest ◽  
Airborne Electromagnetic

27. Viability of an Airborne Electromagnetic System for Mapping of Shallow Buried Metals

2005 ◽  
pp. 653-662
Author(s):  
William E. Doll ◽  
T. Jeffrey Gamey ◽  
J. Scott Holladay ◽  
James L. C. Lee
Keyword(s):  
Electromagnetic System ◽  
Airborne Electromagnetic

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

Geophysics ◽  
2020 ◽  
Vol 85 (5) ◽  
pp. E153-E162 ◽  
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.

COMPUTER DATA PROCESSING AND QUANTITATIVE INTERPRETATION OF AIRBORNE RESISTIVITY SURVEYS

Geophysics ◽  
1975 ◽  
Vol 40 (5) ◽  
pp. 818-830 ◽  
Author(s):  
G. J. Palacky ◽  
F. L. Jagodits
Keyword(s):  
Electric Fields ◽  
Simultaneous Recording ◽  
Quantitative Interpretation ◽  
Geologic Mapping ◽  
Electromagnetic System ◽  
Computer Data ◽  
Type Curves ◽  
Intermediate Data ◽  
Processing Cost ◽  
Airborne Electromagnetic

The recently constructed airborne electromagnetic system called E-Phase measures the intensity of the vertical and horizontal electric fields. Standard broadcasting, VLF, and LF navigation aid transmitters are used as sources of the primary EM field. A system of this kind responds best to horizontal layers of large extent and therefore is suitable for geologic mapping and for the detection of resistive materials such as gravel and permafrost. A successful application of the system would not have been possible without digital recording of the data and subsequent computer processing. An efficient algorithm consisting of three processing steps assures low processing cost and provides for two intermediate data checks. Final outputs are printer plots of apparent resistivity for all flight lines and maps of stacked profiles or contours. Quantitative interpretation was made possible by the simultaneous recording of the data at three transmitter frequencies and by the availability of theoretical solutions for layered media. Instead of generating an atlas of type curves, an interactive program was written which enables the geophysicist to rapidly obtain apparent resistivities assuming a three‐layer model. A close match with the measured data is easy to achieve when a reasonable estimate of two of the parameters (resistivities, thicknesses) can be made initially. The interpretation procedure is demonstrated on a case history, a 1973 survey conducted near Wadena, Saskatchewan.

Predictive filter calculation of primary fields in a fixed-wing time-domain AEM system

Geophysics ◽  
2010 ◽  
Vol 75 (4) ◽  
pp. F97-F106 ◽  
Author(s):  
Adam Smiarowski ◽  
James Macnae ◽  
R. C. Bailey
Keyword(s):  
High Altitude ◽  
Decay Constant ◽  
Secondary Response ◽  
Consistent Difference ◽  
Primary Field ◽  
Low Frequencies ◽  
High Frequencies ◽  
New Process ◽  
Delay Times ◽  
Airborne Electromagnetic

High-altitude data are used to calibrate a least-squares recursion filter that estimates the continually changing primary field of an airborne electromagnetic (AEM) system. The coupling changes in fixed-wing towed-bird systems generate “geometry noise” that in the on-time can be much larger than the ground secondary response. The LSQ filter accurately predicts the high-altitude primary field of a fixed-wing system. The filter is then applied to survey-altitude data to estimate the primary field for subsequent subtraction. After removing the primary field, a spatially consistent difference is detected over a range of delay times, as would be expected from geologic responses. A map of decay constants is produced for the survey area using the data corrected by the predicted primary field. Comparing these time constants with those computed from the conventional method, the maximum decay constant detectable was seven times larger. Thus, the new process can characterize conductors that are seven times more conductive than the conventional processing method. The residual primary field occurs at relatively high frequencies compared to targets of interest. At low frequencies [Formula: see text], we estimate that 28% of the survey-altitude primary field remains whereas only 1% of calibration flight primary is not predicted.

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