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.

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.

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.

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

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

<p>    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——iFTEM. The peak transmit current is 600A, and the peak magnetic moment is 5.0 × 10<sup>5</sup>Am<sup>2</sup>. The exploration depth is 350m. Test flights measurement were taken in 2016. Based on the first-generation iFTEM system, we upgraded the system. The new transmitter has a peak transmit current of more than 1000A and a peak magnetic moment of more than 1,000,000Am<sup>2</sup>. It has multi-wave transmit capability. The static noise of the three-component induction coil receiving sensor is better than 0.1nT/√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).</p>

scholarly journals Development of a Novel Double-Ring Deployable Mesh Antenna

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
Yan Xu ◽  
Fuling Guan ◽  
Xian Xu ◽  
Hongjian Wang ◽  
Yao Zheng
Keyword(s):  
Low Frequency ◽  
Design Concept ◽  
Design Parameters ◽  
Accuracy Measurement ◽  
Double Ring ◽  
Reflective Surface ◽  
Final Design ◽  
Geometric Relationship ◽  
Relationship Of ◽  
Adjustment Test

This paper addresses a type of deployable mesh antenna consisting of the double-ring deployable truss edge frame and the cable net reflector. The structural design concept of the deployable antennas is presented. The deployable truss is designed and the geometric relationship of each strut length is formulated. Two types of radial truss elements are described and compared. The joint pattern and the active cables of the final design concept are determined. The pattern of the cable net is the three-orientation grid. Two connection schemes between the reflector and the deployable edge frame are investigated. The design parameters and the shape adjustment mechanism of this cable net are determined. The measurement test technologies of the antennas on the ground including test facilities, deployment test, and measurement and adjustment test are proposed. The antenna patterns are analyzed based on the real surfaces of the reflector obtained by the reflective surface accuracy measurement. The tests and analytic results indicated that the accuracy of the reflective surface is high and is suitable for low-frequency communication.

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

Model based design of antagonistic shape memory alloy spring devices

2018 ◽  
Vol 29 (12) ◽  
pp. 2619-2640 ◽  
Author(s):  
Efthymios Kolyvas ◽  
Anthony Tzes
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Model Based ◽  
Operational Profile ◽  
Time Work ◽  
Two Factors ◽  
Internal Forces ◽  
Actuation Scheme ◽  
Geometric Relationship ◽  
Relationship Of

Shape memory alloy actuated devices employing a network of antagonistic components can reach an equilibrium of the internal forces by multiple sets of individual force magnitudes. In networks of star topologies particularly, the actuators are placed radially with one end connected at a common node. The ability to produce multiple sets of force equilibria suggests then that similar motions of the common node correspond to different thermomechanical paths. Two factors linked to this behavior are examined in this work, namely the initial design of the antagonistic system and the operational profile used during actuation. A shape memory alloy model is initially constructed based on an elementary hysteresis operator to produce a direct representation of the shape memory alloy behavior in the force–deformation plane. This description enables the identification of the operating point for the actuator by the geometric relationship of these models. In the second part, the placement of the antagonists is guided by the model based on specifications on the range of the workspace and the internal forces. The antagonistic operation is finally compared, in terms of time, work produced, and energy consumption, for a bang-bang (minimum time controller for the actuator) and a bang-off-bang (minimum internal forces for the system) actuation scheme.

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.

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

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.

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