The multicoil II airborne electromagnetic system

Geophysics ◽  
1979 ◽  
Vol 44 (8) ◽  
pp. 1367-1394 ◽  
Author(s):  
Douglas C. Fraser
Keyword(s):  
Noise Sources ◽  
Electromagnetic System ◽  
Contour Maps ◽  
Metallic Mineral ◽  
Order Of Magnitude ◽  
Airborne Electromagnetic ◽  
Recorded Data ◽  
Sand And Gravel ◽  
New Criterion ◽  
Airborne Em

A helicopter‐towed electromagnetic (EM) system has been developed with two orthogonal transmitter coils. Units currently in service have either two or three orthogonal receiver coils. The associated software yields in‐phase and quadrature channels which are generally free of the conductive response of overburden and of the magnetic induction response of magnetite. These geologic noise sources can mask the response of bedrock conductors for all previously developed airborne EM (AEM) systems. The new technique involves energizing conductors with two orthogonal transmitter coils, both operating at approximately the same frequency (e.g., 900 Hz). The subtracting of the secondary field components of one maximum‐coupled coil pair from the other yields in‐phase and quadrature difference channels. These channels may contain as much as an order‐of‐magnitude increase in the signal/noise (S/N) ratio for bedrock conductors in a geologically noisy environment. The new system can also indicate whether a steeply dipping conductor is thin (e.g., width less than 3 m) or thick (greater than 10 m). The thickness parameter provides a new criterion for conductor sorting, complementing the usual parameters of conductance and strike‐length. The geophysical data are digitally recorded, and the profile records and maps are plotted by computer. The traces include the basic recorded data, the EM difference channels, a channel of resistivity, and a channel of conductance. The conductance channel essentially is an automatic anomaly selector calibrated in mhos. The usual application of the system is for metallic mineral prospecting. However, the system has also been used for sand and gravel detection using two well separated frequencies. For such applications, apparent resistivities are computed for each frequency and are displayed as channels on the profile record and as contour maps.

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

Geophysics ◽  
1969 ◽  
Vol 34 (5) ◽  
pp. 729-738 ◽  
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.

Simulated annealing for airborne EM inversion

Geophysics ◽  
2007 ◽  
Vol 72 (4) ◽  
pp. F189-F195 ◽  
Author(s):  
Changchun Yin ◽  
Greg Hodges
Keyword(s):  
Simulated Annealing ◽  
Random Walk ◽  
Boltzmann Distribution ◽  
Model Parameters ◽  
Local Minima ◽  
Model Configuration ◽  
Airborne Electromagnetic ◽  
Starting Model ◽  
Airborne Em ◽  
Cooling Schedule

The traditional algorithms for airborne electromagnetic (EM) inversion, e.g., the Marquardt-Levenberg method, generally run only a downhill search. Consequently, the model solutions are strongly dependent on the starting model and are easily trapped in local minima. Simulated annealing (SA) starts from the Boltzmann distribution and runs both downhill and uphill searches, rendering the searching process to easily jump out of local minima and converge to a global minimum. In the SA process, the calculation of Jacobian derivatives can be avoided because no preferred searching direction is required as in the case of the traditional algorithms. We apply SA technology for airborne EM inversion by comparing the inversion with a thermodynamic process, and we discuss specifically the SA procedure with respect to model configuration, random walk for model updates, objective function, and annealing schedule. We demonstrate the SA flexibility for starting models by allowing the model parameters to vary in a large range (far away from the true model). Further, we choose a temperature-dependent random walk for model updates and an exponential cooling schedule for the SA searching process. The initial temperature for the SA cooling scheme is chosen differently for different model parameters according to their resolvabilities. We examine the effectiveness of the algorithm for airborne EM by inverting both theoretical and survey data and by comparing the results with those from the traditional algorithms.

The airborne electromagnetic discovery of the Detour zinc‐copper‐silver deposit, northwestern Québec

Geophysics ◽  
1981 ◽  
Vol 46 (9) ◽  
pp. 1278-1290 ◽  
Author(s):  
L. E. Reed
Keyword(s):  
Volcanic Rocks ◽  
Channel Response ◽  
Copper Sulfides ◽  
Input System ◽  
Diamond Drill ◽  
Geophysical Surveys ◽  
Airborne Electromagnetic ◽  
Airborne Em ◽  
Two Bodies

In June 1974, a diamond drill operated for Selco Mining Corp. intersected zinc‐copper sulfides in Brouillan Township in northwestern Québec. To date, two bodies have been outlined. These bodies were discovered during a ground follow‐up of a Mark VI Input® electromagnetic (EM) survey. The Input survey covered an area selected on the basis of regional geology and local outcrops of acid volcanic rocks. Conductors were identified that appeared to be associated with potentially favorable geology. They were selected for ground follow‐up. One was the discovery zone. The airborne responses over the zone were less encouraging than those often observed over highly conductive massive sulfides. The low apparent conductivity‐thickness (5 mhos) was suggestive of conductive overburden. However, the character of the profiles suggested a bedrock source. Ground geophysical confirmation identified a drill target. Subsequent to the discovery, more intensive geophysical surveys, both ground and airborne, were carried out. The best EM response suggested a confined source within a much larger mineralized halo. Weaker ground EM response from the halo correlated with the early channel response of the Input system. An airborne EM survey conducted in 1958 over the same area identified both conductive zones. However, they were not followed up. Only with later advances in exploration philosophy, geologic appreciation, and instrumentation were the conductive zones recognized as viable exploration targets.

Resistive limit modeling of airborne electromagnetic data

Geophysics ◽  
2002 ◽  
Vol 67 (2) ◽  
pp. 492-500 ◽  
Author(s):  
James E. Reid ◽  
James C. Macnae
Keyword(s):  
Current Flow ◽  
Integral Equation Method ◽  
Near Surface ◽  
Electromagnetic Data ◽  
Airborne Electromagnetic ◽  
Source Current ◽  
Numerical Model Experiments ◽  
Airborne Electromagnetic Data ◽  
Airborne Em ◽  
Direct Induction

When a confined conductive target embedded in a conductive host is energized by an electromagnetic (EM) source, current flow in the target comes from both direct induction of vortex currents and current channeling. At the resistive limit, a modified magnetometric resistivity integral equation method can be used to rapidly model the current channeling component of the response of a thin-plate target energized by an airborne EM transmitter. For towed-bird transmitter–receiver geometries, the airborne EM anomalies of near-surface, weakly conductive features of large strike extent may be almost entirely attributable to current channeling. However, many targets in contact with a conductive host respond both inductively and galvanically to an airborne EM system. In such cases, the total resistive-limit response of the target is complicated and is not the superposition of the purely inductive and purely galvanic resistive-limit profiles. Numerical model experiments demonstrate that while current channeling increases the width of the resistive-limit airborne EM anomaly of a wide horizontal plate target, it does not necessarily increase the peak anomaly amplitude.

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

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

scholarly journals The Visibility of Earth Transits

2004 ◽  
Vol 202 ◽  
pp. 445-447 ◽  
Author(s):  
T. Castellano ◽  
L. Doyle ◽  
D. McIntosh
Keyword(s):  
Laboratory Experiments ◽  
Ecliptic Plane ◽  
Solar Neighborhood ◽  
Geometric Condition ◽  
The Sun ◽  
Intrinsic Variability ◽  
Noise Sources ◽  
Photometric Detection ◽  
The Earth ◽  
Order Of Magnitude

The recent photometric detection of planetary transits of the solar-like star HD 209458 at a distance of 47 parsecs suggest that transits can reveal the presence of Jupiter-size planetary companions in the solar neighborhood (Charbonneau et al. 2000; Henry et al. 2000). Recent space-based transit searches have achieved photometric precision within an order of magnitude of that required to detect the much smaller transit signal of an earth-size planet across a solar-size star. Laboratory experiments in the presence of realistic noise sources have shown that CCDs can achieve photometric precision adequate to detect the 9.6 E-5 dimming of the Sun due to a transit of the Earth (Borucki et al. 1997; Koch et al. 2000). Space-based solar irradiance monitoring has shown that the intrinsic variability of the Sun would not preclude such a detection (Borucki, Scargle, Hudson 1985). Transits of the Sun by the Earth would be detectable by observers that reside within a narrow band of sky positions near the ecliptic plane, if the observers possess current Earth epoch levels of technology and astronomical expertise. A catalog of solar-like stars that satisfy the geometric condition for Earth transit visibility are presented.

TORSION BALANCE STEP ANOMALIES IN NORTHERN TILLMAN COUNTY, OKLAHOMA

Geophysics ◽  
1945 ◽  
Vol 10 (4) ◽  
pp. 507-525
Author(s):  
K. Klaus
Keyword(s):  
Cross Sections ◽  
Torsion Balance ◽  
Second Derivative ◽  
Contour Maps ◽  
Probability Rating ◽  
Order Of Magnitude ◽  
Wichita Mountains ◽  
Gravity Map ◽  
High Degree ◽  
Quantitative Calculations

The results of a semi‐detailed areal torsion balance survey in Southwestern Oklahoma are shown by means of a gradient‐curvature map, a gravity map, two second derivative contour maps, and gravity and second derivative profiles. Detailed quantitative calculations were made of a number of geological cross sections, two of which are shown in Figs. 8 and 9. Fig. 9 represents the subsurface situation with the highest probability rating, since it combines a high degree of geological probability with the fact that it will reproduce the gravity and second derivative curves of Figs. 6 and 7 very closely. This interpretation embodies a fault with a throw of the order of magnitude of 10,000 feet. If this interpretation is substantially correct, it implies a thick sedimentary section in the down‐thrown block, which might be of great economic interest in prospecting for oil. A comparison of the gravity and second derivative data may be of interest to the geophysicist. The geologist may find the results of this survey interesting because of their possible bearing on the orogeny of the Wichita Mountains.

Sign in / Sign up

Export Citation Format

Share Document