COMPARISON OF AIRBORNE EM COIL SYSTEMS PLACED OVER A MULTILAYER CONDUCTING EARTH

Geophysics ◽  
1973 ◽  
Vol 38 (5) ◽  
pp. 894-919 ◽  
Author(s):  
Ajit K. Sinha
Keyword(s):  
Thin Layer ◽  
Computer Program ◽  
Relative Effectiveness ◽  
Single Frequency ◽  
Master Curves ◽  
Airborne Electromagnetic ◽  
Hidden Layer ◽  
Static Conditions ◽  
Airborne Em ◽  
Layer Problem

A detailed analysis has been made on the relative effectiveness of the four types of coil arrangements used in airborne electromagnetic surveying for the mapping of subsurface inhomogeneities. By comparing the theoretical responses for the four systems over known geologic sections, it has been established that the horizontal coplanar system is the most effective for detecting inhomogeneities in single‐frequency airborne surveys and produces the largest anomaly in multifrequency work. The next largest anomaly in both the cases is obtained in the vertical coplanar arrangement. The multilayer computer program used to derive the theoretical master curves for comparing the performance of the four systems is completely general except for our assumption of the quasi‐static conditions, which is justified in all geophysical induction problems. A study of the “hidden‐layer problem” to determine the best system and conditions for detection of a thin layer sandwiched between two thicker beds has been made with the help of the program. Horizontal coplanar and vertical coplanar systems are again found to be the best and second best systems, respectively, for their detection. It is also clear that a conductive sandwiched bed is much easier to detect than a resistive one.

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.

INTERPRETATION TECHNIQUES FOR A SINGLE FREQUENCY AIRBORNE ELECTROMAGNETIC DEVICE

Geophysics ◽  
1962 ◽  
Vol 27 (4) ◽  
pp. 493-506 ◽  
Author(s):  
W. Gordon Wieduwilt
Keyword(s):  
Field Experience ◽  
Single Frequency ◽  
Electromagnetic Device ◽  
Airborne Electromagnetic ◽  
Exploration Tool

An airborne electromagnetic device, designed to measure electromagnetic anomalies in a manner that readily lends itself to the interpretation of conductivity and type‐body, led to the Aero‐Newmont vertical coaxial coil EM system. This mining prospecting device, applicable chiefly in Canadian‐type mineral environment, is rigidly mounted on an S-55 helicopter. Continued studies in the theory of interpretation for such a device, plus an accumulation of over five years of field experience, have provided a knowledge of the limitations which compliment the interpretation procedure to produce a surprisingly accurate and useful exploration tool.

Improving Speed and Accuracy of Word Recognition in Reading Disabled Children: An Evaluation of Two Computer Program Variations

1988 ◽  
Vol 11 (4) ◽  
pp. 333-341 ◽  
Author(s):  
Andrew L. Cohen ◽  
Joseph K. Torgesen ◽  
Jeffrey L. Torgesen
Keyword(s):  
Computer Program ◽  
Repeated Measures ◽  
Word Reading ◽  
Relative Effectiveness ◽  
Disabled Children ◽  
Repeated Measures Design ◽  
Reading Vocabulary ◽  
Treatment Conditions ◽  
Speed And Accuracy ◽  
Reading Disabled

The present study investigated the relative effectiveness of two versions of a computer program designed to increase the sight-word reading vocabulary of reading disabled children. One version required children to type words into the computer as part of the practice activity; in the other no typing was involved. Subjects were nine reading disabled students, average age 10 years, 7 months. A repeated-measures design was used to expose all subjects three times to two treatment conditions and a no-practice control condition. Accuracy and speed of reading, as well as spelling accuracy for multisyllable words were measured in pre- and posttests. Both versions of the program proved to be equally effective in improving speed and accuracy of reading words, but the typing version was more effective in increasing spelling accuracy. However, students enjoyed the no-typing version better, and they were able to attain mastery levels for new words on this version faster than on the typing version. Implications of these results for reading software design are considered.

Discovery of polymetallic porphyry at the Silver Queen, British Columbia using airborne EM and TITAN-24 DCIP and MT surveys

2013 ◽  
Vol 1 (1) ◽  
pp. T101-T112 ◽  
Author(s):  
Nasreddine Bournas ◽  
Ellen Clements ◽  
Rob Hearst
Keyword(s):  
British Columbia ◽  
3D Inversion ◽  
Ground Survey ◽  
Airborne Electromagnetic ◽  
Polymetallic Mineralization ◽  
Two Phases ◽  
Airborne Em ◽  
Mining Exploration ◽  
Base Metal Mineralization

Airborne electromagnetic, ground direct current and induced polarization (DCIP), and magnetotelluric (MT) surveys have extensively been used in mining exploration and more particularly for the exploration of base metal mineralization. The continuous development of geophysical techniques with advances in the instrumentation and signal processing and the recent development of robust 3D inversion algorithms make possible the detection and accurate delineation of deep-seated mineralization of economic interest. Recently, a deep-penetrating TITAN-24 DCIP and MT survey was conducted over the Silver Queen project area, located in British Columbia, Canada in two phases (2011 and 2012, respectively) by Quantec Geoscience Ltd. on behalf of New Nadina Explorations Ltd. for the exploration of porphyry-style polymetallic mineralization. The ground survey was carried out as a follow-up to the helicopter-borne z-axis tipper electromagnetic survey flown during the spring of 2011 by Geotech Ltd. with the aim to delineate favorable areas for the exploration of porphyry-style deposits. A deep-seated significant zone of anomalously high chargeability occurring in coincidence with a conductive zone was detected by the ground DCIP and MT survey. Drill-testing based on the 3D inversion results of the data led to the discovery of a new significant deep-seated porphyry-style mineralization. The discovery drillhole contained visible disseminated to semimassive sulphide mineralization, gold and molybdenite over 350 m for a total drillhole depth of approximately 800 m and occurs in association with a significant mineralized stockwork zone open at depth.

Automated interpretation of airborne electromagnetic data

Geophysics ◽  
1984 ◽  
Vol 49 (8) ◽  
pp. 1301-1312 ◽  
Author(s):  
G. T. DeMoully ◽  
A. Becker
Keyword(s):  
Data Interpretation ◽  
Earth Model ◽  
Computer Algorithms ◽  
Conductive Layer ◽  
Electromagnetic Data ◽  
Airborne Electromagnetic ◽  
Survey Results ◽  
Airborne Electromagnetic Data ◽  
Airborne Em ◽  
Interpretation Method

Recent improvements in equipment quality make it possible to increase the usefulness of airborne electromagnetic (EM) systems in areas of moderate electrical conductivity for the purpose of constructing simple electrical property maps which can be related to surficial geology. This application of airborne electromagnetics may be demonstrated and evaluated using Barringer/Questor Mark VI Input® survey results in places where independent verifications of the airborne data interpretation are available. For this purpose we have developed a set of computer algorithms which read digitally recorded Input data and interpret them automatically in terms of a simple electrical section that is defined by a single conductive layer whose thickness, conductivity, and subsurface depth are determined from the data. Because this technique is formally based on a one‐dimensional, three‐layer, three‐parameter, horizontally stratified earth model, it is only applicable in regions where the surficial formations are mildly dipping and the conductive layer is covered by, and rests on, highly resistive materials. The interpretation method is illustrated by three field examples. At the first field survey site, in Alberta, Canada, airborne EM survey data are used to map the depth of the interface between coarse and clayey sands. Data from a second survey site, this time in the Western USA, are interpreted to yield the section of a subsurface valley filled with conductive clay. The final example, taken from British Columbia, Canada, involves the mapping of all the three parameters for a weathered volcanic unit.

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