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.

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.

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.

MODEL RESULTS AND FIELD CHECKS FOR A TIME‐DOMAIN, AIRBORNE EM SYSTEM

Geophysics ◽  
1973 ◽  
Vol 38 (5) ◽  
pp. 845-853 ◽  
Author(s):  
Philip H. Nelson
Keyword(s):  
Time Domain ◽  
Scale Model ◽  
Large Lake ◽  
Response Curves ◽  
Channel Response ◽  
Airborne Em ◽  
Good Agreement

The airborne EM system known as Input was calibrated by applying theoretical homogeneous earth response curves to the response obtained on a flight over a large lake of known resistivity. The calibrated response curves for the conductive overburden case agree with field results in that 1) overburden resistivity in excess of 100 ohm‐m produces negligible deflection on the receiver channels, and 2) the maximum channel response occurs between 1 and 10 ohm‐m overburden resistivity. The calibrated response curves for scale model vertical sheets show fair to good agreement with the response to steeply dipping conductors which have been confirmed with ground‐based EM and drilling. The calibrated scale model results also show: 1) The system possesses a “passband” in conductivity‐thickness, with the first channel peaking around 10 mhos and the later channels at progressively higher values, with the sixth channel peaking at 25 mhos. 2) If a conservative detection cutoff is applied, a vertical conductor will not produce a four‐channel anomaly if it is much deeper than 200 ft subsurface for an aircraft elevation of 400 ft. 3) Channel ratios are constant with depth and also fairly constant over the 10–100 mhos range in conductivity‐thickness.

scholarly journals The inversion of time‐domain airborne electromagnetic data using the plate model

Geophysics ◽  
1990 ◽  
Vol 55 (6) ◽  
pp. 705-711 ◽  
Author(s):  
P. B. Keating ◽  
D. J. Crossley
Keyword(s):  
Time Domain ◽  
Digital Processing ◽  
Geophysical Survey ◽  
Inverse Theory ◽  
Great Success ◽  
Plate Model ◽  
Airborne Electromagnetic ◽  
Airborne Electromagnetic Data ◽  
Airborne Em ◽  
Mining Exploration

Airborne electromagnetic (EM) methods were developed in the early 1950s, mostly by Canadian mining exploration companies as a means of economically carrying out prospecting for sulfide deposits associated with volcanics in resistive shield areas. Present interpretation techniques are based on the use of nomograms but the approach is easily amenable to digital processing. For highly accurate interpretation, however, it is necessary to develop quantitative interpretation techniques that can make full use of all the data available. Inverse theory has been used for interpretation with great success in most geophysical disciplines; however, in airborne EM surveying, inversion has only been used for the interpretation of airborne EM data using half‐space and one‐layer models. By introducing some approximations to the rectangular thin‐plate model, it is now possible to apply inverse theory to the interpretation of time‐domain EM data. This approach provides estimates of the parameter errors, the correlation matrix, and a means of assessing the validity of the model. Synthetic profile data are used to demonstrate the validity of the method. The results of the inversion of real anomalies are compared with ground geophysical survey interpretation and drillhole data. The inversion results agree with the known geology of the area and the ground geophysical survey interpretation.

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.

INPUT AEM Results from Project Pioneer, Manitoba

1975 ◽  
Vol 12 (6) ◽  
pp. 971-981
Author(s):  
A. V. Dyck ◽  
A. Becker ◽  
L. S. Collett
Keyword(s):  
Time Domain ◽  
Vertical Axis ◽  
Structural Features ◽  
Geological Mapping ◽  
Geological Survey ◽  
Scale Model ◽  
Potential Contribution ◽  
Input System ◽  
Interpretation Process ◽  
Airborne Em

The results of an airborne EM survey obtained with an INPUT system flown in the vertical-axis-receiver configuration have been assessed by the Geological Survey of Canada as favorable in terms of their potential contribution to the geological mapping carried out in the Project Pioneer study. Manitoba, Canada. Time-domain scale model profiles over the various conductor arrangements presented here have proven indispensable in the interpretation process. An outstanding example of this is the striking modification to an overburden anomaly made possible by the fortuitous location and dip of a conducting dike model below the overburden. The investigation indicates that during the course of an exploration survey, IN PUT data may be used directly to aid in the mapping of structural features or, indirectly in areas of conductive overburden, if the overburden is structurally controlled.

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>

3-D Time-Domain Airborne EM Inversion for a Topographic Earth

2020 ◽  
pp. 1-13
Author(s):  
Yanfu Qi ◽  
Xiu Li ◽  
Changchun Yin ◽  
Huaiyuan Li ◽  
Zhipeng Qi ◽  
...  
Keyword(s):  
Time Domain ◽  
Airborne Em

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.

Sign in / Sign up

Export Citation Format

Share Document