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.

Resistivity/depth mapping with airborne electromagnetic survey data

Geophysics ◽  
1983 ◽  
Vol 48 (2) ◽  
pp. 181-196 ◽  
Author(s):  
Klaus‐Peter Sengpiel
Keyword(s):  
Salt Water ◽  
Mapping Method ◽  
Shielding Effect ◽  
Single Frequency ◽  
Salt Water Intrusion ◽  
Horizontal Gradient ◽  
Model Parameters ◽  
Apparent Depth ◽  
Contour Maps ◽  
Airborne Electromagnetic

Using the homogeneous half‐space as a universal interpretation model, all of the secondary field data obtained with a single‐frequency airborne electromagnetic (EM) system that satisfies the superposed dipole condition can be converted to the model parameters [Formula: see text] (apparent resistivity) and [Formula: see text] (apparent depth). These parameters have been investigated for their behavior above various conductivity models and at various flight altitudes, first for theoretical examples and then for several applications in the field. The values of [Formula: see text] and [Formula: see text] are good approximations of the true resistivity and true depth of an extended, buried conductor only where the shielding effect of the cover is small. Moreover, a depth value has a meaning only within the lateral limits of a target conductor. A method is described to locate these lateral limits and to select acceptable depth and resistivity values by means of the “area of [Formula: see text],” which is derived from the horizontal gradient of log [Formula: see text] and the maxima of [Formula: see text]. The results of the resistivity/depth mapping method are presented in the form of two contour maps. Examples of the practical application of the method, over known sulfide ore bodies and over a salt water intrusion, show that reliable data can be obtained on the depth, dip, and extent of these kinds of conductors, as well as on the approximate resistivity of the conductors and the host rock.

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.

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