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AFMAG

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Journal Article
Journal: Geophysics
Published: 01 August 1971
Geophysics (1971) 36 (4): 723–738.
...Roy J. Greenfield Abstract The buried conducting disk has been suggested by Ward et al (1968) as a suitable model for mineralized zones in the interpretation of AFMAG data. Using an integral equation method, we obtained the secondary magnetic field of a thin disk of arbitrary electrical...
Journal Article
Journal: Geophysics
Published: 01 February 1971
Geophysics (1971) 36 (1): 53–57.
...Keeva Vozoff Abstract New computer techniques permit the calculation of AFMAG and VLF anomalies in the vertical magnetic field component for situations which cannot be conveniently modeled with analog models. Conductivity and geometry of the 'ore' zone, the overburden, and the bedrock can all...
Journal Article
Journal: Geophysics
Published: 01 August 1968
Geophysics (1968) 33 (4): 621–644.
Journal Article
Journal: Geophysics
Published: 01 June 1966
Geophysics (1966) 31 (3): 576–605.
...S. H. Ward; J. O'Donnell; R. Rivera; G. H. Ware; D. C. Fraser Abstract The repeatability of AFMAG measurements has ranged from good to bad since the introduction of the method to industry in 1958. In some applications, e.g. mapping massive sulfide "dikes", the repeatability is generally good, while...
Journal Article
Journal: Geophysics
Published: 01 December 1960
Geophysics (1960) 25 (6): 1290–1293.
... developed a practical scheme (AFMAG) for geophysical prospecting which makes use of this phenomenon in the frequency range from 100 to 400 c/s. Sir Charles Wright et al., on the other hand, have found that at much lower frequencies, .005 to 1 c/s, a substantial verticalcomponent of the field in the vicinity...
Journal Article
Journal: Geophysics
Published: 01 October 1959
Geophysics (1959) 24 (4): 761–787.
... with both amplitudes and directions changing drastically over short periods of time. Hence, use of these fields in geophysical prospecting has been extremely limited. A new development, AFMAG, however, essentially eliminates the time variance in recording these fields without any sacrifice...
Journal Article
Journal: Geophysics
Published: 01 October 1959
Geophysics (1959) 24 (4): 787–788.
...Robert E. Holzer Abstract Dr. S. H. Ward has kindly shown me the manuscript of the preceding paper and has invited me to comment on the origin of the natural audio-frequency signals used by his AFMAG system. He lists five possible sources of signals. Of these, the only natural sources of practical...
Journal Article
Journal: Geophysics
Published: 01 October 1959
Geophysics (1959) 24 (4): 789.
Image
Calculated primary field components (black lines) compared with <b>AFMAG</b> recei...
Published: 06 September 2013
Figure 8. Calculated primary field components (black lines) compared with AFMAG receiver signal levels (gray lines) for the draped flight over the main target of interest. The deviations in the z -component at 1000 and 1500 m are in-phase response from the target. Other deviations are presumed
Journal Article
Journal: Geophysics
Published: 01 April 1985
Geophysics (1985) 50 (4): 656–664.
...V. F. Labson; A. Becker; H. F. Morrison; U. Conti Abstract Experience with the AFMAG method has demonstrated that an electromagnetic exploration system using the Earth's natural audiofrequency magnetic fields as an energy source is capable of mapping subsurface electrical structure in the upper...
Journal Article
Journal: Geophysics
Published: 06 September 2013
Geophysics (2013) 78 (5): E249–E259.
...Figure 8. Calculated primary field components (black lines) compared with AFMAG receiver signal levels (gray lines) for the draped flight over the main target of interest. The deviations in the z -component at 1000 and 1500 m are in-phase response from the target. Other deviations are presumed...
FIGURES | View All (15)
Journal Article
Journal: Geophysics
Published: 01 February 1971
Geophysics (1971) 36 (1): 67–100.
... following conclusions are among those of importance to AFMAG and VLF surveys: 1) the ratio of Re (H) to Im (H) is a function of traverse position and of ground conductivity, as well as of cylinder conductivity and of survey frequency; 2) in no case was a zero phase observed, even for perfectly conducting...
Published: 01 January 1967
DOI: 10.1190/1.9781560802716.ch4
EISBN: 9781560802716
... field methods on the other hand. Of the four natural field methods-telluric, magnetotel-luric, magnetic variationAfmag-only Afmag will be described in detail. Each of these four methods depends upon...
Published: 01 January 1966
EISBN: 9781560802709
..., but when applied with geology, geochemistry, and other methods such as self-potential, magnetics, and perhaps Afmag, then IP can and should be used at least as a tool for more detail. Results did not locate any immediate extensions to the known Ore Knob deposit, but did emphasize the essential part...
Image
A schematic diagram of the Gemini system. The lead helicopter tows the tran...
Published: 06 September 2013
Figure 4. A schematic diagram of the Gemini system. The lead helicopter tows the transmitter (VTEM) while the trailing helicopter tows the three-coil receiver (AFMAG). Both the receiver and the transmitter have GPS units attached (GPS sensors shown as black squares). Both helicopters also have
Journal Article
Journal: Geophysics
Published: 09 July 2012
Geophysics (2012) 77 (4): WB37–WB45.
... is that surveys are costly and time-consuming because many expensive stations must be installed to measure the needed electromagnetic field components on the earth’s surface. It was the desire to collect airborne natural source data that prompted the development of Audio Frequency Magnetics (AFMAG) ( Ward, 1959...
FIGURES | View All (16)
Journal Article
Journal: AAPG Bulletin
Published: 01 December 1964
AAPG Bulletin (1964) 48 (12): 1890–1901.
... in the kind and number of components measured. The methods include Telluric, Magnetotelluric, Wave-tilt and AFMAG, as well as combinations thereof. The Telluric method has already been described in some detail. The E variations in two perpendicular directions, say x and y, are measured simultaneously...
FIGURES | View All (12)
Journal Article
Journal: Geophysics
Published: 22 December 2015
Geophysics (2016) 81 (1): B1–B12.
... by Ward (1959) , and it was then called the audio-frequency magnetic (AFMAG) method. It was developed through the 1980s ( Labson et al., 1985 ), but technological advances minimizing electric noise from the aircraft and enabling the monitoring of sensor position have only recently allowed large, high...
FIGURES | View All (12)
Journal Article
Published: 01 September 2016
Russ. Geol. Geophys. (2016) 57 (9): 1371–1376.
... of artificial sources of excitation of geological sections. Similar experiments were performed later by geophysicists of India ( Murali and Rao, 1983 ). Natural electromagnetic (EM) fields are also used in the AFMAG (audio frequency magnetic) method based on the amplitude-phase processing of NEMFE signals...
FIGURES | View All (4)
Journal Article
Published: 01 July 1963
Bulletin of the Seismological Society of America (1963) 53 (4): 855–856.
.... The coverage of electrical methods is complete, covering static, relaxation, and dynamic. Electromagnetic methods including the pulse techniques are surveyed. The telluric and AFMAG techniques are mentioned but no field case history is described. Seismic and radioactive methods are briefly surveyed...