Rapid, high-accuracy electromagnetic soundings using a novel four-axis coil to measure magnetic field ellipticity

Nam H. Bak, Ben K Sternberg, Steven L Dvorak, Scott J. Thomas

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

A unique high-resolution electromagnetic sounding system, utilizing a four-axis coil and a new calibration technique, has been designed, constructed, and tested. The resulting measurements have an accuracy of approximately ±0.1%. The four-axis coil, which includes three approximately orthogonal coils and a calibration coil, is designed to automatically collect ellipticity data at 20 discrete frequencies in the range 30 Hz-30 kHz. The approximately orthogonal coils detect three components of the magnetic field and the calibration coil injects a calibration signal into the receiving system at the same time that the data are being recorded. A three-dimensional mathematical rotation program was developed to calculate ellipticity, removing the need to know the absolute coil orientation. Equations were formulated for the angular relationships between the approximately orthogonal coils. The actual intercoil angles were computed using a nonlinear optimization analysis applied to the measured data. The system was tested by measuring the ellipticity at one point on the earth's surface for various orientations of the coil. In addition, a close match between calculated and measured ellipticity profiles was obtained in a field test over a known target.

Original languageEnglish (US)
Pages (from-to)235-245
Number of pages11
JournalJournal of Applied Geophysics
Volume30
Issue number3
DOIs
StatePublished - 1993

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ellipticity
sounding
coils
electromagnetism
magnetic field
calibration
magnetic fields
field tests
Earth surface
receivers
optimization
high resolution
profiles

ASJC Scopus subject areas

  • Geophysics

Cite this

Rapid, high-accuracy electromagnetic soundings using a novel four-axis coil to measure magnetic field ellipticity. / Bak, Nam H.; Sternberg, Ben K; Dvorak, Steven L; Thomas, Scott J.

In: Journal of Applied Geophysics, Vol. 30, No. 3, 1993, p. 235-245.

Research output: Contribution to journalArticle

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