1887
Volume 24, Issue 2
  • ISSN: 0812-3985
  • E-ISSN: 1834-7533

Abstract

A portable underwater three-axis magnetic and electric field sensor system with remotely controlled data acquisition has been developed for operation in shallow seawater at ELF. Electric field sensors consist of silver/silver chloride electrodes and magnetic sensors are based on multi-turn induction coils designed and wound to minimise stray capacitances, thus resulting in higher coil resonant frequencies. A Helmoltz coil system was designed for calibration of the magnetic sensors. The three electric and three magnetic field components are sampled simultaneously, multiplexed and transmitted along 1 km of cable to the control station for recording and analysis. This instrumentation enables environmental ELF electric and magnetic fields to be recorded with sensors placed on the seabed to minimise motion-induced noise. The vertical magnetic fields recorded in shallow seawater within and outside the Sydney metropolitan region are presented. Experiments have also been performed with a moving horizontal electric dipole representing a controlled source of known dipole strength and frequency. The dipole is attached to a vessel that is tracked using differential GPS so that the relative geometry between source and sensors is known as a function of time. Comparison of these controlled source emissions with forward modelling over different seabeds gives good agreement for realistic ranges of seabed electrical conductivity.

© 1993 ASEG
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1993-06-01
2026-01-16

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References

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  2. Filloux, J.H. (1987). ‘Instrumentation and experimental methods for oceanic studies. In ‘Geomagnetism’ (ed. Jacobs, J.A.). Vol.1, 144–248. Academic Press, New York.
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  • Article Type: Research Article
Keyword(s): controlled source.; ELF electromagnetic fields; GPS tracking; Helmholtz coils; sensors

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