Unambiguous apparent conductivity for fixed-loop transient electromagnetic data

R. Schaa; J.E. Reid; P.K. Fullagar

doi:10.1071/EG06348

ISSN: 0812-3985
E-ISSN: 1834-7533

Unambiguous apparent conductivity for fixed-loop transient electromagnetic data
Authors R. Schaa, J.E. Reid and P.K. Fullagar
Publisher: Australian Society of Exploration Geophysicists
Source: Exploration Geophysics, Volume 37, Issue 4, Dec 2006, p. 348 - 354
DOI: https://doi.org/10.1071/EG06348
- Received: 18 Jul 2006
- Accepted: 18 Oct 2006
- Published online: 01 Dec 2006

Abstract

We derive an unambiguous apparent conductivity from total magnetic field TEM data for fixed-loop geometry. For single-component fixed-loop TEM measurements, apparent conductivity is either dual-valued or undefined. The ambiguity or non-existence is particularly evident for readings taken outside the transmitter loop, both for step and impulse response data. Therefore, computing apparent conductivity from single-component fixed-loop TEM data can be problematic, especially at intermediate delay times. However, if multi-component fixed-loop magnetic field data is available, an unambiguous apparent conductivity can be derived from |B (t )| at all times, except in the inductive limit. Impulse response measurements can be time-weighted and summed to yield “quasi-|B |” data. Apparent conductivity derived from quasi-|B | amplitudes is dual-valued, but usually only one of the alternatives is geologically plausible. Computing apparent conductivity from |B | or quasi-|B | amplitudes expedites generation of conductivity-depth sections from fixed-loop TEM. A field data example with multi-component SQUID data shows significant improvement in the conductivity-depth section when |B (t )| is transformed rather than the vertical component, Bz, alone; the lateral extent of a conductive target is under-estimated in the Bz CDI

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References

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Article Type: Research Article

Keyword(s): ambiguity; apparent conductivity; fixed loop; TEM; total magnetic field

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Unambiguous apparent conductivity for fixed-loop transient electromagnetic data

Abstract

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