Improving conductivity models using on-time EM data

Daniel Sattel

doi:10.1071/EG998605

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

Improving conductivity models using on-time EM data
Authors Daniel Sattel^a
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^a CRCAMET, World Geoscience Corporation, Locked Bag 6, Wembley, , WA 6014, Phone (08) 9273 6400, , Fax (08) 9273 6466, [email protected]
Publisher: Australian Society of Exploration Geophysicists
Source: Exploration Geophysics, Volume 29, Issue 3-4, Sep 1998, p. 605 - 608
DOI: https://doi.org/10.1071/EG998605
- Published online: 01 Sep 1998

Abstract

Modelling of data from half-sine time-domain airborne EM systems is traditionally limited to the period following the transmitter turn-off, the off-time data. The joint use of on-time and off-time data widens the resolvable range of conductivities. Using a half-sine waveform with a base frequency of 25 Hz and a pulse width of 4 ms, conductivities and conductances as low as 0.5 mS/m and 0.02 S, respectively, become resolvable. Also, with the constraint of on-time data, automated modelling becomes more stable as noise at late time is less likely to be confused with signal.

Conductivity-depth sections of QUESTEM-450 (Lane et ah, 1998) data from Forrestania, Western Australia were modelled using a layered-earth inversion (LEI) and a current imaging technique. The known mineralisation, including massive sulphides and a banded iron formation, is indicated by the off-time data. For both methods, additional use of on-time data led to a model improvement.

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References

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Lines, L. R., and Treitel, S., 1984, Tutorial: a review of least-squares inversion and its application to geophysical problems: Geophysical Prospecting 32, 159–186.
Macnae, J. C., Smith, R., Polzer, B. D., Lamontagne, Y., and Klinkert, P. S., 1991, Conductivity-depth imaging of airborne electromagnetic step-response data. Geophysics, 56, 102–114.
Sattel, D., 1998, Conductivity information in three dimensions: Proceedings AEM 98, ASEG CRCAMET, Session 2.3.
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Ward S. H, and Hohmann, G. W., 1987, Electromagnetic theory for geophysical applications. In: Nabighian, M. N., Ed., Electromagnetic methods in applied geophysics, v. 1, Theory, Investigations in geophysics. Society of Exploration Geophysics, 203–252.

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Article Type: Research Article

Keyword(s): AEM Data; Inversion

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Improving conductivity models using on-time EM data

Abstract

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