1887
Volume 55, Issue 2
  • ISSN: 0812-3985
  • E-ISSN: 1834-7533

Abstract

Interpreting transient electromagnetic (TEM) anomalies in terms of conductive rectangular plates is effective in many situations. However, not all conductors are thin and planar. Triaxial ellipsoid conductors are an attractive alternative: geometrically simple (corner-free), mathematically tractable at early and late time limits, and able to encompass shapes ranging from discs to elongate lenses to equi-dimensional pods. Accordingly a fast magnetostatic algorithm has been developed to compute the resistive limit (RL) response of a ellipsoidal conductor, which may also be permeable. The algorithm has been validated against new analytic resistive limit solutions for spherical and spheroidal conductors and against 3D multigrid finite difference modelling for a triaxial ellipsoidal conductor. A uniformly conductive ellipsoid supports three fundamental current modes in the resistive limit, an independent mode for excitation parallel to each of the principal axes. The RL current density increases linearly with radial distance from the ellipsoid centre. A formula for the time constant of an oblate spheroid has been derived for excitation parallel to its rotational axis, namely , where is the conductivity and and are respectively the minor and major radii.

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2026-01-24
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References

  1. Clark, D.A., S.J.Saul, and D.W.Emerson. 1986. Magnetic and gravity anomalies of a triaxial ellipsoid. Exploration Geophysics17: 189–200.
    [Google Scholar]
  2. Duncan, A.C.2017. Advances in Ground and Borehole EM Survey Technology to 2017: Proceedings of Exploration ‘17, Sixth Decennial International Conference on Mineral Exploration, V. Tschirhart and M.D. Thomas (eds.).
  3. Fullagar, P.K., and R.Schaa. 2014. Fast 3D inversion of transient electromagnetic (TEM) resistive limit data: 84th Annual International Meeting, Society of Exploration Geophysicists, Denver, Expanded Abstracts, pp1827-1831. http://doi.org/10.1190/segam2014‑1157.1.
    https://doi.org/http://doi.org/10.1190/segam2014-1157.1
  4. Gradshteyn, I.S., and I.M.Ryzhik. 1980. Table of integrals, series, and products. Academic Press Inc. 1160p
  5. Grant, F.S., and G.F.West. 1965. Interpretation theory in applied geophysics. McGraw-Hill. 584p
  6. Grimm, R.E.2001. Time-domain measurements and modeling of UXO: Proceedings UXO Countermine Forum 2001, New Orleans. http://www.boulder.swri.edu/~grimm/grimm_uxo01_1.pdf.
  7. Kaufman, A.A.1978. Frequency and transient responses of electromagnetic fields created by currents in confined conductors. Geophysics43: 1002–1010.
    [Google Scholar]
  8. Lamontagne, Y., M.Kolaj, and O.Fernley. 2016. 3D modeling of highly conductive massive sulphides - a Voisey's Bay case study. Society of Exploration Geophysicists Expanded Abstracts.
    [Google Scholar]
  9. Lamontagne, Y., J.Macnae, and B.Polzer. 1988. Multiple conductor modeling using program MultiLOOP. Society of Exploration Geophysicists Expanded Abstracts, 237–240. doi:10.1190/1.1892248.
    https://doi.org/10.1190/1.1892248 [Google Scholar]
  10. Macnae, J.C., A.King, N.Stolz, and P.Klinkert. 1999. 3D EM inversion to the limit. In Three-dimensional electromagnetics, geophysical developments No. 7. M.Oristaglio and B.Spies (eds), 489–501. Society of Exploration Geophysicists.
    [Google Scholar]
  11. Nabighian, M.N., and J.C.Macnae. 1991. Electromagnetic methods in applied geophysics: Investigations in geophysics No. 3, Vol. 2. Society of Exploration Geophysicists, pp. 427-520.
  12. Ontario Geological Survey. 1984. The geology and ore deposits of the Sudbury Structure: Special Volume 1, E.G. Pye, A,J. Naldrett, and P.E. Giblin (eds), 603p.
  13. Schaa, R., and P.K.Fullagar. 2012. Vertical and horizontal resistive limit formulas for a rectangular-loop source on a conductive half-space. Geophysics77: E91–E99.
    [Google Scholar]
  14. Silvester, P.P., and D.Omeragic. 1995. Sensitivity of metal detectors to spheroidal targets. IEEE Transactions on Geoscience & Remote Sensing.33: 1331–1335.
    [Google Scholar]
  15. Smith, R.S., and T.J.Lee. 2002. The moments of the impulse response: A new paradigm for the interpretation of transient electromagnetic data. Geophysics67: 1095–1103.
    [Google Scholar]
  16. Smith, J.T., and H.F.Morrison. 2006. Approximating spheroid inductive responses using spheres. Geophysics71: G21–G25. doi:10.1190/1.2187738.
    https://doi.org/10.1190/1.2187738 [Google Scholar]
  17. Stolz, E.M., and J.C.Macnae. 1997. Fast approximate inversion of TEM data. Exploration Geophysics28: 317–322.
    [Google Scholar]
  18. Urankar, L.1985. Vector potential and magnetic field of current-carrying finite elliptic Arc segment in analytical form. Zeitschrift für Naturforschung A40: 1069–1074.
    [Google Scholar]
  19. Watts, A.1997. Exploring for nickel in the 90s, or "till depth us do part": Proceedings of Exploration ‘97, Fourth Dicennial International Conference on Mineral Exploration, A.G. Gubins (ed.), p. 1003–1013.
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  • Article Type: Research Article
Keyword(s): electromagnetics; Ellipsoid; modelling; resistive limit

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