1887
Volume 29, Issue 1-2
  • ISSN: 0812-3985
  • E-ISSN: 1834-7533

Abstract

Because of the non-uniqueness of the EM inversion problem, one must constrain the inversion procedure in some way to achieve a geologically valid model. All constraints are regarded as subjective except when they agree with the prejudices of the person using the inversion. Conventionally, constraints have included: inverting to models with a small number of parameters; forcing conformation with a priori geological information; or requiring smooth or minimal spatial derivatives with respect to conductivity (Occam inversion).

We prefer to use the constraint philosophy of the damped eigenparameter method (also called the Jupp-Vozoff algorithm). After incorporating a priori geological knowledge in the starting model, this process constrains change to individual model parameters on the basis of the strength of their effect on the data when grouped into eigenparameters. The initial model can thus be regarded as a soft constraint. In this paper, we extend this inversion philosophy to the case where the number of unknown parameters exceeds the number of data points; i.e., an under-determined problem. Inverting to both undetermined and over-determined layered earth models, we have tested this method on two sets of synthetic AEM data: one generated from a 1D model, the other from a 2.5D model.

© 1998 ASEG
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1998-03-01
2026-01-19

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References

  1. Constable, S.C., Parker, R.L., and Constable, C.G., 1987, Occam’s inversion - a practical algorithm for generating smooth models from EM sounding data: Geophysics 52, 289–300.
  2. Farquharson, C.G., and Oldenburg, D.W, 1993, Inversion of time-domain EM data for a horizontally layered earth: Geophys. J. Int. 114, 433–442.
  3. Hohmann, G.W., and Raiche, A.P., 1988, Inversion of controlled-source electromagnetic data: in Nabighian, M.N., Ed., Electromagnetic Methods in Applied Geophysics. 1: Soc. Expl. Geophys., 469–503.
  4. Jupp, D.L.B., and Vozoff, K., 1975, Stable iterative methods for the inversion of geophysical data: Geophys. J. R. Astr. Soc. 42, 957–976.
  5. Knight, J.H., and Raiche, A.P., 1982, Transient electromagnetic calculations using the Gaver-Stehfest inverse Laplace transform method: Geophysics 47, 47–51.
  6. 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.
  7. Oldenburg, D.W., 1990, Inversion of electromagnetic data: an overview of new techniques: Surveys in Geophysics 11, 231–270.
  8. Raiche, A.P., 1994, Modelling and inversion - Progress, problems, and challenges: Surveys in Geophysics 15, 159–207.
  9. Raiche, A.P., Jupp, D.L.B., Rutter, H., and Vozoff, K., 1985, The joint use of coincident loop transient electromagnetic and Schlumberger sounding to resolve layered structures: Geophysics 50, 1618–1627.
  10. Sugeng, F., Raiche, A., and Rijo, L., 1993, Comparing the time-domain EM response of 2D and elongated 3D conductors excited by a rectangular loop source: J. Geomag. Geoelectr. 45, 873–885.
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  • Article Type: Research Article

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