Numerical modeling and inversion of geophysical electromagnetic measurements using a thin plate model
1University of Oulu, Faculty of Science, Department of Geosciences
2University of Oulu, Faculty of Science, Department of Physical Sciences, Division of Geophysics
|Online Access:||PDF Full Text (PDF, 0.8 MB)|
|Persistent link:|| http://urn.fi/urn:isbn:951427119X
|Publish Date:|| 2003-11-08
|Thesis type:||Doctoral Dissertation
|Defence Note:||Academic Dissertation to be presented with the assent of the Faculty of Science, University of Oulu, for public discussion in Raahensali (Auditorium L10), Linnanmaa, on November 8th, 2003, at 12 noon.
Professor Laust B. Pedersen
Professor Peter Weidelt
The thesis deals with numerical methods designed for the modeling and inversion of geophysical electromagnetic (EM) measurements using a conductive thin plate model. The main objectives are to study the EM induction problem in general and to develop practical interpretation tools for mineral prospecting in particular.
The starting point is a linearized inversion method based on the singular value decomposition and a new adaptive damping method. The inversion method is introduced to the interpretation of time-domain EM (TEM) measurements using a thin plate in free-space. The central part of the thesis is a new approximate modeling method, which is based on an integral equation approach and a special lattice model. At first the modeling method is applied to the interpretation of frequency-domain EM (FEM) data using a thin plate in conductive two-layered earth. After this time-domain responses are modeled applying a Fourier-sine transform of broadband FEM computations.
The results demonstrate that the approximate computational method can model the geophysical frequency and time-domain EM responses of a thin conductor in conductive host medium with sufficient accuracy, and that the inversion method can provide reliable estimates for the model parameters. The fast forward computation enables interactive interpretation of FEM data and feasible forward modeling of TEM responses. The misfit function mapping and analysis of the singular value decomposition have provided additional information about the sensitivity, resolution, and the correlation behavior of the thin plate parameters.
Acta Universitatis Ouluensis. A, Scientiae rerum naturalium
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