Geophysical Journal | 2007 volume 29 1

Applied geo-electrodynamics and magneto-telluric experiment

© Shuman V.N.

Key positions of applied geo-electrodynamics are being concretized, which are important from the view-point of applications and reflecting in their main features methodological and technological aspects of modern magneto-telluric science. Special features of classical theory of impedance changes in geo-electrics methods are being analysed. In contrast to standard approach, exact formula of local connection is used between tangential components of complex amplitudes of electric and magnetic field in a point of its registration in a closed border of the interface "land-air",which includes two scalar parameters (impedance) (O.A. Aboul - Atta and W.M. Boerner, 1975), which means its description by unitary space of second number of dimension. This exact vector impedance identity produces two independent imaginary tangential vectors, which orthogonality and equality of norms give two scalar equations, which determine interface under consideration and generalized equation of impedances. On this methodical base new scheme for decision of multi-dimensional inverse problems of deep electromagnetic sounding has been proposed.
The problem of possible presence of toroidal magnetic field B in weakly conducting atmosphere of the Earth is being analyzed which entrance this area of space may take place both at the expense of finite conductivity of air and due to the currents directed along the B field. Attention is concentrated on refinement of theoretical and methodical principles of basic methods of modern geo-electrics, in particular, unification of local magneto-variation and magneto-variation sounding with application of spatial derivatives of field into integrated methodical system - generalized magnetovariation sounding. The concept of 3D tensor of response and non-local marginal conditions of impedance type on the surface of heterogeneous sphere is being considered. It is noted that the classical theorem of uniqueness according to which all the components of electromagnetic field on the closed surface are completely retrievable by exact values of tangential components of magnetic or electric field given in it is true in case of magnetic field B outside of this surface belongs to vacuum type, that is both divergent-less and rotor-less. Let us recollect that in general case tangential component of the current within the surface considered cannot be completely retrieved by only poloidal magnetic field given in it and this fact cannot yet find proper reflection in modern magneto-tellurics.

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