Geophysical Journal | 2006 volume 28 1

Methods and models of electromagnetic sounding systems: state, limitations and new abilities

© Shuman V.N.

Physical mechanisms of producing electromagnetic response registered on the interface "land - air" are being analyzed. Considerations are focused on the problems of generation of thoroidal and poloidal fields with different configurations of the side current, the problems of appearance of bi-modality signs of response in atmosphere and spherical character of its sources. A new type of magnetic field excitation is being studied, inherent to spherical geometry - thoroidal and poloidal current of the source's spherical character, and a specified system of Maxwell equations is being formulated taking into account a new type of the field excitation. From this standpoint fundamental distinctions are being noticed in electrodynamics of spherical and planal sources of the field and the limited character of tensor approach to description of MT-process under conditions of bi-modal excitation of the response is underlined. Classical scheme of electromagnetic soundings theory is suggested to be modernized based upon exact vectorial impedance identity (the vectorial impedance boundary condition) for harmonic fields on the closed interface, which produces two imaginary surface orthogonal and equinormal vectors and a generalized equation of impedances. In the author's opinion this approach in its totality will make possible not only to preserve the most important results of the theory but also to trace the ways for further development of electromagnetic sounding systems.

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