Propagation of ELF Electromagnetic Waves Over a Curved Stratified Ground and its Application in Geophysical Prospecting

Electromagnetic waves radiated by a vertical electric dipole related to deep resource exploration are discussed. According to the tangential components of the field are continuous on the element interface, the spherical harmonic series expression of extremely low-frequency (ELF) electromagnetic waves in the “earth -ionosphere” model is derived, in which the earth is regarded as a curved stratified ground. The Schumann resonance serves to verify the correctness and reliability of the formula and algorithm. And our method is compared with the traditional large-scale electromagnetic method. The forward response curves of the two methods are in good agreement on the ELF band. By comparison, we can find that our method performs best when the distance between the transmitting source and receiving point is greater than 500km. To estimate the effects on the electromagnetic waves associated with resource exploration, we first discussed the ability of our method to identify formations, and then discussed the electromagnetic response characteristics of the earth as two-layer and three-layer models, which are sufficient to show the basic characteristics of the electromagnetic field in the “earth-ionosphere”. The results show that, as an emerging large-scale exploration method, the wireless electromagnetic method can be well used to detect the deep underground electrical structures.