Estimating the macroanisotropy of a horizontally layered section from controlled-source radiomagnetotelluric soundings

Abstract

The possibilities of estimating the macroanisotropic parameters of the earth by radiomagnetotelluric soundings with a controlled source in the form of a horizontal electric dipole (a cable with a finite length) are studied in the case of the measurements in the transition zone of the source, where the galvanic and induction modes of the excited electromagnetic field are both important. The forward problem for the considered high frequency band (up to 1000 kHz) is solved with allowance for the displacement currents in the ground and air. The algorithm of anisotropic 1D inversion of the sounding data is presented. The resolution parameters are estimated from the derivatives of the electromagnetic field components with respect to the model parameters. Based on the synthetic examples, it is shown that joint inversion of the impedance and tipper data in the transition zone of the source constrains the space of equivalent models and makes it possible to determine the macroanisotropy coefficient of the section.