Localized S-inversion of time-domain electromagnetic data

Interpretation of time-domain electromagnetic (TDEM) data over inhomogeneous geological structures is a challenging problem of geophysical exploration. The most widely used approach of interpreting TDEM data is based on the smooth 1-D layered resistivity inversion. We have developed an effective technique of fast TDEM inversion based on thin-sheet conductance approximation that we call S-inversion. In this paper we extend the S-inversion technique, approximating the conductivity cross-section by adding a local inhomogeneous disk with an excess conductance 1S to the horizontal conductive thin sheet used in S-inversion. Localized S-inversion determines the distribution of this excess conductance as a function of a depth and a horizontal coordinate. This new method takes into account the limited horizontal extent of the inhomogeneities, localizing inversion. The numerical modeling results and inversion of practical TDEM data demonstrate that the method resolves local geological targets better than traditional 1-D inversion and original S-inversion. The method can be applied to interpret both ground and airborne TDEM data sets.