A new data constraint for the effective inversion of CSEM data in the intermediate zone

Abstract

Controlled-source electromagnetic (CSEM) data in the intermediate zone show complex characteristics in contrast with the data in the near or far zone. However, there have been few studies on the analysis of the intermediate zone data and their inversion experiments. Thus, we first analyzed the characteristics of the intermediate zone data using the half-space response which is a function of the induction number. We figured out that the data become out of sequence as the frequency increases in terms of the data themselves and the non-uniqueness of the inverse problem increases because of this complex feature. We suggested a new data constraint, named as 'difference between successive frequencies (DBSF)' data constraint, which uses the difference between the data of two successive frequencies for reducing the non-uniqueness in the inverse problem. Through numerical test, we successfully performed the inversion of intermediate zone data by applying the DBSF data constraint to the inversion. This implies that the real field data affiliated to the intermediate zone can be reasonably handled by applying the DBSF data constraint.