ELECTROMAGNETIC SUBSURFACE IMAGING - A CASE FOR AN ADAPTIVE BORN APPROXIMATION

The process of interpretation of electromagnetic data has many facets of which fast approximate interpretation techniques is an intriguing o ne. A new variant of the Born approximation - the Adaptive Born approx imation - is presented and exemplified through 1D and 2D imaging techn iques for transient electromagnetic data. The Adaptive Born approximat ion is generally applicable in approximate inversion schemes for induc tive electromagnetic data as a one-pass imaging algorithm. Though it i s as simple to use as the ordinary Born approximation, it offers a mor e accurate inverse mapping. In the first part of this paper an attempt will be made to give an overview of fundamental concepts in electroma gnetic subsurface imaging relevant for approximate inverse mappings an d to outline major trends in present day modeling and inversion of ele ctromagnetic data. This is of course an impossible task - certainly fo r this author - and much important work will not be mentioned in the l imited space of the following. My apologies to the people who are not mentioned and whose research is not given credit here though it should have been. Naturally, my choice of references reflects the ''schools' ' and circles I have been subjected to, but I hope that the list of re ferences to developments in electromagnetic methods will point to pape rs of importance and thereby to other references for the interested re ader.