Practical 3D EM inversion ? the P223F software suite

Abstract

Over the past 27 years, the AMIRA P223 project series has produced an extensive body of EM modelling and inversion programs used by the minerals, environmental and defence industries for planning and interpreting EM surveys, and for the development of new EM exploration instruments. This project series is now into its final overtime. Historically, the software generated by these projects has been available only to the project sponsors and their designated contractors. All programs are now commercially available through EMIT?s Maxwell graphical user interface. From 2010, the Fortran 90 source code for all programs will be open source. The purpose of this paper is to make the wider EM modelling community aware of the capabilities offered by this extensive, commercially-available software suite. The models for both modelling and inversion include a general 3D full domain finite elements (Loki class), 3D compact finite-elements (Samaya class), 2.5D full-domain finite-elements (Arjuna class), multiple 3D plates embedded in a multi-layered host (Leroi class) and a 1D layered earth (Airbeo and Beowulf). The programs can be used for any frequency or time-domain airborne, ground or downhole EM system. Sources can include multi-vertex closed loops, grounded wires, magnetic dipoles and plane waves. Receiver types can include multi-vertex loops, grounded wires, and magnetic and electric dipoles. Survey types include the variety of airborne configurations, fixed sources with independent surface or downhole receiver lines, moving sources with multiple fixed-offset receivers and magnetotellurics. Inversion for all model classes is based on an iterative, damped SVD method which concentrates on those parameters that most affect the data whilst ignoring those that are irrelevant.