DC resistivity inversion using general-purpose optimisation software

Abstract

DC resistivity sounding data usually are interpreted in terms of a layered earth by an iterative inversion scheme. This paper presents an alternative mechanism for the inversion process by formulating the resistivity inverse problem as an optimisation problem. By invoking the commercial mathematical programming software package called GAMS, an inversion routine has been developed without having to linearise the problem explicitly and without having to know details of the convergence algorithm. The GAMS high-level programming language provides a structure for coding the forward problem, for specifying an initial model and for declaring reasonable bounds on model parameters. GAMS inversion is extremely versatile in allowing ad hoc constraints of any complexity, but converges more slowly than special-purpose resistivity inversion algorithms. After familiarity is gained with the GAMS language, new code for more complex resistivity models or different geophysical methods can be developed in much less time than is required for the development of dedicated geophysical inversion software.