Inversion of magnetometer array data by thin-sheet modelling

A conjugate gradient relaxation method is employed in seeking an iterative solution to a particular 3-D electromagnetic inverse problem. The problem, which is non-linear, is that of modelling observed magnetic fluctuation res ponse functions by a thin-sheet earth structure. The method optimizes data misfit and model roughness, and starting from a base model designed on know n geology produces a series of improved models. Established thin-sheet algo rithms are employed to compute the model responses and sensitivity, and uti lization of a parallel computing system enables reasonable execution times. The method is demonstrated by inverting data generated for a synthetic exa mple. Gaussian noise is added to the synthetic data. The inversion scheme has been applied to geomagnetic induction data which h ave been recorded widely on the Australian continent. Highly conductive str uctures in models given by the inversion method confirm regional conductivi ty anomalies indicated by induction arrow patterns, and give more quantitat ive information about them. The method appears to work well in areas of str ong conductivity contrast such as coastlines.