Advanced Computational Methods of Rapid and Rigorous 3 - D Inversion of Airborne Electromagnetic Data

Abs trac t. We develop a new computa tional meth od for modeling and inverting fre­ qu ency domain airborne electromag ne tic (EM) data. Our method is based on the con­ traction integral equa tion meth od for forward EM modeling and on inversion using the localized quasi-linear (LQL) approximation followed by the rigorous inversion, if necessary. The LQL inversion serves to provide a fast image of the target. These results are checked by a rigorous update of the domain electric field, allowing a more accu­ ra te calcu lation of the predicted da ta. If the accuracy is poorer than desired, rigorous inversion follows, using the resulting conductivity distribu tion and electr ic field from LQL as a starting model. The rigorous inversion iteratively solves the field and do­ main equations, converting the non-linear inversion into a series of linear inversio ns. We test this method on synthetic and field data . The resu lts of the inversion are very encouraging with respect to both the speed and the accuracy of the algorithm, showing this is a useful tool for airborne EM interpretation.