Rapid three-dimensional inversion of multi-transmitter electromagnetic data using the spectral Lanczos decomposition method

In this paper, we develop a new method of three-dimensional (3-D) inversion of multi-transmitter electromagnetic data. We apply the spectral Lanczos decomposition method (SLDM) in the framework of the localized quasi-linear inversion introduced by Zhdanov and Tartaras (2002 Geophys. 1. Int. 148 506-19). The SLDM makes it possible to find the regularized solution of the ill-posed inverse problem for all values of the regularization parameter a at once. As an illustration, we apply this technique for interpretation of the helicopter-borne electro magnetic (HEM) data over inhomogeneous geoelectrical structures, typical for mining exploration. This technique helps to accelerate HEM data inversion and provides a stable and focused image of the geoelectrical target. The new method and the corresponding computer code have been tested on synthetic data. The case history includes interpretation of HEM data collected by INCO Exploration in the Voisey's Bay area of Canada.