Magnetic probability tomography for environmental purposes: test measurements and field applications

Abstract

A new tomographic technique for magnetic data inversion in near-surface geophysical investigations is presented and discussed. It represents a powerful tool for analysing magnetic profiles and/or maps obtained during geophysical surveys carried out for environmental and engineering applications. The inversion technique is based on the cross-correlation integral between the magnetic field measured on earth surface and the theoretical magnetic field produced by an unit scanner dipole positioned in the subsoil at the nodes of a regular grid. The cross-correlation values are then plotted in a 2D map, giving as a result a probability distribution of finding the magnetic dipoles at the selected depth, named dipolar occurrence probability (DOP). The skill of the tomographic technique has been evaluated using theoretical simulations, laboratory experiments with controlled magnetic sources and field measurements for environmental monitoring. Our findings demonstrated that the DOP probabilistic function allows us to localize the presence of metallic buried bodies (hunks), or objects characterized by high magnetic susceptibility contrasts.