Evaluating the effects of magnetic soils on TEM measurements for UXO detection

The task of discriminating UXO from non-UXO items are more difficult when sensor data are contaminated with geological noise originating from magnetic soils. In particular, magnetic material affects the decay curve characteristics in electromagnetic surveys and this can adversely affect inversion calculations that try to estimate parameters of the UXO or determine whether the item is UXO or scrap. This talk focuses on the effects magnetic soils and magnetic viscosity have on time domain and frequency domain electromagnetic sensor data. By forward modelling of a 1-D layered earth model we investigate the sensitivity of surveys to magnetic soils, and attempt to determine the relative strengths of magnetic soils and buried metallic objects. In particular, we consider soil susceptibility models appropriate for Kaho’olawe Island, Hawaii, where the UXO clearance project has been hampered by the presence of highly magnetic basaltic soils. Finally, we investigate how perturbations in signal due to magnetic soil affect the ability to recover parameters of the dipole model presented in Pasion and Oldenburg (2001a).