Comparison between 3D inversion of ERT and Total Magnetic Field Data on an Archaeological Site

Non-destructive geophysical prospecting methods are increasingly used for the investigation of archaeological sites, where a detailed physical and geometrical reconstruction of structures is required prior to any excavation work. In this work the comparison between 3D inversions of ERT and vertical gradient of the total magnetic field (VGTMF) data, to delineate sharp discontinuities (boundary of cavities and fractures in the medium) in the Archaeological Test Site of Sabine Necropolis at Research Area of National Research Council of Rome (Montelibretti, Italy) are shown and discussed. While the VGTMF data inversion has been made minimizing an L-2 norm, the ERT data have been inverted minimizing an L-2 and an L-1 norm, obtaining different information and details. The results are then compared in the volume under the surveyed area: merits and shortcomings of the different techniques are pointed out and analyzed. Both ERT and VGTMF locate the tomb; VGTMF overestimates its barycentre depth and gives a smeared volume; ERT L-1 inversion gives a fine picture of the chamber, delineates the corridor and underestimates the resistivities; ERT L-2 inversion gives a broad image of the chamber, does not delineate the corridor but gives more appropriate resistivities.