3D inversion of ERT data on an archaeological site using GPR reflection and 3D inverted magnetic data as a priori information

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 1996, at the Archaeological Test Site of the Sabine Necropolis at Research Area of National Research Council of Rome (Montelibretti, Italy), a small area had been selected to test the integration of magnetic, GPR and ERT techniques. The magnetic data were acquired as Vertical Gradient of the Total Magnetic Field (VGTMF), and were inverted minimizing an L-2 norm. The GPR data were acquired as single-offset measurements on a regular grid and processed to obtain time slices of reflection amplitude. The ERT data were acquired with dipole-dipole array along parallel profiles in both E-W and N-S directions. In this work we reprocess the data collected in 1996 performing a 3D inversion of ERT data using GPR data and 3D inversion results of the magnetic data. We inverted ERT data according to both L-2 and L-1 norm minimization. Both the mean apparent resistivity and different resistivity distributions derived from processed GPR and 3D inversion of VGMTF data were used as starting model. The results are then compared in the volume under the surveyed area: merits and shortcomings of the different techniques are pointed out and analyzed. From the results of the different applied techniques, it comes that both ERT and VGTMF locate the searched tomb as a volume, while GPR mainly identified the ceiling of the tomb. VGTMF data inversion obtained from minimization of the L-2 norm properly locates both the chamber and the corridor but produces smeared overestimated volumes. 3D inversions of ERT data with a priori information give an accurate picture of the chamber and delineates the corridor, even if the resistivity values are underestimated if compared to the expected resistivity of void. Results are compared with the archaeological findings as the area was unearthed and verified in 2001.