3D inversion of ERT data on an archaeological site using GPR reflection and 3D inverted magnetic data as a priori information
2015
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, ground-penetrating radar, and electrical
resistivity tomography techniques.
The magnetic data were acquired as the vertical gradient of the total magnetic field and were
inverted by minimizing an L-2 norm. The ground-penetrating radar data were acquired as singleoffset
measurements on a regular grid and processed to obtain time slices of reflection amplitude.
The electrical resistivity tomography data were acquired with dipole–dipole array along parallel
profiles in both east–west and north–south directions.
In this work, we reprocessed the data collected in 1996 performing a three-dimensional inversion
of electrical resistivity tomography data using ground-penetrating radar data and three-dimensional
inversion results of the magnetic data. We inverted electrical resistivity tomography data according
to L2 and L1 norm minimization. Both the mean apparent resistivity and different resistivity distributions
derived from processed ground-penetrating radar and three-dimensional inversion of the
vertical gradient of the total magnetic field data were used as a starting model.
The results were 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 electrical resistivity
tomography and vertical gradient of the total magnetic field locate the searched tomb as a volume,
whereas ground-penetrating radar mainly identified the ceiling of the tomb. Vertical gradient of the
total magnetic field data inversion obtained from minimization of the L2 norm properly locates both
the chamber and the corridor but produces smeared overestimated volumes. Three-dimensional
inversions of electrical resistivity tomography 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 with the expected resistivity of void. Results are compared with the archaeological findings
as the area was unearthed and verified in 2001.
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