Acquisition and processing of electric, magnetic and GPR data on a Roman site (Victimulae, Salussola, Biella)

A multi-method geophysical survey has been carried out on a Roman archaeological site, where part of an apse had previously been found and then refilled by archaeologists during an excavation test. Magnetic gradient measurements were performed over the whole study area and a sub-area of interesting anomalies beside the excavation test site was found. Two-dimensional filtering of a more detailed magnetic gradient map and 2D inversion of magnetic profiles were performed, using an on-purpose implemented software, in order to reduce the effect of noise and to stress the eventual presence of buried structures in agreement with the archaeologists’ hypothesis. Resistivity tomography and GPR profiles were carried out along some selected profiles to obtain information on the vertical distribution of the anomalous bodies. GPR profiles, carried out in the area containing the test excavation, supplied good results, particularly when processed as time slices. The whole structure of the apse was clearly outlined. The authors were then able to suggest to the archaeologists further excavation tests on the basis of GPR results and of the filtered magnetic gradient map. A comparison of the results of the applied surveying methodologies has supplied an example of the relative strengths and weaknesses of the different electric, magnetic and GPR techniques.