High-frequency GPR investigations in Saint Vigilius Cathedral, Trento

In this paper, we present the results of high frequency GPR measurements performed on the pillars of Saint Vigilius cathedral in Trento to monitor the construction conditions as well as to detect the internal defects of the pillars. Tomographic measurements were performed using a pair of 1GHz Mala antennas at three heights along the pillars. The distribution of the propagation velocity was therefore determined in horizontal planes within the pillars and the data were then translated to images of the relative permittivity. Reflection measurements were performed using the very high frequency 3GHz IDS antenna. The results detected some minor spaces where the stones were not perfectly attached. However, significant internal defects with dimensions larger than 15cm should be excluded according to GPR results. Based on vertical profiles on all the accessible sides of the pillars, the size and layout of the stones used to construct the outer parts of the pillars were recovered. Thickness variations of two sample vaults were also monitored using the profiles measured across them.