GPR survey in the Crypt of the Cathedral of Otranto

A study of the problem of deterioration of stone buildings of cultural importance, integrating different non destructive techniques (microclimatic and Ground Penetrating Radar) is proposed. It is well known in fact that this deterioration can be attributed to the presence of water and/or moisture in the porous material that occurs in water-damaged and humid buildings, due to poorly manufactured constructions and inadequate maintenance. The distribution of moisture within stone mainly depends on not suitable environmental condition and by the presence of wet buried structures in the ground. The Ground penetrating radar (GPR) survey was carried out inside the Crypt of the “Cattedrale di Otranto” (Lecce, South Italy). The careful analysis of the 0.4 m spaced GPR parallel profiles, acquired in the Crypt, using a Sir2 GSSI radar system with a 500 MGHz antenna, allow us to distinguish the wet and moisture zone. GPR data were displayed in time slices form to obtain both the amplitude and the moisture variations map. Moreover GPR data were displayed in the form of frequency slices to evidence absorption losses probably linked to higher moisture content. The GPR data were compared with microclimatic data, acquired in a precedent campaign of measures. Microclimatic and GPR data are in good agreement and suggest that an important channelling of moisture has origin in the subsoil.