Intensity of scattering fot lithotype characterization of an excavated pre-Trajan wall structure

The study is focused on the characterization of a pre-Trajan wall structure, decorated with mosaics. The wall is located below the Crvptoporticus of the 'Baths of Trajan' complex, at Rome historical centre. The surveyed wall is 15 m large and 0.9 m wide, with an height ranging from 3 to 5 m. GPR survey was planned with the aim to reconstruct the inner geometry, characterizing materials constituting the wall and mapping the fractures. The 900 MHz gives the best trade-off between resolution and depth of investigation and the wall is surveyed with horizontal and vertical profiles, spaced 20 cm apart, using plywood panels in order to safeguard the integrity of the mosaics. Through data interpretation we map the fractures or joints between travertine blocks and we characterize the construction materials and the quality of travertine blocks analyzing the scattered energy. We show that the effective intensity of scattering can be a useful tool for defining the different lithotypes. Furthermore analysing the time slice obtained from profiles in true amplitude, we observe that the energy amount is directly related to the lithology, because of the different attenuation exhibited by the two materials forming the wall.