A ground-penetrating radar survey for archaeological investigations in an urban area (Lecce, Italy)

Abstract

A ground-penetrating radar (GPR) survey, using mostly a 500 MHz antenna, was carried out in an urban area (Lecce, Italy) to obtain a detailed characterization of the most superficial layers, where presumably archaeological structures are buried, and to quickly identify anomalous zones for excavation. In the area, the presence of remnants of a historical Franciscan friary (built in 1432 and pulled down in 1971) and, probably, of more ancient (Roman and/or Messapic) features was expected. The geological setting (mainly wet calcarenite named “Pietra Leccese”) was not the most favourable for the application of GPR methodology because of an expected high attenuation of electromagnetic energy. The low penetration depth of the signal, not exceeding 1 m and even using a 100 MHz antenna, made it possible to obtain information only between the ground level and the top of the calcarenitic basement. Data recorded along parallel profiles, 1 m spaced, prevented the clear identification of the walls of the historical building constructed in “Pietra Leccese” blocks, because of the weak contrast in the electromagnetic parameters with respect to the hosting material. On the other hand, the analysis of the radar sections allowed for identification and reconstruction of the shape and extension of a barrel-vault cavity, subsequently confirmed by archaeological excavations. Time slice representations were used as a tool to locate other features including modern-day urban utilities and the planimetric development of the barrel-vault cavity.