Testing a new low-frequency GPR antenna on karst environments of central Italy

A new unshielded low-frequency GPR antenna, centred on a frequency of about 40 MHz, has been recently developed by IDS Ingegneria dei Sistemi Spa, a leading Italian GPR manufacturer. The antenna is being tested. The Engineering Geology Laboratory of the L´Aquila University, with consolidated experience in GPR investigations, used it on two karst areas of central Italy, where available underground data were compared to GPR results, thus verifying depth and accuracy of the new antenna. The study areas were: i) the Lepini karst massif, characterized by diffuse underground caves and karst conduits (for which detailed speleological and geological data were available); and ii) the Gran Sasso Massif, with welldeveloped surficial karst morphologies (for which geological data were also available); GPR data on the latter study area were also provided by another IDS antenna with a central frequency of 100 MHz (maximum investigation depth: about 10 m). The radar time window was set to 640 ns, implying a maximum penetration depth of about 30 m at a standard propagation velocity of 10 cm/ns. In the Lepini massif, the depth of some strong anomalies, due to the occurrence of known caves, was in good agreement with the location obtained from speleological surveys. On the Gran Sasso Massif, data from the new 40 MHz antenna were compared to those recorded with the 100 MHz antenna, showing that the prototype is a very powerful tool to investigate deep cave and karst morphology.