GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.2 - POSTER GNGTS 2023 After the unification of Italy in 1860, many historical buildings of this district risked being demolished by the military to expand the barracks. In 2019 the complex was included in the UNESCO "Arab-Norman Palermo and the Cathedral Churches of Cefalú and Monreale" itinerary. The San Paolo D'Alga Church, used until few years ago as a gym for the barracks cadets, was investigated using ground penetrating  radar surveys (Capizzi et al., 2021). Thanks to these geophysical analyses, old perimeter walls, different from the current ones, were partially recognized and an archaeological campaign began. GPR surveys At the square of the Carabinieri were acquired 158 georadar profiles, parallel to each other, with aninterdistance of 50 cm. A total of about 4250 linear meter of GPR profile were acquired. Geophysical surveys were carried out using a multichannel georadar system (RIS MF HI-MOD system of IDS (Ingegneria dei Sistemi s.p.a.) which is equipped with a 200-600 MHz multi-frequency antenna, which allows high performance in detecting anomalies in the subsoil. This system can generate, capture, amplify, filter, and storing signals and enable to view the data acquired in real-time. Test profiles were performed to choose the acquisition parameters and to optimize the signal during the scan phase. All profiles were acquired with both antennas to have a good surface detail (600 MHz) and an adequate depth of investigation (200 MHz). The data were initially processed with ReflexW software (Sandmeier, 2016). The acquired data are usually noising and this makes subsequent interpretation difficult. For these reasons, some pre-processing steps results necessary. The data processing operations flow is completely arbitrary choice, mainly depending on the raw data quality. Parameters elaboration criteria chosen should not excessively affect data originality to avoid an over-processing that could lead to unrealistic representations. In this way, each GPR profile has been analyzed to eliminate the consistent and inconsistent noise present in the original data. In particular, the following pre-processing operations were applied: a) Static correction: this operation facilitates a correction for each trace in time direction and is applied to eliminate time delays related to trigger errors. b) The Butterworth type frequency filter: is a filter that eliminates electromagnetic noise characterized by frequencies other than those of the transmitted signal. For data captured with the 600 MHz antenna, a 100-1200 MHz band pass filter was used, and for data captured with the 200 MHz antenna, a 35 -600 MHz band pass filter was used. c) Energy decay: a tool useful for highlighting low ranges of amplitudes acquired signal against the highest ones. A gain curve is applied in time domain on the complete profile. d) Background removal: this 2D filter allows to eliminate temporally consistent noise and moreover is useful to make some signal portions, previously covered by noise, more visible.