Remote sensing techniques in archaeology. From Space to Ground investigation through the microwave spectrum: SAR and GPR detection

The goal of this research is to investigate underground anomalies which could be interesting from the archaeological point of view through observations collected both by SAR (Synthetic Aperture Radar) sensors and GPR (Ground Penetrating Radar) prospection. In particular, the two Etruscan and Roman test sites of Vulci and Veio were considered; they are located respectively near Montalto di Castro (80 km North of Rome) and near Isola Farnese (10 km North of Rome). During previous years both sites have been investigated with optical and full polarimetric SAR images. The choice of areas of interest was suggested by the previous studies carried out by the University of Rome “Sapienza” that gave us a complete overview of the area. Regarding Vulci previous researches, we observed one mark corresponding to part of the ancient moat of Vulci visible in Entropy (H) and Alpha Angle () products. By analyzing the H/plane and after survey in situ, we noticed the presence of very short grass, that probably allowed SAR penetration that could detect small targets (pieces of tuffs?) under the ground. Regarding Veio previous studies, we were able to analyse only one SAR dual-polarimetric product (containing less information about the scattering mechanism respect to full-polarimetric data), not sufficient for identifying the hidden structures detected in optical data. This is the reason why we went on in the analysis of full polarimetric data. As a final step, GPR prospection for the validation of SAR results was carried out in order to confirm what observed from satellite, both for well known archaeological marks and for assumed underground structures. For this purpose we employed two different SIR System (GSSI), equipped with a 500 MHz bistatic antenna with constant offset and a 70 MHz monostatic antenna. Ancillary information (meteorological conditions, geologic maps, archaeological maps, cartography) and surveys in situ allow a critical and scientific approach for data interpretation, in particular regarding SAR imagery. The well known utility of GPR prospection in archaeology demonstrated its usefulness for the detection of underground archaeological structures of Veio and Vulci, giving us a complete overview of the microwave portion of the spectrum, from satellite to ground investigation.