Antonio Trogu

Integrated geophysical and aerial sensing methods for archaeology: A case history in the Punic site of Villamar (Sardinia, Italy)

In this paper, the authors present a recent integrated survey carried out on an archaeological urban site, generally free of buildings, except some temporary structures related to excavated areas where multi-chamber tombs were found. The two methods used to investigate this site were thermal infrared and ground penetrating radar (GPR). The thermography was carried out with the sensor mounted under a helium balloon simultaneously with a photographic camera. In order to have a synthetic view of the surface thermal behavior, a simplified version of the existing night thermal gradient algorithm was applied. By this approach, we have a wide extension of thermal maps due to the balloon oscillation, because we are able to compute the maps despite collecting few acquisition samples. By the integration of GPR and the thermal imaging, we can evaluate the depth of the thermal influence of possible archaeological targets, such as buried Punic tombs or walls belonging to the succeeding medieval buildings, which have been subsequently destroyed. The thermal anomalies present correspondences to the radar time slices obtained from 30 to 50 cm. Furthermore, by superimposing historical aerial pictures on the GPR and thermal imaging data, we can identify these anomalies as the foundations of the destroyed buildings.

Time-lapse electrical resistivity tomography to delineate mud structures in archaeological prospections

Archaeological sites in rural areas are often characterized by structural remains that are made of mud or raw brick, and that produce a very small contrast in physical characteristics, as the surrounding materials of both anthropogenic and natural origins have similar lithological and mineralogical properties. The main measurable differences are due to changes in compaction and porosity and, as a consequence, in permeability, which influence the hydrological behaviour of the subsurface materials. In this paper, we present some applications based on Electrical Resistivity Tomography (ERT) surveys that are routinely applied in archaeological prospection, carried out over two different weather conditions. Measurement of the changing resistivity, corresponding to different moisture conditions in the subsoil, allowed us to identify archaeological strata and structures surrounded by natural, undisturbed soil. A number of tests carried out on a physical model permitted a further definition of the acquisition parameters and methodologies to be used to secure the best results. The field surveys were carried out in the necropolis of “Pill’e Matta” (IV BC - V AD), located in the suburbs of the metropolitan area of Cagliari, in the southern part of Sardinia, and in a Punic and Roman site near the village of Terralba, located in the Campidano plane, in the western part of Sardinia. The results show that time-lapse prospecting can increase the resistivity contrast between archaeological structures and soil.

Time and Spectral Multiresolution Remote Sensing for the Study of Ancient Wall Drawings at San Salvatore Hypogeum, Italy

Historic and prehistoric sites are often a serious challenge for geophysical techniques, which could give enhanced and essential information to define identity and health of cultural heritage assets. Multispectral remote sensing techniques have been applied to ancient wall pictures of a hypogeum actually under a rural church in San Salvatore (Italy). Multispectral survey was jointly done with state of art surveying for historic architecture and was compared with a 40s’ photographic survey. This integration has been the way to fully explore and exploit the signs present in wall drawings evidences of hypogeum frequentations. Adopting multiresolution approach for the construction of scientific datasets and maintaining full dimensionality for their evaluation and interpretation, jointly with some synoptic images, allowed us to build a user friendly Decision Support System potentially used by authorities assigned to the conservation, restoration and management of ancient heritage goods. In this case study, the informative layering showed to be a very effective method to find cross-information present in different surveys data, which are essential for planning restoration activities but also for dissemination and fruition of cultural heritage sites. The application of applied geophysics techniques to cultural heritage and artistic targets proved to be a disciplinary strategic application field.

Terrestrial remote sensing and microtremor measurements for the study of the vibrations of a rock mass with large underground cavities

This note describes an experimental study aimed at evaluate the vibration properties of a limestone rock vault, subjected to the forcing action produced by an intense vehicular traffic. The site of study occupies an area of about 3,000 m2. The subsoil of the site is characterised by shallow underground cavities due to the past quarry activities. Ambient vibration measurements were done by means of seismometer stations placed on the ground surface. Microtremor stations were arranged above the cavity and in the surrounding area. An innovative coherent radar sensor was installed inside the underground cavity in order to measure time series of displacement related to different reflector points located on the internal surface of the vault. The experimental vibration properties were derived by means of frequency analyses of both seismic and interferometric data in order to compare the results achieved by using the seismic transducers and the unconventional microwave sensor. Furthermore the preliminary results of numerical simulations were discussed.