Joint Interpretation of Geophysical Data for Archaeology: A Case Study

Abstract

Interpret-joints within geophysical data recorded in a complex area where ruins do not outcrop and only earthenware remains within the surficial layer are present. The study area, located in central Italy, consists of Roman, medieval and modern ruins that are included in reworked sediments. The geology is formed by inhomogeneous alluvial sediments (sand and gravel) several meters thick with diamagnetic character. To reduce the ambiguity in the subsurface reconstruction, a joint interpretation of georadar, magnetic and electrical tomography data was performed. The georadar was chosen to reconstruct detailed subsurface features, the electrical tomography to distinguish resistive bodies (stones, voids, etc.) from conductive (cavities filled by clay) and, because of the diamagnetic character of in situ sediments, the magnetic method was chosen to detect the earthenware ruins. The geophysical data were controlled by excavation, which detected silos of 1 m in diameter and a concrete layer at a few centimeters from the topographic surface. Time slices in the georadar data allowed us to detect the silos and to define the lateral edge of the concrete layer. Silos were also indirectly detected by the magnetic data because of the earthenware present in the filling sediments. Electrical tomography detected the concrete layer and an ancient anthropogenic surface of few centimeter depths. The study demonstrates that, because the geophysical methods are based on different physical characteristics, they can have different resolution and therefore detect different bodies.

Georadar data collection, anomaly shape and archaeological interpretation – a case study from central Italy

“…The low resistivity (60-200 ohm.m) was attributed to alluvial sediments and the high resistivity (>200 ohm.m) to stone structures. On the basis of the geoarchaeological knowledge acquired in the region, and the geophysical results of previous investigations (Orlando, 2005), we decided to apply georadar and magnetic methods in the study area, which is about 1 km away from the previously studied area. The surveyed area, 50 m long and 33 m wide, is located on a football field where some slab-covered tombs were discovered when the field was dug up.…”

“…Ground-penetrating radar (GPR) has become more common in archaeological studies over the past 20 years (Goodman et al, 1995;Malagodi et al, 1996;Basile et al, 2000;Piro et al, 2000Piro et al, , 2003Conyers, 2004;Orlando, 2005). Performance of GPR essentially depends on two main elements: the geo-archaeological setting of the study area, which is independent of the researcher, and the acquisition and processing of data.…”

Two different approaches for georadar data processing: A case study in archaeological prospecting

“…The exploitation of georadar in archaeological applications is very common (Barone et al, 2007;Martino et al, 2006;Abbas et al, 2005;Orlando, 2005;Tallini et al, 2004;Leckebusch, 2003;Piro et al, 2002;Basile et al, 2000;Conyers and Goodman, 1997;Malagodi et al, 1996). The georadar is usually exploited in a configuration, where the receiving and transmitting antennas are separated by a small fixed offset and are moved very close to or in contact with the ground-interface and for each position a time domain trace is collected.…”

“…In fact, the depth resolution depends on the frequency and on the electromagnetic velocity of the probing radiation of the investigated structures; moreover thin resistive structures, depending on the thickness as function of frequency of electromagnetic signal, can originate resonance phenomena. The lateral resolution depends on antenna frequency, depth and distance of profiles, the latter can induce on the time slices a stretching of the anomalies in the normal direction of profiles (Orlando, 2005) because of the different sampling of the underground. Also, it is necessary to account the role of the losses in the investigated medium, which entails to reducing the peak antenna frequency in order to achieve a good penetration depth.…”

Ground‐penetrating radar investigations into the construction techniques of the Concordia Temple (Agrigento, Sicily, Italy)

“…Prospect. 14, 47-59 (2007) Published online 8 January 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/arp.300 Conyers and Goodman, 1997;Basile et al, 2000;Leckebusch, 2003Leckebusch, , 2005Sciotti et al, 2003;Orlando, 2004;Watters, 2004;Nuzzo, 2005). In particular, GPR is well suited to investigate the foundation geometry of archaeological buildings where it is impossible to apply any destructive technique (Lü ck, 1997;Perez Gracia et al, 2000;Jol et al, 2002;Leucci, 2002;Nuzzo, 2004;Tallini et al, 2004;Abbas et al, 2005).…”