**5. Conclusions**

A geophysical prospection of a prehistoric archaeological site in Sardinia, Italy, is proposed. In particular, results from an Automated Resistivity Profiling (ARP) survey over a 2.28 hectares area are analyzed and discussed in comparison with Ground Penetrating Radar (GPR) sections over the same area. The purpose of the prospection was to reveal the archaeological potential of a wide area surrounding a site accidentally discovered and partially excavated in the 1970s when a necropolis and

related archaeological findings (e.g., fragments of large stone statues and funeral monuments) were found. The site was abandoned until the joint archaeological-geophysical scientific project (2013–2015) in which the ARP and GPR prospections were carried out.

The ARP survey covered a wide area localized at the northern side of the historic archaeological site. Apparent resistivity data were simultaneously acquired at three di fferent depths of investigation (0.5 m, 1 m and 1.7 m) and exhibit a wide range of variability (from 15 Ω·<sup>m</sup> to 250 Ω·m). The most intense planimetric patterns of the apparent resistivity maps were characterized by wide resistive regions with irregular shapes and linear spatial extensions of the order of tens of meters, but even some conductive anomalies were found which were characterized by sub-regular shape and dimensions of possible archaeological interest. Some small apparent resistivity patterns presented spatial coherence but weak local resistivity contrast; therefore, it is di fficult to assign them to archaeological features without more detailed measurements of the possible artifacts.

In order to verify preliminary interpretations, the tridimensional distribution of apparent resistivity measures was compared with high resolution GPR data acquired along linear profiles. In most cases, the results show a good correspondence between apparent resistivity anomalies and GPR signals. Based on the agreemen<sup>t</sup> between ARP and GPR datasets, it was possible to define the surveyed area in five classes which varies in function of the two kind of signal intensities and their complementary spatial features. Two very promising and neighboring wide areas were delimited for an approximate total extension of 4190 m<sup>2</sup> in the southern part of the surveyed region, corresponding to the limit of the archaeological restricted area (inside and outside). GPR comparison was possible only for one of them (and was positive), but their continuity and ARP data parameters (intensity and spatial features) are evidence of their global archaeological potentiality. Of the other four large resistive regions (in the range of 190–390 m2), two were characterized by the spatial correspondence of strong ARP and GPR anomalies, while the others, presenting high apparent resistivity contrast and shapes potentially attributable to non-geological origin, presented GPR signal of medium amplitude or locally covered by strong noise. Consequently, they were classified as susceptible in the first case to include buried archaeological evidence, and in the second case, suggested further investigations with other complementary geophysical methods and archaeological trials. The remaining wide area (17,830 m2) showed a complex scattered distribution of planimetric patterns with low resistivity contrast which could be indicative of the presence of in situ archaeological features, less sensitive than possible accumulation of stone fragments to volume analyses, such as ARP.

In order to validate ARP apparent resistivity patterns and nominal map depth, two sample pseudo-sections were inverted, substantially confirming their validity but obtaining few di fferences in terms of hierarchy of most resistive values between top and bottom subsoil and partially in terms of depths in correspondence with the most conductive layers. The depth values of the pseudo-sections and the ERTs bottom interfaces are still compatible with the geological investigations summarized in Section 2.2 considering the ordinary spatial variability of geological features.

In the present case study, the ARP method was confirmed as a reliable and expeditious geophysical technique able to investigate wide regular surfaces and to identify areas likely to contain archaeological features. Thanks to the simultaneous acquisition of positioning data by means of a di fferential GPS system mounted in the middle of the electrical array, ARP data were instantly geopositioned and an accurate georeferencing was automatically performed. Very good performances were evidenced in indicating large subsoil volumes with a high apparent resistivity contrast. Some spatially coherent patterns were also recognizable with weak apparent resistivity contrast for which further investigations could be useful. Overall, ARP proved to be an e ffective geophysical technique for the preliminary assessment of the archaeological potential of investigated areas and to direct more concentrated, expensive and time-consuming higher resolution prospections. Furthermore, joint interpretation of ARP and GPR measurements could be used to di fferentiate potential archaeological zones, demonstrating the e ffectiveness of the integration of both extensive non-destructive methods to address preliminary researches concerning archaeological studies.

**Author Contributions:** Conceptualization, L.P., S.V.C., A.T. and G.R.; Data processing, L.P., S.V.C. and A.T.; Funding acquisition, G.R.; Investigation, L.P., S.V.C., A.T. and G.R.; Methodology, L.P., S.V.C., A.T. and G.R.; Validation, L.P., S.V.C., A.T. and G.R.; Writing—original draft, L.P. and S.V.C.; Writing—review and editing, L.P. and S.V.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by *Regione Autonoma della Sardegna*, LR 7/2007. The APC was funded by *Fondazione di Sardegna.*

**Acknowledgments:** The authors are grateful to Luigi Noli and Mario Sitzia for their essential technical support during the surveys and GEOCARTA © for the acquisition of ARP data. The authors wish to thank the Archaeological Superintendency of Cagliari and Oristano (*Soprintendenza Archeologia, belle arti e paesaggio per la città metropolitana di Cagliari e le province di Oristano e Sud Sardegna*) for the courtesy and for the permission to carry out the surveys in the site of study and to publish the results of geophysical researches.

**Conflicts of Interest:** The authors declare no conflict of interest.
