Atomic archaeology? Using portable gamma surveying techniques to identify buried archaeological features

Traditionally, archaeological aerial surveyors fly routes selected on the probability of site visibility and record only what they perceive as significant. This approach to aerial reconnaissance has come under criticism in recent years with respect to productivity, bias and cost. Through panchromatic imagery with sub-metre resolution and high-resolution multispectral products, modern commercial satellites are capable of recording fine details of both extant sites and archaeological cropmarks. They are not limited by fuel costs, airspace laws, pilot time or conflicting regions of interest. In addition, the multiple wavelength images and powerful image analysis software available offer the facility to manipulate images in order to maximise the visibility of surface details and to detect any variations in the non-visible spectrum. The present paper employs a comparative analysis of above-ground remotely-sensed data recovered on various dates and with various methods of acquisition (QuickBird and Corona satellite imagery; WWII vertical aerial photography and recent oblique aerial photographs), in order to discuss the potential of satellite imagery to reveal buried archaeological features in the area of southern Dobrogea (Romania) and to assist in the reconstruction of past landscapes. It outlines some of the methodological approaches employed, highlights areas for further research and presents some preliminary outcomes.

Electromagnetic (EM) surveys have been used at the Cahokia Mounds State Historic Site in southwestern Illinois to locate and define a number of buried archaeological features. Two instruments, Geonics EM31-D and EM38 conductivity meters, were employed to locate portions of a wooden stockade known as the Central Palisade; delineate a number of leveled earthen mounds; and explore a broad, flat area in the central portion of the site known as the Grand Plaza. EM surveys, together with limited excavation, provide a cost effective and nondestructive means of exploring a site as large and complex as Cahokia. Archaeological excavations confirmed that EM surveys were able to locate the Central Palisade, and more importantly, that they provided information on anthropogenically modified terrain within the Grand Plaza. The EM survey documented buried ridge and swale topography and borrow pits within this area. This evidence of landscape modification challenges previous conceptions about the extent of earthmoving at this important Mississippian center and suggests a promising area of application for EM surveys in archaeology.

The importance of visible built heritage and archeolandscapes for preservation of collective memory and identity is widely acknowledged across disciplines regarding heritage protection and valorisation. The complex analysis of archaeolandscape transformations through time needs multilevel geospatial information. To this purpose, it is necessary to consider different domains of technological tools but also an appropriate geospatial framework, applying a multi-scale, multitemporal and multi-sensor approach. In this way, the capabilities of new technologies can be further expanded aiming towards to an effective integration and improvement of preservation strategies and protection methodologies for cultural heritage sites. This paper illustrates the integration of in situ surveying campaigns, close range photogrammetry, aerial and satellite remote sensing imagery for identify change detection at the “Nea Paphos”, a UNESCO protected archaeological site of Cyprus. In particular, this paper examines the evolution of a buried archaeological feature (amphitheatre?) which is already known to experts but has not yet been excavated. Changes of shape and size have been documented, interpreted and mapped using resources covering a temporal arch of circa last 50 years. While soil and vegetation marks of the buried feature are very clear in the historic aerial imagery, these traces are disturbed on the recent images. An integrated method of detecting natural and physical consequences for evolving landscapes, using remote sensing techniques, airborne, and 3D photogrammetric models developed using open-source tools has been applied. Such integration is envisaged to (1) provide new kind of information and possible scenarios for retrieving geospatial knowledge of evolving archeolandscapes and their multiple layers of history and to (2) enable archaeologists, public administration and conservation professionals to pursue specific tailored-made preservation strategies of- specific archaeological sites and to support them in more informed decision making.

With the increased demand to facilitate the archaeological work either in well-known archaeological sites or the crude sites, geophysical methods plays an important role. The Geophysical methods have been used since 1946 with increasing frequency for archaeological investigations and currently the branch of archaeogeophysics is widely applied. The wide varieties of geophysical methods applied in archaeological work relies principally upon existing reasonable contrast in physical properties between the buried archaeological feature and the surrounding subsoil. Understanding the archaeological properties of the physical contrasts, in terms of density, thermal conductivity, electrical resistance, magnetic or dielectric properties, remains fundamental issues of choosing and applying the discipline geophysical techniques. In this regard, we tried to introduce a brief outline for the common and applicable techniques in archaeological investigations. The physical principles and field instrumentation involved for the acquisition of data with each method are considered, as well as some common results from the worldwide case studies. Generally, the archeogeophysical survey results can be used to guide excavation and to give archaeologists insight into the patterning of non-excavated parts of the site as well as it is often used where preservation of the sensitive sites is the aim rather than excavation.

With the increased demand to facilitate the archaeological work either in well-known archaeological sites or the crude sites, geophysical methods plays an important role. The Geophysical methods have been used since 1946 with increasing frequency for archaeological investigations and currently the branch of archaeogeophysics is widely applied. The wide varieties of geophysical methods applied in archaeological work relies principally upon existing reasonable contrast in physical properties between the buried archaeological feature and the surrounding subsoil. Understanding the archaeological properties of the physical contrasts, in terms of density, thermal conductivity, electrical resistance, magnetic or dielectric properties, remains fundamental issues of choosing and applying the discipline geophysical techniques. In this regard, we tried to introduce a brief outline for the common and applicable techniques in archaeological investigations. The physical principles and field instrumentation involved for the acquisition of data with each method are considered, as well as some common results from the worldwide case studies. Generally, the archeogeophysical survey results can be used to guide excavation and to give archaeologists insight into the patterning of non-excavated parts of the site as well as it is often used where preservation of the sensitive sites is the aim rather than excavation.

This paper aims to present the potential of observations of the Earth’s surface by means of remote sensing (survey), specifically via direct (active) visual prospection from low altitude to identify and map small components (such as postholes) of archaeological contexts, namely aboveground post-built structures dated to the Early Iron Age (appr. 800–380 B.C.). This work gives an example of archaeological data on buried settlement constructions identified by aerial reconnaissance (i.e., by a non-invasive method), the interpretation—and primarily dating—of which is based on information achieved by excavation practice (recently performed predominantly during rescue campaigns). This research points to the fact that nonetheless to the traditional idea on the limited potential of crop-marked archaeological heritage in terms of dating (the ability of cropmarks displayed over pits, ditches, graves, etc., to produce exact ground-plans of even small buried features, so that their original function and dating can be determined) the number of more or less precisely datable archaeological sites and features buried under the surface is growing, including wooden structures once constructed on the ground (i.e., not sunken under the ground) and leaving on cereal crops just tiny spots/dots regularly spaced into lines. These are features (constructions) with identical ground plans (postholes placed in 4 × 3 and/or 3 × 3 patterns) of which commonly just one in a group of them situated on one site is enclosed by a perimeter line—a foundation for a wall or a trench for a palisade. Consequently, a retrospective survey of air-photo analog archives and digital repositories now brings new evidence on the chronological setting of many crop-marked Early Iron Age sites that previously remained undated.

Generally, in order to detect shallow archaeological features, such as tombs, cavities, walls, etc., ground penetrating radar (GPR) data are acquired along parallel profiles. In some cases, the data collected using the GPR method are difficult to interpret owing to the presence of low signal-to-noise (S/N) ratio. These signals can be generated by several factors that significantly influence the radar profiles. To enhance the interpretation of radar sections, three-dimensional data acquisition, radar signal processing and time-slice representation are used. The archaeological investigated as a test site was the Sabine Necropolis (700–300 BC) at Colle del Forno (Montelibretti, Roma), believed to contain unexplored underground dromos chamber tombs. The measurements were carried out along parallel profiles in a test area, using Sir System 10 (GSSI) equipped with different antennas operating at 100, 300 and 500 MHz. The spatial interval used during the survey was 20 cm. To enhance the S/N ratio, a band-pass filter and subtraction of an average trace on the field data has been applied; furthermore, the two-dimensional migration technique on all profiles collected was used in order to move diffraction effects. A time-slice representation technique was adopted to obtain a planimetric correlation between anomalous bodies at different depths. The results indicate that the three-dimensional data acquisition, processing and the time slice representation can help determine the location, depth and shapes of buried features.