Apostolos Sarris

Use of engineering geophysics to investigate a site for a building foundation

The combination of geophysical data and geotechnical measurements may greatly improve the quality of buildings under construction in civil engineering. A case study is presented here at a vacant building site. Initially, boreholes indicated a complex geology. A dipole–dipole configuration was selected for electrical resistivity tomography (ERT) implementation and the data were processed and interpreted by applying 2D and 3D inversions. An electromagnetic survey was also carried out at a different time periods and successfully used to verify the results of the resistivity measurements. It is demonstrated that engineering geophysics is able to provide solutions for determining subsurface properties and that different prospection techniques are necessary for developing a reasonable model of the subsurface structure.

Efficient ERT measuring and inversion strategies for 3D imaging of buried antiquities

ABSTRACT The optimum processing technique (2D vs. 3D inversion) to interpret and visualize parallel and/or orthogonal two‐dimensional surface Electrical Resistivity Tomography data collected from archaeological sites is examined in this work. A simple modification of a standard resistance‐meter geophysical instrument was implemented in order to collect parallel two‐dimensional sections along the X‐, Y‐ or XY‐direction in a relatively short time, employing a pole–pole array. The sensitivity analysis showed that the distance between the parallel 2D lines must be smaller or, at the most, equal to the basic inter‐electrode spacing in order to produce reliable 3D resistivity images of the subsurface. This was confirmed by modelling and inversion of both synthetic and real data. Direct comparisons of the quasi‐3D images, resulting from a posteriori combination of the inverted 2D sections, with the full 3D inverted resistivity models indicated the superiority of the 3D inversion algorithm in the reconstruction of buried archaeological structures, even in complex archaeological sites. Due to the inherent three‐dimensionality of many archaeological targets, quasi‐3D images suffer from artefacts. The combination of a single survey‐direction with a full 3D processing and interpretation scheme is adequate to image the 3D subsurface resistivity variation in detail. Furthermore, the implementation of a quasi‐Newton Jacobian matrix update technique reduced the processing time by one‐half without any significant loss of accuracy and resolution.

A large scale geophysical survey in the archaeological site of Europos (northern Greece)

Abstract The results of a large scale exploration of an archaeological site by geophysical means are presented and discussed. The operation took place in the site where the ruins of the ancient city of Europos are buried. This site is in northern Greece. Resistivity prospecting was employed to detect the remnants of wall foundations in the place where the main urban complex of the ancient city once stood. The data were transformed in an image form depicting, thus, the spatial variation of resistivity in a manner that resembles the plane view of the ruins that could have been drawn if an excavation had taken place. This image revealed the urban plan of the latest times of the life of the city. Trial excavations verified the geophysical result. Magnetic prospecting in the same area complemented the resistivity data. The exact location of the fire hearths, kilns and remnants of collapsed roofs were spotted. Magnetic gradient measurements were taken in an area out of the main complex of the ancient city and revealed the location of several kilns. One of these locations was excavated and a pottery kiln was discovered. The resistivity prospecting in one of the graveyards of the ancient city showed anomalies which were expected and corresponded to monumental tombs. The locations of a few of them were excavated and large burial structures were revealed. Ground probing radar profiles were measured over the tombs which showed pronounced resistivity anomalies, so far unearthed. The relatively high resolving ability of the method assisted the interpretation in the sense that a few attributes were added. In the presented case, it was concluded that a particular tomb consists of two rooms and that it is roofless.

Orthogonal Equations of Multi-Spectral Satellite Imagery for the Identification of Un-Excavated Archaeological Sites

This paper aims to introduce new linear orthogonal equations for different satellite data derived from QuickBird; IKONOS; WorldView-2; GeoEye-1, ASTER; Landsat 4 TM and Landsat 7 ETM+ sensors, in order to enhance the exposure of crop marks. The latest are of significant value for the detection of buried archaeological features using remote sensing techniques. The proposed transformations, re-projects the initial VNIR bands of the satellite image, into a new 3D coordinate system where the first component is the so called “crop mark”, the second component “vegetation” and the third component “soil”. For the purpose of this study, a large ground spectral signature database has been explored and analyzed separately for each different satellite image. The narrow band reflectance has been re-calculated using the Relative Spectral Response filters of each sensor, and then a PCA analysis was carried out. Subsequently, the first three PCA components were rotated in order to enhance the detection of crop marks. Finally, all proposed transformations have been successfully evaluated in different existing archaeological sites and some interesting crop marks have been exposed.

Urban archaeological investigations using surface 3D Ground Penetrating Radar and Electrical Resistivity Tomography methods

Ongoing and extensive urbanisation, which is frequently accompanied with careless construction works, may threaten important archaeological structures that are still buried in the urban areas. Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) methods are most promising alternatives for resolving buried archaeological structures in urban territories. In this work, three case studies are presented, each of which involves an integrated geophysical survey employing the surface three-dimensional (3D) ERT and GPR techniques, in order to archaeologically characterise the investigated areas. The test field sites are located at the historical centres of two of the most populated cities of the island of Crete, in Greece. The ERT and GPR data were collected along a dense network of parallel profiles. The subsurface resistivity structure was reconstructed by processing the apparent resistivity data with a 3D inversion algorithm. The GPR sections were processed with a systematic way, applying specific filters to the data in order to enhance their information content. Finally, horizontal depth slices representing the 3D variation of the physical properties were created. The GPR and ERT images significantly contributed in reconstructing the complex subsurface properties in these urban areas. Strong GPR reflections and high-resistivity anomalies were correlated with possible archaeological structures. Subsequent excavations in specific places at both sites verified the geophysical results. The specific case studies demonstrated the applicability of ERT and GPR techniques during the design and construction stages of urban infrastructure works, indicating areas of archaeological significance and guiding archaeological excavations before construction work.

Exploring natural and anthropogenic risk for cultural heritage in Cyprus using remote sensing and GIS

Abstract On site observation is the most common way of monitoring cultural heritage sites and monuments in Cyprus. However, this procedure that includes data collection, periodical observations, and multivariate risk assessment analysis is difficult to accomplish with the traditional practices and methods since it is time consuming and expensive. Furthermore, many archaeological sites and monuments are located at inaccessible areas, far away from the main road network and urban areas. Satellite remote sensing and Geographical Information Systems (GIS) can successfully confront this problem by providing the scientists with integrated monitoring of the study areas and the unique advantage to store and manipulate a large amount of spatial and attribute data simultaneously. Actually the monitoring and identification of several natural and anthropogenic hazards in the vicinity of the cultural heritage sites in Cyprus, seems to be one of the main priorities of its governmental and municipal authorities. This study aims to integrate both satellite remote sensing techniques and GIS in a multidisciplinary approach, for monitoring anthropogenic and natural hazards with the use of archived and up-to-date multitemporal remotely sensed images in the study area, namely in areas nearby cultural heritage sites and monuments in Cyprus. In this study anthropogenic hazards include urbanisation and extended land use changes in the surroundings of archaeological sites and natural hazards concern seismicity and sea erosion.

A large-scale magnetic survey in Makrygialos (Pieria) Greece

A large-scale magnetic survey was conducted in the archaeological area of Makrygialos. The site was threatened due to the construction activities carried out in the area, as part of the national highway re-route project. Geophysical prospection contributed to the archaeological evaluation of the site, which was based mainly on the salvage excavations that took place prior to and after the geophysical survey. Magnetic prospecting was applied on a routine base, in order to cover a large area in a short period of time. Also, magnetic susceptibility was used to acquire detailed information of the stratigraphy of the ditches revealed by the excavations. The Le Borgne contrast was calculated and was used as an index of the magnitude of the magnetic anomalies. Geophysical data were processed by a number of filtering techniques, including the removal of regional trends and Hanning smoothing. Fourier transformation was applied and bandpass filtering procedure was based on the examination of the power spectrum of the data. In addition, two-dimensional inversion filtering was performed at specific parts of the data set, in an effort to rectify the significant geophysical anomalies of the site and obtain more information about their width and magnetization. The results of the geophysical survey were able to highlight a system of three curvilinear ditches, which excavation data suggested were probably dug during the Neolithic period. Various linear and geometrical anomalies, related to subsurface structures, are included among the other geophysical features encountered at the site. The geophysical prospecting techniques were able to map more than 60,000 m2 of the site, a large portion of which has now been destroyed by the construction activities for the national road. In this way, geophysical maps can be used as a valuable source of information for the future study of the site. The present case study illustrates the impact of geophysical exploration in the management of archaeological sites threatened by large-scale construction projects.

Evaluating the Potentials of Sentinel-2 for Archaeological Perspective

The potentials of the forthcoming new European Space Agency’s (ESA) satellite sensor, Sentinel-2, for archaeological studies was examined in this paper. For this reason, an extensive spectral library of crop marks, acquired through numerous spectroradiometric campaigns, which are related with buried archaeological remains, has been resampled to the spectral characteristics of Sentinel-2. In addition, other existing satellite sensors have been also evaluated (Landsat 5 Thematic Mapper (TM); Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER); IKONOS; Landsat 4 TM; Landsat 7 Enhance Thematic Mapper Plus (ETM+); QuickBird; Satellite Pour l’Observation de la Terre (SPOT); and WorldView-2). The simulated data have been compared with the optimum spectral regions for the detection of crop marks (700 nm and 800 nm). In addition, several existing vegetation indices have been also assessed for all sensors. As it was found, the spectral characteristics of Sentinel-2 are able to better distinguish crop marks compared to other existing satellite sensors. Indeed, as it was found, using a simulated Sentinel-2 image, not only known buried archaeological sites were able to be detected, but also other still unknown sites were able to be revealed.

Cultural heritage management and monitoring using remote sensing data and GIS: the case study of Paphos area, Cyprus

Cultural heritage (CH) sites are threatened from a variety of natural and anthropogenic factors. Innovative and cost effective tools for systematic monitoring of landscapes and CH sites are needed to protect them. Towards this direction, the article presents a multidisciplinary approach, based on remote sensing techniques and Geographical Information System (GIS) analysis, in order to assess the overall risk in the Paphos district (Cyprus). Paphos region has a great deal of archaeological sites and isolated monuments, which reflect the long history of the area, while some of them are also listed in the UNESCO catalogue of World Cultural Heritage sites. Several natural and anthropogenic hazards have been mapped using different remote sensing data and methodologies. All data were gathered from satellite images and satellite products. The results from each hazard were imported into a GIS environment in order to examine the overall risk assessment based on the Analytic Hierarchy Process (AHP) methodology. The results found that the methodology applied was effective enough in the understanding of the current conservation circumstances of the monuments in relation to their environment as well as predicting the future development of the present hazards.

Early Copper Age Settlements in the Körös Region of the Great Hungarian Plain

Abstract This article discusses research carried out by the Körös Regional Archaeological Project from 2000 to 2006 at Early Copper Age Tiszapolgár Culture sites on the Great Hungarian Plain. To build a model of social organization for the period, we incorporated information from regional geomorphological studies, soil chemistry analysis, archaeological surface surveys, remote sensing, and systematic excavations at Early Copper Age sites in the Körös Valley of southeastern Hungary. Previous models characterized the transition from the Neolithic period to the Copper Age as an abrupt shift from a tell-based, sedentary, agricultural lifeway to one based on mobile cattle herding. By studying the transition between these periods on multiple geographic and temporal scales, we have identified a more gradual process with widespread regional variation in cultural patterns. Similar social processes characterize the transition between chronological periods and cultural phases in other parts of the world, and we suggest that a multiscalar approach is effective for building comparative archaeological models of long-term social change.