Two‐dimensional and three‐dimensional resistivity imaging in archaeological site investigation

Abstract

In this work, the application and the effectiveness of two-and three-dimensional non-linear inversion algorithms in processing and interpretation of electrical resistivity tomography (ERT) data collected from archaeological areas are investigated in the framework of a new field technique for gathering three-dimensional pole^pole tomographic data in a relatively small amount of time using standard archaeological prospection equipment. The inversion routine, for both the two-dimensional and the three-dimensional case, is based on a smoothness constrained algorithm and the forward modelling calculations are carried out using two-dimensional and three-dimensional finite element solvers respectively.Resultsofcombined two-dimensionalinversions (quasi-three-dimensional) are compared with the fullthree-dimensionalinversions.Comparisonsare carried out inrelationto the optimum survey direction of gathering the tomographic data using the pole^pole array for synthetic data arising from three-dimensional structures commonly encountered in archaeological sites.The response of the algorithms in the presence of noisy data was also tested. The algorithms were also used in the processing of real data collected from the archaeological sites of Sikyon and Europosin Greece.The results from the synthetic and therealdata indicate the superiorityofthe three-dimensionalinversion algorithms in processing tomographic data. The reconstructed three-dimensional images do not suffer from the artefacts encountered in the quasi-three-dimensional approach, owing to the three-dimensional nature of the archaeological features. Most importantly, both synthetic and real data results indicate that a single survey direction is adequate to produce a valid three-dimensional subsurface image when full three-dimensional inversion is used in contrast to the quasi-threedimensional approach, which would require that two survey directions be used to obtain satisfactory results

Ground penetrating radar and electrical resistivity tomography for locating buried building foundations: A case study in the city centre of Thessaloniki, Greece

“…Given the three-dimensional nature of the problem studied, we decided to acquire dense survey lines, to allow full 3D processing of the data (Papadopoulos et al, 2006). We measured a dense grid of parallel -and a few perpendicular -2D ERT lines.…”

“…Note that this approach is much more time-consuming compared to the 2D one and can be applied only in areas where several parallel ERT lines (i.e., > 4) are collected. Although the data acquisition is a set of 2D measuring sections, it has been shown that in this case fully 3D imaging is possible when inversion is performed by fully 3D algorithms (Papadopoulos et al, 2006;. Also, the data have to be collected along dense parallel traverses, which ideally should be spaced at intervals equal to the spacing of the electrodes along the traverse.…”

2D and 3D imaging of the metamorphic carbonates at Omalos plateau/polje, Crete, Greece by employing independent and joint inversion on resistivity and seismic data

“…This inversion technique employed finite elements using 2256 cells for the calculation of the apparent resistivity data (forward problem) and the blocky (robust) inversion (Claerbout & Muir, 1973). This gives reasonably accurate images of three-dimensional structures, bigger than 5x5x10 m, enabling the 3D imaging of the subsurface using costeffective 2D electric tomography techniques (Dahlin & Loke, 1997;Papadopoulos et al, 2006;Tsokas et al, 2008;Chang et al, 2011). The depth slices (Fig.…”

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

“…This data set can be inverted for the true subsurface resistivity by using 2D or 3D inversion algorithms and the resulting estimated models can be interpreted accordingly (Papadopoulos et al 2006). Electrical resistivity tomography is a method adapted to the recognition and study of 2D structures perpendicular to the profile and to the identification of the various geological layers, including the surface cover, but is more expensive and time consuming than the electromagnetic survey.…”