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.

3D Inversion of Automated Resistivity Profiling (ARP) Data

“…In special cases where a more quantitative interpretation is necessary, the 3D resistivity inversion of the data can provide additional information about the burial depth and the depth extent of buried relics (Papadopoulos et al, 2007). Th e resistivity inversion scheme starts by lineariz-…”

Geoelectrical imaging in the interpretation of geological conditions affecting quarry operations

“…The acquisition strategy of combining 2D sections can be considered to be a roll-along procedure for 3D surveying. This measuring strategy allowed a 3D inversion of the data, which gives increased detail and accuracy of the resulting resistivity model when compared with 2D inversion (Dahlin et al 2007;Papadopoulos et al 2007). …”

“…The resistivities are adjusted iteratively until an acceptable agreement between the input data and the model responses is reached (Dahlin 2001). However, large variations in the physically defined parameters may result in small variations in the observed data, hence damping and smoothness constraints are often included in the software to stabilize the process (Papadopoulos et al 2007). In this study, the standard software values for damping and smoothness were used.…”

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

“…Further, the combination of geophysical methods offers high resolution, detecting features in the order of a few tens of centimetres depth and/or thickness to several metres. Resistivity methods, and more specifically electrical resistivity tomography (ERT), (Tsokas et al, 1994;Diamanti et al, 2005, Papadopoulos et al, 2007, Tsokas et al, 2008a, Tsourlos and Tsokas, 2011 and ground penetrating radar (GPR) (Savvaidis et al, 1999;Leucci, 2002;Piro et al, 2003;Linford, 2004;Tsokas et al, 2007) are two of the most popular methods for doing so.…”