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

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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.

In this work a study of the effect of surface topographical variations on several dc resistivity arrays is presented. A 2.5-D finite‐element modeling scheme is used to examine the performance of several arrays over buried features that exist below a range of different topographical terrain contexts, such as valleys, hills, and steep slopes. A mesh‐generating algorithm allows a realistic representation of terrain topography. The results confirm that topographical variations can have a significant impact on the field resistivity data values for all resistivity arrays. Further, topographical variations can be treated flexibly using a realistic resistivity forward modeling process. Thus, topographic effects, to the degree they can be modeled, are predictable and should be taken into account when designing surveys and interpreting data.

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