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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This work explores the applicability and effectiveness of electrical resistivity tomography in mapping archaeological relics in the shallow marine environment. The approach consists of a methodology based on numerical simulation models validated with comparison to field data. Numerical modelling includes the testing of different electrode arrays suitable for multi-channel resistivity instruments (dipole-dipole, pole-dipole, and gradient). The electrodes are placed at fixed positions either floating on the sea surface or submerged at the bottom of the sea. Additional tests are made concerning the resolving capabilities of electrical resistivity tomography with various seawater depths and target characteristics (dimensions and burial depth of the targets). Although valid a priori information, in terms of water resistivity and thickness, can be useful for constraining the inversion, it should be used judiciously to prevent erroneous information leading to misleading results. Finally, an application of the method at a field site is presented not only for verifying the theoretical results but also at the same time for proposing techniques to overcome problems that can occur due to the special environment. Numerical and field electrical resistivity tomography results indicated the utility of the method in reconstructing off-shore cultural features, demonstrating at the same time its applicability to be integrated in wider archaeological projects.In contrast to the previous applications, the use of electrical resistivity method is uncommon in submarine archaeology, and only limited studies have been presented (Passaro 2010). ERT data acquisition is accomplished through a fixed cable that can float on the water surface or can be submerged in the sea bottom. These marine surveys can be undertaken with standard resistivity meters. The main challenge for mapping the subsurface stratigraphy in marine environments is the highly conductive nature of the seawater in comparison with the resistive sediments (Lagabrielle 1983). However, there are some issues that need to be solved concerning the installation of the electrodes and the most appropriate modelling and inversion approaches to cope with the special conditions that are found in such environments (Loke and Lane 2004).This study investigates the efficiency of ERT for mapping archaeological relics buried beneath the sediment-water interface in shallow marine environments. In order to undertake a thorough study of an archaeological survey in this environment, extensive testing was performed with numerical modelling and synthetic data. Initially, different electrode arrays were tested in

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