Three-Dimensional Electrical Resistivity Tomography Schemes Optimized for Imaging Wall Foundations

This paper describes the application of three-dimensional electrical resistivity tomography (ERT) in urban environments to detect wall foundations or similar structures. In this study, a specific measurement strategy based on optimized 3D measurement arrays with surface electrodes is proposed and tested. As this type of survey can be used for archaeological prospection, a special design was chosen to make the survey as non-invasive as possible. The 3D ERT measurement scheme therefore used layouts that placed electrode lines on each side of the wall. Using an optimization method based on the Jacobian matrix, only the optimal cross-line and in-line measurements were selected. The proposed scheme was tested using synthetic models and was also applied to the investigation of the foundations at two sites of the Byzantine walls of Thessaloniki, Northern Greece, near the Cassandrian Gate. Additional 2D ERTs were performed on each wall segment intersecting the wall perpendicularly to test the results of the 3D ERTs.

The presented results of the synthetic data support the effectiveness of the measurement scheme and at the same time provide important information about the maximum depth of investigation and about the influence of the shape of the structure, which must be considered as a priori information in the inversion process. The selected sections of the 3D inversion of the field data compare well with the respective 2D ERT results. Overall, the proposed 3D ERT measuring scheme has proven to be an effective non-destructive prospecting method.