Considerations on the electrode spacing to electrode diameter ratio in electrical resistivity tomography (ERT): an operational approach

To develop small-scale, shallow, and high-resolution electrical resistivity surveys (e.g., for archaeological or agricultural purposes) the available literature highlights few requirements in terms of distance between two adjacent electrodes or electrode’s length embedded in the soil. Nevertheless, there are no studies about the influence of the electrode’s diameter and/or the electrode’s diameter to electrode spacing ratio. Thus, this work proposes to investigate this ratio in relatively small-scale surveys (electrode spacing from 10 cm to 100 cm) to define an operational approach. The analysis has been conducted comparing the apparent resistivity data acquired by means of electrodes different in terms of diameter and materials. The apparent resistivity was chosen to avoid the introduction of further errors/approximations caused by the inversion procedure. Overall, six different types of electrodes have been employed and tested. The results of the data analysis emphasize the necessity of take into account the electrode diameter to electrode spacing ratio in the case of small-case Electrical Resistivity Tomography (ERT) surveys.