New prototype for 4D self-potential tomography in near-surface geophysical exploration

We describe the design and the development of a new prototype to obtain Self-Potential (SP) tomographic images (2D, 3D and 4D) of subsoil. The method of SP is a passive geophysical prospecting method. the data are generally measured on the earth surface as potential drops across a passive dipole, normally consisting of a pair of grounded electrodes, moving along a selected direction. Starting from the measure of the natural electric field along selected profiles and\or maps, we evaluate the probability to identify in subsoil positive and\or negative charge accumulation zones. The prototype has been implemented assembling some hardware components of National Instruments and developing ad hoc a software in C++ and VB language. The system allows to measure the SP voltage differences between electrodes regularly distributed along selected profiles and\or maps (maximum 128 channels). In real time the software produces a high resolution tomographic image representing the probability to find electrical sources in subsoil. The main applications of this prototype regard the near surface geophysical exploration in areas characterised by high hydrogeological hazard. In particular the system is able to depict the groundwater circulation system in landslide body, to describe the spatial and temporal dynamics of pollutant diffusion processes in aquifers and to localise seepage phenomena in dam embankment.