The ERT inversion process involves solving both the forward and inverse problems. The solution to the forward problem uses the finite element method to compute the potential electrical response in the soil due to the current source. The reverse problem is solved by an iterative inversion routine to approximate the resistivity distribution. By interconnecting a network of boreholes, a 3-D representation of the area being investigated can be developed. D.C. electric currents that are injected into the formation to measure electrical resistivity.
Voltage used depends primarily on the electrical properties of the formation.
The outputs of the data collection process are measurements of resistance. The data acquisition rate is sufficiently rapid for detailed measurement of large subsurface regions in reasonable amounts of time. For example, at the Savannah River Project, one cross-borehole data set could be obtained in approximately one hour. The data acquisition system is computer-controlled and can be operated by personnel with minimal training. Operation requires a technician to interact with the data collection system on a periodic basis to start the automatic program that performs data collection and to connect electrodes in other boreholes to the acquisition systems.