Zonge Electrical Tomography Acquisition System

For a number of years, Zonge International has been involved in the development of instruments for electrical resistance tomography (ERT) in connection with ongoing research and development at the Lawrence Livermore National Laboratory, a facility funded by the U.S. Department of Energy. ERT is being used to generate resistivity images of the 'plane' defined by the space between two boreholes or other electrode strings. ERT is presently being applied to monitor leakage at hazardous waste sites, to monitor dynamic fluid injection processes that are often involved in waste site remediation. Other applications for ERT technology exist and are simply waiting for the availability of equipment and software that can economically acquire the necessary resistivity data required and the software required for its interpretation.

ERT involves the acquisition of hundreds, even thousands of 4-electrode resistivity measurements that are possible between multiple strings of electrodes. For example, given two strings of 15 equally-spaced electrodes (30 electrodes total), there are 632 different dipole-dipole measurements that can be made (including all reciprocal measurements) involving transmitter and receiver dipoles with a fixed length of 2 electrode spacings. The dense data provide the basis for solving sophisticated inverse computer models of the conductivity distribution in the ground. When both resistivity and IP are measured, the resulting data set relates to the complex impedance of the earth and the term EIT (Electrical Impedance Tomography) is sometimes used to describe the technique.

Obviously, there are too many measurements to be acquired manually. To efficiently measure all the desired transmitter-receiver electrode combinations requires a computerized acquisition system that automatically switches both transmitter and receiver electrodes and has multi-channel measurement capabilities. The Zonge ERT/EIT acquisition system has unique capabilities for the efficient acquisition of ERT or EIT data sets. With the Zonge ERT/EIT system, acquisition of the dense data sets is now economically feasible. Such data sets are required to generate conductivity images using sophisticated inversion software. These capabilities greatly improve the usefulness of the venerable resistivity measurement for problems wherein the resistivity method is traditionally applied. Moreover, the capability of ERT/EIT to generate 'images' of conductivity distribution greatly expands the applicability of the electrical resistivity method to many problems in engineering and hazardous waste site characterization and monitoring, and in geophysical and groundwater exploration as well.