Optimization of DC resistivity data acquisition: real-time experimental design and a new multielectrode system

With the recent introduction of multielectrode acquisition systems and twoand three-dimensional imaging software, there has been a marked increase in the use of direct-current (DC) resistivity techniques for addressing a wide variety of environmental, hydrogeological, and engineering issues. To determine the location and physical characteristics of relatively small targets distributed over wide areas, deployments of laterally extensive arrays of densely spaced electrodes for long recording periods may be required. For many academic and commercial projects, such large expenditures of effort are not plausible. We introduce the concept of real-time experimental design, in which relatively limited datasets that contain the most important subsurface information are recorded in a cost-optimized sense. Real-time experimental design, which involves a number of "data acquisition - data analysis - update survey design" cycles, requires highly flexible recording equipment. To meet this need, we have developed a distributed data acquisition system in which waveforms are digitized and partially processed at each electrode before being rapidly transmitted to a central computer for storage, further processing, display, and preliminary interpretation. The individual data acquisition unit at each electrode has a high input impedance and a large dynamic range that ensures the recording of high-quality digital data. Versatile software controls the functions of all electrodes (e.g. whether they operate as current or potential electrodes) and the waveform of the transmitted current.