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Lawrence Livermore National Laboratory, Livermore, California, U.S.
Lancaster University, U.K.
Multi-phase Technologies, LLC, Sparks, Nevada, U.S.
Corresponding author: daily1@llnl.gov
Editor's note: This paper is a condensation of a review titled "Electrical resistance tomography—Theory and practice," to be published in Near Surface Geophysics, vol. 2, D. Butler, ed., by SEG in 2004. See page 472 for a case study on this topic.
| The first 20% of the full text of this article appears below. |
Electrical resistance tomography (ERT) is a method that calculates the subsurface distribution of electrical resistivity from a large number of resistance measurements made from electrodes. For in-situ applications, ERT uses electrodes on the ground surface or in boreholes. It is a relatively new imaging tool in geophysics. The basic concept was first described by Lytle and Dines as a marriage of traditional electrical probing (introduced by the Schlumberger brothers) and the new data inversion methods of tomography. Development of both the theory and practice of ERT was confined mostly to the late 1980s and the 1990s. Tomographic inversion added important new capabilities as it was more general, accurate, and rigorous at spatial imaging of geophysical electrical resistance data than earlier pseudosection or curve fitting methods.
An early application of geophysical ERT was to image laboratory core samples under test but practical field scale use of ERT was delayed by the lack of suitable measurement and test equipment. ERT requires the same four electrode resistance measurement used by the Schlumberger brothers (two electrodes to inject current and two other electrodes to measure the resulting potential); however, tomography requires addressing tens or hundreds of electrodes and making hundreds or thousands of such measurements in a timely fashion. Clearly, the available manual measurement systems that were designed for one, or perhaps a few measurements at a time, were not practical for ERT. High-speed, automated systems were needed.
The first system for practical application of geophysical ERT was constructed at Lawrence Livermore National Laboratory by two of the authors (Daily and Ramirez) in 1989. This system combined a commercial geophysical resistivity instrument (capable of producing the switched dc signal and making the synchronous voltage measurement), a commercial multiplexer capable of connecting the resistivity instrument to 20 electrodes and a computer to control the process
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