HR: 0800h
AN: NS31B-0379    [Abstracts]
TI: A Novel Design for High-Speed Imaging in Laboratory Scale Electrical Resistivity Imaging
AU: * Mitchell, V
EM: vmitchel@stanford.edu
AF: Geophysics Department, Stanford University, 397 Panama Mall, Stanford, CA 94305, United States
AU: Neice, A
EM: aneice@stanford.edu
AF: Stanford University School of Medecine, 300 Pasteur Dr, Stanford, CA 94305, United States
AU: Knight, R
EM: rknight@stanford.edu
AF: Geophysics Department, Stanford University, 397 Panama Mall, Stanford, CA 94305, United States
AB: Electrical resistivity imaging (ERI) is seeing increased use for the study of near-surface processes. The quality of an image obtained with this method, however, is often degraded as a result of the spatial variability of the measurement resolution. Improving the accuracy of images obtained through ERI requires a more complete understanding of the information contained in measurements, especially with respect to the resolution and sampled volume. To this end we have developed a high-speed resistivity imaging system to study dynamic hydrologic processes at the laboratory scale. Drawing on technologies developed independently for medical and geophysical applications, we have created a system that incorporates the high sampling rates of medical devices with the flexible spatial and temporal sampling configuration which can be achieved with current geophysical instruments. The 48-electrode system can be programmed by the user to collect voltage data using a number of 3- or 4-electrode arrays, switching between arrays at frequencies on the order of kilohertz. A number of voltage measurements may be collected using many different electrode spacings in seconds, rather than minutes as required by instruments currently used for geophysical applications. Consequently, the system is able to gather a suite of measurements in a sufficiently short time so that imaged processes may be assumed to be static during data collection. This simplifies inversion of the data and minimizes temporal smearing. The noise of the data acquisition system is characterized using a Hele-Shaw cell filled with a saline solution to create a two- dimensional medium with homogeneous resistivity structure. A number of salinities and switching rates are tested to identify any resistivity-dependence and frequency-dependence in the measurement noise. With comprehensive characterization of the noise distribution, the system can be used to image hydrologic processes accurately at the laboratory scale, using a high sampling rate to avoid temporal smearing and realistic electrode arrays to quantify the resolution and support volume of resistivity measurements.
DE: 0594 Instruments and techniques
DE: 1835 Hydrogeophysics
DE: 1895 Instruments and techniques: monitoring
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting