HR: 11:30h
AN: NS12A-05    [Abstracts]
TI: A Pitfall in the Design of 3D Surface Resistivity Arrays
AU: * Nyquist, J E
EM: nyq@temple.edu
AF: Department of Geology Temple University, 1901 N 13th Street, Philadelphia, PA 19122 United States
AU: Roth, M J
EM: rothm@lafayette.edu
AF: Department of Civil and Environmental Engineering Lafayette College, 319 Acopian Engineering Ctr., Easton, PA 18042 United States
AB: Multielectrode arrays, computer-controlled data acquisition, and commercially available resistivity inversion software have increased interest in 3D resistivity imaging. Recent research has demonstrated the advantages of using 3D inversion in areas where off-line heterogeneities would otherwise distort 2D results. For convenience in the field, multielectrode arrays used to collect 3D resistivity data are typically laid out on a Cartesian grid with potential measurements acquired using electrode pairs oriented along the X and Y axes. The current flow away from a given injection electrode, however, has radial symmetry in the case of a homogeneous, isotropic half-space, and near-radial symmetry otherwise, unless the ground is extremely heterogeneous or anisotropic. Consequently, many of the voltage measurements made using standard electrode combinations are tangential or nearly-tangential to the voltage equipotentials, resulting in the worst possible signal to noise ratio. Using data collected in karst terrain near Easton, PA, we compare results from a standard pole-dipole measurement sequence with measurements made using the same pattern of electrodes, but choosing potential electrode pairs oriented along lines radiating from the injection electrode. The remarkable improvement in data quality illustrates the importance of considering the potential gradient when designing resistivity data collection schemes.
DE: 0925 Magnetic and electrical methods
DE: 0994 Instruments and techniques
SC: Near-Surface Geophysics [NS]
MN: 2005 Joint Assembly