Miller, B.V., Payne, J.D., Killion III, W.F., and Adams, R.F., 2019, Geophysical surveys and geospatial data for Bob Kidd Lake, Washington County, Arkansas: U.S. Geological Survey data release, https://doi.org/10.5066/P9I4W2P0.
Summary
DC Resitivity Methodology Direct current (DC) resistivity transects were surveyed using an IRIS Syscal Pro Switch 96 instrument (IRIS Instruments, Inc., Orléans, France). Steel electrodes were hammered into the ground at a fixed distance along the profile. These were connected to the instrument using copper wires and junction boxes. The number of electrodes on each profile and their spacing is shown below: Line 1: 180 electrodes, 5 meter spacing Line 2: 48 electrodes, 2 meter spacing Line 3: 48 electrodes, 2 meter spacing Line 4: 24 electrodes, 2 meter spacing Line 5: 36 electrodes, 2 meter spacing On Line 1, the roll-along method was used to extend the line to its full extent. In this method, 48 electrodes are picked up and [...]
Summary
DC Resitivity Methodology
Direct current (DC) resistivity transects were surveyed using an IRIS Syscal Pro Switch 96 instrument (IRIS Instruments, Inc., Orléans, France). Steel electrodes were hammered into the ground at a fixed distance along the profile. These were connected to the instrument using copper wires and junction boxes. The number of electrodes on each profile and their spacing is shown below:
Line 1: 180 electrodes, 5 meter spacing
Line 2: 48 electrodes, 2 meter spacing
Line 3: 48 electrodes, 2 meter spacing
Line 4: 24 electrodes, 2 meter spacing
Line 5: 36 electrodes, 2 meter spacing
On Line 1, the roll-along method was used to extend the line to its full extent. In this method, 48 electrodes are picked up and moved to the end of the line. Then, new data is collected in this configuration. Data were collected on each line using three array types: Reciprocal Schlumberger, Dipole-Dipole, and Reverse Dipole-Dipole (additionally, a Wenner-Schlumberger array was collected along Line 2 to facilitate the interpretation of the GEM-2 data). The dataset contain data from the Reciprocal Schlumberger arrays for each line as well as the Wenner-Schlumberger for line 2. Following data collection, the data were downloaded from the IRIS Pro instrument and stored digitally for processing.
DC Resistivity Processing
Data were imported into the Workbench Electrical Resistivity Tomography Module (Aarhus Geophysical, Inc.; version 5.5.0.0) using the “Syscal” data import options. The data were then manually despiked and any negative resistivity values were removed. The data were subsequently inverted using “Aarhus 2D” inversion option. The “Smooth” Inversion setting was chosen with model converging to the L2 norm. The number of layers of the starting model was set to 20. The vertical model discretization was set to the default for each given combination of line length and electrode spacing. The starting value was set to “Auto”. The lateral and vertical constraints were set to the “Medium” settings. The Prior Constraint was set to “Unconstrained”. The inversion was set to stop at 50 iterations or when the convergence condition was satisfied.
