Figure 1.Schematic arrangements of tripotential quadrupole electrode configurations and β for surface (a), borehole-borehole (b), and surface-borehole (c) survey designs. Borehole-borehole surveys are arranged in vertical circulating (vc) and β vertical circulating mode (βvc). C = current electrode, P = potential electrode. (After Hagrey, 2008)
Figure 2.Resolution (R) and relative resolution with the comprehensive data set (rel. R) of an optimized electrode configuration data set for survey designs of surface, borehole-borehole, and surface-borehole. Note that the R borehole curve overlaps that of rel. R surface.
Figure 3.(a) Model of plant root growth simulated by an adaptive refined grid (after Wilderotter, 2001). (b) Corresponding 2D starting resistivity model with conductive (root = 20 -m)/resistive (root = 500 -m) root zone within the partially saturated soil (100 -m). Dots show the positions of 16 surface and 16 borehole electrodes.
Figure 4.Reconstructed 2D inversion models of electrical resistivity for conductive (a) and resistive (b) root zones with number of data points and root mean square errors for six quadrupole electrode configurations (rows) and three survey designs (columns). Dots show positions of surface and borehole electrodes and solid lines outline root zones. All models have error 0.5%.
Figure 5.Experiment setup and first resulting model of electrical resistivity tomography measurements on a young hibiscus plant in the laboratory: (a) two surface and four vertical electrode arrays (solid dots) placed symmetrically around the plant; (b) 3D tomograph inverted from crosshole measurements only.
and β for surface (a), borehole-borehole (b), and surface-borehole (c) survey designs. Borehole-borehole surveys are arranged in 
root = 20 
-m)/resistive (
0.5%.