Geoscience Reference
In-Depth Information
fIGURe 2.3
Veris 3100 mobile electrical resistivity equipment. (From Corwin, D.L., and Lesch, S.M.,
Comput. Electron. Agric.
, 46, 11-43, 2005a. With permission.
measuring EC
a
using the principles of ER (Figure 2.3). In the case of EMI, the EMI conductivity
meter is carried on a sled or nonmetallic cart pulled by a pickup, ATV, or four-wheel-drive spray
rig (Cannon et al., 1994; Carter et al., 1993; Corwin and Lesch, 2005a; Freeland et al., 2002; Jaynes
et al., 1993; Kitchen et al., 1996; Rhoades, 1992, 1993). Both mobile ER and EMI platforms permit
the logging of continuous EC
a
measurements with associated GPS locations at time intervals of
just a few seconds between readings, which results in readings every few meters. The mobile EMI
platform permits simultaneous EC
a
measurements in both the horizontal (EM
h
) and vertical (EM
v
)
dipole configurations, and the mobile ER platform (i.e., Veris 3100) permits simultaneous measure-
ments of EC
a
at 0 to 30 and 0 to 90 cm depths. No commercial mobile system has been developed
for EMI, but several fabricated mobile EMI rigs have been developed (e.g., see Figure 2.4).
To establish where soil sample sites are to be located based on the spatial EC
a
data, the third
essential component of EC
a
-directed sampling is needed (i.e., statistical sample design). Currently,
two EC
a
-directed soil sampling designs are used: (1) design-based sampling and (2) model-based
fIGURe 2.4
Mobile dual-dipole electromagnetic induction equipment developed at the United States Salin-
ity Laboratory. (From Corwin, D.L., and Lesch, S.M.,
Comput. Electron. Agric.
, 46, 11-43, 2005a. With
permission.)
