Geoscience Reference
In-Depth Information
from the ground surface reflection coefficient in a straightforward manner. Theoretically based
site-specific calibrated equations or empirically derived relationships are used in the final step to
calculate θ values from soil ε r values. The empirical relationship most commonly used to calculate
θ from ε r for soils was developed by Topp et al. (1980) and is given by:
2
3
θ
=− +
0 053
.
0 0292
.
ε
0 00055
.
ε
+
0 0000043
.
ε
r
(1.1)
r
r
Additional information on the application of GPR to soil volumetric water content determina-
tion can be found in three of the Chapter 12 case studies.
1.5 AGRICUltURAl GeophySICS oUtlook
New developments in the overall discipline of geophysics are ongoing, with innovative methods,
equipment, and field procedures continuing to be introduced. The same is particularly true for
agricultural geophysics. Many concepts being tested and initiated at present will eventually become
commonplace for agricultural geophysics. In this regard, the following is a list summarizing the
probable future trends (some previously mentioned) for agricultural geophysics.
1. New agricultural applications will continue to be discovered for the geophysical methods
already used in agriculture (resistivity, electromagnetic induction, and GPR).
2. Geophysical methods not traditionally employed in the past for agricultural purposes will
find significant use in the future. The geophysical methods likely to make inroads into
agriculture include magnetometry, self-potential, and seismic. Agricultural opportunities
for other geophysical methods, such as nuclear magnetic resonance, induced polarization,
and seismoelectric, may also exist.
3. The incorporation of GPS receivers will become the norm, especially with regard to real-
time kinematic (RTK) GPS, which will allow geophysical measurement positions to be
determined with horizontal and vertical accuracies of a few centimeters or less. Guid-
ance devices, video display tracking systems, or even simple on-the-go guesstimates of
the spacing distance between transects, when used with an accurate GPS, can provide the
capability of efficiently conducting geophysical surveys over large agricultural field areas
without the need to mark out a well-defined grid at the ground surface. For some geophysi-
cal methods, the computer processing procedures used for horizontal mapping of measure-
ments may require some modification for input of data collected along a set of transects
with somewhat irregular orientations and spacing distances.
4. Geophysical surveying with more than one sensor will become a standard approach
because of the variety of field information required to make correct agricultural manage-
ment decisions. Multisensor systems based on a single geophysical technique have already
been produced, and these systems are certainly beneficial to agriculture. Examples include
GPR systems having more than one transmitter and receiver antenna pair (the individual
transmitter and receiver antenna pairs can have the same frequency or different frequen-
cies), or continuously pulled resistivity electrode arrangements containing more than one
four-electrode array. However, multisensor systems based on more than one geophysical
technique still need to be developed for agricultural purposes, something likely to happen
in the near future. For reference, the physical properties responded to by the different geo-
physical methods are reviewed in Table 1.2.
5. Multiple geophysical data sets integrated and analyzed together along with other geospa-
tial information can provide agricultural insight not available when analyzing each geo-
physical data set separately. Geostatistical analysis techniques can be especially useful in
this regard. GISs are particularly well adapted for integration and geostatistical analysis of
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