Geoscience Reference
In-Depth Information
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General Considerations
for Geophysical Methods
Applied to Agriculture
Barry J. Allred, M. Reza Ehsani, and Jeffrey J. Daniels
ContentS
1.1 Introduction: Geophysics Definitions, Development Chronology, Investigation Scale .......... 3
1.2 Geophysical Methods Applicable to Agriculture.................................................................... 5
1.2.1 Resistivity Methods ..................................................................................................... 5
1.2.2 Electromagnetic Induction Methods............................................................................ 5
1.2.3 Ground-Penetrating Radar Methods............................................................................ 6
1.2.4 Magnetometry Methods............................................................................................... 6
1.2.5 Self-Potential Methods................................................................................................. 6
1.2.6 Seismic Methods.......................................................................................................... 6
1.3 Aspects of Agricultural Geophysics Data Collection and Analysis ....................................... 7
1.3.1 Selecting the Proper Geophysical Method................................................................... 7
1.3.2 Investigation Depth and Feature Resolution Issues ..................................................... 7
1.3.3 Field Operations: Station Interval, Stacking, Survey Line/Grid Setup, and
Global Positioning System (GPS) Integration.............................................................. 8
1.3.4 Analysis of Geophysical Data...................................................................................... 9
1.4 Potential Agricultural Uses for Geophysical Methods ........................................................... 9
1.5 Agricultural Geophysics Outlook ......................................................................................... 13
References ........................................................................................................................................ 14
1.1 IntRodUCtIon: GeophySICS defInItIonS, developMent
ChRonoloGy, InveStIGAtIon SCAle
Geophysics can be defined several ways. In the broadest sense, geophysics is the application of
physical principles to studies of the Earth (Sheriff, 2002). This general definition of geophysics
encompasses a wide range of disciplines, such as hydrology, meteorology, physical oceanography,
seismology, tectonophysics, etc. Geophysics, as it is used in this topic, has a much more focused
definition. Specifically, geophysics is the application of physical quantity measurement techniques
to provide information on conditions or features beneath the Earth's surface. With the exception of
borehole geophysical methods and soil probes like a cone penetrometer, these techniques are gener-
ally noninvasive, with physical quantities determined from measurements made mostly at or near
the ground surface. (Note: Some large-scale airborne surveys are carried out with geophysical mea-
surements collected by airplanes and helicopters positioned well above the surface, but these types
of surveys are not within the scope of this topic.) The geophysical methods employed to obtain sub-
surface information from surface-based measurements include resistivity, electromagnetic induc-
tion, ground-penetrating radar, magnetometry, self-potential, seismic, gravity, radioactivity, nuclear
magnetic resonance, induced polarization, etc.
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