Geoscience Reference
In-Depth Information
The integration of Global Positioning System (GPS) receivers with geophysical equipment is
becoming more and more common, particularly with regard to agricultural applications. GPSs
can provide accurate determinations of measurement locations while the geophysical survey is in
progress. As a result of GPS integration, marking off a well-defined grid in the field is no longer
required, thereby allowing rapid geophysical data collection over large areas, especially in regard to
horizontal soil electrical conductivity mapping with resistivity or electromagnetic induction meth-
ods. The importance of GPS to agricultural geophysics will undoubtedly continue to experience
growth in the near future; therefore, a detailed discussion on aspects related to GPS is certainly
warranted and can be found in Chapter 9.
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Depth sections and contour maps are two of the most common geophysical data analysis end prod-
ucts. Two-dimensional depth sections characterize the distribution of some geophysically measured
property beneath a measurement transect along the surface. Different geophysical methods employ
different computer processing steps to produce these depth sections. Contour maps are typically
used to show the horizontal spatial pattern of some geophysically measured property. Various
spatial interpolation algorithms are employed by the computer software used to generate these con-
tour maps. Where there is a choice, careful consideration is needed in selecting the interpolation
algorithm so as not to introduce features on the contour map that do not truly exist or to remove
features that are actually present.
Rather than focusing just on a single geophysical data set at a time, the integration of sev-
eral geophysical data sets along with other spatial information is an approach that can potentially
improve agricultural data interpretation for a particular farm site. Integration of multiple geophysi-
cal and nongeophysical spatial data sets is accomplished using a geographic information system
(GIS). A GIS is a powerful data analysis tool that is just beginning to find widespread use in agri-
cultural geophysics. Because GIS is expected to become essential to agricultural geophysics in the
future, a detailed discussion on some important GIS elements is definitely relevant and is presented
in Chapter 10.
1.4 potentIAl AGRICUltURAl USeS foR GeophySICAl MethodS
Past research indicates a wide range of potential uses for the three geophysical methods predomi-
nantly employed in agriculture (resistivity, electromagnetic induction, and ground-penetrating radar).
Table 1.1 serves to emphasize the variety of possible applications by listing just a few of the numer-
ous ways that these three geophysical methods can provide valuable information for agriculture
purposes. The resistivity and electromagnetic induction case histories in Chapter 11 and the ground-
penetrating radar case histories in Chapter 12 provide in-depth descriptions for many of the agri-
cultural geophysics applications listed in Table 1.1. However, some aspects regarding the last four
agricultural geophysics applications listed in Table 1.1 warrant further mention at this juncture.
Figure 1.1 provides two examples of GPR drainage pipe detection. Figure 1.1a and Figure 1.1b
are GPR time-slice amplitude maps. Each map represents the reflected radar amplitudes (and radar
energy) returning to the surface from a particular depth interval. Lighter shaded elements on gray-
scale GPR time-slice amplitude maps typically denote subsurface features that reflect significant
amounts of radar energy. The lighter shaded elements with linear trends found in Figure 1.1 are
indicative of buried drain lines. Shown in Figure 1.1a is the subsurface drainage pipe system in a
northwest Ohio agricultural field, and depicted in Figure 1.1b is the subsurface drainage pipe system
for a central Ohio golf course green. In addition to GPR, magnetometry methods have exhibited
some success in locating buried drainage pipes (Rogers et al., 2005, 2006). An example regarding
the application of magnetometry methods to locate subsurface drain lines at a dairy operation in
Oregon is included in Chapter 8.
