Past research indicates a wide range of potential uses for the three geophysical methods predominantly 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 numerous 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 agricultural 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 grayscale 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.
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