ABSTRACT
Geophysical methods measure changes in some physical property (i.e., density, seismic velocity, electrical conductivity, electrical resistivity [ER], magnetic susceptibility, dielectric permittivity) of the subsurface without direct access to the sampled volume (Daniels et al., 2003; Allred et al., 2008). Over the last three decades, the use of geophysical methods has signicantly increased in soil investigations. ¤e geophysical methods most commonly used in these pursuits include electromagnetic induction (EMI), groundpenetrating radar (GPR), transient EMI, galvanic resistivity, and magnetics. ¤ese methods are used to infer and better understand the spatial variability of soils and soil properties, and to guide observations and sampling. Selection of the most suitable geophysical method oen requires an understanding of the soil properties that in¥uence the method’s response, and whether, and to what extent, a selected soil property a¦ects the measured physical property (Allred et al., 2008). Whereas surface geophysical methods allow more continuous coverage than traditional approaches, they are limited in their capacity to resolve and characterize many pedologic features. Recent improvements in instrumentation and the integration of geophysical methods with other technologies (global positioning systems [GPS], data processing soware, and surface mapping programs; e.g., geographic information systems [GIS], Geoso, and Surfer) have fostered the expanded use of geophysical methods in soil investigations. ¤e impetus has been the needs to improve quality control, provide more comprehensive coverage, and increase the e¬ciency of eld operations. In agriculture, the three most commonly used geophysical methods are EMI, GPR, and Electrical resistivity (Allred et al., 2008). ¤is chapter will focus on two of these geophysical methods: GPR and EMI. ¤e initial uses, expansion, and present-day applications of
GPR and EMI in agriculture have been summarized by Collins (2008) and Corwin (2008), respectively. As numbers of applications have become diverse and numerous, with a considerable amount of literature written on the uses of these geophysical methods in soil science, it is impossible for this brief discussion to cover all of these applications and papers.
