Dielectric permittivity is the capacity of a material to polarize under the influence of an electric field. Thus, in most subsurface environments, the contrast in dielectric permittivity (ε) is the primary factor that controls GPR signal return. However, under certain conditions (e.g., in the presence of magnetite), magnetic permeability can strongly influence radar attenuation and velocity, and such effects can be considered (Van Dam and others, 2013). Furthermore, the magnetic permeability is often not high enough to impact the interpretation of GPR data and can be considered negligible. While wave impedance can be depicted as a relation between electrical conductivity, dielectric permittivity, and magnetic permeability, conductivity does not significantly influence reflection. Thus, if a portion of energy is reflected to the surface, the remaining part of the wave continues traveling through the subsurface and may reach another reflector or dissipate completely. Radar waves respond to these contrasts according to Snell’s law and Fresnel’s equations, which describe how EM waves are refracted, reflected, and transmitted. Radar reflection occurs at interfaces with sufficient wave impedance contrast, and the amplitude of the reflected signal is dependent on the contrast magnitude. The receiver antenna measures the strength (i.e., amplitude) of the reflections off subsurface features and time required to detect them. The portion of the transmitted wave field that penetrates and propagates through the subsurface is the radar (i.e., Radio Detection And Ranging) signal used to image the subsurface. GPR uses high-frequency pulsed radio waves that are generated by and spherically spread out from a transmitter antenna. The ground-penetrating radar method relies on the principles of electromagnetic theory. The progression of the survey is represented by dashed lines. All subsurface anomalies, such as the draining pipe, are observed by the GPR. Reflected waves penetrating the subsurface travel at different velocities based on the dielectric permittivity (ε) of the media in which they encounter.

GPR is a popular method owing to its rapid data collection, high spatial resolution (e.g., sub-meter), and because qualitative/semi-quantitative interpretations are possible in real time during collection.

With such configurations, data are gathered at or near walking speeds, which allows for the high-resolution imaging of near-subsurface interfacial geometry. However, the most common deployment includes a transmitter and receiver tied together at a fixed (or common) offset. The possible configurations and applications of GPR are numerous. The GPR method is ideal for subsurface investigations requiring an understanding of geologic structure or the location of discrete objects. The result of a GPR survey resembles a cross-section, which can depict the subsurface electrical structure and/or reveal features of interest. This information can be used to determine the depth to- and geometry and magnitude of subsurface reflectors.

The amplitude variations and wave velocity-dependent travel time of the returning signal are measured and recorded by the GPR receiver. If a wave pulse encounters a material interface of sufficiently different electromagnetic properties, some of the energy is reflected back while the remainder continues to propagate. GPR capitalizes on the effects that the electrical properties of matter (i.e., dielectric permittivity, electrical conductivity, and magnetic permeability) have on electromagnetic (EM) energy propagation. Ground penetrating radar (GPR) is an electromagnetic geophysical method that transmits radio wave pulses at select center frequencies into the ground to study the subsurface.

Ground penetrating radar price