Ground penetrating radar (GPR) is now a well-accepted geophysical technique. The method uses radio waves to probe “the ground” which means any low loss dielectric material. In its earliest inception, GPR was primarily applied to natural geologic materials. Now GPR is equally well applied to a host of other media such as wood, concrete, and asphalt. The existence of numerous lossy dielectric material environments combined with the broad radio frequency spectrum leads to a wide range of GPR applications. The same methodology can be applied to glaciology and to nondestructive testing of concrete structures; the spatial scale of applications varies from kilometers to centimeters.

The most common form of GPR measurements deploys a transmitter and a receiver in a fixed geometry, which are moved over the surface to detect reflections from subsurface features. In some applications, transillumination of the volume under investigation is more useful. Both concepts are depicted in Figure 1.1. An example of GPR response is shown in Figure 1.2. Use of radio waves to sound the earth was contemplated for decades before results were obtained in the 1950s (El Said, 1956; Waite and Schmidt, 1961). Waite’s demonstration of ice sheet sounding with aircraft radar altimeters leads to radio echo sounding in many locations around the world. From this start, there was a gradual transition of the concepts to sounding soils and rocks, which began in the 1960s, and has continued ever since.