Ground penetrating radar (GPR) data are acquired by reflecting pulses of radar energy produced on a surface antenna, which generates waves of various wavelengths that propagate outward. They spread into the ground in a cone as the waves propagate downward. As these waves move in the ground, they can be reflected from buried objects, features, or bedding surfaces.
The reflected waves then travel back to the ground surface and are detected and recorded at a receiving antenna that is paired with the transmitting antenna. The two-way travel times of the waves into the ground, to the reflection surface and back to the receiving antenna, are recorded in nanoseconds (ns). As the radar waves propagate through various materials in the ground, their velocity changes depending on the physical and chemical proprieties of the material through which they are travelling. A reflected wave is generated when waves’ propagating velocity changes at contacts between different materials in the ground radar.
Some reflected waves will then travel back to the ground surface while the remaining energy continues to propagate deeper and can be reflected again from additional interfaces, until all the energy finally dissipates with depth. Only the reflected energy that travels back to the surface antenna is recorded and visible for interpretation. If buried surfaces that reflect energy are orientated in such a way that the reflected waves move away from the surface antenna, that energy will not be recorded, making those interfaces effectively invisible using GPR method.