Appendix 1 : how ground penetrating radar (GPR) works

Abstract

Ground penetrating radar (or GPR) uses the transmission and reflection of radio waves (typically 25 to 2 GHz) in imaging the subsurface. Radar waves, introduced in the ground, may reflect back to surface when they intersect objects or surfaces of varying dielectric permittivity. Thus a GPR system requires a source antenna and receiving antenna (built to measure the same frequency). *Note that the plural of electrical devices is antennas; antennae are exclusively for animals such as insects. The transmitting antenna generates a pulse of radiowaves that the receiver detects at a set time interval: the longer the time interval, (potentially) the deeper the waves will have travelled into the ground (or to a nearby surface object) and back again. When the ground has a slow radarwave velocity, so a buried object may appear deeper than in ground with a fast transmissive velocity. [excerpt]