Ground penetrating radar is a non-destructive geophysical method that produces a continuous cross-sectional profile or record of subsurface features, without drilling, probing, or digging. Ground penetrating radar (GPR) profiles are used for evaluating the location and depth of buried objects and to investigate the presence and continuity of natural subsurface conditions and features.
Ground penetrating radar operates by transmitting pulses of ultra high frequency radio waves (microwave electromagnetic energy) down into the ground through a transducer (also called an antenna). The transmited energy is reflected from various buried objects or distinct contacts between different earth materials. The antenna then receives the reflected waves and stores them in the digital control unit.
GPR works by sending a pulse of energy into a material and recording the time required for the return of any reflected signal. A series of pulses over a single area make up what is called a scan, or trace. Reflections are produced whenever the energy pulse enters into a material with different electrical conduction properties (dielectric permittivity) from the material it left. The strength, or amplitude, of the reflection is determined by the contrast in the dielectric constants of the two materials. This means that a pulse which moves from dry sand (diel of 5) to wet sand (diel of 30) will produce a very strong, brilliantly visible reflection, while one moving from dry sand (5) to limestone (7) will produce a weak reflection.