Recognized as one of the most powerful remote sensing geophysical survey instruments available today, ground penetrating radar (GPR) is a safe, non-invasive geophysical investigation method for "looking" underground to image subsurface features. Operating GPR equipment and interpreting its results requires in-depth training and field experience.
GPR works by sending a radio signal or series of signals into ground. The returning signals provide information about changing ground characteristic with depth.
GPR works best when there are well defined differences in the electromagnetic properties of materials being surveyed: gradual change is not easy to detect. This makes GPR a very good detector of pipes.
GPR is not without its limitations. GPR radio wave signals are absorbed by the ground with some soils (clay, saline) greatly limiting exploration depth. GPR effectiveness is thus site specific and varies greatly from place to place. GPR also responds to changes in soil type, density, water content, as well as many other buried objects; making unique identification of the desired target difficult. (i.e. you can not see the individual tree in the middle of the forest).
GPR survey will not work in certain clay soils when they are waterlogged, nor will they work in saline water. The reason for this is that in conditions equivalent to a heavily ionized solution the signal produces a current in the ground and no signal is returned. This loss of signal depends upon the mineral content of the soil.