Ground Penetrating Radar (GPR)
GPR uses electromagnetic waves which are reflected at interfaces where the electric or magnetic properties of the penetrated material change: Media with different dielectric constants (permittivity) show as a pattern in the radargram. Higher frequencies allow for better resolution, but the signal strength decreases faster with depth. In moist clay rich soil the penetration of the radar waves diminishes rapidly; measuring through muck and clay is principally a problem, even in dry conditions. Good results are achieved in dry sandy soils or solid rock.
We use a Sensor & Software pulse EKKO pro with 50 and 100 MHz antennae.
The advantages of GPR can be brought to bear primarily in technological applications: In dry solid construction materials of buildings, bridges, dams, etc. disturbances can be easily and precisely detected.
In the right circumstances GPR is a possible method for placer exploration. But because moisture preserving layers such as humus, muck and clay absorb the electromagnetic waves, the method, in many places in northwest America, does not deliver the necessary depth penetration for placer prospecting. In discontinuous permafrost conditions the radargrams show pseudo-topography at layer interfaces.