GPR emits electromagnetic (EM) waves to the subsurface and calculates the time these waves need to travel through the various subsurface material...

GPR emits electromagnetic (EM) waves to the subsurface and calculates the time these waves need to travel through the various subsurface material and get back to the GPR receiver. This two-way travel-time, along with a few other parameters such as the dielectric, provide the user an estimate of the target depth.