What ground penetrating radar does is transmits very high rates of radar energy (pulses) in to the ground looking at soil disturbances. As the radar pulses travel through the ground the energy bounces off buried matter and is detected by a receiving antenna. The ability to see a target (hyperbolas) on the computer screen depends on the dielectric values of the target's material and the material that the radar is traveling through prior to hitting the target. Finding a target like buried piping system is not a great issue because there will always be visible contrast between soil conditions and target material. The best way to detect buried pipes would be to set up a grid pattern and scan each section length wise you can track the direction on the piping system.
Bob Perry
TOPOGRAPHIX.com

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I am the website owner or are you referring to this reply posting website?