A method to collect clear profile with Ground Penetrating Radar in tunnel

At present, we are using commercial ground penetrating radar (GPR) to inspect tunnel walls, conduct an underground geological structure assessment and anticipate geology behind the tunnel face. A variety of metal objects, include portal frame, forklift, and excavator, can cause back reflection in the GPR profile during the test in the tunnel. Typically end users of GPR are unable to appropriately interpret the GPR profile because they are unware of what is actually coming from back reflection in the air and projection into the ground penetrating radar profile or from subsurface. They really need some method to identify real reflection signals from underground sources.

The GPR antenna transmits electromagnetic (EM) waves that can travel all space, including the air, the interface between the ground and the air, and the subsurface. During EM travel in the air, there is some back reflection from the air object to be recorded in the GPR profile during data collection in the field. We need to measure and recognize and elimate this back reflection interference noise. We have made electromagnetic waves absorbent block configuration for the GPR antenna that can complete cover the GPR antenna. We have done the comparative experiments tests with and without electromagnetic waves absorbent block have been conducted in the field, the results show that, without this block, GPR profile recorded many back reflection from the air objects, while the GPR antenna with covering electromagnetic waves absorbent block can only record the refection from surbsurface during data collection in the field, and it is clear GPR profile. This allows the GPR end user direct interpret the GPR profile only with reflection from surbsurface as it may completely eliminate back reflection from the air object.