Tri-band ground penetrating radar for subsurface structural condition assessments and utility mapping

This paper describes the operating principles and use of an impulse ground penetrating radar (GPR) system that operates with three center frequency bands to enable more agile sensing of structural conditions and utility mapping. The operation of a GPR is typically a tradeoff between low-frequency waves that penetrate well, but lack good spatial resolution with high-frequency waves that do not penetrate well but have better spatial resolution. A complication is that many GPRs use short-duration impulse-shaped signals with mixed time and frequency content. The electronic generation of impulse signals is hardware dependent. Most are capable of producing only a single type of electromagnetic wave with fixed frequency content. The result is limited sensing capability. Many structures and subsurface conditions are unpredictable and better sensed with a variety of different wavelengths. A workaround presented here is a system that combines three fixed frequency sensing bands with center frequencies of 400 MHz, 1.6 GHz and 2.3 GHz. This system can sense at three different depths and resolutions and provide a wider coverage of subsurface conditions. Results from tests aimed at sensing subsurface conditions in concrete structures, roadways and buried utility location are presented. In each of these three cases the system performs differently and better or worse for different frequency bands.