Towards Underground Void Detection with In-pipe Ground Penetrating Radar

Dramatic voids and how to find them: In-pipe condition assessment of sewer pipes

“…To enhance the signal we multiply the field values with a gain that compensates for exponential attenuation of the signal amplitude with increasing TWTT. We also apply filtering in frequency domain to remove the horizontal lines that appear in the radargram due to reverberation from the concrete pipe [142] (such region with reverberation lines is shown with an arrow in Figure 4.2a). The result of these two processing steps is shown in Figure 4.2b.…”

“…Comparing Figure 4.11b to Figure 4.6b reveals that air-gap adversely affects the 2D rotational radargram more than its longitudinal counterpart. This is because the reflections paths are intrinsically longer in the rotational case due to the curvature of the sewer wall [142]. Hence, it is important to try to keep the air-gap zero in rotational in-pipe GPR surveys.…”