Using interference to determine the phase change of a reflected GPR pulse

In this paper we describe a method to detect cavities in roadbeds by determining the phase change of a GPR reflection. All GPR reflections interfere with each other, creating ripples in the power spectrum. The reflection from the road surface always has an Opposite phase compared to that of a reflection from a cavity, creating a ripple with a x radians phase shift. Subtracting the power spectrum of an ensemble average of time domain data reduces the number of ripples caused by interferences between reflections from the layers in the roadbed. The Fourier transform of the resulting signal gives the phase of the ripple, and consequently the phase change of the reflection. Applying this method to field data confirms the applicability of the method.