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Time-frequency spectral analysis of step frequency continuous wave and impulse ground penetrating radar

Time-frequency spectral responses of an in-house built step-frequency continuous wave (SFCW) GPR (Y akumo) developed by Tohoku University and a commercial impulse GPR were studied and compared. The Yakumo SFCW GPR operates from 50 MHz to 1.5 GHz, and the center frequency of the commercial impulse GPR is 500 MHz. Both GPRs were probed on top of an embedded steel pipe overlaid by a concrete pavement. The time domain radargram signals were transformed to the time-frequency domain through a continuous wavelet transform with Morlet wavelet as the mother wavelet. The study reveals, with a definite buried pipe as a reflector, how the spectral responses in both the frequency domain and time-frequency domain are changed by two different bandwidths and two different ray paths of the GPR wave propagation into materials.