Application of the reassignment time-frequency method on an acoustic signals backscattered by an air-filled circular cylindrical shell immersed in water

In this paper, the time-frequency representations of the Spectrogram (SP), the Reassigned Spectrogram (RSP), the Smoothed Pseudo-Wigner-Ville (SPWV) and the Wavelet Transform (WT) were used. These techniques are applied for analyzing experimental acoustic signal backscattered by an air-filled tube immersed in water. From the time-frequency images obtained, one can go up easily with certain characteristics of the acoustic waves such as the attenuation and the group delay of each circumferential wave. A comparative performance study of these four time-frequency representations was used. The reassigned spectrogram was chosen for its better localization and good resolution of the signal components in the time-frequency plane. It allows a better visibility of the circumferential waves which are propagated around the target. The estimated parameters from the reassigned spectrogram time-frequency image are in very good agreement with those obtained by the theoretical methods.