Time-frequency processing of underwater echoes generated by explosive sources

Abstract We study the advantages and performance of an ‘impulse sonar’ that uses the short, energetic pulses emerging from underwater explosions as its sources. This transient analysis is carried out for various simple targets of interest, in the time-domain, in the frequency domain and in the combined time-frequency domain. The first two, more traditional, approaches are contrasted with a third and more recent processing scheme in the combined time-frequency domain, which utilizes the windowed or pseudo-Wigner distribution (PWD). This third processing approach exhibits the time-evolution of the target resonances in a more informative way and it is seen to offer additional advantages for target identification purposes. We display calculations showing the quite different patterns generated by the echo of each target, which can then be used unambiguously and remotely to characterize them. The procedure, implemented here for the PWD, could be repeated using any of the many distribution members of the general bilinear class.