TIME-FREQUENCY PROCESSING OF UNDERWATER ECHOES GENERATED BY EXPLOSIVESOURCES

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 ta rgets of interest, in the time-domain, in the frequency domain and in the combined time-frequency domain. The first two, more traditional, a pproaches are contrasted with a third and more recent processing schem e in the combined time-frequency domain, which utilizes the windowed o r pseudo-Wigner distribution (PWD). This third processing approach exh ibits the time-evolution of the target resonances in a more informativ e way and it is seen to offer additional advantages for target identif ication 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, implem ented here for the PWD, could be repeated using any of the many distri bution members of the general bilinear class.