Detection of underwater transient acoustic signals using time-frequency distributions and higher-order spectra

The authors demonstrate the application of the Wigner-Ville time-frequency distribution, the bispectrum, the time-varying bispectrum, and Gerr´s third-order Wigner distribution to some underwater acoustic data. They also demonstrate the merit of including higher-order spectral information when signaturing underwater acoustic sources. It is pointed out that conventional signal analysis procedures do not utilize all the information available in many practical signal analysis problems. It is shown that the use of higher-order spectral analysis improves time, frequency, and time-frequency analysis methods and provides the analyst with important additional information. Time-varying higher-order spectra are not well developed and are difficult to interpret. Phase coupling cannot be detected without some form of ensemble averaging. This important feature of the stationary bispectrum, where for single signal realization problems ensemble averages are often replaced by temporal averages, does not carry through to time-varying higher-order spectra