Abstract:

Fluctuations in signals and noise are an inherent characteristic of the undersea acoustic environment. The effects of the fluctuations were usually considered a nuisance to be avoided to ignored. However, within the last few years, it has been recognized that the fluctuations in the acoustic power amplitudes received by a sonar system could be exploited to achieve additional signal-to-noise ratio (SNR) gains, enhanced resolution, clutter suppression and elimination, and unalerted autodetection/classification. This paper demonstrates that a similar capability can be achieved by exploiting the phase fluctuations in the acoustic pressures of the signals and the noise. In fact, since the phase is independent of the pressure amplitude, the phase-dependent algorithm is able to enhance the sonar's performance on some phase-stable signals, which have fluctuation amplitudes that will cause the other techniques that exploit the amplitude fluctuations to fail. The new technique for exploiting phase fluctuations is described, and results from measured data are presented that show SNR gains of more than 6 dB, complete clutter elimination, and unalerted automatic detection/classification (submerged/not submerged) of signals from submerged sources. [Work sponsored by ONR and NRL.]