The application of evidential
reasoning to the problem of identifying passive, narrow-band
sonar signals has been explored. The main acoustic sources considered are
propulsion and auxiliary equipment found aboard surface and subsurface
ships and submarines. The specific acoustic emitters of interest include
various types of rotating or periodically varying emitters of underwater
acoustic energy, such as propellors, propellor shafts, components of
reciprocating engine, turbines, auxiliary equipment such as pumps and
generators, and various resonating components.
Because of the nature of acoustic sensors and preprocessing steps,
acoustic energy is typically presented in the form of a power spectrum
spanning a particular frequency range. The low frequency end of this range
is often higher than the actual (fundamental) frequency of the emitter.
Instead, what is detected is some subset of the harmonic frequencies
associated with the fundamental frequency.
This leads to an approach consisting of several steps: extraction of
harmonic frequencies, association of harmonic frequencies into correlated
sets, determination of the fundamental frequency associated with the
harmonic set, identification of the acoustic source, and identification of
the platform containing the source.
John D. Lowrance,
Artificial Intelligence Center
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