|A Fresh Look At Broadband Passive Sonar Processing
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Traditional passive broadband sonar processing has been constructed by performing
spatial decomposition (beamforming) followed by a temporal filter (Eckart weighting)
structured to maximize deflection for signal present while minimizing deflection under
noise only conditions. This processing, while approaching optimality in the stationary
single signal stationary noise case, is not well suited for clutter rich environments and
spectrally diverse new target sets. Techniques such as the Smoothed Coherent Transform
(SCOT) and the PHAse Transform (PHAT) as well as a new ad hoc construction referred to as
Subband Peak Energy Detection (SPED) are finding increased usage in modern sonar systems.
This paper analyzes the underlying signal model along with a forensic discussion that
details the sources of the performance gains over traditional processing. A conclusion
that 'passive broadband' is fundamentally a Direction of Arrival (DOA) estimation is
developed from this analysis. Based on this conclusion higher resolution techniques
including Spectral Capon Quadratic and a Fixed Subspace Dimension Spectral MUSIC is
applied to generate a similar broadband output. A comparison of performance to the Navy's
current broadband schemes against common real data is presented.
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