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A Fresh Look At Broadband Passive Sonar Processing

Robert Zarnich
PEO (USW) ASTO-D1 Undersea Warfare
2531 Jefferson Davis Highway
Arlington, VA 22242-5169
tel: (703) 604-6013, Ext. 515
email: zarnich_robert@hq.navsea.navy.mil

Abstract 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.

Presentation (pdf format)



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