Classifying Continuous Active Sonar Echoes for Target Recognition

Classification and tracking are two important techniques for enhancing active sonar performance. Classification rejects unwanted clutter using echo analysis, and tracking provides a history of target motion while rejecting clutter that doesn’t support realistic target motion. Continuous active sonar (CAS) has been proposed as an alternative to conventional pulsed active sonar (PAS), largely in order to provide tracking updates at a much higher rate than is possible with PAS. Unfortunately, these faster updates come at the cost of reduced classification performance, at least for CAS that uses linear frequency modulated waveforms. In this case, maximizing the update rate requires sub-band processing. Classification of echoes from these sub-bands is expected to be relatively poor, since the full bandwidth is favoured for classification. An alternate processing scheme for CAS uses full-band processing, which is typically used for PAS. This potentially maximizes classification performance rather than providing faster updates as in the sub-band approach. A risk of this scheme is the potential for complications in echo signals arising from coherence loss caused by the long duration of CAS waveforms. One facet of a recent Canada-U.S. sea trial, TREX13, focused on conducting experiments that allow direct comparison of the performance of CAS and PAS in shallow water. In this paper, DRDC’s echo classification software was tested with sonar echoes from TREX13. The software, which was originally developed for PAS applications, was used to evaluate whether CAS echoes can be classified as accurately as PAS echoes.