Striation processing of continuously active sonar data

Abstract

Previous work by the authors has shown that striations associated with the waveguide invariant can provide a new physics-based tracking constraint that improves tracking performance in pulsed active sonar data. A necessary pre-processing step is to isolate the target return from the direct arrival and other target echoes. Striation-based beamforming can be used as an optional pre-processing step to preserve the multipath structure in the beamformer output of a horizontal line array. Recent interest in continuously active sonar (CAS) processing has motivated research to determine how striations might be similarly exploited for tracking when the sonar is operated with a high duty cycle. In CAS signals, the direct arrival is almost always overlapping in time with the target echo return and the standard time-gating technique cannot isolate the echo return. In this paper, a time-dependent filter is introduced to isolate and extract the CAS echo spectrum. The conditions in which striation-based beamforming should be applied to preserve the striation structure in the beam output are also explored. The physics-based signal processing algorithms discussed here are expected to provide valuable information about the target’s multipath structure, which can be exploited in an extended Kalman filter for enhanced tracker performance.