Signal-to-Reverberation Ratio Comparison of Linear Frequency Modulated Continuous Active Sonar and Pulsed Active Sonar

Abstract

Continuous active sonar (CAS) waveforms provide an advantage over conventional pulsed active sonar (PAS) waveforms, which is, they can be processed to provide a higher target update rate through subpulse processing. Performance in reverberation limited conditions is particularly important in shallow water. This article compares the signal-to-reverberation ratio (SRR), echo level, and reverberation level of simultaneously transmitted linearly frequency modulated (LFM) PAS with an equal bandwidth LFM CAS waveforms processed with different CAS subpulse durations in a littoral environment. Data from an experimental sea trial showed that the LFM PAS waveform outperformed the full-band LFM CAS waveform in terms of SRR by 3.0 ± 2.1 dB. The SRR of the CAS waveform degraded by less than the expected 3 dB per halving of the subpulse bandwidth and duration. Energy spreading loss, which increases with bandwidth, was shown to be the dominant cause of the deviation from expected degradation rate. The detection performance of the full-band LFM CAS waveform was approximately equal to that of the LFM PAS waveform as measured by a receiver operating characteristic analysis.