Testing the feasibility of a concurrent comparison of continuous and pulsed active sonar

Abstract

The performance of continuous active sonar (CAS) was compared to conventional pulsed active sonar (PAS) during the TREX13 (Target and Reverberation Experiment 2013) sea trial. The approach was to execute a one-hour CAS run followed closely by a one-hour PAS run to limit the environmental variability between runs and allow a fair comparison. This approach was possible because the sonar source and receiver were fixed to the seabed. A different approach was required for a more recent sea trial, LCAS15 (Littoral Continuous Active Sonar 2015), where the source and receiver were towed from a ship. Ship motion increases variability in sonar performance, therefore a simultaneous comparison of CAS and PAS was desired so that any motion effects were the same for both waveforms. The approach of transmitting CAS and PAS concurrently in two separate frequency bands was taken. The risk with this approach is that potential differences in propagation in the two bands could bias the comparison. A run in which equivalent CAS waveforms were transmitted simultaneously in the two bands was therefore performed to establish a baseline for the performance difference between the bands. Doppler-corrected replicas were required in all of the correlation processing due to the high Doppler sensitivity of the long-duration, wideband CAS waveforms. Preliminary results from the LCAS15 sea trial will be presented.

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“…However, matched filter gain may decay due to the more limited bandwidth used in each time interval. To experimentally examine the advantages and limitations of CAS (or HDCAS) with respect to the more traditional PAS mode [193], a series of sea trials have been conducted. Among others, the 2013 sea campaign Target and Reverberation Experiment (TREX‐2013) conducted in the Atlantic was partly devoted to evaluate the impact of pulse duration on echo statistics [194] and evaluate sonar performance with respect to environmental spreading effects, the target's physical extent and Doppler effects [190, 195]; the Littoral Continuous Active Sonar (LCAS) joint research and multinational project started in 2015 and, led by NATO STO CMRE, aims at the evaluation of CAS performance in littoral waters, generally characterised as a high‐reverberation environment, hence more challenging for CAS.…”