Military sonars must detect, localize, classify, and track submarine threats from distances safely outside their circle of attack. However, conventional pulsed active sonars (PAS) have duty cycles on the order of 1% which means that 99% of the time, the track is out of date. In contrast, continuous active sonars (CAS) have a 100% duty cycle, which enables continuous updates to the track. This should significantly improve tracking performance. However, one would typically want to maintain the same bandwidth for a CAS system as for the PAS system it might replace. This will provide a significant increase in the time-bandwidth product, but may not produce the increase in gain anticipated if there are coherence limitations associated with the acoustic channel. To examine the impact of the acoustic channel on the gain for the two pulse types, an experiment was conducted as part of the Target and Reverberation Experiment (TREX) in May 2013 using a moored active sonar and three passive acoustic targets, moored at ranges from 2 to 6 km away from the sonar. In this paper, preliminary results from the experiment will be presented. [Work supported by the U.S. Office of Naval Research.]

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