Well, an obvious proposal would be to send out a drone and transmit the sonar ping from a different location.
You're right in that a broadcast is required, but I don't see why the broadcast should have to come from the sub itself.
You're right in that a broadcast is required, but I don't see why the broadcast should have to come from the sub itself.
While water motors are not exactly my area of expertise, I would also expect that drone/torpedo motors are significantly louder than submarine engines and that launching or recovering a drone is itself a fairly noisy event that exposes the sub to traditional acoustic tracking.
In terms of noise, keep in mind that submarines have all sorts of concessions already. A diesel-electric sub is quieter than a nuclear sub, but it has to surface every two days or so to get air to run its very noisy diesel generators.
I think a battery powered electric drone should be far quieter than any sub technology we have (steam/nuke is loud, diesel is louder). The quiet systems we have are all electric and therefore have limited energy capacity.