And there is no reason to doubt the Chinese in this matter, unless you (or someone) dislike Chinese and are allowing that to cloud their judgement
- The Chinese did not record the signal, they just listened to it. This reduces the credibility a lot. It's very easy to hear what you want to hear - to imagine you hear a weak signal that is not there.
- The Chinese picked up the signal at the surface. It is unlikely that it could be heard that far from the bottom.
- The signal could not have traveled the distance between the Chinese and the Aussie detection. Signal attenuation due to both distance and energy losses (from non-adiabatic compression of ocean water) of ultrasonic signals prohibit it. It *could not have done it.* This isn't a matter of it maybe didn't do it - this distance is orders of magnitude too far. Even ducting wouldn't do it - and if it were being ducted, only one of the two parties would have heard it, since they were listening at greatly different depths.
- The US detector was recorded. It showed a solid signature. The people doing the US detection are experts at this thing.
None of this is to imply that the Chinese did anything wrong other than being over-eager - a common problem in SAR/