Low power high freq radio waves? These should rapidly attenuate underwater, so not much of giveaway, but could be enough for proximity scans around the sub. Is

Low power high freq radio waves? These should rapidly attenuate underwater, so not much of giveaway, but could be enough for proximity scans around the sub. Is there some spectrum of emissions from an even stealthy sub, some kind of "local presence"? The immediate massive obstacles would result in distortions to such a self-presence profile. So the sensors could be trained to detect such local distortions, almost like some fish have a lateral line of nerves supposedly helping detect current flows etc. [1]. [1]:https://en.m.wikipedia.org/wiki/Lateral_line https://en.m.wikipedia.org/wiki/Lateral_line