Hacker News Reader

Comment by idoh | Hacker News Reader

How would the proximity sensors work? The can’t go active sonar…

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

>...So the sensors could be trained to detect such local distortions, almost like some fish have a lateral line ...

Turns out, this has been modeled already (2007):

[1]:https://www.photonics.com/Articles/Fish_Navigation_System_Re...

Ultrasound, magnetic, eddy-current metal detection, conductivity detection by conducting current through water, red light, VNIR, antineutrino detectors...

Optical, perhaps? How much light is at these depths? How do the subs avoid terrain?

I remember (barely) from a diver friend that colors disappear below 20 meters (everything appears blue, unless a bright light is shone), and sun light disappears completely below 70 meters. You'd assume that an optical system with flood lights could theoretically work, but then it would be pretty simple to monitor for light at these depths (for counter-intelligence/retaliatory purposes)

Subs avoid terrain using charts and dead reckoning, including inertial navigation systems. They typically come to periscope depth occasionally to get a navigational fix. In 2005 a US submarine allided with an underwater mountain due to a navigational error.

https://www.cbsnews.com/news/whos-to-blame-for-sub-accident/

There is little or no light at typical operating depths. Lidar can work to a limited extent in some water conditions but it's not something to rely upon for collision avoidance.

>Lidar can work to a limited extent in some water conditions but it's not something to rely upon

And, of course, it's an active sensor. An adversary could detect the emitted light.

Reply on news.ycombinator.com