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> Submarines do have their own sonar, but using it comes at a price – loss of stealthiness.

• encryptluks2 4y ago
  Is there not reliable alternatives to sonar that would maintain stealth?
  • mlindner 4y ago
    They're in a place where there is no lights and no sound. You have to emit something whether that be in the form of sound or in the electromagnetic spectrum in order to receive a reflection back and emissions remove stealth. Not to mention that sonar is highly disruptive to many forms of sea life as it's incredibly loud.
    • walrus01 4y ago
      the only thing I could possibly think of are receive-only apparatus like magnetometers, which are themselves used by low flying aircraft and surface ships to locate submarines. And likely of very limited value in underwater navigation unless you're in a research submarine literally hovering a few meters above some rocky metallic outcroping on a seamount. Or something thermal sensor based, there's rumored to be systems that submarines can use passively to follow and track other submarines by the waste heat put into the water.
      • pueblito 4y ago
        I suspect the real purpose of the Poseidon nuke torpedo is to avoid the difficulties of detecting subs by over-pressuring an enormous area all at once, like fishing with dynamite
      • etiam 4y ago
        I'm not sure how practical they are for mapping but the sensitivity of some such sensors is so outrageous you can definitely measure well beyond a few meters of distance. https://en.wikipedia.org/wiki/SQUID https://en.wikipedia.org/wiki/SQUID Managing the interference is probably the main issue. Actually, I see now the Wikipedia entry lists prospecting among the uses, so I guess it's quite possibly not only practical but even practiced.
        • walrus01 4y ago
          My understanding of the physics is that SQUIDs only work at distances of max of 50-100mm, not more...
          • etiam 4y ago
            You seem generally very knowledgeable about this environment and I'm by no means an expert in the SQUID, but the way I understand it it's effectively a magnetometer with sensitivity down to about femtotesla scale. Clearly that could in principle pick up the magnetic effects of many objects well beyond a decimeter, even with consideration of the field rapidly declining with distance. The main problem in using it, as I understand it, is rather that picking up everything the sensor could detect would usually result in an unmanageable deluge of unwanted information, and it's a normal operation context to filter the signal for distance so as to not pick up too much interference from equipment, staff, etc. But personally I don't see any reason it would be impossible to arrange it to band-pass instead of low-pass in that filtering.
    • ge96 4y ago
      https://www.youtube.com/watch?v=EAqUelpwEl8 https://www.youtube.com/watch?v=EAqUelpwEl8
  • Arainach 4y ago
    What do you propose? Any sonar-equivalent involves broadcasting (in this context, broadcasting nearly continuously). Any broadcast makes it trivial to locate you. Submarines go to great lengths to be as quiet as possible so that the acoustics of the engine, ship, etc. can't be caught in a microphone. Any sort of EM radiation is child's play to trace compared to that. The content of the message and the frequency of the message don't matter - any sort of signal means you can be monitored and your location determined.
    • throwaway09223 4y ago
      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.
      • Arainach 4y ago
        The threat model isn't a torpedo, it's knowing where the enemy's subs are (and aren't). "There's a sub within half a mile of this point" is likely 90% as bad as "there's a sub exactly here" for most missions. 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.
        • throwaway09223 4y ago
          Sure, all valid issues. It for sure would expose the general vicinity. 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.
      • maxwindiff 4y ago
  • throwaway09223 4y ago
    Sure. You can transmit the sonar from a different location. A hidden sub could send out a drone to make the sonar pings from a different location. You'll be giving away the location of the drone, rather than the sub. There's still an issue around detecting that a sub is in the general vicinity, of course.
    • walrus01 4y ago
      or more conventionally, you build a fleet of oceanographic survey ships which operate in the open navigating international waters, collecting vast data sets of bathymetric information... obviously not perfect yet. https://en.wikipedia.org/wiki/Pathfinder-class_survey_ship https://en.wikipedia.org/wiki/Pathfinder-class_survey_ship there is also the danger that a drone emitting sonar pings may be indistinguishable to a third party from a live torpedo, and makes it look like you're preparing to attack somebody you really don't want to start a war with (China, etc).
    • lazide 4y ago
      Your drone would need to be really close to the sub to provide any useful information - so close that you’d definitely be exposing the submarines locations unless it was quieter than the sub. Which good luck with that. Any active sonar would likely paint the submarine anyway too for any passive sonar listeners. Overall, unlikely to be useful.
      • throwaway09223 4y ago
        It could be a mile or more away.
        • lazide 4y ago
          How do you figure? RF (nor light) transmit effectively under water. How would it be useful to them at that distance?
          • throwaway09223 4y ago
  • fsckboy 4y ago
    I believe there have been successful experiments to detect underwater mountains by their gravitational pull, but I don't think it's an operational system type thing. https://ieeexplore.ieee.org/document/5345843 https://ieeexplore.ieee.org/document/5345843 and also, I wanted to mention another submarine navigation technique that the Soviet Russians pioneered. I thought it was called Crazy Ivan but I just looked that up and that's Soviet Russian submarinery, but not this one. The idea is to carefully map the ocean floor features in a particular area, and water currents, and know your boat well, and use that information to "blindly run a route" at high speed. I'm not an expert but something like, when submarines are traveling at speed, stuff like sonar (at least the quiet kind) is useless because of all the turbulence around the boat, so the Russians figured out they didn't need to be stealthier to evade US subs in the Baltic, they just needed to know where they were and then go fast. The goal was to get to the open sea were it's easier to get loast in the vastness. Maybe these Navy subs were trying something like that.