Submitted by Leumas404 t3_y7qalt in askscience
I’m just wondering if the Navy or someone could use a system to catch a section of a sonar pulse from an enemy sub in the water and use the information about the curvature of the sonar pulse to instantly derive the enemy’s location? I imagine this would eliminate the need to bypass enemy counter sonar stealth tiles.
Yes, this is called passive sonar: https://en.wikipedia.org/wiki/Sonar#Passive_sonar
Not only can you detect enemy sonar pulses, you can also detect other sound sources, such as engine noise. Submarines almost exclusively operate using passive sonar (as opposed to actively sending out pings) so that they can remain hidden.
Yes, and for this reason submarines don't use active (pinging) sonars when they are trying to stay undetected. In fact any noise a submarine makes can be used to detect it, so submarine designers go to a lot of effort to make their submarines as quiet as possible, with things like machinery noise from the engines, and noise from the propellers, being particularly important. While detecting the noise of an otherwise hidden submarine can give you a good idea of the direction it is from you, using directional sound detectors, it it somewhat harder to determine the distance it is, unless you have several listening devices that are separated by a large enough distance to get a good triangulation.
If you haven't seen it, watch the Hunt for the Red October. It's a classic movie, and gives a good sense of how submarines try to find one another, and how they try to avoid being found. "One ping only" is a classic moment from that film.
Any noise coming out of a submarine will reveal its location. Through various detectors (hydrophones) arrayed along the hull, a sub can use triangulation to pin point another submarine, engine noise, cavitation of the propeller (Red October used an impeller interesting concept). Attack subs can also tow a long array of hydrophones to listen to subs much further away.
The US Navy maintains a series of listening devices along the east coast to listen to Soviet subs. It was named SOSUS (SOund SUrveilleance System).
[removed]
One ping for ranging just before a torpedo launch because once you start the launch sequence, your target knows your there.
Could you theoretically develop a sonar network that was constantly sending out pulses kind of like a WiFi network. So friendly ships would have access and basically have a map of the waters?
Obviously the ocean is massive and you wouldn’t be able to do this everywhere. But important strategic locations, especially defensive ones, I feel like this could work.
I can't think how you could ever make it so that only friendlies could use it, unless the pulse emitting devices were moving, on a pre-known pattern.
Moving emitters wouldn’t be too difficult and would also allow the system to follow a submarine or fleet around as well
Never heard of encryption?
Can you use the background noise spectrum for detection? Or are submarine hulls too sound absorbant and the reflection back to your sensors too weak?
How're you going to encrypt the direction of origin from a sound wave bouncing off something?
Yes, it's called passive sonar.
Not only that, the US Navy has an array of hydrophones (underwater microphones) across the globe that can not only pinpoint the location of virtually every ship/sub in the world but have developed extraordinarily sophisticated algorithms to decode the unique acoustic signature of every ship. Said another way: all ships emit sound (engine, prop moving through water, etc.) and every ship (even ships made from the same design/blueprint) have enough unique differences that result in slightly different sounds when in operation.
Fun fact: this system has also been used to track whales - groups of whales and individual whales with their unique acoustic ID.
[removed]
The comment you replied to talked about using the waves to create a 'sonar network' that would send 'out pulses kind of like a WiFi network. So friendly ships would have access and basically have a map of the waters', suggesting a data transmittion through water, using sonar frequencies.
If they had a data transmission system in place, then they could encrypt it. If they did not then how is it similar to a WiFi network, and how would it provide a map, and gated access?
The comment I replied to did ask about making a sonar network, so I'll ask - how are you going to encrypt your sonar to make the location info they inherently contain private?
If using sonar as a communication means, that's fair I suppose, despite being obscenely inefficient. But I don't think anyone was asking "can we make a network with sound waves instead of radio waves" because the answer would be obvious.
I interpreted it as numerous pulse devices which would make a continually up to date sonar map, which would then inherently be available to anyone within the mapped area if the emitters didn't continuously move on an undeterminable path.
This comment is primarily just explaining that I guess we interpreted the question differently.
[removed]
[removed]
This is probably relevant to what you're thinking about, although it's not quite the same thing https://en.m.wikipedia.org/wiki/SOSUS
Note the civilian used in section, where it's been used to track whales and seismic activity
if you encode the outgoing signal as white noise, it won't clearly correlate to reflections from the environment, as you would have to subtract the random additive noise from the emitter, which would drown out the quieter reflection.
however , if you know the sequence from the emitter in advance (say you know the random key) , then you can subtract it from your inbound signal, enhancing the signal to noise .
its a bit like radar jamming, or selective availability in gps.
I learned about this playing Tom Clancy's SSN - submarine combat sim! Always running passive if there are enemies around.
Realism was the focus, which made it super slow for how arcade-like it felt.
The ocean is heterogeneous to sound waves, so such a system would be extremely complex and error-prone. Not to mention disruptive to aquatic life. Whales are pissed about international shipping.
[removed]
[deleted]
Each Boat and surface vessel has a noise signature as effective as a fingerprint. The technology has been used for a long time and can program torpedos to select targets.
[removed]
Sonar is like flash photography in a dark room.
When it is activated, everyone knows where the flash is. But also everyone can briefly see everyone else in the reflections
This is grossly implausible for sonar for a variety of reasons, including (but almost certainly not limited to):
[removed]
[removed]
[removed]
You need information to be inherent to the signal in order to receive information from it. Either you need a big coherent wave that comes from an unknown direction (so that you can detect alterations in the received wavefront) or you need random noise coming from a known location (so you can detect the direction of increased noise).
Each information (i.e. non-randomness) factor adds disambiguity to the resulting detected signal. A signal of known origin and coherent timing gives you the best bet of detection the direction and range to another object.
What comes back from your coherent active sonar is already fuzzy. Any fuzziness in the input to that process increases fuzziness in the output. Eventually the fuzziness is high enough you're getting no useful information.
[removed]
[deleted] t1_iswebqu wrote
[removed]