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VolcanicBear t1_isy00yr wrote

Reply to comment by hearnia_2k in Can a submarine’s sonar pulses be detected and used to pinpoint location of origin? by Leumas404

How're you going to encrypt the direction of origin from a sound wave bouncing off something?

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hearnia_2k t1_isydusb wrote

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?

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VolcanicBear t1_isygac5 wrote

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.

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SamQuan236 t1_isynqc2 wrote

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.

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Coomb t1_it8w7cx wrote

This is grossly implausible for sonar for a variety of reasons, including (but almost certainly not limited to):

  • potentially very substantial added complexity to receiving microphones in order to extract spectral information from a sonar return (depending on spectrum used)
  • the extremely low bandwidth available from sonar pulses from emitters a practical distance away (at least tens to hundreds of kilometers if not more) because of the attenuation of higher frequency sound in water
  • the high frequency dependence of attenuation and dispersal of sound in water
  • the extremely challenging noise environment at usable frequencies
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