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Situation

A species lives on a planet with heavy fog, and as such, they rely on a conjunction of hearing, smell, and sight. The fog only allows for vision at 500 feet (~152 meters) . They have basic echolocation capabilities. The rifle "sight" uses echolocation for long ranged weapons, with a top range of one mile (~1600 meters).

Differences to Normal Rifle Sights

  1. Inherently less accurate. Sound travels slower than light, and the locating sound needs to travel both ways in order for the creature to get information about their targets.
  2. More reliable in more settings. Only places that there may be issues are loud urban areas or space.

Question

Would this echolocation rifle "sight" be feasible? If so, what are some of the pros and cons I forgot about the "sight"?

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    $\begingroup$ Err... Various navies seem to do quite well with sonar. $\endgroup$ – jamesqf Nov 3 '17 at 18:09
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    $\begingroup$ @jamesqf Depending on the size and accuracy of the sonar systems navies use, it may not be practical to strap that onto a rifle. We need to accurately pinpoint human sized targets at a distance of one mile, and I don't know if that idea is sound. $\endgroup$ – OneSurvivor Nov 3 '17 at 18:20
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    $\begingroup$ Echolocation would be "active", where an ocular scope is "passive". You can't sense an eyeball looking through glass (unless maybe you have a hairy neck) but you could certainly sense a ping from an echoscope. Your snipers better get those shots off quickly. $\endgroup$ – EightyEighty Nov 3 '17 at 20:40
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    $\begingroup$ Building on @EightyEighty's comment: You can identify what you're shooting at with a visual scope. You cannot with an echolocation scope. Submarines use large computers to identify their enemy (vs. their friend). An echolocation scope can tell you how close something is... but it can't tell you what it is. Which is why bats only use it for collision avoidance. $\endgroup$ – JBH Nov 4 '17 at 0:45
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    $\begingroup$ @OneSurvivor said: ". . . I don't know if that idea is sound." Ha! I see what you did there. $\endgroup$ – EightyEighty Nov 4 '17 at 23:50
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If I get the question right OP asks for feasibility of a targeting device based on sound reflection.

Under stated conditions answer is no.

As discussed, e.g., here the upper limit of ultrasound range in air is about 200 meters, probably much less with heavy fog.

Situation is very different in water.

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  • $\begingroup$ Yep, that's what I'm asking. $\endgroup$ – OneSurvivor Nov 3 '17 at 18:37
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    $\begingroup$ I understand losses are often related to wavelength would lower frequency have better range? $\endgroup$ – user25818 Nov 3 '17 at 19:18
  • $\begingroup$ It’s true the range for ultra Sonic’s is short. I saw one reference for bats as only having a range of 67m. You can change the wavelength but you then have other problems. In the extreme imagine shouting. How far might the sound carry? Under the right conditions you might be heard a mile away, but target resolution would not be in the gunsight league, more like north south east or west if that. $\endgroup$ – Slarty Nov 3 '17 at 19:28
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    $\begingroup$ @notstoreboughtdirt: lower frequencies actually carry much better. You can hear low rumbles many miles away, unfortunately such sounds have wavelength in the order of tens of meters and thus: would require a transmitter/receiver of the same magnitude; won't be able to discriminate anything smaller. Think how difficult is to pinpoint direction of a far away thunder. $\endgroup$ – ZioByte Nov 4 '17 at 9:02
  • $\begingroup$ Low frequency echolocation might be able to identify that there's a building out there, but good luck trying to "see" anything smaller. $\endgroup$ – Keith Morrison Nov 5 '17 at 6:01
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I'm the random submarine guy, and man do I have some things for you.

See, when we're alone out in the water, we try to be as quiet as possible for our own good. It helps us identify what's in the water near us, minimizes false positives, and helps us stay undetected should a potential enemy show up in our patrol area.

There is only one really good tactical reason you would ever broadcast active sonar pings in the water, outside of testing - when you suspect you are not alone, but you are absolutely postive you still have the upper hand once you announce your presence to the enemy.

This sort of situation really only comes up in battle groups and task forces, because that is essentially the only way to ensure a tactical advantage. Even then, when you go active, you light up the water with a ping - an enemy may suddenly find himself with his torpedo tubes pointed directly at you, when before he wasn't even sure you were there. Most submarine commanders, in wartime, will take the shot they have right before they try to evade, and you stand a very good chance of dying.

To point this up a bit, in 8 years of service, I never once heard either of my boats go active anywhere other than for testing in undeniably friendly water.

Another thing about active sonar - you're still guessing, a bit. Yes, the guys who were listening are almost absolutely positive that the thing behind you is a whale, but now? Everything sounds like ping. You have what the computers can sort out, which might be an enemy submarine, or it might be a cruise liner through a thermocline that's making it seem to be in the wrong place. Good commanders maintain an awareness of what they think is out there, and that helps bridge the gap in the tactical picture.

So, you point the rifle, start the sight, send a broadcast, probably get shot at, and you get a range ping back... But from what, who knows? It would be hard to tell the difference between a rock and a riot shield.

Now stop for a minute, and consider your own, ordinary human hearing. You can probably readily identify the sound of a car shifting into reverse - it's pretty distinctive. Your brain can also pull apart the sounds from a three way conservation, identify who is speaking without looking, and give you an idea of how far away they are. As an electrician, on the boat, I knew when we lost an electrical bus the second after it happened because ventilation fans whine a bit when they're winding down. Electricians were already running for the engine room by the time anyone was talking on the announcement systems - we all knew that sound.

It's your world, so by all means, if echo sights are a thing, then by golly they're a thing. But if you want a more explainable, realistic technology, what these guys need is parabolic microphones, silencers, and lots and lots of patience.

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  • $\begingroup$ Interesting point, I will have to look a bit farther into that. Thanks for the answer! $\endgroup$ – OneSurvivor Apr 25 '18 at 4:11
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Your single biggest issue is that using a such a system is a good way to have the shooter end up dead before they're in any way prepared to shoot at anything.

There are already systems that use the sound of a shot to triangulate the source, such as Boomerang, which means that within seconds of the shot the area could be getting pasted by return fire or heavier weapons. Note that's with someone actually having made the shot. In the echolocation system proposed, the sensor is, by definition, going to be advertising its position in order to function, and one of the downsides of active sensors is that they typically can be detected at a significantly greater distance than the distance they can detect anything at.

So if someone tried to field such a system, the immediate reaction would be to deploy sensors that listen for an echosounder, which would detect it at a far greater distance than the "sight" would detect anything, and then send a high velocity and/or high-explosive hello back at the shooter's position.

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How wedded are you to sound versus a laser? You can get all the same results but faster and more precise. Plus, if you time gate when the receiver "looks" for the reflected laser, you can effectively filter out the fog. This process is better described here. This could actually be a weapon sight, though determining if it is pointed at a person versus a rock would require careful survey of the battlefield first, or tracking motion. But it would deliver accurate enough location information to allow for a hit from a traditional rifle.

Your echolocation system would work better if there were remote sensors placed around the battlefield that could passively listen and perhaps actively transmit. We have real world systems like this to include the GUIK SOSUS network, and even actual infantry/armor applications. Here is a really detailed look at military acoustic systems, some of which kinda do what you are proposing (though using sound to pinpoint a person is very tricky). Almost all are passive though, since that works pretty well in the air. Seismic sensors to register walking, vehicles could also help.

A proposed sniper system would involve the use of passive acoustic triangulation to get an approximate location of an enemy, then use an area munition rather than a single bullet. Something like the proximity minigrenade in the XM25 that allows for an effective kill just from "being close".

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Tactically, no they aren't

1) If you are focusing in on produced sound you inherently require your target to make loud enough identifying sound (which they may dampen) and you are relying on your target not to employ deceptive sounds (which they could easily make).

2) if you are doing true echolocation and emitting a sound pulse in order to locate a target based on received responses you have just revealed your location. This inherently botches loads of ground tactics requiring surprise like sniping. Even submarines don't constantly emit pulses and just sit and wait. Furthermore what if your opponent is static and geometrically blended into the landscape, you have given him your position without knowing his thus you are likely to be disadvantaged.

3) The apparatus needed to do this would certainly be unwieldy with the distance and level of detail needed to be operationally effective.

In short, this would be useful against an enemy who couldn't counter it. But because it is easily countered it is in short tactically detrimental.

At most it would see more usage in defensive facilities.

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Ultrasonic imaging would likely be an impractical way of acquiring vision in dense fog. However there are frequencies of electromagnetic radiation that are not absorbed and reflected by water vapor to the same extent as visible light.

Here is a link to a publication by FLIR, an industry leader in infrared imaging, about using infrared to see through fog. One interesting conclusion is that to see high levels of detail using small lenses (such as through a scope) the sensors need cryogenic cooling.

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