How Sonar Works

and you come up with this on your own. That had a direct burying to our topic today, and that topic would be sonar sound navigation and ranging. Well, that pretty much covers it, so, well, that's exactly what it is. It's one of those nice, nice words that sort of covers it. So yeah, no, it's it's it's very it's very much exactly what sounds like. It's using sound to navigate and to to find the distance from other objects.

As it turns out, there a lot of ways to use sonar um and we'll get into that, uh in a minute, but there are also a lot of different types of applications, uh, different ways to use it as in like um, different kinds of equipment that that can be used to find depth and identify things in the water and even map the sea floor if you want to do that. Yep. And uh, actually, the you know, we're not the only ones to to use sonar, not by a long shot. True. Dolphins and whales use it

to man to other animals. Yes, that would be an echolocation, Yes, yeah, exactly. That's what the sonar is based off of. It's the idea of the way sound travels. And so if you sound travels and waves, it's a it's actually a physical uh thing. It's you know, we don't see it, but it is a physical effect. When you make a sound, you are causing stuff to bang against each other. Sounds

so so scientific, it's true. So when sound travels, it's really lots of air molecules bouncing against each other until well really just until it disperses, so it keeps on going. I mean. And we detect sound, of course through hearing, but there are other ways to detect it. There there are sounds that are outside of our range of hearing that we can sense, Like there's some that are so low that you know, you can't hear it. But you

can feel it. That's thrumbing feeling. And when sound hits a really solid object, uh, it bounces it, it refracts off as some of it reflects back and uh and that's where we get the whole echo effect. So when you're in the right kind of environment and you speak and you hear that echo, that's those sound waves bouncing back and coming back to you. Well, you can use this to find your way around an environment. Well, um, so where does sonar come from? Then we have to

figure out exactly. Uh really when that all started taking place, And I think it was really probably, I mean, people have been doing it for a long time. Yeah, you could, you could identify things and under the surface of the water. But why are you creating him? Because my favorite man of all time did some experiments with listening to sound through water. Okay, Leonardo da Vinci. We just finished talking about him a second ago, which I'll try and make

sure that the podcast published in the right order. But no, Leonardo da Vinci back in experimented with with listening to sounds through water. He would in sort a tube into into water and put his ear to the two like a straw. Yeah, pretty much like a straw larger than a straw. Mr da Vinci, why are you listening to

your drink if you had a drinking problem. So, but yeah, he would use this to to kind of listen to UH to the two noises, with the idea that if you could create the right system, you would be able to detect when things were approaching through the water. Now, during da Vinci's time, this wasn't really that big a problem. Things usually approached on the water, and if they were in the water, they weren't really something you needed to worry about. The UH frogmen of his day not not

so effective. But getting all the way up to the eighteen or the nineteenth century, rather the eighteen hundreds, UH, you started to some some lighthouses would have underwater bells that would be UH placed around the area to warn ships of of hazards. So ships could actually listen as they approached land and they heard bells, they knew they were coming up on shoals, and they could they could

alter their course before running aground. And then UH in around nineteen six, UH was an early passive sonar system. Will explain what that means UH in a minute. But they were using strings of microphones towed by ships, which is again something that dates up to the present and different form, but by en um and of course thinking back on it, that's you know, world War One, the

British and American scientists had developed an active sonar system. Um. You know that that was a big concern at the time because of course the German uh U boats were patrolling and it was some scary stuff. Yeah, actually it was.

It was a very intimidating weapon, definitely. I mean there had been some sorry I keep kinding, so there had been submarines before that, but sure, but the German U boats in World War One were a very effective way of taking control of the Atlantic Ocean and the shipping back and forth between the continents. So sonar was something that they were very rapidly trying to work out exactly.

And it's funny because well not funny, but it's it's interesting to me that really the the event that kind of started all this off wasn't World War One, because by then they they were pretty far into it. But they did have an interest, yes, yes, to talk about to talk about how this really started off. You really got to look back to a certain event that happened in nineteen twelve. What was that event, Well, there was a little boat that happened to sink. Yeah, that little boat. Yeah, yeah,

don't let go, um my heart will go on. Yeah, the Titanic disaster. Titanic disaster. Following that, that's when we saw the first patent for underwater echo ranging demands. So that was that was where the first patent was filed UM and it was filed at the British Patent Office by Lewis Richardson, who was a meteorologist UM and he had come up with this idea of creating a way

to locate objects underwater using sound. You would you would fire sound out, you would measure the sound that comes back, and through that you would figure out what was there, how far away it was, whether it was moving or not. I mean, these were all the concepts now back in nineteen twelve, they didn't really have a way of achieving this.

He panted to the idea, but it wasn't until like Chris said, around nineteen eighteen that we started to really see accelerated development because then you had a wartime use for it, and it was really important to find a way to to detect those submarines those U boats. Yeah, icebergs were were obviously concerned, especially in the North Sea and areous like that. UM because you know, as as is in the case of many cliches, there is an

element of truth in it. The tip of the iceberg really is, you know, the smallest part, and so much of it is underwater, and you can't tell without some kind of device, and I think that's uh. The earliest, earliest sonar or the earliest echolocation devices were not very precise.

In fact, they were so imprecise that they could tell you that there was an iceberg, but could not tell you where the iceberg was, So you you might know that there's an iceberg somewhere within a two mile radius of your ship, which is not entirely helpful, although I guess it tells you to keep an eye out so that you you don't see it before you hit it. You know, you you know, to keep an eye out

for for icebergs. UM. By the by the time World War two came around, that's when the because early sonar was really led by the British, they made the biggest advances in sonar technology. They didn't call it sonar, they called it as DICK A S D I c UH and UH. The A S D was actually a code. It was it was so that the people outside of the top secret development wouldn't know what the scientists were working on. So people say, well, what does as DICK stand for? Well, it kind of stands for keep your

nose out of it MR. So it wasn't really until World War Two that the United States actually outpaced the British in this technology. And uh, and that's when you know, the term sonar started to pop up, and that eventually became the de facto term for the technology. Right right now, we should probably uh at this point go into the two basic, very very very basic types of sonar, so active and passive. Active and passive, And I think passive

is the easiest one to explain. Yes, basically, you're receiving the sounds of the water around you. You're listening, yes, so simply listening. So passive passive sonar is where you have some sort of sound collection device, usually a hydrophone, which is just a microphone that you can use in

the water. You would have hydrophones placed and you may have a couple of different passive sonar stations so that you have hydrophones directed in specific areas, so that way you can tell where the sound is coming from, not just that there is sound, and you listen carefully for any kind of indication of other activity in the water. And it's interesting because as I was doing my research, I discovered that that if you were a trained sonar operator, yes,

and you heard a submarine. Let's say you're in a submarine and you heard another submarine, right, you could actually identify where that submarine what was from, based upon the sound you heard. Yes, that is correct, it is. That is to me as phenomenal. Well, every uh, as I understand it, every ship of any kind, submarine or ship or you know, I guess boat, depending on what's on

the boat has its own audio signature. Could be the engines, um or basically anything that's going on, if they are electronics on board that make a noise, if you know, fans, things like that. Some those things can help identify um another vessel in the water to the listening vessel. Yeah.

For example, in the United States, most of the submarines were operating on a sixty hurts alternating current power system, but in Europe they were operating on fifty hurts power systems, So just the the frequency of the sound would be enough to indicate to you whether you were listening to a US ship or a European ship. And uh, you couldn't necessarily if everything was running the way it should, you might not hear anything at all, or you might

hear very little. Um. It was if you didn't sound proof all of your equipment, like if if the various elements weren't uh weren't insulated properly, then stuff would rattle and you could you could actually hear the rattling. In fact, one source I read said that, uh, you know, the location of a submarine might be given away by someone accidentally dropping a wrench onto the floor the deck. I guess, um, I assume they're decks and submarines. I've never been a

board one. Yes, so yes, if you were to drop a wrench to the deck, it could create a sound that someone another sonar operator might be able to pick up and say, all right there there support. Um, so it's it's a pretty interesting thing. And passive sonar, by the way, was more important for submarines because if they use the active method, they would actively be giving away their location. Yes, that's because active active sonar systems are

giving off a pulse of sound yea often called a ping. Yes, So you ping the sound out and uh, and then they wait for the sound waves to come back. And based upon how long it takes uh and how much how strong the signal is, that's how you kind of determine what it is your your hearing or you know, how far away the the object is and you know

what it might be. You know, how many how many submarine movies have you seen where they do that tense moment where nobody's moving a muscle they got wait wait, you know, and there's just like you know, you watch the beads of sweat rolled down the submariners faces. Yes, there's the there's the one that I quoted at the beginning of this podcast. Um, yeah, no, no that, but

there are many you know that that. And that's the thing is you have to be very very quiet and that kind of a situation because any little thing can be up by the ping. And here's what's really interesting to me is that the ping is well really anything could be picked up by passive sonar. I know, I just want to make it okay, I got you. I was about so active, but with you stopped at one of three the active sonar. The basis of that really rests in the fact that we know how fast sound

travels through water. But we we do, but it's really complicated. You would think, oh, it's got to be some constant right, not exactly actually constantly constant. Yeah, The speed of sound traveling through water depends on several things. Depends on the temperature of the water, the salinity of the water, and the depth of the water, and all of these things affect the density of the water. Which makes sense, right.

If you've got more molecules packed together, sounds going to travel faster through that because the molecules hit each other more quickly, Like it doesn't take much for a molecule they'll run into another molecule. The sound travels much much further and much faster. Um if you've got them spread out, then they lose some of their energy as they are moving, and so it doesn't travels far and it doesn't travels quickly. So the rule of thumb is that it's four thousand,

three eight feet per second. And then you have to add all these modifiers in right right now, there are some some things that you can do. Uh. There is a system that I read about, the a n B q H DASH one speed of sound measuring system, which is, you know, a modern sonar system. Um. But it evaluates the depth and temperature and salinity of the water to get an idea of how the speed of sound is

going to travel through that particular water at the time. Obviously, that's probably a very expensive piece of equipment because it's doing those calculations for you. But that's what modern computing technolo gets you. Um. But yeah, it gives you uh, you know, sonar technicians can use that equipment to get an idea of what's going on with a lot better accuracy, and also helps them avoid being detected by other sonar equipment because they have an idea of you know, what's

the current conditions are underwater where they are right. So if you're using active sonar, you might be using it for uh. Well if in wartime you would have ships and and even aircraft using active sonar to try and detect submarines and then drop depth charges down to to

disrupt the submarines. Ah, yes, uh, so active sonar in wartime is often used by by vessels that can move fast enough so that it's not it's not a big deal about giving away your location like destroyers for example, exactly exactly, if you're a submarine, you don't tend to use active sonar as often. Um Yeah, especially when you're submerged in trying to avoid detection, because that's you can't move nearly as quickly as a the enemy destroyer you're

coming after you. Right, So so if you're also you could be using active sonar, not just in wartime, but also if you're mapping the ocean floor, then you want you want to be as accurate as possible, which means you have to have you know, you have to factor in all those elements we were talking about before, the

salinity and temperature and depth and all that. Um. If you if you're just using sonar as a fish finder, because there are plenty of products on the market that do that, you don't have to worry quite that level of accuracy because you're not you're usually not talking about the same kind of distances involved that we're talking about, and usually the you know, the depth is not as big a factor. So really in that case, uh, you know, you could use a constant speed for the sound through

water and not be so inaccurate. You're looking for schools of fish. You're going to be moving around anyway, so it's not like it's um, it's not like the kind of precision work you need to do with these other elements, right. Actually that that's one of the things that I found fascinating during part of the the sent our Technicians training. They actually uh are known to record things that are just natural sounds, like the sounds of fish, um, tectonic plates.

I'm not sure. I'm not sure what kinds of sounds does give off really low, low groaning ones. Yes, my back, but that's but that's the the trick is you once they understand what those things are, they can eliminate them. They go, oh, well, that's just a large school of fish, you know. Oh that's you know, an alien spaceship that's crashed underwater, that kind of stuff. Um, I make a joke,

but no, that that that Uh. I was wondering about that when I was reading about civilian uses for so in our technology and I was thinking, Wow, how do they know, you know, what is a school of fish? And obviously if you're on a lake and it's it's probably going to be the stuff that's moving around underwater. It's not likely to be in any submarine. But you know, detecting a fish versus you know, a snake or some other type of nest monster. We've gotten very silly, very quickly.

Well no, I mean people have been using that kind of equipment to try and determine whether or not there Yeah, so in our equipment. Yes, there are plenty of monster hunters who have tried to use like a fish finder, yeah, essentially. But that's the thing is that there there are schools of fish in Lockness and schools of eels as well. So you get a school of fish or a school of eels that's going to give you a reading. And then people say, hey, look there's a monster down there.

Not necessarily, And I have to say, you know, I've mentioned before in the podcast that I'm a skeptic. Out of all the things to be skeptical about, the lucknest monster was the one I held onto the longest because I want to believe it's real. I don't believe it's real, but I want to so badly. Um, in a cottage on the shore, there's a shadow on the door. No different kinds of sonar like side scan sower. UM. This is a device used to find objects on the sea

floor and figure out what they are. UH. They usually have a toe fish or a toebody, which is a UM basically a sophisticated device that goes in the water and is towed behind the ship, and UH a device that processes the signals on the top. UM. What happens is they used the the sound energy which is transmitted in a fan shaped pattern and UH goes about a hundred meters down or so. Basically they used the information that comes back to create a an image of what's

on the sea floor. So if they get a really strong signal UM back, that appears as a light image on the screen, whereas weaker signal would show darker images. So UH sort of a black and white image. I don't know if it's actually black and white because I was reading copy and they didn't bet but i'd be bright green and dull, right right. But you can get an idea of what the bottom of the area you're looking at. I guess it could be a lake or

the ocean. UM. They don't they don't offer the same kind of depth information as the military would use to say, oh, well, we you know, we're about to run aground. It's not the same kind of application of sonar. Also, we should add that at certain depths, once you get really really deep, the water gets so dense that it can refract sound waves. So you you start to lose the ability to really map the ocean floor with sound because the water itself

is so dense that it's it's it's mucking things up. Also, I guess I should go ahead and mention as well. We've talked a lot about the sonar. The sonar really has three main elements to it. Oh, yes, there's a transmitter which transmits the sun right right right. I can't believe we didn't. We didn't really talk about it. But there's a transmitter that's that's what passes on the signal. Uh, it's an electric signal that goes to a transducer. Now, transducers what they do is they convert one kind of

energy into another kind of energy. In the case of sonar, it's converting sound electricity rather into sound right. Active for this is for active sonar, clearly. And then you've got a receiver that receives the signals when they come back um and and then you usually have a display, so there's a transmitter, transducer and receiver. This is for again

active sonar. With the passive sonar, you just need receivers really microphones, hydrophones, UM and and there are plenty of stationary UH sonar UH stations and I guess stationary stations, thank you, Jonathan, you're both repetitive and redundant. But at any rate, there are plenty of these in the ocean. The lots of different militaries have them station stationed at different spots along the coast to detect things like possible

incoming submarines, that kind of thing. UH. And I wanted to mention very quickly about an interesting sound that was detected. Oh do you want to? Yes, I do, I definitely want to. There was a sound detective in It was actually detected several times over the summer of U in the Pacific Ocean by by a hydrophone array. And the sound was a very low frequency sound generated over a pretty extended UH time frame several I think it's several

minutes long. And it's called the bloop. The bloop is UM this odd sound that that we're not really sure what made this noise. If it was organic, then it would have to be a creature larger than any that we've previously identified. So if it were a whale, it would have to be such an enormous whale that we've never seen it. Uh ever, yeah, so be be ginormous,

right to use the technical term. It's more likely that the blue is a h was some sort of geological byproduct, right, But at any rate, this sound was located or the location of the sound is probably somewhere around fifty degrees south hundred degrees west. What's interesting to lovecraft Ian fans is that that's not that far off from the supposed coordinates of Realier, which is Cathulu's city of the Deep.

So some people have jokingly, tongue in cheek, said that this noise was dead Cathulu snoring because in his house, and really a dead Cathulu lies dreaming. Alright then, and also, let's some we can actually play the sounds. So what we're gonna do here is we're gonna just take a second, we're gonna play the sound. This is a sound that's off of the U. S. Government's websites, and it is specifically the sound sped up sixteen times. Now, I don't

know about you, but I think that was Catlu. I was pretty certain it was a bunch of people flushing all at the same time. Could have also been that it might have been during the Super Bowl. Wait, it was the summer of ninety seven, so it couldn't have been. I don't know anything about sports, but even I know it doesn't happen in the summer. It was World Cup. It was a World Cup, except that wouldn't have been It wouldn't have been a World Cup. Okay, so our

speculation goes awry. Also, we had someone on Facebook I think, asked us about the blue Yes, there that goes and that goes out to you random Facebook person. All right, UM, so, uh, you know, I did look up some other interesting related technology like LDAR, which is a light detected light detection and ranging system doesn't use sound, uses light, but it is used. Bath Memetric lighter is used to determine the depth of water. UM. It uses lasers, pulses of lasers

sent out at two frequencies. UM. There's an infrared pulse which is a lower frequency and then reflects off the surface, so you know where the surface of the water is and then it uses green lasers that have a higher frequency that reflects off the bottom of the area. Interesting, and it works pretty similar to echolocation because it's getting a reading for the top and the bottom of the depth, so you can get an idea of how deep the water is. And they use this um from aerially generally,

well from they're mounted on aircraft. UM so according to Noah and I mean the National Oceanic and Atmospheric Administration, not the guy with the big boat. That's the second time you've made that joke on this pod, not this

particular episode, but in the series. Yeah, well you know, but yeah, and depending on how clear the water is, they can determine depths up to fifty meters And this is really useful for those, uh, really hazardous areas where it's might be difficult to get a reading from a vessel,

a waterborne vessel. It would be dangerous to put a ship there, exact reefs and shoals and that sort of thing, which is exactly why you'd want to know what it's like, you know, underneath the surface of the water, so you can get an idea for navigation purpose. I mean, really, sonar just don't mean to interrupt. But the reason why sonar it was so important early on is because light does not travel through water very well. It's just normal light, and you know, you go down just a couple hundred

feet and it's it gets dark really fast. And anybody who's swam in the Atlantic Ocean knows that it's not exactly the clearest water. Uh So it will be especially difficult to see in in you know, water with a lot of salinity and trabidity. And of course if you get it at pretty intense depths, then you don't want to have any windows in your device at all because

the pressure is too great. Um. Before we get to the next segment, I was going to mention too that you can you can actually sonar from uh you know, from the air as well, if you're using a sona buoy, which is basically a buoy that is equipped with sonar equipment that is lowered I guess by a helicopter would

probably be the best. Uh that's where I've actually seen it done, where they lower it into you know, so there's floating on the surface of the water that they can get readings um from anything that might be in the area. Yeah, that's pretty cool. That's often used in in wartime as well, because it's a way for you know, you send a helicopter out to the general region where you believe there's a submarine. You use these to try

and locate the submarine. Then you use the depth charges, which are really just explosives that that sink into the water before exploding. UM, and then try to damage or or disrupt the submarine in some way whereas the submarine is trying desperately to or the people in the submarine anyway, or trying desperately to avoid detection. Or sometimes they'll use things like UM decoy explosions. So you create enough uh noise in the water and it becomes very difficult to

pinpoint a specific object. UM. And I know you wanted to discuss that it's not all the sonar is not all necessarily beneficial, that it can actually have a negative impact on the environment. Right, we're actually the creatures living in the environment. We mentioned that that whales and dolphins

use echolocation in order to navigate their environments. UM. Sometimes there have been reports that that the low frequencies used in sonar equipment have disrupted that they're this marine life that in some cases there may be instances where it has spooked a pot of whales, for example, and and and so there there's some studies that suggest that some whales are suffering from a kind of um uh well, sort of a pressurization sickness because they're surfacing so quickly

that they are uh it's kind of like whales getting the bends. Yeah, actually it's exactly like wells getting the bends. Because the report I saw was actually from a uh uk organization called Marine Connection, which is a pro um uh water life organization, and they had cited a study from the magazine Nature from two thousand three which was citing an instance in which ten beaked whales uh surface too quickly off the Canary Islands um in two thousand two,

and and they got the bends. The whales got the bends. And apparently the situation is especially prominent for deep diving animals such as a beaked whale. And it may be related to the terrain underneath the water. If it's really steep um sharp drop off, that may affect the way that the sound waves are traveling underwater and maybe especially

confusing um. Noah also mentioned that there might be problems for deep diving species, but said that more study needs to be done on on these kinds of strandings to find out if it's limited to the surroundings, if it actually is the c floor that is playing into it, or whether it is strictly the sonar itself, you know, before they can make a decision as to what's going on.

But the Marine Connection has asked the uh, um, they've actually gotten involved and suggested to the European Parliament and it asked for a ban on high intensity sonar in certain areas. Um. So you know, there there are concerns that it may cause uh some some harm basically that they can swim into uh dangerous terrain to it. That is also an issue if they're they're momentarily confused, but in dangerous waters, that could be long enough for there

to be a serious problem. So yeah, there there are some concerns about this technology, which we've been using for almost a century now, uh yeah, and we're still some of them, like the passive systems. Of course, that's not a problem because the passive systems, all they're doing is listening. They're not sending out any signals, so not all sonar

is bad sonar even from a marine life standpoint. Oh no, it's still an incredibly useful technology, right, you just have to learn how to use it responsibly so that you're not causing harm to the environment or to marine life in particular. Well, I guess that pretty much wraps up a discussion on sonar. This was one of the Pallette's pet pet topics. He's he likes the topic as well. I think the video series brought that out, and they've had our radar and sonar moments, so that was a

lot of fun. If you guys have any suggestions for topics, stop by on Facebook or Twitter and let us know our handled there is tech Stuff hs W, or you can use the old fashioned method of send us an email that's text stuff at how stuff Works dot com and Chris and I will talk to you again really soon.

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