TechStuff Classic: How Sonar Works

Dive dive boop boop boop. So I talked a lot about echolocation in recent episodes, this is the episode where we really looked at the tech behind sonar. So listen as Chris and I explore the incredible world of sonar. I hope you enjoy. Have I got this straight? Jonesy, A forty million dollar computer tells you you're chasing an earthquake, but you don't believe, and you come up with this on your own that had a direct bearing 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 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 cea floor if you want to do that. Ye, 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 other animals. Yes, that would be an echolocation, Yes, yeah, exactly, that's what the sonars 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. That sounds so so scientific. It's though, 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 scrumbing feeling from from from and when sound hits a really solid object, 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, right, 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 publish in the right order. But no, Leonardo da Vinci back in experimented with with listening to sounds through water. He would insert a tube into into water and put his ear to the tube like 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 frogman of his day not not so effective, but getting all the way up to the eighteen or the nineteenth century, rather they 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 sixteen. Uh it was an early passive so in our 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 in a

different form. But by um and of course thinking back on it, that's you know World War one, right, the British and American scientists had developed an active so in our 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 something sorry I keep coming, there had been submarines before that, but sure, 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 it's 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 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. Oh really, and what was that event? Well, there was a little boat that happened to sink. Oh yes,

that little boat. Yeah, yeah, don't they go um, my heart will go onto Yeah, the Titanic disaster, Titang 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 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 he panted 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 various 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 right 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 just 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 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. Right, you would have hydrophones play and you may have a couple of different passive sonar stations so that you have hydrogen phones 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 did 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, I believe there are 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, they're

they're support um. So it's it's a pretty interesting thing. And the 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. Yeah,

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 and how much how strong the signal is, that's how you kind of determine what it is, your your hearing. You know how far away 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 don't wait wait, you know, and there's just like you know, you watch the beads of sweat rolled down the submariner's faces. Yes, there's the there's the one that I quoted at the

beginning of this podcast. Um, yeah, no, no, but there are many you know that that then that's the thing is you have to be very very quiet and that kind of a situation because any little thing can be picked 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 an Okay, I got you. I was about for the rhyme. I sorry, so active, but with the rhyme of an ancient you stopped at one

of three. Chris and I will be back in just a moment to continue our discussion about sonar, but first let's take a quick break to thank ours. Answer 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 the and 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 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 technology

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 it 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 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 the enemy destroyers are 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 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. There. You're looking for schools of fish. They're going to be moving around anyway, so it's not like it's um, it's not like 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 sentar technicians training. They actually, uh are known to record things that are just natural sound,

like the sounds of fish, um tectonic plates. I'm not I'm not sure what kinds of sounds does give off really low groaning ones, yes, kind of like 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 an enemy submarine. But you know, detecting a fish versus you know, a snake or some other type of monster, we've gotten very silly, very quickly.

Well no, I mean people have been used saying that kind of equipment to try and determine whether or not there are yeah, so 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 Locknest 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 lock best 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 and a cottage on the shore. There's a shadow on the door. No different kinds of sonar okay, side

scan center UM. This is a device used to find objects on the sea floor and figure out what they are. They usually have a tow fish or a tow body, which is a UM basically sophisticated device that goes in the water and is towed behind the ship, and a device that processes the signals on the top UM. What happens is they use the the sound energy which is transmitted in a fan shaped pattern and goes about a

hundred meters down or so. Basically, they used the information that comes back to create 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 you get 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 it might be photo bright green and dull, right right, But you can get an idea of what the 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 around. 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. Yes, there's a transmitter which transmits the sound right right, 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 to receive or 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. We have a bit more to say about sonar technology, but before we get to that, let's

take another quick break to thank our sponsor. There was a sound detective in n 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 it would be be ginormous, right to use the technical term. It's more likely that the bloop is ah 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 Reallyer, 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 dead Cathul 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. I think that was 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 it was the 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 lidar, which is a light

detected light detection and ranging system. Doesn't use sound, he uses light, but it is used mathemetric 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 it reflects 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 reading for the top and the bottom of the depth, so you get an idea of how deep the water is. And they use this um from aerially generally, well from their 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 and this is really useful for those, uh, really hazardous areas where it's might be difficult to get a reading from a vessel water borne vessel. It would be dangerous put a ship there exactly reefs and shoal 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, like 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. Sure, I was going to mention too that you can you can actually use sonar from uh, you know, from the air as well. If you're using a sona boy, which is basically a buoy that is equipped with sowner equipment that is lowered I

guess by helicopter would probably be the best. Uh. That's where I've actually seen it down 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 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 you know, sometimes they'll use things like UM decoy explosions so you create enough 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 that 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 spooped 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 welles getting the bens. Because the report I saw was actually from a uh UK organization called Marine Connection, which is a pro um water life organization, and they had cited to 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 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 no. UH 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. Right, So yeah, there there are some concerns about this technology, which you know, we've been using for almost a century now regularly. 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, that wraps up this classic episode of tech Stuff how sonar works. It was fun to go back and revisit that and listen to a version of Jonathan that's eight years younger than I am today. Holy cal Uh. I look forward to bringing you more of these classic episodes

in the future. If you have any suggestions of topics that should cover in current episodes of tech Stuff, because new splash. I cannot travel back in time and record a new classic episode that that the way Back Machine will not let me do that. It's apparently some sort of I don't know. They call it a Grandma paradox. I don't understand. But if you have a suggestion for a future episode, let me know. Send me an email. The addresses tech stuff at how stuff works dot com.

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