How Sonar Works (Submarine Shadow Zone) - Smarter Every Day 249
Do you guys do things like that? That's a NO GO. That last 15 seconds has got to go. ....That' a No Go....Okay, cool. Nice. When you talk about weapon systems on a nuclear submarine, there's a very fine line between what's unclassified and what's classified. What you just saw was me getting my hand slapped for asking a question that crossed that line. This is the next video in the Smarter Every Day deep dive into how nuclear submarines work We're on the USS Toledo. And I'm about to talk to a very important person.
Do you remember in a previous episode, we talked to chief Luth? You don't look excited about it. -That's cause there's no poppers out here yet. -(Destin Laughs hard) Well that happens to be the guy over sonar for the entire nuclear submarine that we're on. Sonar operators do their thing HERE in the control room.
This information is processed and then distributed on monitors throughout the boat. For this discussion we'll be located down HERE in the officer's wardroom. So here's how this interview went down. I interviewed chief Luth on the boat. I had to hand over physically the cards and all my data to the Navy, the Navy then scrubbed what was classified, what wasn't...long story short.
This is an amazing video. And we're going to deep dive into the hardcore physics of how sonar works. Let's go get smarter every day. (Smarter Every Day jingle, with sonar ping at end) When you think about subs, you think about sonar, but this is a very sensitive thing, because if this is a cat and mouse game, this is how you do the cat part. And so I guess the mouse part too.
So to make sure that we don't say anything, we're not supposed to say we have Executive Officer Andrews here. Thank you. And so if I say something wrong or he says something he's not supposed to say you're going to... you're going to... -Yup! Yup. Okay. So this is a sensitive topic. Okay. I'm Destin Hi, I'm Garrett.
Garrett? Yep. Okay. And so what is your role on the boat? I am the Sonar Division Lead and Chief Petty Officer. Okay. That means you're over sonar for the whole boat? Correct.
So my understanding with sonar is that, sir, am I allowed to sit here? Okay. So my understanding was sonar is it's kinda like echolocation. Um, you ping, you listen for a return off of an object. And then, um, based on the shape of the sound that comes back, we'll say "shape of the sound", you can figure out what's out there. I would say that you are partially right. -Okay.- But mostly wrong. (Both laugh)
Okay. So, so is it because of the ping part? -Uh, yes. Okay. You're smart. And like me, you probably have a good idea of how sonar works, SONAR which stands for sound navigation and ranging works like this. You're going along and then you ping and then you listen for an echo The amount of time it takes for that echo to return to you. [Underwater Pinging Sounds with echoes]
AND how much sound bounces back gives you an idea of how far away and how big the object is. This is exactly the same way dolphins and bats use echolocation to navigate using sound. This method is called ACTIVE SONAR because you're actively sending out a sound in waiting for a return. We're going to talk more about that in a few minutes, but for now we're about to learn about something called PASSIVE SONAR, which is something I don't know a whole lot about So this underway specifically is a bad underway for me to tell you, tell you that you're wrong because we're using a whole bunch of active sonar. Since we're under ice, we're trying to navigate around icebergs and find ice keels and make sure we're not running anything. Um, we're using a lot of active sonar this underway.
Normally we're a hundred percent passive. And um,..... OK so the reason you'd want to have passive sonar is because anytime you emit anything from the boat, people can see that is that right, sir? [Silently nods] That's right? He's very tight-lipped I kinda like this. Okay. So, so active sonar as I understand you ping you make it sound any kind of emission. You're looking for the return, passive sonar... This is something I don't know about. So passive sonar, we're just listening.
So what we're doing is listening to see what's up in the water. And, uh, once we find something we can gain it and we can, we know what bearing it's down, um, and, uh, maneuver the ship and determine which direction the sound is coming from. Uh, we can even classify, uh, what is making the sound based on how the sound was made..
OK, Chief Leuth is talking about acoustic signatures. The ability to identify what's out in the water, just from the sound. When you and I listened to sound, it looks like THIS in my head. It's just a wave form. And I'm like, "oh, that's louder. That's not as loud" but sound is actually way more complicated than that. In order to analyze TRUE sound,
you need something called a spectrogram. And that's what this is. You can see that you have all the different frequencies displayed here, and it's a function of time and you can see which frequencies are hot at different times. [Deep Voice] The lower frequencies are down here [High Voice] And the higher frequencies are up here. If you analyze a spectrogram, you can come up with all kinds of amazing things. For example, let's look at a spectrogram of an Alabama summer night and look at all the different sounds that we might be able to discover. [Mockingbird chirps line up with graph] [The shape of the curve corresponds with the sound] If we zoom in, we can see the whistle of the bird as it changes its pitch, creating a bird call.
[Bird call changes every 3 chirps or so, as you can see on the graph] We also see these faint, horizontal bands on the screen as well. Let's take a look at what's going on here. [Crickets Chiirping} If we isolate the frequency and increase the gain, that we can clearly hear the hum of the summertime crickets. [Crickets chirping sounds like high pitched white noise] If we zoom in on this second lower frequency band and boost the gain again, we can hear tree frogs and toads from all around the immediate area. And then you can see something down here in the even lower frequencies. You want to guess what that might be? [Distant train horn] Yep! That's a train going on in the distance, but all the bird calls keep going on above it.
You just did signature recognition with your ears. You compared a sound, you heard in a certain frequency band to known sounds in your database. That's exactly what the Navy does, except they do it in a much deeper level, pun intended.
Think about this. Your phone can identify music based on what it can hear. Imagine how much money and effort has gone into developing algorithms to operate on a submarine, to identify. What kind of boat is out there in the ocean? Human made machinery stands out like a sore thumb, but the Navy also has to filter out what they call "biologics" sounds of pistol shrimp clicking or whales off in the distance.
All this is rolled into tremendous efforts, put into signal processing and machine learning algorithms, just to figure out how the Navy can process all the sounds in the ocean. So passive sonar. So I'm assuming you're using multiple frequencies? And those frequencies will affect what you're hearing come back? Is that true? [Clicks teeth...Inhales... thinking deeply] Uh, yes, it is true. Um.
Are you trying to, are you buffering? You're trying to figure out what you can say? - Yes. - Okay. So... You can just avoid it. You can just say, I don't wanna talk about it. Let's just.
It's just the question you asked. I can't answer it without getting into classified stuff. Well, don't, don't worry about it.... So passive, PASSIVE sonar. I assume that means you're having to use multiple frequencies in order to see shapes of different things. Is that the deal? Uh, we're looking at a large band of frequencies, um, to determine where a contact is coming from.
So if you're listening to a boat, that's out there, let's say you got something that's running off a diesel engine and you got a knocking cylinder or something. It's one thing to hear that that's just listening, but that's not sonar. You're using the term passive sonar. So that implies that you're hearing something bounce off something else? Uh....no. No. So I mean that, that is part of it. Um, and there is some different propagation paths or different ways that sound could take coming from the source coming to us.
I I'll draw you a picture real quick about what we're looking at and I'll make a little more sense. Chief Leuth is about to draw. What's called a bearing rate graph. This seems intimidating at first, but it's not. I promise you WILL understand it. Just stick with it.
This is one of the most important tools that submariners use to see the world. Okay. So we have a... this is a waterfalling display. So the newest data is coming from the top and the older stuff is scrolling down. You have a line of bearing at the top. So in this case we'd be going, course North,
Um, and then if we saw a line coming down right here, this could be a contact. So it would be a contact bearing zero nine zero. My broadband operator would take his cursor. He could, uh, put it on top of this trace and listen to see what it sounds like and based on how it sounds, we can classify the contact.
Okay. So we're about to get into the deep water. Just say no, if I go too far. Okay. But I've observed enough to, I think, be able to ask questions here. So if this is, if this is the boat here, so can we draw a boat? What are these called? The bow planes. Uh, about planes out front stern planes back AFT. Okay. And you got the rudder back here? Yes, sir. Okay. So, so this right here, that would be the line of bearing and boat?
Correct. Okay. So if, if we have a contact right here, straight off the nose and that's going to be right at zero, and if we're going straight at it, then I would expect this. This is time right? -It is time to time versus bearing, correct.
So I would expect the line from that to be just like that. Is that true? Exactly. Exactly right. Okay. So if, if we have something else, I think this is what you're about to tell me...If we have a contact here and the boats going forward. Can you please draw?
Are we okay, sir? We're good. Okay. Can you please draw what that would look like on that graph? So we're, we're moving forward at a certain velocity, the contact's off to the right. So the contact is kind of in time, it's going to be moving down here to the right. Correct. And it's actuallygoing to look a lot, like the first thing I drew and it's range dependent.
So you could have something that looks like this. Um, like I had there originally, if he's like, I'd say at mid range. But if he is at a much closer range, he's still gonna start at the same bearing, but he's going to go through those bearings a lot faster.
I always think about it. Like you're walking down the mall or something. And if you see somebody all the way down or walking towards him, you don't have to turn your head very far because they are pretty much in the same position, relative to you. But when they get real close, if you want to keep looking at them you have to turn your head, and that's kind of where this, this bearing rate comes from.
Cause you're going through bearings relative to you faster. So bearing rate means a measure of angle over time. So it's the angular.
It's the amount of rate that you're moving to look. Right, the change in bearing over time. -Change in bearing over time.... So imagine you're in the submarine, moving along in a straight line. If another boat comes along and you hear its sound with the hydrophones, which are installed on the outside of the boat, the Navy calls this a CONTACT, Just like your two ears, tell you the direction that a sound is coming from.
If you have multiple, hydrophones set up correctly on the outside of your boat, you can also tell which direction the contact sound is coming from. That angle from the nose of your boat to that contact is called the bearing. And that is very important for submariners. In this case, the contact is moving. So the bearing is 20 degrees, 30, 60, 90, 120 150... And if it's running parallel, it doesn't quite make it to 180.
And that's how you measure the bearing, which is basically just the angle from your boat. Now let's do something a little strange. Let's unwrap this polar coordinate graph and let's add a time component to it by scrolling the graph down and plotting the bearing we see as a function of time, Watch this closely.
Contact. There's 20 degrees, 30 degrees, 60 90, 120, 150. And we've lost contact. The shapes you see on this graph could literally mean life or death for submariners. For example, if you see a vertical line on this graph, that COULD mean danger. Let's say you're stationary and you're trying to hide.
And someone figures out where you are. If they start moving right at you, they're bearing rate will remain constant. Look at the graph. There's a vertical line. Flip that scenario around.
And let's say you've found a contact that you want to interrogate. As you close the gap between you and the contact, your bearing rate also remains constant, meaning it also graphs as a vertical line, vertical lines on a bearing rate chart means you're on a collision course. And it means from my perspective that probably one party or the other knows the other one's there.
And they're going to check it out and say, hello. If a boat is crossing in front of you, you'll see a very different kind of curve, [Boat engine noises moves right to left] a boat going behind you. You'll see something totally different. The ability to understand these curves is a skill that submariners develop over time til it becomes second nature. So imagine how complicated this gets.
If you have multiple contacts in relatively close proximity, Watch this and try to figure it out. This is how submariners see the world. Where is this boat relative to you? Submariners are like Neo in the matrix. They don't just see lines. They can see the code and understand what they're looking at.
Let me give you a visual aid and see if you can see now what was being plotted on the bearing rate graph. How did you do now? Now let's take this one step deeper. So what happens when we start to change the heading of the boat? Not only does the chart get incredibly complicated, but you have to do a rotational coordinate transform in your head all the while. Keeping track of time. This bearing rate graph is an incredible tool to use math, to literally see beyond the hull. Every major room I went into in the Toledo had one of these hanging on the wall.
Got it. How am I doing? Like, like in terms of understanding it, where am I at? Am I like...? You're pretty good. Pretty good. I'm like at kindergarten though... That's all we want you to know.. That's where you want me? That's where we want to keep it. [Destin laughs] Okay.
I'm impressed how fast you picked that up. Or, understood the bearing right thing. -Ok So, so this is like first glance. This is where you start. And then I've worked with radar stuff before. There's a thing called a waterfall chart. You're dealing with stuff like that as well. Yeah. So if you worked with radar before radar and active sonar,
which is not really what we're talking about right here, but radar, radar and active sonar are almost identical except for the frequency in which they're happening at. I mean, in a lot of ways, it is the same thing except for radars happening in the GHz range and we're happening in the Hertz range. -Gotcha. That's good. So you're also....
if you can't answer, don't answer. So you're also doing... That's no go -That's a no go? No Go That last 15 seconds has got to go. That's a no go. Okay, cool [awkward nerd laugher]
Nice. So we started to dig deeper into active sonar. And we had conversations about the signal to noise ratio and how they filter out different signals. And at some point the conversation switched to what was classified and what wasn't Each hydrophone is. Hold on. I'm reading his body language. Don't go that deep.
Yeah, no, that's good I can show you in the manual is good to go a hundred percent good to go. It's an unclassified manual. RP 33. I can go run and get it real quick. If you want. In the end Executive Officer Andrews was very patient with me and he didn't totally shut down the conversation and let us keep going. So if we have something out here that we're contacting here, I know this is an issue with radar. I don't know if this is an issue with sonar, but like, as we create, if, if we're, if we're pinging we're doing active sonar, and then we get that return coming back, what can happen if I understand correctly is some of this that goes up, hits the ice and then comes down.
So instead of getting a distance from here to here, back to here, you get here, here, here, here, or here, here, here, here, here you get multipath. So basically there's multiple ways that you can get returns to the vessel. Is that true? That is true. And, uh, even when we're not under ice,
the signal can interfere with the bottom, -The what? The bottom of the ocean. Okay. And we can also get a return off the bottom of the ocean. Oh, okay. So the, the problem is more complex than I thought. So you, you have things like that as well. Correct. -Got it. And so... You have ways to take this into account? -Yes.
Multipath gets incredibly complicated geometrically and to prove a point. We're going to play a game. You are now the sonar operator on the USS Toledo. You've been authorized by the captain to use active sonar, to tail, a mysterious craft that's in front of you, the Nautilus.
First of all, we're going to do this in open ocean. You are behind the Nautilus and you are going to issue a ping. And you're going to watch the return to see where the Nautilus is. [Sweeping sonar ping] [Echoey Return] Okay. By that return, it's clear that it's in front of you
and it's off to the right a little bit. Right? But that's not how sonar works. You're under the ice and you're over a sea floor. So let's take a different view.
This is what it's actually like. [Sweeping Ping] [Return from floor] [Return from Ice] [Return from Nautilus] [Bounce echos overlap] I'm going to slow it down and watch closely. The first return to the submarine is actually not from the Nautilus.
It's from the bottom of the ocean. So how do you figure out, which one is the real return? Is the difficulty of multipath. There are multiple paths that the sound can take to the contact and on the return path. So that means one sonar contact gives you multiple returns at your hydrophones. If that's true, how do you know it's real? Like, how do you know it's here and not here? Furthermore, what if there's actually a school of Nautilus is out there? How do you know that it's just one contact and not five.
That is a challenge that I don't know the answer to. We're good. We're good. You got to get the manual. He's got to make sure that it's all clear RP, 33, you can actually Google this, this breaks it down a lot more. And there's a lot of good stuff in here. I asked a ton of questions and there was a lot of things they just weren't willing to talk about. But when I got off the sub, I found this document and it details a lot of the things that submarines have to consider for example, and this is crazy, but this is real. The speed of sound in water changes with temperature, pressure and even salt content because of that, it can bend sound.
So because these three things change on different places at the globe. And even in the depth of the water, wherever you are, you have to understand the conditions of the water around you at all time. So that you know, the speed of sound in the water around you. The Navy likes to display this data by graphing the speed of sound in water versus the depth of that water. This is commonly referred to as the SVP or this sound velocity profile. To measure the sound velocity profile, a device called an expendable bathythermograph is used.
And just looking at these things shows you that they're really expensive, which tells you this data must be really important. You chunk one of these things overboard and it travels the water column, measuring the temperature the whole way you can then graph the sound velocity profile. And you know how fast sound travels at each depth. And you know, then what that will do to your sonar waves. If you're a surface ship, since speed of sound generally increases the deeper you go down, the speed gradient could bend your sonar waves up, making them bounce off the surface, creating what's called convergence zones around your boat.
At certain ranges and depths, you could detect contacts, but at other ranges, you can't. This means a crew could acquire a contact and then lose it only to acquire it again at a different range. What!? Bending sonar is...it gets weirder. Let's keep going.
If you're a submarine and you find a few rapidly changing temperature layers. Known as Thermoclines, your sonar waves might bounce back and forth like light in a fiber optic cable. This is a formation called a sound channel. To me one of the craziest things that bending sound can do underwater for a submarine is make it disappear.
If a surface ship is using sonar to look for submarines because the sound travels faster the deeper it goes down. This lensing effect means that some of the sound will curve up and other parts will curve down. Creating what's literally called the SHADOW ZONE. This is super spooky important stuff that they wouldn't talk to me about on the boat. If you go back to that document, I found earlier, you'll see a section, describing an equation to calculate what's called "BD" or the best depth. Interestingly, that particular equation is redacted Shadow Zone!?. What!?
I mean, this is amazing. And we're talking like the bleeding edge of physics here. If you had the ability to measure and had total perfect knowledge of everything to do with the ocean water around you, you could literally find a spot to put your submarine that people could not detect you. They could not hit you with sound and get sound back. And you're just there. You're a silent killer, just sitting there in the ocean. That's amazing. That being said, though, even if you had perfect knowledge of the salinity and the thermoclines and the bathymetry, and you could find that spot, you still have to get there. And the act of getting there has its own challenges associated with that.
Think about the earth and its waterways. There are choke points all over the globe that boats are forced to go through. If I activate this heat map of global shipping throughout the world, you can easily identify the areas with the highest traffic density. For example, the Panama canal. If you cross the Pacific, one of the busiest places of the world is the Strait of Malacca, which is why Singapore is so important. You can see Sri Lanka, the Strait of Hormuz, the Suez canal, Gibraltar, the English channel.
But think about submarine traffic. It probably looks a little different depending on what your mission is. If your job is to hide, you're probably going to avoid these shipping lanes because you might be detected. One of the most strategic places on earth is the body of water, bordering Europe, Asia, and North America. The Arctic Ocean, Not only is it important because you can access these areas easily, but it's also a shortcut for Russia to gain access to the Atlantic Ocean.
Think about it. The Bering Strait between Alaska and Russia is narrow and shallow, which means it's easier to see what goes through, but at the exit of the Atlantic ocean, it's different. For American submarines based in the East coast, like the USS Toledo, there's a path to the Arctic through friendly territory, the Canadian islands for Russian submarines, looking to enter the Atlantic. There's pretty much only one thing that makes sense. The why that G I U K gap, which is an acronym, which stands for the gap between Greenland, Iceland, and the United Kingdom.
The G I U K gap is deeper and in international waters. So as submarine can pass through this area, more stealthily, According to unclassified web sources, because of its tactical importance, this area is absolutely full of all sorts of acoustic listening devices and hydrophones in order to detect submarine traffic. This was ultimately my question when I got on a sub, right? When I get in a car, I've got a windshield and I can look out the windshield and I know where I'm going. You are the eyes ofthe boat. -Yes, yes, sir.
Yeah. So you're using geometry to steer a multi-million dollar... or is this a billion dollar vessel? I don't know what this is. It's in a very expensive vessel. Appreciation. [Both laugh] So there's multiple levels of math that you're using here, right? Yes. All the time. In fact,
I thought it was funny cause I told my geometry teacher that I would never use this stuff because I hated class in high school. and now I'm using more advanced geometry than I even knew was possible in high school. -Really... So I'd like to go back and talk to him [Laughs] (Destin) And tell him, thank you? Yeah. This episode of Smarter, Every Day. Is sponsored by Audible.
And I'm going to tell you about a book today that you've heard about your entire life, but you may not have listened to it and you're missing out. And I'm going to tell you why you should listen to "20,000 Leagues Under The Sea" by Jules Verne. So 20,000 Leagues, let's start here.
20,000 Leagues does not refer to the depth that the Nautilus goes. It refers to the distance, traveled underwater by captain Nemo in the Nautilus In 1867, Jules Verne went to this big exposition called the Exposition Universelle And when he was there, he saw this model of a French Navy submarine called the Plongeur. When he got this thing in his head, he started thinking about how fantastic it would be to go on a voyage with some crazy captain named captain Nemo.
And he came up with all the different technologies that would be required for such a voyage. And he nailed it. Like this is to the point where it's literary prophecy A nuclear submarine is pretty darn close to what Jules Verne came up with.
And it's amazing. So when you read it, it's almost like hardcore science fiction in a historical setting. So it takes your brain, many different places. It's amazing.
You can get this by going to audible.com/smarter or texting the word smarter to 500-500. That gets you a credit every month you can use on any book you want. I've got all kinds of stuff like comedy, things about negotiating.
There's all kinds of stuff in audible. You can get. However, there's a new thing called a plus catalog. Audible is way more than just audio books. There's all kinds of podcasts, original content. If you go to the plus catalog, you can get anything you want in there all the time for free.
There is way more content here than you would ever need. 20,000 Leagues Under the Sea is amazing. And I'm grateful if you use the "smarter" at the end of your URL, because that lets them know you came from Smarter Every Day and encourages them to support Smarter Every Day in the future. Speaking of support, you are sticking with the submarine series and I'm grateful. I am.
The turnout on the series has been fantastic and it was far more than I ever anticipated. I'm doing this because I love this content. I learned a lot on the boat, but doing the research for these videos, I go even deeper. This one was interesting though, because I had to learn stuff apart from what they told me on the boat.
And I had to like be clever about what goes in. It was, it was difficult to make this video and I hope you enjoyed it. Anyway. I'm grateful that you're here. Please consider subscribing to smarter everyday. If you're into that sort of thing, if not, no big deal. I'm going to continue to try to earn that subscription anyway. One day, one day, maybe you'll consider it Anyway. Thank you so much.
I'm Destin, you getting smarter every day. Have a good one. Bye. Well, thank you very much. I appreciate your time. This was a, this was very exciting for me, sir. I appreciate it. Uh, that was, uh, that was rather fun just to watch your body language.
Yeah... [Laughs] ...Wow. [Laughing]