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Transcript of SONAR
What is Sonar?
Sonar stands for SOund Navigation
And Ranging. It's a system for the
detection of objects underwater and
for measuring the water's depth by
emitting sound pulses and detecting
or measuring the return after being
Sonar was first tested in the early 1900's
as a morse code/echolocation hybrid.
Types of Sonar
There are two types of sonar- passive
sonar and active sonar.
Passive sonar listens for other sound
waves using electronic listening
equipment. It's not as reliable as active sonar meaning you can't see a picture but you can hear sounds but it
doesn't harm wildlife like porpoises and dolphins
which use echolocation for hunting and navigation.
Active sonar produces and emits a burst of
sound/"ping". Active sonar picks up inanimate
objects, like mountains and other
geographical objects. Sound waves bounce
back when they hit an object, determining the
size and distance.
Active Sonar Pings
What you just heard (this video)
demonstrates roughly what
active sonar "pings" sound like.
These pings are used to help locate
things on the surface of or under
water. Active sonar is often used in
things such as drowning victim
Today, we will mainly talk about active sonar,
and its role in locating underwater mountains.
Without sonar, we wouldn't know about these
underwater wonders of the Earth.
Side Scan Sonar—
Side-scan sonar is a type of sonar system that is used to efficiently create images of large areas on the sea floor.
Side-scan sonar emits a fan shaped acoustic wave directly perpendicular to its direction of travel. As the "ping" travels outward, the seabed and other objects reflect the sound waves. The travel time of the pulse along with it's amplitude (vibration) are recorded, and then sent to a console which interprets and displays information recorded. With every new sonar pulse, the console calculates and displays another tiny section of the seafloor until it stitches together a large continuous image of the seabed.
1. Depth of acoustic pulse
2. Vertical beam angle
3. Range of acoustic pulse
4. Swath width across seabed
5. Tow depth of scanner
6. Port and starboard channel seperation
7. Horizontal beam width
- Side Scan Sonar — http://www.starfishsonar.com/technology/sidescan-sonar.htm
Discovery of SOUND BENEATH THE SEA
History of Sonar
Now that we're familiar with the usage of sonar and how it works, let's take a look at the history of how sonar helped us discover underwater mountains and other objects buried deep within the ocean.
During World War II, sonar was mainly used on submarines to detect enemy submarines and boats nearby, incoming projectiles, or other things like that. After the second world war, sonar was developed to help create seabed maps, locate undersea mountains, etc.
Passive sonar was mainly used because active sonar was so loud.
Some of the things that sonar has helped discover are listed to the side:
Passive sonar listens but does not transmit any signals or sound waves. This type of sonar is essentially used for listening for active sound waves, like ones used by neighboring submarines (active sonar) and and underwater creatures like whales (bio-sonar/active sonar) to determine the distance/size of the object. Passive sonar is not always the most reliable source because sometimes cannot pick up sound waves because ocean currents might redirect the sound waves.
Scientists discovered the location of the famous sunken cruise-liner, the
, and later a map of the site where it sank is made using sonar imaging. The titanic was found on 1985.
FIRST MAP OF SEAFLOOR
After the second world war, sonar was adapted for use in the scientific field- specifically in the field of Oceanography. Sonar was used to measure the depth of the ocean, or to map areas under the ocean's surface.
In the 1960's, the first complete map of the sea floor and all the mid-ocean ridges was published.
1.What are the two kinds of sonar?
2.What is a con of Sonar?
3.Sonar discovered a famous ship's remains, what was it called and when?
Final Question: How loud is an active sonar ping?
Bonus: Many underwater mountains were found by?
rescues, or searching for things deep beneath the ocean's surface. The shipwreck of the famous ship,
, was found using active sonar. Active
sonar can only locate physical objects, as the
sound emissions physically bounce off of
objects and return to the emitter.
A piece of passive sonar
We hope you enjoyed
Diagram: How sonar works
Left: A sonar map of the
Kaikoura Canyon, next
to New Zealand
Right: Digital sonar
rendering of a part of the
seafloor- red = higher
and blue = lower
THE MID-ATLANTIC RIDGE
The Mid-Atlantic ridge is a mid-ocean ridge under the Atlantic Ocean, and is part of the largest mountain range in the world. The Mid- Atlantic ridge was first suggested by Matthew Fontaine Maury, in 1850. It was later discovered by a team of scientists during the expedition of HMS
, and the claim was confirmed in 1925 by sonar.
Left: The location of the Mid-Atlantic ridge
PROS/CONS OF SONAR
Although sonar is a great discovery, and has proven to be useful in the aid of many other discoveries, yet it has it's limitations.
Sonar is an easy way to make undersea maps and to detect underwater objects that would otherwise be impossible to see.
Sonar also provides a large, tractable amount of information for interpretation or inferences.
Active sonar harms and can kill marine animals such as whales and dolphins- you may not realize it, but sonar pings are actually as loud as a rocket blast. Marine animals such as dolphins and whales who require hearing to survive and have very sensitive ears will most likely be killed by an acoustic wave emitted by a sonar device if they are too close to the source. If they aren't killed, they are often left deaf and thus no way to survive; so it's just as bad as killing them.If the animal is far away it could also be confused by the sound as it thinks it is prey, only to find a submarine or boat and ends up going on a wild goose chase.
Above: A dolphin killed by a deadly sonar blast
Locating Underwater Objects
Above: A digital sonar rendering
of the seabed.
A Prezentation by:
All in all, sonar is a great resource as it has revealed many things about geography that we wouldn't know without it. Heck, without sonar, Alfred Wegener's Theory of Continental Drift wouldn't even be proven! Or would've taken longer to prove. (Such a drama killer, Jay ;C)
However, sonar harms and kills hearing dependent wildlife, such as dolphins or whales, so we have to be careful about where and when we use it. Active sonar should not be overused. There have already been several whales and dolphins killed because of our carelessness.
SO, ANY QUESTIONS?
Now that we're done with our presentation, we'd appreciate it if you gave us some feedback, and we can answer any questions about the presentation you might have, such as:
What are your thoughts about sonar?
Should we still use sonar, even with the cons?
Which is better: passive sonar or active sonar?
Do you want to see another slide again?
If we didn't give enough information and you are confused about a part, we'll straighten it out for you.
Or any other questions you have about SONAR!
Now, it's time for the......
Let's see if you were paying attention, shall we?
Now its time for the trivia questions!
Above: Examples of sonar
Shadow zones are places where
sound waves cannot reach or detect a certain area. Objects behind soft sand slopes will most likely not be detected because the angle from which the sonar was produced will be blocked by the sand mound. Shadow zones don't have an echo bouncing off them so you can only see a black spot on the sonar map. Also they can be a place where convection currents meet. The sonar is interfered with when the relativity warm water and the cold redirects it.
Now you're thinking, "Wow, with active sonar and side sonar, we can probably detect anything underwater, right? Wow, that's so cool! Imagine what we'd find at the deep sea bottom..."
Well, sorry to burst your bubble, but you're wrong.
You see, there are these things called shadow zones. The concept is similar to the shadow zones we learned about earlier that have to do with S-Waves — in underwater acoustics, shadow zones are places where very little sound energy penetrates. Inside these 'shadow zones', we can detect very little to nothing using sonar, as the sound waves won't be able to penetrate the 'sound-wave barrier' of these shadow zones.
Above: Diagram of shadow zones
Above: Acoustic Shadows
by Jonathan and Alex
by Jonathan and Alex
by Jonathan and Alex
by Jonathan and Alex
Shadow zones are places where
sound waves cannot do it's work due to either objects that sound cannot pass through, soft sand that sonar doesn't move back from very well, or a slope. Shadow zones don't have an echo bouncing off them so you can only see a black spot on the sonar map. Also they can be a place where warmer and colder water meet. The sonar is bounced back from the warm water causing it to go to the cooler water.
Right: Shadow Zones
Bat using echolocation
to find prey
find a school
Sound waves from
bouncing off a island
Proofread by Jay
(Proofread by Jay)
1906 - First Passive Sonar Device
Lewis Nixon invents the first Sonar type listening device as a method for detecting icebergs, as he is emotionally struck by the
incident. Interest in Sonar development was increased during World War I, as there needed to be a way to find underwater submarines.
Left: Lewis Nixon, naval architect
1915 - Active Sonar (ASDICS) Invented
Paul Langévin invented the first Active Sonar-type device for the detection of submarines (to help the British with World War I), using the piezoelectric (electricity produced by mechanical pressure on certain crystals) properties of quartz.
In order to keep this project secret, there was no mention of sound or quartz in the name. Instead, the word used to describe the work was 'ASD'ics; where 'ASD' stood for Anti-Submarine Detection; hence the term ASDICS.
He was a little too late to help with the war effort — however, his work heavily influenced later Sonar designs.
Abovve: Paul Langévin, physicist
1918 - Acoustic Communication Systems
Above: An advanced acoustic communication system
Following Paul Langévin's invention of Active Sonar, Sonar became more widely spread. By 1918, both the US and Britain had incorporated Active Sonar into vessels such as submarines and fishing boats.
Acoustic communication systems were also used in 1918. An acoustic communication system is a sonar device where there is both a sound transmitter and receiver on either side of the projection path. The invention of other devices such as the acoustic transducer and efficient acoustic projectors made more advanced forms of Sonar possible.
From the three of us
SONAR THROUGH THE AGES
1939-1945 - World War II
The term 'Sonar' (SOund Navigation And Ranging) is first used by Americans and advanced models of sonar are used to track and locate underwater enemy submarines. The British equivalent of Sonar, ASDICS (Anti-Submarine Detection Investigation Committee) is used for the same purpose.
Sonar played a heavy role in WW2, allowing ships to detect enemy submarine fleets before it's too late, and allowing submarines to track and hunt down enemy carriers. Sonar turned the tides of the war- while the Allies focused on developing anti-submarine technologies such as sonar and military tactics, the Axis focused on offensive strategies such as the German Type VII Submarine and the wolfpack formation. In the end, Allied development on sonar effectively rendered these tactics useless and Allied homing torpedoes decimated the Axis' navy craft. Without sonar none of this would've been possible.
Extra research on sonar done by Jonathan Hou
Presented as a timeline
Sonar continues to develop and improve but has all in all been perfected to serve it's purpose.