SONAR: Sound Navigation and Ranging

Introduction

Sound waves can reflect from objects. This property is used not only by animals in echolocation but also by humans in technology.

One important application of reflected sound waves is SONAR. SONAR is mainly used for underwater exploration.

What is SONAR?

SONAR stands for Sound Navigation and Ranging.

It is a technique in which sound waves are sent into water. These waves reflect from underwater objects, and the reflected waves are studied to find information about those objects.

SONAR is used to determine the distance, direction and speed of underwater objects such as submarines and shipwrecks.

Why is SONAR Used Underwater?

Sound travels much farther in water than light. Therefore, sound waves are very useful for underwater applications.

In SONAR, ultrasonic waves are commonly used because they can be directed and detected effectively for locating underwater objects.

Working of SONAR

The working of SONAR can be understood in the following steps:

  • A ship sends ultrasonic waves into water.
  • The waves travel through seawater.
  • The waves strike an underwater object such as a submarine or shipwreck.
  • The object reflects the waves back.
  • The reflected waves are received by the ship.
  • By measuring the time taken by the waves to return, the distance of the object can be calculated.

Diagram: Working of SONAR

Working of SONAR Underwater Seawater Ship with SONAR Ultrasonic waves sent Underwater object Sent wave Reflected wave Distance of object SONAR finds distance by studying the reflected ultrasonic waves.

Explanation of the Diagram

The diagram shows a ship sending ultrasonic waves into seawater. These waves travel through water and strike an underwater object. The object reflects the waves back to the ship. By measuring the time taken for the waves to return, the distance of the object is found.

Formula Used in SONAR

In SONAR, the sound wave travels from the ship to the object and then comes back to the ship. Therefore, the total distance travelled by the sound wave is twice the distance of the object.

\(2d = vt\)

Therefore,

\(d = \frac{vt}{2}\)

where,

  • \(d\) = distance of the underwater object from the ship
  • \(v\) = speed of sound in seawater
  • \(t\) = total time taken by the sound wave to go to the object and return

Example

A naval SONAR signal sent into seawater returns after \(0.90\,s\). The speed of sound in seawater is \(1530\,m\,s^{-1}\). How far is the object?

Given,

  • Total time taken by the signal, \(t = 0.90\,s\)
  • Speed of sound in seawater, \(v = 1530\,m\,s^{-1}\)

The given time is for the sound wave to reach the object and come back. So, the time taken to reach the object is:

\(\frac{0.90}{2} = 0.45\,s\)

Now,

\(\text{Distance} = \text{Speed} \times \text{Time}\)

\(d = 1530 \times 0.45\)

\(d = 688.5\,m\)

Therefore, the object is \(688.5\,m\) away.

Another Example: Depth of Ocean

A SONAR signal sent to find the depth of the ocean takes \(4\,s\) to return. If the speed of sound in seawater is \(1500\,m\,s^{-1}\), find the depth of the ocean.

Given,

  • Total time, \(t = 4\,s\)
  • Speed of sound in seawater, \(v = 1500\,m\,s^{-1}\)

Using,

\(d = \frac{vt}{2}\)

\(d = \frac{1500 \times 4}{2}\)

\(d = 3000\,m\)

Therefore, the depth of the ocean is \(3000\,m\).

Uses of SONAR

  • SONAR is used to locate submarines underwater.
  • It is used to find shipwrecks.
  • It is used to measure the depth of the ocean.
  • It helps in underwater exploration.
  • It helps to find the distance, direction and speed of underwater objects.

SONAR and Echolocation

SONAR works on the same basic principle as echolocation.

Echolocation SONAR
Used by animals such as bats, dolphins and whales Used by humans in underwater technology
Uses reflected sound waves to locate objects Uses reflected ultrasonic waves to locate underwater objects
Example: bat locating prey Example: ship locating a submarine

Important Terms

1. SONAR

SONAR stands for Sound Navigation and Ranging. It is a method of locating underwater objects using reflected sound waves.

2. Ultrasonic Waves

Sound waves with frequencies more than \(20\,kHz\) are called ultrasonic waves.

3. Reflected Waves

Sound waves that return after striking an object are called reflected waves.

4. Seawater

Seawater is the medium through which sound waves travel in SONAR.

5. Echo Time

The total time taken by a sound wave to reach an object and return after reflection is called echo time.

Important Points

  • SONAR stands for Sound Navigation and Ranging.
  • SONAR is used for underwater exploration.
  • In SONAR, ultrasonic waves are sent into water.
  • The reflected waves are analysed to locate underwater objects.
  • SONAR can determine the distance, direction and speed of underwater objects.
  • SONAR can be used to locate submarines and shipwrecks.
  • Sound travels much farther in water than light, so it is useful for underwater applications.
  • The distance of an underwater object can be calculated using \(d = \frac{vt}{2}\).
  • The factor 2 is used because the sound wave travels to the object and comes back.

Conclusion

SONAR is an important application of reflected sound waves. It stands for Sound Navigation and Ranging. In SONAR, ultrasonic waves are sent into water and the reflected waves are analysed to determine the distance, direction and speed of underwater objects. It is useful for locating submarines, shipwrecks and measuring ocean depth. SONAR works on the same basic principle as echolocation.

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