SONAR stands for Sound Navigation and Ranging. SONAR is a process of communicating or detecting objects underwater. It is generally used by ships and submarines to detect underwater objects like rocks and icebergs, which cause a serious risk to the ships. Submarines also communicate with the help of SONAR, and during wars, military ships and submarines detect underwater torpedo and missile attacks with the help of SONAR. So, it serves for plenty of uses, but let’s first understand the working of SONAR.
Working
SONAR works on the principle of ultrasonic waves. It consists of a transmitter and a receiver mounted on a ship. The transmitter generates ultrasonic waves, which travel through water. When these waves strike an underwater object or the seabed, they get reflected. The reflected waves are received by the receiver and converted into electrical signals. By analysing these signals, information about underwater objects, depth, and obstacles can be determined.
Below are the terms related to the working of the SONAR:
- Emitter & Transmitter: An emitter or transmitter is a device that produces ultrasonic sound waves and sends them in different directions from the ship or submarines.
- Receiver: A receiver, sometimes also called a detector, is a device that detects and receives the echo coming from the transmitted waves coming from different objects and analyses them to find the distance of the objects and many more such things.
- Ultrasonic Waves: Ultrasonic waves, or ultrasound, are sound waves that have a frequency greater than 20 kHz (or 20,000 Hz).
Depth Measurement by SONAR
Let’s consider an example: A ship emits ultrasonic waves in water using the emitter and receives a wave back after time t, and we know the speed of sound in water is v. If d is the distance from the object and the ship, then the total distance covered by the wave from emitter to receiver is 2d. Therefore, the speed of the sound in this case is defined as:
Simplify for d,
This is the required expression to determine the distance of the object from the ship. This method is convenient.
Uses
- For underwater communications, ships and submarines use special sonars.
- Sonar is used in medical imaging to detect cysts and cancer cells, and this process is known as a sonogram.
- It is used by the military to track enemy warships and submarines.
- Sonar is often used to monitor pipelines that transport oil and gas to detect potential damage.
Hunting Mechanism of Bats
Ultrasonic waves are generated by bats. When these waves collide with another, they are reflected to the bat's ears. Bats understand the nature of these waves' reflections and thereby determine the object's location over their prey. This process is called echolocation.
Solved Examples
Problem 1: What exactly is a sonic boom?
Solution: When an object travels through the air at a faster rate than the sound, it makes a high-energy sound. This force is strong enough to break glasses and cause structural damage. The sound emitted is close to that of a thunderclap or an earthquake. These objects exert a huge amount of energy on the air, causing shock waves to propagate through it. Sonic booms are the result of these shock waves, which create extraordinarily large and noisy sound waves.
Problem 2: A ship sends out a signal that returns from the seabed and is detected by the receiver of the ship after 3.4 s. If the speed of ultrasound through seawater is 1530 m/s, calculate the the distance of the seabed from the ship?
Solution : Given that,
The time for transmission and receiving of sound wave, t is 3.4 s.
The speed of ultrasound through water, v is 1530 m/s.
Therefore, the formula to calculate the distance of the object from the ship is:
d = (v × t) / 2
Substitute the given values in the above expression.
d = (1530 m/s × 3.4 s) / 2
= 5202 m / 2
= 2601 m
Therefore, the distance between the ship and seabed is 2601 m or 2.6 km.
Problem 3: A military submarine emits a sonar signal, which returns from an underwater cliff ahead of it in 1.2 s. If the speed of sound in seawater is 1525 m/s, how far away is the cliff from the submarine?
Solution : Given that,
The time taken by the pulse to return after striking the cliff, t is 1.2 s.
The speed of the sound in seawater, v is 1525 m/s.
Therefore, the formula to calculate the distance of the object from the ship is:
d = (v × t) / 2
Substitute the given values in the above expression.
d = (1525 m/s × 1.2 s) / 2
= 915 m
Therefore, the distance between the submarine and the cliff is a
Problem 4: A ship on the surface of water sends a signal and receives it back from the submarine inside the reflected water after 4s. Calculate the distance of the submarine from the ship (Given: The speed of sound in water is 1450 m/s.
Solution: Given that,
The time taken by the signal to return to the ship, t is 4 s.
The speed of sound in water, v is 1450 m/s.
Therefore, the formula to calculate the distance of the object from the ship is:
d = (v × t) / 2
Substitute the given values in the above expression.
d = (1450 m/s × 4 s) / 2
= 2900 m
Thus, the distance between ship and the submarine is 2900 m or 2.9 km.
Problem 5: A SONAR picks up a reflected signal after 5.5 s. How far away is the body?
Solution: Given that,
The time taken by the signal to return to the ship, t is 5.5 s.
And it is known that, the speed of sound in water, v is 1450 m/s.
Therefore, the formula to calculate the distance of the object from the ship is:
d = (v × t) / 2
Substitute the given values in the above expression.
d = (1450 m/s × 5.5 s) / 2
= 3987.5 m
Thus, the distance between ship and the submarine is 3987.5 m or 4 km.
Unsolved Problems
Question 1: A ship uses SONAR to detect an underwater object. The echo is received after 2.5 s. If the speed of sound in seawater is 1500 m/s. Calculate the distance of the object from the ship.
Question 2: A fishing boat sends ultrasonic waves toward the seabed and receives the reflected signal after 4 s. Find the depth of the sea if the speed of sound in water is 1450 m/s.
Question 3: A SONAR device receives an echo after 1.8 s. If the speed of ultrasound in seawater is 1520 m/s, determine the distance of the underwater obstacle.
Question 4: A submarine detects two underwater objects using SONAR. The first echo returns after 1.6 s and the second after 3.6 s. If the speed of sound in seawater is 1510 m/s. Calculate the distance between the two objects.
Question 5: A ship receives two echoes while using SONAR, one from the seabed after 5 s and another from an underwater rock after 2 s. If the speed of sound in water is 1500 m/s. Calculate the depth of the sea and the distance of the rock from the ship.