SONAR

Simple explanation of SONAR technology used to detect underwater objects using sound waves.

1. What Is SONAR?

SONAR stands for Sound Navigation And Ranging.

It is a technique that uses sound waves to detect and locate objects underwater. Ships, submarines, and researchers use SONAR to find the depth of the sea and to locate underwater rocks, wrecks, and other objects.

2. Basic Idea Behind SONAR

The main idea is simple: send a sound pulse into water and listen for its echo.

If the sound hits an object, it reflects back. By measuring how long the echo takes to return, the distance of the object can be calculated.

2.1. Steps in SONAR Operation

  1. A device called a transmitter sends a short, sharp pulse of high-frequency sound into water.
  2. The sound travels through water until it hits an object (like the sea floor or a submarine).
  3. The sound reflects back as an echo.
  4. A receiver on the ship or submarine picks up this echo.
  5. The time taken for the echo to return is measured and used to calculate the distance.

3. Distance Calculation in SONAR

The distance to the object is found using the time taken for the echo to return and the speed of sound in water.

The basic formula is:

\( \text{Distance} = \dfrac{v \times t}{2} \)

Where:
\( v \) = speed of sound in water
\( t \) = total time taken for the pulse to go to the object and come back
The division by 2 is done because the sound travels to the object and then back to the source.

3.1. Example

If the speed of sound in water is taken as \( 1500\, \text{m/s} \), and the echo returns in \( 2 \) seconds, then:

\( \text{Distance} = \dfrac{1500 \times 2}{2} = 1500\, \text{m} \)

This means the object is 1500 metres below or away from the SONAR device.

4. Types of SONAR

SONAR systems can be grouped in two simple ways:

4.1. Active SONAR

In active SONAR, the system sends out sound pulses and listens for the echoes. This is useful for detecting and locating objects.

4.2. Passive SONAR

In passive SONAR, the system does not send any pulse. It only listens to sounds produced by other sources, such as ship engines or marine animals. It is more like a sensitive underwater microphone.

5. Uses of SONAR

SONAR has many important applications underwater.

5.1. Navigation and Safety

  • Helps ships avoid underwater rocks, icebergs, and other obstacles.
  • Used by submarines to move safely without colliding with objects.

5.2. Measuring Depth (Echo Sounding)

SONAR is used for echo sounding, which means measuring the depth of the sea or ocean. This helps in creating sea maps and studying the ocean floor.

5.3. Locating Objects

  • Finding shipwrecks and lost equipment.
  • Searching for underwater mines.
  • Tracking fish schools in fishing operations.

6. Advantages and Limitations of SONAR

SONAR is very useful underwater, but it also has some limitations.

6.1. Advantages

  • Works well in dark or muddy water where light cannot reach.
  • Can cover large distances underwater.
  • Provides information about both distance and direction of underwater objects.

6.2. Limitations

  • Accuracy depends on knowing the exact speed of sound in water, which changes slightly with temperature, salinity, and pressure.
  • Very strong sound pulses may disturb marine life.
  • Reflections from uneven surfaces or layers in water can sometimes cause confusing signals.