What is SONAR? Explain the working and application of SONAR. Why are ultrasonic waves used in SONAR?

SONAR (Sound Navigation And Ranging) is a technique that uses sound pulses to detect and measure underwater objects and distances; it works by sending a sound “ping,” receiving the echo, and calculating distance from the time of flight; it uses ultrasonic waves (above 20 kHz) because they give narrow beams, better resolution, and precise ranging under water.

How SONAR works (active mode):

1. A transmitter drives a transducer (often piezoelectric) to emit a short pulse of high-frequency sound into water.
2. The pulse travels through water at about 1500 m/s (varies with temperature, salinity, and depth).
3. The sound hits a target (seafloor, fish school, submarine) and reflects back as an echo.
4. A receiver (the same or another transducer) detects the echo. Electronics measure the time delay (Δt).
5. Distance is calculated using d = (v × Δt) / 2, dividing by 2 because the pulse travels to the target and back.

In passive SONAR, the system does not send a pulse but only listens for sounds made by objects (like ship engines or marine life). Passive systems are useful for stealth and for identifying sound “signatures.”

Applications of SONAR:

• Depth sounding and seabed mapping: Measure ocean depth and draw bathymetric maps; locate underwater hazards for ships.
• Navigation and collision avoidance: Submarines and autonomous underwater vehicles use SONAR to see the environment.
• Fish finding and fisheries: Detect fish schools and estimate biomass.
• Search and rescue / archaeology: Find wrecks, black boxes, and artifacts on the seafloor.
• Military uses: Detect or track submarines and underwater mines (active and passive systems).

Practical notes: Very high frequencies give sharp detail but are absorbed more quickly, so they work best for short-range, high-resolution tasks (harbors, fish finders). Lower frequencies travel farther and suit long-range detection (ocean surveys), but with lower image detail. Modern systems use beamforming arrays and signal processing to improve accuracy and reduce false echoes.