Passive sonar.

Passive sonar.

• A. Receives sound to detect objects
• B. Emits sound to detect objects
• C. Uses light waves
• D. Measures current speeds

Answer: (A)

Passive sonar works by listening for sound in the water rather than sending out sound pulses. It uses hydrophones to pick up noises produced by other ships, submarines, marine life, or natural water movement. By analyzing where those sounds come from and how they change over time, the system can infer the direction to the source and, with advanced processing, estimate bearing and sometimes range. Because nothing is emitted, the listener remains covert, which is a major advantage in many marine situations. Light waves aren’t used for this purpose underwater because light is quickly absorbed and scattered in seawater, while sound travels farther with less attenuation, making it the better medium for detecting objects. Measuring current speeds would involve a different tool or method (such as acoustic Doppler techniques) and is not what passive sonar does.

Passive sonar works by listening for sound in the water rather than sending out sound pulses. It uses hydrophones to pick up noises produced by other ships, submarines, marine life, or natural water movement. By analyzing where those sounds come from and how they change over time, the system can infer the direction to the source and, with advanced processing, estimate bearing and sometimes range. Because nothing is emitted, the listener remains covert, which is a major advantage in many marine situations. Light waves aren’t used for this purpose underwater because light is quickly absorbed and scattered in seawater, while sound travels farther with less attenuation, making it the better medium for detecting objects. Measuring current speeds would involve a different tool or method (such as acoustic Doppler techniques) and is not what passive sonar does.