Active sonar relies on which of the following to determine range and bearing?

• A. Transmission of sound waves and reception of their echoes
• B. Listening for ambient noises without emitting sound
• C. Measuring surface wave patterns
• D. Observing electromagnetic reflections

Answer: (A)

Active sonar determines range and bearing by emitting a sound pulse and listening for its echoes. The time delay between sending the ping and receiving the echo tells you how far away the target is, because you multiply that delay by the speed of sound in water. Bearing comes from the direction the echo arrives, which is found using the sonar’s array of transducers and beamforming or by scanning to locate the angle of arrival. In short, range comes from time-of-flight of the emitted sound, and bearing comes from the direction from which the echo returns.

This is why the other options don’t fit: listening only to ambient noise without emitting sound doesn’t provide a range measurement; measuring surface wave patterns isn’t how you locate submerged targets; and electromagnetic reflections aren’t used underwater, since sound, not electromagnetic waves, propagates effectively in water.