What are the two main types of sonar?

• A. Digital and Analog
• B. Active and Passive
• C. Long-range and Short-range
• D. Surface and Subsurface

Answer: (B)

Two main types of sonar are defined by whether they transmit sound or only listen. Active sonar emits a loud acoustic pulse and then listens for echoes. By measuring the time it takes for the pulse to return and analyzing Doppler shifts, it can determine a target’s range, bearing, and even speed, providing detailed information about what’s out there. Passive sonar, on the other hand, does not transmit any sound. It simply listens to sounds in the water, using the characteristics of those sounds—such as frequency, duration, and direction—to detect, locate, and identify sources like ships or submarines. Because nothing is emitted in passive mode, it’s stealthier but may offer less precise range unless the target itself produces distinctive acoustic cues.

Think of the other pairings as describing capabilities or environments rather than fundamental operation modes: digital versus analog relates to how the signal is processed, not whether the system transmits; long-range versus short-range describes performance, not the method; surface versus subsurface refers to the environment rather than the sensing approach.