Which device emits underwater sound and analyzes echoes to gain information on the seabed, biology, or military targets?

• A. Adhesion
• B. Silt
• C. Active Sonar
• D. Aphotic Zone

Answer: (C)

Active sonar is an underwater acoustic device that both emits sound pulses and analyzes the echoes that return. The transmitted sound travels through water, bounces off the seabed, organisms, or objects, and the time delay and characteristics of the returning echo are used to estimate distance and infer what the target is like. By mapping echo patterns, researchers can reveal seabed features, study habitats and biology (like fish schools), or detect military targets such as submarines or ships. This is different from passive listening, which only receives sounds without emitting anything. The other terms aren’t devices with this capability: adhesion is a surface property, silt is sediment that can distort sound, and the aphotic zone is a depth range where there is no light.