Active Sonar

Active sonar transmits an acoustic pulse and times the returning echo to detect, locate, and classify underwater targets. Range follows from the two-way travel time and the local sound speed near 1500 m/s, so a 1-second round trip places a target about 750 m away. Source levels for military and survey systems often exceed 220 dB re 1 microPa at 1 m, and detection is set by the active sonar equation balancing source level, two-way transmission loss, target strength, and reverberation or noise. It contrasts with passive sonar, which only listens. Active operation reveals the listener’s position and can disturb marine mammals.