How does SONAR measure sea depth?

Watch an ultrasound pulse travel to the seabed and return as an echo.

Seabed Depth = ? Ship sends ultrasound and detects the echo
Echo time 0.0000 s
Speed in seawater 1500 m/s

Press Start Animation to send the ultrasound pulse.

Animation slowed down for learning. Displayed echo time represents the actual journey.