Sonar measures depth by timing how long a sound pulse takes to return from below.

The longer version

A transmitter sends a short pulse downward, and a receiver starts a clock. The pulse travels through water at a known speed, reflects from the bottom or from an object, and comes back; half the round-trip time multiplied by that speed gives the distance.

Speed in water is not fixed, so temperature, salinity and depth all have to be allowed for. Echoes from fish, thermoclines or a soft muddy floor can mislead, and narrow beams and pulse shaping improve resolution where the bottom is uneven. Animals that find their way by listening use the same timing principle.

Where this entry sits

Sound and Music gathers facts about how vibrations move through air and water, how ears turn them into meaning, and how instruments and notation shape what listeners hear. Expect echoes, pitch, volume, acoustics, and the odd silence in between. The full list sits on the Sound and Music page, where every entry is listed in order.