Echo Sounder

An instrument that measures water depth by timing sound pulses reflected from the seabed.

A transducer sends a pulse through the water and receives the returning echo. The instrument uses the elapsed time and an assumed speed of sound in water to calculate and display a depth, often as a numerical value and a scrolling trace.

The displayed depth may be referenced to the transducer, the waterline or the bottom of the keel, depending on the configured offset. Aerated water, weed, soft sediment, steep slopes, interference and incorrect settings can produce misleading readings, so the reference and limitations must be understood and the result compared with other navigational information.