Sounding (Depth)

A measurement of water depth or the act of obtaining that measurement.

Traditional soundings use a lead line, while echo sounders determine travel time of acoustic energy between transducer and seabed. A charted sounding is normally reduced to chart datum, whereas an onboard display may show depth below transducer, keel or surface depending on its offset.

Bottom slope, sound speed, weeds, aeration, transducer angle and multiple echoes can affect readings. Units, datum, offset, survey age and tide must be known before comparing a live depth with a charted value.