Single-beam echo sounder produces soundings by transmitting short pulses of acoustic energy down towards the seabed and detecting those pulses reflected. The depth under the survey vessel is then calculated from the 2-way travel time of pulses and the mean speed of sound over the water column :

Distance = 0.5 x (Travel Time) x (Sound Velocity)

By this way a vessel with a single-beam echo sounder produces lines of soundings, and a map of contours can be constructed by interpolating the depth values between the survey lines.

A Typical Single-beam Echo Sounding Plan