Editing Hydrographic survey (section)

===Single-beam echosounders===
{{main|Echo sounder}}

Single-beam [[echosounder]]s and fathometers began to enter service in the 1930s which used [[sonar]] to measure the depth beneath a vessel. This greatly increased the speed of acquiring sounding data over that possible with lead lines and sounding poles by allowing information on depths beneath a vessel to be gathered in a series of lines spaced at a specified distance. However, it shared the weakness of earlier methods by lacking depth information for areas in between the strips of sea bottom the vessel sounded.<ref name="noaahistorysurvey"/>