回音测深术，又称回声，是一种使用声音的脉冲波技术，从表面或潜艇直接向下垂直，依靠声波来测量到达底部的距离。

为避免再次发生1912年铁达尼号的灾祸，德国物理学家亚历山大·伯姆引导一些研究，找出了一个发现冰山的方法。他发现回声的技术，可惜对于认出冰山的性能不太理想，却是一种非常好的工具用来深测海洋的深度。Behm 于1913年得到发明的专利权。

Echo sounding is a type of SONAR used to determine the depth of water by transmitting sound pulses into water. The time interval between emission and return of a pulse is recorded, which is used to determine the depth of water along with the speed of sound in water at the time. This information is then typically used for navigation purposes or in order to obtain depths for charting purposes. Echo sounding can also refer to hydroacoustic "echo sounders" defined as active sound in water (sonar) used to study fish. Hydroacoustic assessments have traditionally employed mobile surveys from boats to evaluate fish biomass and spatial distributions. Conversely, fixed-location techniques use stationary transducers to monitor passing fish.