Multiple echo evaluation
Introduction
Echo-sounding or depth sounding is the use of sonar to measure distances, usually to determine the depth of water (bathymetry). It involves transmitting acoustic waves into water and recording the time interval between the emission and return of a pulse; The resulting time of flight, together with knowledge of the speed of sound in water, allows the distance between the sonar and the target to be determined. This information is typically used for navigation purposes or to obtain depths for mapping purposes.
Echo sounding can also be used to target other targets, such as schools of fish. Hydroacoustic assessments have traditionally employed mobile ship-based surveys to assess fish biomass and spatial distributions. In contrast, fixed location techniques use stationary transducers to monitor fish passage.
The word sounding is used for all types of depth measurements, including those that do not use sound, and is not related in origin to the word sound in the sense of noise or tones. Echo sounding is a faster method of measuring depth than the previous technique of lowering a sonar line until it hits the bottom.
History
The German inventor Alexander Behm obtained German patent No. 282009 for the invention of the echo sounder (device for measuring the depths of the sea and the distances and courses of ships or obstacles using reflected sound waves) on July 22, 1913.[1][2][3].
One of the first commercial echo sounding units was the Fessenden Brazometer, which used the Fessenden oscillator to generate sound waves. It was first installed by the "Submarine Signal" company in 1924 on the M&M liner SS Berkshire.[4].
Technique
Distance is measured by multiplying half the time from the outgoing signal pulse to its return by the speed of sound in water, which is approximately 1.5 kilometers per second [T÷2×(4700 feet per second or 1.5 km per second)]. In precise echo-sounding applications, such as hydrography, the speed of sound must also be measured, typically by deploying a sound speed probe in water. Echo sounding is effectively a special purpose sonar application used to locate the bottom. Since a traditional pre-SI unit of water depth was the fathom, an instrument used to determine water depth is sometimes called a Fathometer (which could be informally translated as ).