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Depth sounding, often simply called sounding, is measuring the depth of a body of water. Data taken from soundings are used in bathymetry to make maps of the floor of a body of water, such as the seabed topography. Soundings were traditionally shown on nautical charts in fathoms and feet.
A deep-sea lead, the heaviest of sounding leads, was used in water exceeding 100 fathoms in depth. [21] This technique has been superseded by sonic depth finders for measuring mechanically the depth of water beneath a ship, one version of which is the Fathometer (trademark). [22] The record made by such a device is a fathogram. [23]
Echo sounding is a special purpose application of sonar used to locate the bottom. Since a historical pre-SI unit of water depth was the fathom, an instrument used for determining water depth is sometimes called a fathometer. Most charted ocean depths are based on an average or standard sound speed.
The fathometer is an echo sounding system for measurement of water depth. A fathometer will display water depth and can make an automatic permanent record of measurements. Since both fathometers and fishfinders work the same way, and use similar frequencies and can detect both the bottom and fish, the instruments have merged. [2]
The earliest and most widespread use of sound and sonar technology to study the properties of the sea is the use of a rainbow echo sounder to measure water depth. Sounders were the devices used that mapped the many miles of the Santa Barbara Harbor ocean floor until 1993. Fathometers measure the depth of the waters. It works by electronically ...
Sonar: use of underwater sound propagation to measure depth; Fathometer or fishfinder: a device to locate fish at various water depths; Echo sounding: a technique using sound pulses to measure depth; sounding line: a length of rope used to measure water depth
To measure the bearing, several hydrophones are used, and the set measures the relative arrival time to each, or with an array of hydrophones, by measuring the relative amplitude in beams formed through a process called beamforming. Use of an array reduces the spatial response so that to provide wide cover multibeam systems are used.
Since a traditional pre-SI unit of water depth was the fathom, an instrument used for determining water depth is sometimes called a fathometer. The first practical fathometer was invented by Herbert Grove Dorsey and patented in 1928. [8]