The Speed of Sound in Water
Abstract
The introduction of the echo sounder into routine hydrographic surveying, replacing dependence on use of the lead line, produced a major change. It must be remembered that a sounder actually registers a time interval and that the speed of sound must be known to convert the time to depth. The International Hydrographic Bureau resolved that 1500 metres per second should be adopted as a standard velocity. Most Canadian waters are cold enough that this causes an overestimate and for calibration the value of 1463 metres per second (800 fathoms per second) is frequently used. Since fresh water has to have a temperature of 14.2°C before this speed is attained most soundings in deep lakes will be overestimated with this calibration. The velocity of sound in water depends upon temperature, concentration of dissolved constituents (for which salinity is the conventional quantity in oceanography) and pressure. The actual value at a given location and time may be evaluated by use of one of the procedures reviewed in this paper.
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