The Velocity of Sound in Sea Water

Abstract

In the sonar detection of underwater objects an accurate knowledge of the velocity of sound in sea water, and its variation with chemical composition and temperature, is desirable. Eight samples of Caribbean Sea water collected at various depths were studied with respect to sound velocity, density, and chemical composition. At both 20° and 30°C the velocities (determined with a 3-megacycle ultrasonic interferometer) were about 4 meters/second higher than the values in Kuwahara's tables, for which an accuracy of 3 meters/second is claimed. The salinities determined by chemical analysis agreed closely with those calculated from the densities; a slight increase of salinity with depth was noted. In another series of experiments, the sound velocity, density, and adiabatic compressibility were determined over a wide range of concentration for pure solutions of each of the seven salts which are the major constituents of sea water. It was found that the compressibility and sound velocity observed for sea water agree to 0.1 percent with the values obtained by linear summation of the effects of the individual salts, each taken at the proper concentration. Finally, removing over 90 percent of the dissolved air was found to increase the sound velocity only by about 0.5 meter/second (the order of magnitude of the experimental error) in sea water, as well as in distilled water.