Sound Absorption at 50 to 500 kc from Transmission Measurements in the Sea

Abstract

The absorption coefficient of sound in sea water has been obtained by a series of direct transmission measurements at several moderately high frequencies in a sheltered deep water bay in Puget Sound. Advantage was taken of the isothermal and isosaline properties existing during certain seasons of the year in this location. The fluctuations normally encountered in such a measurement were minimized by the utilization of fixed buoys, a radio link for range determination by acoustic travel time, and a method of space averaging. Values obtained, in decibels per kiloyard at a temperature of 10°C and a salinity of 30 parts per thousand, are: 14.4±0.3 at 60 kc, 35.7±0.7 at 142 kc, 57±3 at 272 kc, and 101±3 at 467 kc. Although the frequency dependence of the absorption coefficient given by these measurements follows the normal relaxation law, the magnitudes are lower than those given by Del Grosso by 4 to 10 db/kyd.