Sound absorption measurements at 10–60 kHz in near-freezing sea water

Abstract

Sound propagation measurements at various frequencies between 10 and 60 kHz were made in April 1974 under the pack ice near Pt. Barrow, Alaska. With a stationary transmitter at mid-depth, a series of sound level versus depth profiles at ranges between 40 and 1300 m were obtained and used to calculate the absorption coefficient. Although the sound speed profile contained many small irregularities which caused undesirable fluctuations, it had no large features that would change the average intensity at the ranges and depths at which the sound was received. The average temperature and salinity were −1.6 °C and 32.3 0/00, respectively. The calculated absorption values in decibels per kiloyard were 2.5±0.5 at 10 kHz, 4.5±0.5 at 20 kHz, 8.3±0.5 at 30 kHz, 10.7±0.4 at 40 kHz, and 13.9±0.5 at 60 kHz. These values indicate a relaxation frequency, assumed due to MgSO4, of 27±5 kHz, a value much lower than that predicted by the Schulkin–Marsh equation, but about the same as that determined by Greene in similar low-temperature water. Subject Classification: 30.20, 30.80; 35.24.