Intensity decay laws for near-surface sound sources in the ocean

Expressions derived for the acoustic intensity decay with range in shallow water by Marsh and Schulkin [J. Acoust. Soc. Am. 34, 863–864 (1962)] and Weston [J. Sound Vib. 18, 271–287 (1971)] have been adapted to describe the intensity-range variation in the deep water situation, where the sound speed at the surface is equal to the sound speed at the base of the water column. The modified equations take account of the surface decoupling loss which occurs at frequencies below 100 Hz for source depths less than 25 m. The levels predicted by these equations are compared with experimental data obtained in deep water in the Indian Ocean. It is found that the mean difference in measured and predicted levels at frequencies of 25 and 50 Hz is less than 2 dB, and rms level differences are within 4 dB.