Analysis of deep ocean sound attenuation at very low frequencies

The attenuation coefficient of low-frequency, deep ocean acoustic waves is computed for various assumptions regarding the depth profile and the frequency dependence of the scatterers. The calculations are made for a realistic velocity profile by means of a perturbation technique proposed by Guthrie [Ph. D. dissertation, The University of Auckland (1975)]. It is shown that excellent agreement with experimental data is obtained when the attenuation function is independent of frequency and decreases exponentially with depth with a characteristic depth of 200 to 500 m. A surface value of 0.11 dB/km gives good agreement with the data. At frequencies below 50 Hz the attenuation in the water column is comparable to the attenuation in the sediments for the lowest order normal modes.