Long-range sound propagation in the shallow-water part of the Sea of Okhotsk

Experimental data on the long-range propagation of explosion-generated sound signals in the shallow-water northern part of the Sea of Okhotsk are analyzed. The propagation conditions in this region are characterized by a fully-developed underwater sound channel that captures the rays crossing the channel axis at angles lower than 3°. The experimental data reveal a small increase in the duration of the sound signal in proportion to the range with the proportionality factor lower than 0.00025 s/km. The frequency dependence of attenuation exhibits a pronounced minimum whose position on the frequency axis is close to the critical frequency of the first “water” mode (about 160 Hz). The increase in the attenuation coefficient at lower frequencies is confirmed by the field calculations performed with the wave-field computer code and is explained by the sound energy loss in the bottom sediments. At frequencies higher than 200 Hz, as in the Baltic Sea, the most probable reason for the attenuation to exceed the absorption in sea water is sound scattering by internal waves.