Underwater Sound in the Arctic Ocean
AVCO MARINE ELECTRONICS OFFICE NEW LONDON CT
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A summary of the U.S. Navy Underwater Sound Laboratory experimental program to investigate acoustic phenomena in the Arctic is given. As the sound velocity is an increasing function of depth, propagation is characterized by upward refraction and surface reflection. A rough-surface model of the ice cover accounts for both forward and back-scatter. The roughness-wavelength spectrum calculated from reverberation measurements is similar to that for the sea surface although the level is higher. Forward scatter loss depends on total roughness and is responsible for severe attenuation of high frequencies. Propagation and reverberation data both imply an R.M.S. roughness of from two to three meters, which is consistent with under-ice profile measurements. Propagation of explosive waves is described by normal mode and ray theories. At short ranges convergence zones are observed. Because the ice cover shows a critical angle dependence, the time dispersion of the wave train at long range in deep water is well defined. In shallow water, the bottom may produce reflection modes, or reduced dispersion of the refracted mode.