Applied Underwater Acoustics

2.2. Sound Propagation in a Viscous Fluid

In the foregoing discussion, dissipation in the medium supporting the propagation of a sound wave was neglected, apart from allowing the imaginary part of the acoustic wave number to be nonzero but infinitesimally small in order to ensure the convergence of certain integrals. Over shorter ranges and at lower frequencies, the effects of losses in the medium may be negligible but, as frequency increases and ranges become greater, the attenuation experienced by a propagating sound wave may grow to a significant level. In the ocean, the predominant attenuation mechanisms are the molecular relaxation of magnesium sulfate [14] and boric acid [15], as discussed in Section 1.5.9. In pure water, viscosity is the ...