Low-frequency sound transmission through water-air interface: A comparison between Ray and wave theory

Studying low frequency sound transmission through water-air interface can help understand airplane-generated sound for acoustic remote sensing and effects of airborne sources on marine life. In this paper ray theory and wave theory are utilized to evaluate the acoustic transparency. Ray theory is first used to calculate the energy of the plane and spherical wave that transmits from water to air. Wave theory is then utilized to study spherical wave transmission through water-air interface. By comparing the results obtained from two theories, it is found that acoustic transparency can be derived using both ray and wave theory. Because acoustic transparency derived using ray theory is slightly smaller than that of the wave theory, it is thus called Enhanced Transparency as opposed to Anomalous Transparency proposed by Godin. By incorporating the inhomogeneous wave, wave theory does provide more significant transparency, especially in low frequencies. The results have been further extended to liquid-gas interface.