Transmission of acoustic-gravity waves through air-water interface.

Abstract

It was demonstrated recently that air-water interface, which is usually an almost perfect reflector of acoustic waves, becomes anomalously transparent and the power flux in the wave transmitted into air increases dramatically, when a compact sound source in water approaches the interface within a fraction of wavelength [O. A. Godin, Phys. Rev. Lett. 97, 164301 (2006)]. Powerful underwater explosions and certain natural sources, such as underwater landslides, generate very low-frequency waves in water and air, for which both fluid buoyancy and compressibility simultaneously serve as restoring forces. In this paper, analysis of sound transmission through air-water interface is extended to acoustic-gravity waves (AGWs). It is found that, as for sound, the interface becomes anomalously transparent for sufficiently shallow compact sources of AGWs. Depending on the source type, the increase in wave power flux into air due to diffraction effects can reach several orders of magnitude. Physical mechanisms responsible for the anomalous transparency are discussed. Excitation of an interface wave by an underwater source is shown to be an important channel of AGW transmission into atmosphere, which has no counterpart in the case of sound.