Sound transmission through water–air interfaces: new insights into an old problem

A water–air interface is usually an almost perfect reflector of acoustic waves. It was found recently that the interface becomes anomalously transparent and the power flux in the wave transmitted into air increases dramatically when a compact underwater sound source approaches the interface within a fraction of wavelength. The phenomenon is robust with respect to the roughness of the interface and to the variation of air and water parameters and may have significant geophysical and biological implications. This review article discusses the properties of the interface and the physical mechanisms leading to the anomalous transparency.