The bubble distribution and acoustic characteristics of the subsurface sea layer

Abstract

The upper sea layer contains bubbles with different concentrations and is characterized by abnormal linear and nonlinear acoustic characteristics. The study of the upper sea water layer characteristics such as the acoustic nonlinear parameter, gas bubbles distribution, sound absorption and cavitation strength is presented. Methods of nonstationary linear and nonlinear sound scattering were applied in order to separate the scattering by resonant gas bubbles from the scattering by other micro-inhomogeneities (such as solid particles, plankton etc). The investigations of acoustic nonlinearity in the upper sea water layer were carried out using probing systems. At the same time the temperature, velocity of sound and sound absorption were measured. We have obtained data for the distribution of bubbles, the acoustic nonlinearity and the cavitation strength in the upper sea water layer. As result, new relationships between cavitation strength, the nonlinear parameter and the bubble distribution for typical sea water were obtained. It is shown that in subsurface layer to depths of 7-10 meters an increase of acoustic nonlinearity and simultaneous drop of cavitation strength of sea water are observed. We connect it with the presence of gas bubbles which always are present in subsurface sea water.