I.N. Didenkulov, S.I. Muyakshin, D.A. Selivanovsky
Air bubbles in subsurface ocean layer play an important role: they influence on gas exchange between the ocean and the atmosphere, sound propagation and ambient noise generation. Bubbles in a liquid are oscillators and exhibit strong acoustic nonlinearity, that make possible their detection with the nonlinear acoustic methods. It is described in the paper a nonlinear acoustic method – the difference frequency method for measurement of bubble concentration in the subsurface ocean layer. Measurements were done with a unit which allows one to detect individual bubbles with radii from 10 to 80 mcm at depth from 1 to 7 m. Simultaneously with the registration of acoustic response from bubbles at the difference frequencies the linear scattering at 1200 kHz frequency was also registered. Results of measurements of spatial and frequency bubble distributions obtained by linear and nonlinear acoustic methods are given and discussed in the paper. It was shown in particular that even for weak winds the spatial bubble distribution in the horizontal plane is strongly inhomogeneous.