Abstract: A linear and nonlinear two-frequency acoustical technique has been used to make in situ measurements of gas bubbles profiles in the Baltic Sea. At three pairs of frequencies namely 30/35, 57/63 and 110/115 kHz spectral components of linear and nonlinear backscattered signal were extracted and their wind and depth dependences have been calculated. Preliminary results of nonlinear backscattering from the subsurface layer of gas bubbles in different hydrological conditions are presented.