Abstract
The properties of the nonlinear phenomenon in water, including sea water,
have been well known for many decades. The feature of the non homogeneous
distribution of the speed of sound along the depth of the sea is very
interesting from the physical and technical point of view. It is important
especially in the observation of underwater area by means of acoustical
method (Grelowska et al., 2013; 2014). The observation of the underwater
space has been carried out for more than hundred years. In the second half
of the twentieth century we observed very intense trend of development of
the measuring methods of underwater sound speed. It was done mainly in the
linear sound propagation aspect. At the end of 20th century nonlinear
devices were invented. Thus, from this point of view, knowledge on the
nonlinear properties of the sea water is the matter of interest. The
phenomenon of nonlinear distortion of elastic waves, and the same the
efficiency of nonlinear transfer of energy from the primary wave to the
higher harmonic components depend on properties of the medium, especially
on the material constant known as the nonlinearity parameter B/A. The
Baltic Sea is a specific reservoir with untypically low salinity and low
depth (Grelowska, 2000). In the paper results of investigation of
nonlinear properties of the South and the Central Baltic by means of
thermodynamic method are presented.
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