Abstract: In the paper the interpolation method of two variables using bicubic Hermite’s pieces has been shown. Basics preceded theory of Coons’ pieces and bicubic one, which are the introduction to interpolation method of bicubic Hermite’s pieces. For determination the surface using this method hypothetical data have been used. As an example of the small area with differences of the vertical distribution of the sound speed in water estuary of the Vistula river has been assumed.