Diffraction focusing of acoustic fields in oceanic waveguides smoothly varying along the track

With the use of adiabatic and WKB approximations for the mode representation of an acoustic field excited by a tone source in an oceanic waveguide smoothly varying along the track, dependences of the characteristic spatial scales of the phenomenon of diffraction focusing are obtained. Conditions that should be satisfied for the formation of zones of diffraction focusing of the acoustic field in such a waveguide are formulated.