ON DESCRIPTION OF MODE AMPLITUDE FLUCTUATIONS IN THE OCEAN

Results of Tindle and Guthrie, Felsen and other authors on studying th e relationship between ray and mode representations of a field in a ra nge-independent waveguide are used to describe wave scattering in a wa veguide with large-scaled random inhomogeneities of refractive index. The notion of Fresnel zones for modes is introduced, which is analogou s to the usual Fresnel zones introduced for rays. Using the Fresnel zo nes for modes one can simplify the analysis of mode scattering at larg e-scaled inhomogeneities in waveguides. Simple formulae to calculate f luctuations of mode amplitudes are obtained. They are quite similar to the well known formulae of geometrical optics and those of the Rytov method. Unlike their ray prototypes, the formulae presented here allow one to describe field fluctuations not only at the waveguide regular points but at the caustics as well.