The notion of Fresnel zones for modes is introduced which is analogous to the usual Fresnel zones introduced for rays. It is shown that by using Fresnel zones for modes one can simplify the analysis of mode scattering at large-scale inhomogeneities in multimode waveguides. The mode amplitude variations due to scattering by an opaque screen and by refractive index inhomogeneities are considered. In the latter case the formulas obtained in the scope of this approach are statistical averaging suited and similar to those of geometrical optics and the Rytov method widely used to calculate fluctuations of ray complex amplitudes. The results of a tank experiment carried out to test the predictions concerning the mode scattering by an opaque screen are presented.

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The propagation of intensive acoustic noise is of fundamental interest in nonlinear acoustics. Some of the simplest models describing such phenomena are generalized Burgers' equations for finite amplitude sound waves. An important problem in this field is to find the wave's behavior far from the emitting source for stochastic initial waveforms. The method of numerical solution of generalized Burgers equation proposed is step-by-step calculation supported on using Wavelet Analysis. For simulating the wave evolution we used 4096 (212) point realizations and took averaging over 1000 realizations.

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