Search

On the example of an underwater sound channel typical of the Philippine Sea [1–3], it was established by numerical simulation using mode theory that during experimental studies of the propagation of explosive signals by R.A. Vadov [1–3], manifestation of a weakly divergent beam in the spatiotemporal structure of the acoustic field was observed for the first time: at certain locations of the corresponding points in the oceanic waveguide, in addition to classical quadruples of pulses, additional acoustic signals with small time delays with respect to them. [ABSTRACT FROM AUTHOR]

Abstract—Numerical modeling with the use of mode theory was used to investigate the regularities of the spatial (depth and horizontal distance) distribution of the acoustic field intensity formed by multiple interaction of a caustic beam with a layered bottom in a shallow oceanic waveguide with an underwater sound channel open to the bottom. It has been established that at the values of the sound velocity at the upper boundary in the sedimentary layer, less than the sound velocity at the bottom in the water layer, the formation of a multi-beam structure of the acoustic field is possible. It was found that, starting from certain distances, newly formed beams can play the main role in the spatial distribution of the acoustic field intensity. [ABSTRACT FROM AUTHOR]

Using the geometrical acoustics approximation and parabolic equation, we investigated the regularities in the spatial distribution of the acoustic field intensity generated by interaction between a caustic beam and bottom irregularities in a relatively shallow oceanic waveguide with an underwater sound channel open to the bottom. It is shown that when certain conditions are met, a multibeam structure of the spatial distribution of the acoustic field intensity is formed in the oceanic waveguide. [ABSTRACT FROM AUTHOR]

Using approximate analytical calculations based on the WKB and adiabatic approximations for the mode representation of the field, as well as numerical simulation based on the theory of adiabatic modes, geometric acoustic approximation, and the parabolic equation method, the patterns of the formation and propagation of caustic and weakly diverging acoustic beams in a horizontally inhomogeneous refractive oceanic waveguide are studied. The horizontal distance regions are determined at which the dependences of the acoustic field intensity on the horizontal distance typical of caustic and weakly diverging beams are retained. The study considers the processes involved in reformation of caustic and weakly diverging beams in an oceanic waveguide with increasing water layer depth and constant sound speed profile, which near the source characterized an underwater sound channel open toward the bottom. The conditions are formulated for an effectively matched transition of shallow-water waveguide modes refracted in the thermocline and interacting with the bottom to purely refracted modes of the underwater sound channel in a relatively deep water part of the oceanic waveguide. [ABSTRACT FROM AUTHOR]

The paper considers the regular patterns that can be manifested in the behavior of the invariant of the spatial-frequency interference structure of an acoustic field in oceanic waveguides that are homogeneous and inhomogeneous along a track. Using the WKB and adiabatic approximations, an analytic expression is obtained for the invariant that, when certain conditions are fulfilled, reduces to the well-known classical expression independent of the mode numbers, their parity, or the emission frequency. It has been established that the approximate classical expression for the invariant correctly describes the slope of interference lines only in ranges of variation in the grazing angles of modes where the dependence of the cycle length of their corresponding Brillouin waves on the ray parameter is quite smooth and monotonic. The paper studies the formation of the spatial-frequency interference structure of an acoustic field propagating from a shallowwater isovelocity waveguide to a relatively deep-water waveguide with a near-surface sound channel. [ABSTRACT FROM AUTHOR]

It is established that the existence of weakly divergent beams in an oceanic waveguides leads, in a certain time interval and depth range, to the formation of a characteristic triplet structure of wavefronts. It is explained that a weakly diverging beam of rays represents an Airy wave in the spatiotemporal structure of the acoustic signal field in an oceanic waveguide. [ABSTRACT FROM AUTHOR]

Scattering of a tonal low-frequency (up to 400 Hz) acoustic signal on a rough surface during its propagation along stationary paths in a shallow water area is considered. A calculation technique of estimating the spectral power density of the signal scattered at wind waves (reverberation) given an arbitrary angular distribution of the wind wave is developed based on the Bragg scattering model. The obtained results are compared with the results of numerical simulation of resonant sound scattering at surface perturbations according to an algorithm proposed by the authors, as well as with the results of experimental investigations. [ABSTRACT FROM AUTHOR]

The problem of scattering from a rough sea surface is considered for a harmonic low-frequency (200–400 Hz) acoustic signal propagating in a shallow water area. An experimental study of the azimuthal reverberation dependence is carried out on the basis of the bistatic location scheme with the use of linear phased arrays. By comparison with calculations, the formation of the frequency-angular characteristics of reverberation is investigated for various wind directions with respect to the path of acoustic signal propagation. [ABSTRACT FROM AUTHOR]

It is shown that an increase in the sound velocity gradient in the bottom sediment layer results in the formation of additional zones of diffraction focusing of the acoustic field generated by a vertical line array in the water layer. It is also established that, depending on the sound velocity step at the upper boundary of the sediment layer, the diffraction focusing of the acoustic field in the main focusing zones can be enhanced or reduced. [ABSTRACT FROM AUTHOR]

Features characterizing the formation of the spatial (in depth and horizontal distance) interference structure of an acoustic field generated by a point tone source or a vertically distributed tone source in a shallow-water oceanic waveguide are considered. The waveguide is modeled by a three-layered fluid medium. The main object of the study is the effect of the acoustic parameters of the sediment layer on the formation and structure of the spatial regions within which the diffraction focusing of the acoustic field takes place. [ABSTRACT FROM AUTHOR]

The effect of the diffraction focusing of an acoustic field on the space-time intensity distribution of narrow-band pulsed signals in multimode oceanic waveguides is analytically and numerically studied. The laws governing this effect and its specific features are illustrated by the results of calculations based on the standard ray approximation and the mode theory for the acoustic field in an isovelocity waveguide. [ABSTRACT FROM AUTHOR]

Laws manifesting themselves in the formation of the space-frequency distribution of the intensity of the acoustic field generated by a point source of wide-band radiation are considered. Most attention is concentrated on the study of the effect of diffraction focusing on the formation of the interference structure of the acoustic field. [ABSTRACT FROM AUTHOR]