B. G. Katsnel’son

Low-frequency horizontal acoustic refraction caused by internal wave solitons in a shallow sea

The effect of internal wave solitons on the sound field generated by a point source in a shallow sea is considered. In the framework of the theory of “horizontal rays and vertical modes,” the sound field pattern governed by the aforementioned hydrodynamic effect is investigated. It is shown that solitons can induce time-periodic focusing and defocusing of horizontal rays propagating at shallow angles to the internal wave front. This may result in the formation of “dynamical” horizontal sound channels, which, in its turn, results in considerable temporal fluctuations of the field along the acoustic track oriented along the internal wave front. For the sound field calculations, an approach is developed on the basis of the parabolic approximation in the horizontal plane and the mode representation in the vertical direction. The results obtained can be used for remote monitoring of internal wave packets in a shallow sea.

Acoustic effects caused by high-intensity internal waves in a shelf zone

The sound field fluctuations caused by high-intensity, solitonlike, quasi-plane internal waves crossing a fixed acoustic path at different angles are numerically modeled for natural conditions of the shelf zone of the Sea of Japan. The horizontal refraction of sound is considered for the case of an acoustic path parallel to the internal wave front.

Space-Frequency Distribution of Sound Field Intensity in the Vicinity of the Temperature Front in Shallow Water

The sound field produced by a low-frequency (100–1000 Hz) point source in a shallow water region in the presence of the temperature front is considered. It is shown that the latter anisotropic inhomogeinity leads to a substantial horizontal refraction and to a number of related effects: a redistribution of the sound field in the horizontal plane, changes in the spectral and mode contents of a pulse in the course of its propagation, and changes in the arrival times at the receiver. A theoretical analysis and a numerical modeling are carried out for the Polar Front of the Barents Sea.

Determination of the Absorbing and Scattering Properties of the Sea Floor in a Shallow Water Environment by the Spectra of Wide-Band Signals

Sound propagation in a shallow sea is considered within the framework of the two-component model of the sea floor. The porosity and the coefficients of absorption and volume scattering are treated as the parameters characterizing the sea floor. These parameters are determined on the basis of the comparison between the experimental and theoretical frequency spectra of a signal received from a wide-band source. A conclusion is made about the relative contributions of different mechanisms of losses (absorption or scattering) in the sea floor at different sound frequencies.

Intensity variations of high-frequency sound pulses due to the motion of shallow-water internal solitons

Intensity variations of high-frequency sound pulses due to the motion of internal solitons in shallow water are investigated in terms of the ray approximation. It is shown that ray distortions cause intensity fluctuations of about 3–5 dB. It is found that rays with turning points near the upper boundary of the thermocline play the dominant role in the formation of these fluctuations. Formulas for estimating the fluctuation frequencies predominantly observed in the spectrum of intensity variations are presented.

Rearrangement of the horizontal space-time structure of the sound field in shallow water in the presence of moving internal waves

The rearrangement of the space-time structure of the sound field in a shallow-water waveguide with a moving intense internal wave packet is considered. The analysis is performed in terms of an approach characterized by space-time horizontal rays and vertical modes. It is shown that, within the time the packet travels over the acoustic track (about an hour), considerable spatial and temporal fluctuations occur in the field intensity and interference structure.

Horizontal refraction of sound in a shallow water and its experimental observations

Basic results of theoretical and experimental studies of acoustic effects caused by horizontal refraction in a shallow water are reviewed with special emphasis on the effect produced by intense internal waves on the propagation of broadband signals. Theoretical calculations and experimental data testifying to the manifestation of three-dimensional acoustic effects in the SWARM’95 experiment are presented.

Characteristics of the Diffraction of Acoustic Waves in Stratified Sound Channels

The results of calculations performed in the framework of the approximate approach developed by the authors are presented for the diffraction of sound waves by a stiff spheroid in an acoustic waveguide. The scattered sound field is analyzed as a function of the following parameters of the problem: the spheroid dimensions, its position relative to the sound source and the receiver, the vertical profile of sound velocity in the waveguide, and the acoustic parameters of the waveguide bottom.

Space-time sound field interference in the horizontal plane in a coastal slope region

The nonstationary interference structure formed in the horizontal plane in the field of a point source in a coastal slope region is analyzed on the basis of the space-time horizontal ray concept. For a model that includes the typical bathymetry and sound velocity profile, the space, time, and frequency dependences of the sound field are considered for different waveguide modes. The characteristic scales of the field variability in space and time are estimated. The frequency-time diagram is analyzed for the region of the interference of direct and reflected waves. The variability of the field interference structure in the presence of mesoscale perturbations is considered.

Sound field phase front variations in shallow water in the presence of intense internal waves

The method of vertical modes and horizontal rays and the method of parabolic equation in the horizontal plane are used to study space-time fluctuations of the phase front of the sound field in the presence of a train of internal waves passing through the acoustic path. The possibility of measuring the distortions of the phase front with a simultaneous filtering of modes by a horizontal array is analyzed. A numerical simulation is carried out for the conditions corresponding to the Eastern coast of United States and the Barents Sea.