The possibility of reconstruction of two-dimensional random inhomogeneities in a shallow sea by frequency shifts of the spatial interference structure of the sound field

Fluctuations of frequency shifts of the spatial interference structure of the sound field in the oceanic waveguide, caused by a two-dimensional field of a random perturbation, are described. Various schemes of observation point spacing are considered. The possibility is shown to reconstruct the spatial spectrum of waveguide perturbations by measuring the spatial spectrum of the frequency shift of the interference pattern. The results of the theoretical treatment are illustrated by the examples of background internal waves and bottom roughness. The sensitivity of monitoring based on measurements of frequency shifts of the interference structure of the sound field is estimated. For medium perturbations by background internal waves, the fluctuations of liquid layer vibrations, sound speed, and temperature, which are minimum detectable by frequency shifts of the interference pattern, were estimated.     

Long-range reverberation in a randomly inhomogeneous shallow water with the use of focused radiation

The low-frequency bottom reverberation in a randomly inhomogeneous shallow water is investigated within the framework of a numerical experiment using vertical transmitting arrays focusing the acoustic field at various distances from the sea bottom. It is assumed that the main source of sound velocity fluctuations in the medium is represented by background internal waves. To focus the field, a phase conjugation of acoustic waves from a probe source positioned at the focusing point is used. It is demonstrated that the reverberation level is mainly determined by the presence of internal waves and may vary by 5–20 dB as the distance from the focusing point to the sea bottom increases up to H/2, where H is the channel depth.     

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.     

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.     

Application of Vertical Receiving Arrays for Underwater Acoustic Communication in an Inhomogeneous Waveguide under an Ice Cover

Doklady Physics - The results of experimental studies of underwater acoustic communication at frequencies of 500–1000 Hz using vertical chains of hydrophones (linear arrays) are presented....     

On the feasibility of normal wave selection in a shallow-water waveguide

Long-range propagation of low-frequency narrowband sound signals in the near-bottom acoustic channel with random inhomogeneities caused by internal waves and a rough bottom is investigated in the framework of numerical and field experiments. The feasibility of selecting the signal components corresponding to different normal waves is analyzed. The problem of selecting such components is considered for signals of long duration exceeding the characteristic time of the stationary state of the channel.     

Use of Linear Receiving Arrays for Observing Horizontal Refraction of Low-Frequency Sound in Shallow Water with a Strongly Inhomogeneous Waterlike Bottom

Acoustical Physics - Numerical simulation is applied to study the features of a low-frequency (55 and 137 Hz) acoustic field and its recording by linear horizontal and vertical arrays in a...     

Sound scattering by spatially localized inhomogeneities in a shallow-water waveguide in the presence of internal waves

A method is developed for solving the problem of sound scattering by concentrated inhomogeneities in a waveguide of small depth in the presence of internal waves (IW) typical of an oceanic shelf. The sound field fluctuations related to the motion of a model scatterer (a soft spheroid) and to the propagation of the IW are calculated and analyzed. It is shown that the field of internal waves considerably affects the scattered sound field even when the source-receiver and source-scatterer distances are relatively small (about several kilometers). This effect depends not only on the amplitude of the IW, but on their propagation direction as well.     

Attenuation of sound in shallow-water areas with gas-saturated bottoms

Acoustical Physics - We investigated the specific features low-frequency (50–300 Hz) sound propagation in shallow-water areas to relatively small distances r ≈ 3H–50H from the...