The paper describes monitoring of seismic survey parameters conducted during 4-D seismic surveying at the Pil’tun-Astokh hydrocarbon deposit on the northeastern shelf of Sakhalin Island at the boundary of the near-coastal Pil’tun gray whale feeding area. Acoustic measurements were performed in the frequency range of 2–15000 Hz using 12 autonomous underwater acoustic recorders, of which three were deployed at the 10-m isobath and nine were equipped with digital radiotelemetry channels and deployed at the 20-m isobath along a line extending 20 km. In real time, the shore-based radio receiver station received over the digital radiotelemetry channels acoustic data from nine observation points, measured in the frequency range of 2–2000 Hz. The influence of the hydrology and bathymetry on the seismic survey pulse propagation to the near-coastal zone is studied experimentally and theoretically.

A problem of sound propagation in a shallow-water waveguide with a weakly sloping penetrable bottom is considered. The adiabatic mode parabolic equations are used to approximate the solution of the three-dimensional (3D) Helmholtz equation by modal decomposition of the acoustic pressure field. The mode amplitudes satisfy parabolic equations that admit analytical solutions in the special case of the 3D wedge. Using the analytical formula for modal amplitudes, an explicit and remarkably simple expression for the acoustic pressure in the wedge is obtained. The proposed solution is validated by the comparison with a solution of the 3D penetrable wedge problem obtained using a fully 3D parabolic equation that includes a leading-order cross term correction.

The problem of sound propagation in a randomly inhomogeneous oceanic waveguide is considered. An underwater sound channel in the Sea of Japan is taken as an example. Our attention is concentrated on the domains of finite-range ray stability in phase space and their influence on wave dynamics. These domains can be found by means of the one-step Poincare map. To study manifestations of finite-range ray stability, we introduce the finite-range evolution operator (FREO) describing transformation of a wave field in the course of propagation along a finite segment of a waveguide. Carrying out statistical analysis of the FREO spectrum, we estimate the contribution of regular domains and explore their evanescence with increasing length of the segment. We utilize several methods of spectral analysis: analysis of eigenfunctions by expanding them over modes of the unperturbed waveguide, approximation of level-spacing statistics by means of the Berry-Robnik distribution, and the procedure used by A. Relano and coworkers [Relano et al., Phys. Rev. Lett. 89, 244102 (2002); Relano, Phys. Rev. Lett. 100, 224101 (2008)]. Comparing the results obtained with different methods, we find that the method based on the statistical analysis of FREO eigenfunctions is the most favorable for estimating the contribution of regular domains. It allows one to find directly the waveguide modes whose refraction is regular despite the random inhomogeneity. For example, it is found that near-axial sound propagation in the Sea of Japan preserves stability even over distances of hundreds of kilometers due to the presence of a shearless torus in the classical phase space. Increasing the acoustic wavelength degrades scattering, resulting in recovery of eigenfunction localization near periodic orbits of the one-step Poincaré map.

An experimental study aimed at the measurement of arrival times and effective velocities of acoustical pulses propagating approximately along the edge of the continental shelf was conducted in the Sea of Japan in early autumn. In a posteriori theoretical analysis and modeling of sound propagation in this experiment modal structure of acoustical field along the path was described and a number of general conclusions on the formation of such fields in course of sound propagation over distances of tens and hundreds of kilometers were formulated. An algorithm for predicting effective velocities of long-range propagation of acoustical pulses in shallow water was developed on the basis of these conclusions. The algorithm is based on the averaging of group velocities of the first modal component of the pulse over the entire track. It was shown that on the considered path of approximately 136 kilometers horizontal refraction is one of the major factors contributing to the dispersion of pulsed signals. This effect also causes additional delays as compared to the sound propagation along the respective geodesic path on the Earth’s surface. Implications of the importance of taking the horizontal refraction into account in estimation of arrival times in the modeling of long-range propagation and the solution of acoustical ranging problems are also discussed.

The article discusses the results of experiments conducted in September 2017 to prove the applicability of positioning underwater objects during their operation at depths substantially...