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Passive localization of a sound source in the deep ocean is investigated in this study. The source can be localized by taking advantage of a cross-correlation function matching technique. When a twosensor vertical array is used in the deep ocean, two types of side lobe curves appear in the ambiguity surface of the localization. The side lobe curves are analytically expressed and they are then used as indicators of the localization result instead of the scanning point with the maximum power. Simulation and experiment demonstrate the performance of the proposed passive localization method. [ABSTRACT FROM AUTHOR]

The characteristics of scattering due to interface roughness are usually described by the backscattering matrix for reverberation modeling. The backscattering matrix based on the Bass perturbation theory has significant differences from that based on the empirical scattering rule (Lambert's rule), especially at low grazing angles. In a waveguide environment with a point source, it is very difficult to extract the quantitative characteristics of the backscattering matrix at low grazing angles from the experimental data because of the difficulties in acquiring low-grazing-angle scattering data and separating the scattering data between different modes (grazing angles). In contrast, the use of single-mode excitations as sources in shallow-water waveguides enables acquisition of good quality low-grazing-angle scattering data. In this paper, the characteristics of the backscattering matrix were obtained from different single-mode reverberation experiments in shallow-water. The experiments were carried out at different sites during different seasons off the coasts of China. Model-data comparisons were made and the results showed that at low grazing angles (2 °-5 °), the backscattering matrices based on the Bass perturbation theory were in good agreement with the experimental data, but the backscattering matrices based on Lambert's rule were not. [ABSTRACT FROM AUTHOR]

The nonlinear progressive wave equation (NPE) is a time-domain model used to calculate long-range shock propagation using a wave-following computational domain. Current models are capable of treating smoothly spatially varying medium properties, and fluid-fluid interfaces that align horizontally with a computational grid that can be handled by enforcing appropriate interface conditions. However, sloping interfaces that do not align with a horizontal grid present a computational challenge as application of interface conditions to vertical contacts is non-trivial. In this work, range-dependent environments, characterized by sloping bathymetry, are treated using a rotated coordinate system approach where the irregular interface is aligned with the coordinate axes. The coordinate rotation does not change the governing equation due to the narrow-angle assumption adopted in its derivation, but care is taken with applying initial, interface, and boundary conditions. Additionally, sound pressure level influences on nonlinear steepening for range-independent and range-dependent domains are used to quantify the pressures for which linear acoustic models suffice. A study is also performed to investigate the effects of thin sediment layers on the propagation of blast waves generated by explosives buried beneath mud line. [ABSTRACT FROM AUTHOR]

The sea floor is considered to be a thin surface layer overlying an elastic half space. In addition to layers of this type being thin, they may also have shear wave speeds that can be small (order 100 m/s). Both the thin and low-shear properties, viewed as small parameters, can cause mathematical and numerical singularities to arise. Following the derivation presented by Gilbert [Geophys. J. Int. 133, 230-232 (1998)], the surface layer is approximated as a thick, finite-thickness interface, and modified ocean bottom fluid-solid interface conditions are derived as jump conditions across the interface. The resultant interface conditions are incorporated into a seismoacoustic parabolic equation solution, and this interface-based solution is benchmarked against existing solutions and previously derived modified fluid-solid interface jump conditions. Accuracy quantification is given via dimensionless interface thickness parameters. [ABSTRACT FROM AUTHOR]

Using vector acoustic sensors for marine geoacoustic surveys instead of the usual scalar hydrophones enables one to acquire three-dimensional (3D) survey data with instrumentation and logistics similar to current 2D surveys. Vector acoustic sensors measure the sound wave direction directly without the cumbersome arrays that hydrophones require. This concept was tested by a scaled experiment in an acoustic water tank that had a well-controlled environment with a few targets. Using vector acoustic data from a single line of sources, the three-dimensional tank environment was imaged by directly locating the source and all reflectors. [ABSTRACT FROM AUTHOR]

The traditional Pekeris treatment of the shallow water acoustic waveguide is marred by a seeming paradox: The so-called nonorthogonality of the propagation modes. This anomaly is due to the use of mistaken orthogonality criteria, and is easily exorcised by the use of normal coordinate theory (which leads to the correct orthonormality conditions for any linear conservative system). [ABSTRACT FROM AUTHOR]

Reflectivity measurements can be used in inversion techniques to obtain estimates of the physical characteristics of seabed sediments. In addition, computation of posterior probability distributions (PPDs) [S. E. Dosso, J. Acoust. Soc. Am. 111, 129–142 (2002)] provide an uncertainty of each parameter estimate obtained by a simulated annealing inversion. In this work, PPDs are calculated for experimental reflection loss data to evaluate the sensitivities associated with the parameters in the Biot-Stoll poro-elastic model for sediments. The data comes from a lab tank experiment in which reflection loss from a sandy sediment was measured as a function of grazing angle for frequencies between 75 kHz and 150 kHz. The sampling for the PPDs is based on the least-squares error between simulated reflection coefficient data and values modeled with the reflection module of OASES. [H. Schmidt, ‘‘OASES Version 2.1 User Guide and Reference Manual,’’ Department of Ocean Engineering, Massachusetts Institute of Technology, 1997.] The PPDs resulting from the lab data are compared with those obtained for simulated data, and the effects of experimental error on the results are explored. [ABSTRACT FROM AUTHOR]