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In this study, the conventional beamforming (CBF) and the minimum variance distortionless response (MVDR) beamforming with a line hydrophone array mounted on an infinite rigid cylindrical baffle are proposed. Based on decomposing the sound field into a summation of harmonics, a model is introduced to compute the noise cross-spectral matrix in the spherically isotropic noise field. Some design examples are given with different array configurations and different kinds of incident signals. In comparison with the acoustically transparent array, the effects of the baffle scatter on the array gain and white noise gain are examined. Simulation results show that the baffled array has an advantage over the transparent array in a wide range of elevation angles.

The noise spatial correlation coefficient between two array elements deployed vertically in real deep ocean environment is not consistent with that in isotropic ambient noise field because of surface-distributed wind driven noise sources. Therefore, it is necessary to analyze the performance of vertical line array spatial gain properly. A method for modeling wind-driven ambient noise field is described. By using the described method the noise response on array hydrophones can be calculated. Furthermore, the formula of array spatial again in nonisotropic ambient noise field is developed. Spatial correlation coefficient between two elements are simulated with the described method and compared with that in isotropic noise field. And simulations are performed to analyze the difference of vertical line array spatial gain between nonisotropic noise field and isotropic noise field. Besides, the array spatial gain as a function of element number is also analyzed.

Cylindrical arrays are widely used in sonar systems for underwater target detection. For the sake of reducing calculation, each line of hydrophones at the same azimuth direction aligned with the cylinder axis are hardwired together in practice and thus, each line array with omnidirectional sensors becomes a directional sensor steered to broadside. As a result, the cylindrical array can be treated as a circular array with directional elements. In this paper, a model is introduced for computing the array gain and the white noise gain of an acoustically transparent cylindrical array. The three-dimensional acoustic field is described by the angular spectral density function and the steering vectors are represented by the cylindrical harmonic expansions, based on the derived noise cross-spectral matrix. Simulation results of array gains and white noise gains with the conventional beamformer (CBF) and the minimum variance distortionless response (MVDR) beamformer for different situations are presented, which has a guiding significance for practical applications.

In this paper, Argo data combined with altimetry data were used to investigate the effect of eddy on Sound Speed Profile (SSP) in Northwestern Pacific Ocean. A combination of the closed contours method and the Okubo-Weiss method is used to detect the eddy. Statistics of SSP anomalies induced by eddy have been calculated by removing the climatology from Argo profiles in eddy. Then effects of eddy on close range Direction of Arrival (DOA) estimation have been studied with a conventional beamforming method. Results suggest that the DOA estimation performance may deteriorate due to presence of the eddy. The deterioration occurs when the receiver is placed near the direct path range. This is because the direct path range is sensitive to the SSP anomalies and the presence of the eddy may lead to the receiver falling in/out of the direct path range.

Underwater sensors will diverge from the initial position because of the ocean current when the underwater sensors are deployed in the deep ocean. Assuming that the xy-plane coincides with the sea surface, a local Cartesian x-y coordinates system is set up in such a way that, when the sensors and sources are projected onto the local xy-plane, its origin coincides with the initial point of the sensors and the x-axis is parallel with east direction and positive y-axis is parallel with north direction. The depth of sensors can be obtained from press transducers, and the accurate position of the sources can be obtained from the GPS receiver attached to the ship and depths of the sources are preset. When the minimum time arrivals are snapped to a certain name, multipath time delay arrivals relative to the minimum time arrivals can be extracted from the measured signal and results of standard ray approach. The horizontal distance between the sensors and the sources can be estimated by matched time delays measured with ones calculated by BELLHOP model. Then the position of underwater sensors can be estimated by three points distance intersection method. Simulations and experiments are performed to demonstrate the feasibility of the method in the deep ocean. With the proposed method, the position of the underwater sensors can be localized in the deep ocean successfully.

An ensemble Kalman filter (EnKF) approach is proposed to perform sequential tracking of water column sound speed profile (SSP) using a moving acoustic source. First, the SSPs are discretized in depth and range, and are expressed by the empirical orthogonal functions (EOFs). Second, the acoustic source state information and the first three orders of EOF coefficients are expressed as the state variable, and the acoustic field information received by the vertical line array are the measured values. Successively, the state variables and measured values are used to establish the state-measure model. Last, the EnKF is utilized to track the state variables. The simulation results show that the root mean square error of SSP and the absolute error of source are all small, and thus the acoustic source tracking-positioning has high accuracy.

Waveguide sound propagation in continental slope with a varying-gradient water-sediment interface and special environment is very complex. Given three different gradients for shelf break areas and a defined gradient for the continental slope, numerical simulations with a full-wave range-dependent acoustic model show that the energy distributes distinctly in different depth in the sound field, in which the slope enhancement and mudslide effect are robust with different bottom properties. The greater gradient slope transfers more energy from shallow to the deep areas, but the transmission loss will be similar between different gradient slopes with range reaching to 20 km because of the significant bottom loss. Comparing to the effects on sound intensity by varying sediment thickness and sediment sound speed gradient, the latter influences more in the bottom loss. One purpose of this paper is the feasibility of these effects in ocean continent transition zone for a short range (10 km – 30 km). Another purpose is the acoustic propagation characters affected by different gradient slope in this region. These results provide a better interpretation on acoustic signals at whole depth for deployed hydrophone in continental slope.