Localizing a source of radial movement at moderate range using a single hydrophone can be achieved in the reliable acoustic path by tracking the time delays between the direct and surface-reflected arrivals (D-SR time delays). The problem is defined as a joint estimation of the depth, initial range, and speed of the source, which are the state parameters for the extended Kalman filter (EKF). The D-SR time delays extracted from the autocorrelation functions are the measurements for the EKF. Experimental results using pseudorandom signals show that accurate localization results are achieved by offline iteration of the EKF.

Moving source localization with a single hydrophone using multipath time delays in the deep ocean.

The physical properties of a reliable acoustic path (RAP) are analysed and subsequently a weighted-subspace-fitting matched field (WSF-MF) method for passive localization is presented by exploiting the properties of the RAP environment. The RAP is an important acoustic duct in the deep ocean, which occurs when the receiver is placed near the bottom where the sound velocity exceeds the maximum sound velocity in the vicinity of the surface. It is found that in the RAP environment the transmission loss is rather low and no blind zone of surveillance exists in a medium range. The ray theory is used to explain these phenomena. Furthermore, the analysis of the arrival structures shows that the source localization method based on arrival angle is feasible in this environment. However, the conventional methods suffer from the complicated and inaccurate estimation of the arrival angle. In this paper, a straightforward WSF-MF method is derived to exploit the information about the arrival angles indirectly. The method is to minimize the distance between the signal subspace and the spanned space by the array manifold in a finite range-depth space rather than the arrival-angle space. Simulations are performed to demonstrate the features of the method, and the results are explained by the arrival structures in the RAP environment.

https://iopscience.iop.org/article/10.1088/1674-1056/21/12/124301/pdf

A reliable acoustic path: Physical properties and a source localization method

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 two-sensor 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.

Passive localization in the deep ocean based on cross-correlation function matching.

This paper presents a technique for calculating tracks of striations observed in the plot of acoustic intensity versus range and frequency. The striations result from the interference in acoustic propagation below the critical depth. The key of this technique is modeling Lloyd's-mirror interference fringes based on the ray-based description of the normal modes. Then, as the striations are interpreted as sampling fringes at different frequencies and ranges, a method to calculate their tracks is proposed based on the fringe model. Finally, experimental observations of striations are compared with results from the presented technique.

Acoustic-intensity striations below the critical depth: Interpretation and modeling.

Reconstructing Sound speed profiles worldwide with Sea surface data

Research on the underwater target scattering can provide important theoretical support for target detection. The scattering model of cylindrical shell is established in this paper. It is found that the forward target strength is much stronger and varies with angles of incident wave less significantly than backward target strength. The received forward signal strength fluctuates with the target moving due to the interference between direct signal and scattering signal, which is most significant when the target approaches the baseline. An experiment is carried out in an anechoic tank to validate the scattering model. The method of acquisiting forward scattering in the tank is proposed. The forward and the backward target strengths are achieved by using the pulse compression technology, and they are about 3dB less than the modeling results. The forward scattering phenomena of quiescent and moving targets are measured, which are similar to modeling results with different target types.

http://iopscience.iop.org/article/10.1088/1674-1056/19/5/054301/pdf

Lei Bo

Papers

A reliable acoustic path: Physical properties and a source localization method

Physical model of acoustic forward scattering by cylindrical shell and its experimental validation

Research on the temporal-spatial distributions and the physical mechanisms for the sound speed profiles in north-central Indian Ocean