Passive source depth estimation using beam intensity striations of a horizontal linear array in deep water

Depth estimation for broadband sources with a vertical line array in deep water

In deep water, deploying a short vertical line array (VLA) is an effective way for source localization. In the past decade, most studies focused on localizing sources at the short to moderate ranges in the reliable acoustic path or the direct arrival zone (DAZ), with a VLA deployed near the ocean bottom. Little work has been done for the end part of the DAZ and the zones outside the DAZ. In addition, a VLA deployed at other depths rather than near the bottom is rarely studied. This paper proposes a near-surface source depth estimation method by matching the measured time delay with a library of modeled values under different source depths calculated by a simple formula. This method is suitable for zones, which contains two paths (one is reflected from the sea surface) with very close arrival angles, of a VLA deployed not only near the bottom, but also at other depths of the water column. Source depth estimation strategy for the end part of each zone, which faces the problem of poor depth resolution, is also analyzed. Simulation and experimental data of the airgun and explosive sources in the South China Sea are used to demonstrate the method.

Sources depth estimation for a tonal source by matching the interference structure in the arrival angle domain

A publication by McCargar and Zurk [J. Acoust. Soc. Am. 133(4), EL320-EL325 (2013)] introduced a passive source depth estimation method for a moving tonal source with a vertical line array (VLA), utilizing the depth-dependent modulation in the arrival angle domain caused by the interference between the direct and surface-reflected acoustic arrivals. Under the isovelocity approximation, this method can estimate the depth of sources at close ranges, but the depth estimation error will increase with the increase in source range, as the impact of the sound speed profile on sound propagation is ignored. This paper presents a theoretical formula for calculating the modeled interference structure in the arrival angle domain with the knowledge of the sound speed profile. By matching the measured interference structure obtained from the beamforming of the acoustic data received by the VLA with the modeled structure under different assumed source depths, the tonal source depth estimation is achieved, even for sources at the remote part of the direct arrival zone. The performance of this method is verified by simulation data, as well as experimental data radiated from a towed source and a non-cooperative passing ship.