Reliable Acoustic Path and Direct-Arrival Zone Spatial Gain Analysis for a Vertical Line Array

Abstract

A method is developed in this paper to calculate the spatial gain of a vertical line array when the plane-wave assumption is not applicable and when the oceanic ambient noise is correlated. The proposed optimal array gain (OAG), which can evaluate the array’s performance and effectively guide its deployment, can be given by an equation in which the noise gain (NG) is subtracted from the signal gain (SG); hence, a high SG and a negative NG can enhance the performance of the array. OAGs and SGs with different array locations are simulated and analyzed based on the sound propagation properties of the direct-arrival zone (DAZ) and the reliable acoustic path (RAP) using ray theory. SG and NG are related to the correlation coefficients of the signals and noise, respectively, and the vertical correlation is determined by the structures of the multipath arrivals. The SG in the DAZ is always high because there is little difference between the multipath waves, while the SG in the RAP changes with the source-receiver range because of the variety of structure in the multiple arrivals. The SG under different conditions is simulated in this work. The “dual peak” structure can often be observed in the vertical directionality pattern of the noise because of the presence of bottom reflection and deep sound channel. When the directions of the signal and noise are close, the conventional beamformer will enhance the correlation of not only the signals but also the noise; thus, the directivity of the signals and noise are analyzed. Under the condition of having a typical sound speed profile, the OAG in some areas of the DAZ and RAP can achieve high values and even exceed the ideal gain of horizontal line array 10 logN dB, while, in some other areas, it will be lowered because of the influence of the NG. The proposed method of gain analysis can provide analysis methods for vertical arrays in the deep ocean under many conditions with references. The theory and simulation are tested by experimental data.

Vertical Correlation and Array Gain Analysis for Vertical Line Array in Deep Water

“…Qiu et al discussed the spatial gain of the VLA laid in the reliable acoustic path and the direct-arrival zone, respectively. It also demonstrates that when the signal is in the reliable acoustic path, higher array gain can be obtained [18]. In this paper, based an experiment in the Deep South China Sea, the vertical correlation of the sound field in the direct-arrival zone and shadow zone are analyzed, and the correlation coefficient of the noise field is calculated.…”

Investigating the reliable acoustic path properties in a global scale

“…Duan et al utilized RAP multipath time de-lays recorded by a single hydrophone for localizing a moving source (Duan et al, 2014), while the interference structure of RAP was leveraged to estimate source depth with robust performance (Duan et al, 2019). Recently, Qu et al conducted a comprehensive spatial gain analysis for vertical line arrays in RAP regions (Qiu et al, 2018), and Tompson incorporated RAP as a crucial sound propagation factor in deep ocean acoustic networks, achieving impressive performance in high SNR scenarios (Thompson, 2009).…”