Spatial Gain Analysis For Vertical Line Array In Deep Ocean

The vertical line array is an important part of the underwater early warning detection network.It has less difficulty to be deployed into water compared with the horizontal array and has small workload.The vertical array can be quickly put into the sensitive waters to perform tasks.The direct-arrival zone and the reliable acoustic path are both important acoustic channels in the deep ocean with special physical properties and detective advantages.In this paper,A method is developed in this paper to calculate the spatial gain of a vertical line array by considering the influence of both acoustic signals and oceanic noise.Firstly,we introduce the multi-path effects and ray theory.Then the sound propagation properties and detection advantages of the direct-arrival zone and the reliable acoustic path are analyzed using ray theory.Secondly,the definition of vertical correlation coefficient was given.The vertical correlation of sound field is mainly affected by the effect of multi-path effects.The calculation method of array gain based on the spatial correlation coefficients of signals and noises is developed.The proposed optimal array gain can be given by an equation in which the noise gain is subtracted from the signal gain.Therefore,the BELLHOP computation model was used to calculate the signal gain in the direct-arrival zone and the reliable acoustic path.The two-dimensional distributions of signal gain in above two regions were simulated and the gain results under different conditions were compared,include different source frequencies,different source depths,different numbers of array elements,and different separations of neighboring hydrophones.Thirdly,the vertical correlation and vertical directionality of oceanic noise in deep water were summarized.Based on the noise's typical directivity “double peak” structure,the signal directionality and noise directionality were compared.In addition,the two-dimensional distribution of the optimal array gain in the direct-arrival zone and reliable acoustic path was simulated,which provides the evaluation of array performance,the design and deployment of vertical array with reference.Finally,the experimental data measured in South China Sea were analyzed,the theory and simulation are tested by experimental data.