Phase fluctuation of cross-spectrum by dividing a vertical linear array for shallow water source depth discrimination

Abstract

This study proposes a depth-dependent characteristic for discriminating source depth by dividing a vertical linear array (VLA) in shallow water with a typical downward-refracting sound-speed profile. Theoretical analysis of the phase fluctuation of cross-spectrum between the wide-band acoustic field recorded by the upper-half VLA and that recorded by the lower-half VLA was conducted. Results showed that the number of zero crossing points of the phase fluctuation of cross-spectrum had significant separability for the surface and submerged sources. The effects of velocity gradient, SNR, thermocline depth fluctuation, and array aperture on depth separability were investigated using simulation analysis, which is important for the application of depth discrimination method in real marine environments. Furthermore, the effect of array tilt on depth separability was illustrated and improved using a modified sound field summation method. On this basis, the VLA acoustic data collected in the South China Sea were processed to verify the detection ability of the current method on submerged sources.