Using the phase characteristic for source depth discrimination with a horizontal line array for a broadband source

Abstract

A solution to the problem of source depth discrimination in a shallow water waveguide is proposed for the case of a horizontal line array and low-frequency broadband sources. The method divides the horizontal line array into two subarrays with the same number of elements and then calculates the cross-power spectrum of beamforming pressure outputs of the subarrays. Depth-dependent features of phase fluctuation in the cross-power spectrum are analyzed using longitudinal correlation, and depth-separable decision metrics are defined. These decision metrics are poorly impacted by the energy distribution of the signal spectrum. Depth discrimination relies on the phase variation of the cross-power spectrum, and thus does not require mode space information or geoacoustic parameters as the prior knowledge, but sufficient effective horizontal apertures. Due to the application of beamforming, array gain can be obtained to improve the input signal-to-noise ratio of the phase feature-based discriminators. Simulations and Monte Carlo methods are applied to performance predictions and method comparison. The impact on the performance of signal-to-noise ratio, horizontal aperture, and array overlap is numerically studied. Finally, the method is experimentally demonstrated with data from a bottom-mounted horizontal line array deployed in the South China Sea, and the applicability of array overlap is illustrated.