Arrival structure of a distance source on the horizontal line array in deep ocean

The arrival signals of the horizontal line array (HLA) in the waveguide are not plane waves. The direction of maximum array output will not be the exact direction of the source. The acoustic pressure field can be expressed in terms of a normal mode expansion. The output of the HLA for a distance source in the waveguide is then constructed by summing up contributions of the normal mode response to each of the modes weighted in accordance to the frequency-wavenumber response of the array. The low and high order modes arrive at shallow and steep grazing angles, respectively. In deep ocean, a source away from the sound channel axis couples strongly with high order modes while weakly with low order modes. The direction of maximum output of a HLA deviates significantly from the horizontal direction.