Striation-based beamforming for a ship of opportunity in shallow water.

Abstract

Coherent multipath arrivals in oceanic waveguides generate complex interference patterns that degrade the performance of conventional beamforming (CBF) on horizontal arrays, often causing azimuthal bias and sidelobes-especially in the endfire direction. These limitations stem from grazing-angle multipath propagation in the vertical plane. As a physics-based alternative, this study proposes striation-based beamforming (SBF), which leverages the waveguide invariant. SBF consists of three steps: (1) estimating the time-domain Green's function of an unknown broadband source via ray-based blind deconvolution, (2) resampling this Green's function along striation slopes (relative frequency shifts) aligned to the first arrival, and (3) applying CBF to the resampled Green's function. Anchoring to the first arrival-corresponding to the minimum grazing angle-allows SBF to reduce azimuthal bias and sidelobes. This study also introduces a simplified variant, termed CB1, which applies CBF exclusively to the first arrival, bypassing the resampling step. CB1 offers substantial computational savings while achieving performance comparable to SBF. Experimental results using a bottom-mounted horizontal array confirm CB1's effectiveness in tracking the azimuth of a ship of opportunity in shallow water.