Beam Converging and Slope Search Processing by Striation-Correlation-Based Beamforming in Shallow Water

In this article, we investigate the feasibility of using striation-based beamforming (SBF) methods to address the performance degradation of conventional beamforming (CBF). The research results demonstrate that the process of SBF utilizing interference striations along the horizontal array can exploit phase coherence among signals to achieve beam converging–allowing to form the same directivity for different modes, which can thereby help restore beam resolution and ensure array gain. Furthermore, this paper expands the striation-correlation-based beamforming (SCBF) to utilize array data generated from the cross-correlation of CBF beam output (BO) and array pressure signals (named as SCBF-BO). This SCBF-BO method can eliminate source spectrum and truncation time limitations inherent in SBF applications while maintaining the beam converging capability. Finally, the SCBF-BO algorithm for search of different slope values is proposed. The main-lobe position of SCBF-BO's BO is approximately independent of the striation slope used, but processing along the optimal slope maximizes the convergence gain of SCBF-BO. The slope search of SCBF-BO overcomes the dependence of SBF methods on previously obtaining slope information from the external acoustic intensity image processing. Moreover, the coherent processing of both amplitude and phase enables the slope search of SCBF-BO to achieve the optimal BO performance quickly when the signal-to-noise ratio of the selected BO exceeds 0 dB. Simulation results under Pekeris waveguide and summer thermocline conditions, as well as the synthetic aperture of approximately 959 m horizontal array in the northern Yellow Sea experiment conducted in winter 2011, are provided as illustrations.