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The array gain degrades significantly suffering from a decrease of signal spatial coherence caused by imperfectly correlated acoustic channels with spatial and temporal fluctuations. For a long linear array collecting signals in the range-dependent ocean waveguide, the amplitude and phase of the received signals show more viriation over the elements, which causes the signal coherence to attenuate seriously. The gain of traditional beamformers, such as the conventional beamformer (CBF), minimum variance distortionless response beamformer (MVDR-BF), and eigenvalue beamformer (EBF), will deviate from their ideal values. In this paper, a matched-phase weighting beamformer (MPBF) is proposed to obtain high gain in an ocean waveguide. The variational phase of acoustic channel transfer functions over the elements can be compensated for by matched-phase weighting, and then, the acoustic channel spatial coherence can be restored to achieve a high gain. The weighting-matrix of MPBF is obtained by the received signals; hence, environmental parameters or channel transfer functions do not have to be estimated. Simulations and experiments considering a long horizontal uniform linear array (HLA) in the slope region receiving a narrow-band signal from a deep-water source (upslope waveguide) are performed. The results demonstrate that MPBF can achieve a higher gain than CBF, MVDR-BF and EBF in a complex ocean waveguide.

Matched-Phase Weighting Beamformer to Improve the Gain of a Long Linear Array in the Range-Dependent Ocean Waveguide