Application of Striation-based Beamforming for Enhanced Passive Azimuth Estimation with Horizontal Line Array in Shallow Water

The dispersion of normal modes in shallow water leads to interference striations with certain slopes on intensity spectrogram of the range-frequency domain, which also causes the performance of conventional beamforming (CBF) to degrade in both array gain and output fidelity. The striation-based beamforming (SBF) has been proved to be one effective technique to improve these problems for pulse signals but the phase shift related to the waveguide invariant can deflect its main-lobe to a position that is not corresponding to the source azimuth. In this paper, the phase delay introduced by waveform truncation is analyzed. It is shown that the phase shift related to the waveguide invariant can be compensated when the header truncation point (HTP) is exactly set at the arrival point of the dominating modes (APDM) from the source to the reference array element. Simulation and experimental results show that the arrival point of signal peak (APSP) could be one effective estimation of the APDM. SBF is applied successfully on such specially truncated signals for enhanced passive azimuth estimation without the knowledge of waveguide invariant or the source range.