Phase correction in extended towed array method

Abstract

An important issue in research on passive ASW operations is to improve signal-to-noise ratio (SNR) and bearing resolution for targets emitting low frequency signals. Passive Synthetic Aperture Sonar (PSAS) is one of the techniques believed to improve these characteristics. In the past decades, various passive synthetic aperture techniques have been investigated, such as Extended Towed Array Method (ETAM), Fast Fourier Transform Synthetic Aperture (FFTSA), and Maximum Likelihood (ML) algorithm. ETAM is shown to be superior in performance to the other two algorithms. Estimation for phase correction factor is the core idea in original ETAM. Firstly, the cross-correlations of signals on multi-pairs of overlapped hydrophones are estimated, secondly the average value of the cross-correlation phase angles is taken as the least-square estimation for the phase correction factor. However, when the phase angle is close to the discontinuous point, the above estimation method will lead to large estimation error. In this paper, a modified phase correction method in ETAM is proposed, and the discontinuity of phase angle is eliminated to ensure the accuracy of the phase correction estimation. Simulation and experimental results show that the modified method can effectively improve the stability of ETAM.