Array shape calibration based on coherence of noise radiated by non-cooperative ships

Array shape calibration is commonly categorized into active calibration and self-calibration, yet both methods have their drawbacks and are generally considered less optimal. This paper proposes a novel approach based on the coherence of noise radiated from non-cooperative ships. Firstly, the time-varying law of the frequency domain coherence of ocean ambient noise received by a titled hydrophone pair when a ship passes by is investigated, which reveals the relative location of the hydrophones and passing ship. The array shape can be calibrated by analyzing the ambient noise coherence and horizontal acoustic path difference between passing ships and different hydrophones. The calibration results are consistent which are obtained from the three sections of data collected near the shipping lanes in the Qingdao offshore. One of the calibrated result is employed to simulate the coherogram of ambient noise when the ship passes by. It is shown that the simulation is in good agreement with the measured results. The main error sources are also analyzed and simulated in this paper, and the results show that the method is basically feasible and reliable.