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Ref.: in IEEE/OES COA'2016, Harbin (China), 9-11 January 2016.
Distant ship noise has been utilized for geoacoustic inversion and ocean monitoring for many years. In a shallow water experiment, Makai 2005, a 4-element acoustic vector sensor array was deployed at the stern of the research vessel R/V Kilo Moana. The recorded engine noise of R/V Kilo Moana during its dynamical positioning was analyzed by the DEMON (Detection of Envelope Modulation on Noise) method. The strongest modulation frequency band of the ship noise was found by a group of band-pass filters for further data processing. Multipath arrivals in the vertical particle velocity have higher signal-to-noise ratios than those in the horizontal particle velocities because of steep arrival directions. By exploiting this advantage, the cross correlation of the broadband ship noise between the pressure and the vertical particle velocity can be used for multipath information exploration. Since the ship noise is often characterized as continuous broadband noise plus strong tonal noise, the cross correlation of the tonal noise would dominate that of the broadband noise, and consequently cover the multipath arrival pattern. Therefore, the spectral weighting functions are applied to reduce the noise contamination and ensure sharp multipath peaks in the cross correlation. For the engine noise emitted by the dynamically positioned ship, a short correlation time of 0.4s was used in order to keep the time delay fluctuation details of multipath arrivals. Clear multiple arrivals are seen in the cross correlation of different arrivals, and verified by the ray tracing program TRACEO. The results demonstrate the potentials of only one acoustic vector sensor in applications of source localization and geoacoustic inversion.