Passive moving source ocean acoustic tomography with uncertainty quantification using relative arrival times from a...

An ocean acoustic tomography inversion with uncertainty quantification has been performed in the Santa Barbara Channel using relative arrival times obtained from the radiated noise of a ship of opportunity received by two 32-element vertical line arrays, at ranges from approximately 1.8 km at the closest point of approach to approximately 2.5 km at the maximum receiving range. The sound-speed estimate agrees [with a root mean square (rms) difference of 0.71 m/s] with an estimate performed about 40 min later [Gemba et al. (2022). J. Acoust. Soc. Am. 151(2) 861-880] using a controlled source and absolute travel times. The estimate using relative arrival times is less constrained (1.42 m/s rms uncertainty) than with absolute travel times (0.89 m/s rms uncertainty). The relative proximity of the ship noise source to the surface and the geometry at these short ranges result in a depth-varying interference between surface-reflected and direct arrivals. The interference effect on the estimated time delays is larger when computed with respect to a single element but minimal when estimated between adjacent elements. The relevant equations for relative travel time ocean acoustic tomography are presented.