Ocean shipping is the major contributor to ambient noise in the ocean. Specifically, tonal sounds from large container ship propellers can persist for over 100 km. In this talk, we examine the Doppler spread of tonal sources measured on the US continental shelves received by a near bottom vector sensor. The directional intensity information, and ship position from the Automated Identification System (AIS) provide a-priori information to match the observed signals to a bottom model. The low rotation rate of the massive propellers provide single digit frequencies that penetrate through the thick sediment layers overlaying bedrock. Doppler spread of a propeller tone, caused by the source motion, becomes concentrated at discrete frequencies corresponding to preferential angles of propagation. These modes are readily predicted from a plane wave reflection coefficient, matching resonances to a probable sound speed and density profile of the lithosphere below the source. On the Eastern US Shelf along the New England Bight passing ships confirm a sediment thickness exceeding 1 km. This noise-of-opportunity technique supplements the course global sediment thickness maps to date, which in turn improves regional models of low-frequency sound propagation via better knowledge of the sub-bottom sediment structure and composition.
Dall'Osto et al. (Wed,) studied this question.
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