Abstract

The Intensity Vector Autonomous Recorder (IVAR) is a bottom deployed system measuring particle velocity and pressure. Results using IVAR in the Sediment Characterization Experiment (SBCEX) conducted off New England (spring 2017), involving active sources have been presented [P. H. Dahl and D. R. Dall’Osto, IEEE J. Ocean. Eng. (2019)]. Here, passive ship noise is studied from a 200-m length cargo vessel that is tracked over a 10 km course a 15 knots for which the closest point of approach (CPA) to the IVAR deployment location (1.25 m above the seafloor) was 500 m, as confirmed by Automatic Identification System (AIS) data. The time-frequency interference pattern of the noise as the vessel closes and opens in range is studied by way of vector acoustic field indicators. These are non-dimensional ratios of second-order quantities, e.g., kinetic energy over potential energy, which preserve magnitude over the track. Inferences on the seabed made from study of the field indicators are compared with geoacoustic models emerging from studies related to SBCEX. The aspect-dependent source level of the vessel is also estimated, with method tested on a known, omni-directional source towed past IVAR from the research vessel R/V Endeavor. [Study supported by Office of Naval Research.]

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