Vector sensor measurements of dispersed arrivals from explosive signals, underwater sound (SUS)

Abstract

In 2017 and 2021, ONR experiments south of New England examined the effect of the environment on sound propagation. A series of small explosive ordinance called SUS, models Mk-64 (1.1 oz) and Mk-82 (1.8 lbs), were deployed at various ranges (1-40 km) from a vector sensor positioned a 1.5 m above the seafloor. These studies focused on two areas: (1) the New England Mud Patch (NEMP) where 75 m of water overlay a thick 10-m layer of surficial mud; (2) a 60 km south-southwest of the NEMP where the continental shelf transitions to the slope. SUS provide a strong impulse signal, exciting both water-borne and sediment-borne arrivals. Owing to geometric dispersion, a time-frequency representation of the signals reveal distinct arrivals associated with the propagating normal modes. Forward models based on mode theory are presented to demonstrate the effects of bathymetry, oceanography and sediment structure on dispersed SUS signals. The model facilitates both the extraction of vector information, and inverting it to determine geo-acoustic properties of the environment. Measured vector data are also presented, including examples on the continental slope where the 3D propagation effects encountered will need to be considered for successful modeling and inversion.