Observations of scattered surface duct arrivals from acoustic transmissions in the Beaufort duct using a tomographic array during 2016–2017

The 2016–2017 Canada Basin Acoustic Propagation Experiment (CANAPE) was conducted to assess the effects of the changing Beaufort Gyre on low-frequency underwater acoustic propagation and ambient sound. A 150-km radius ocean acoustic tomography array was deployed with six transceivers and a distributed vertical line array (DVLA) measuring the impulse responses every 4 h with broadband signals centered from 172.5 to 275 Hz. The nominal transceiver source depth was 175-m, placing them near the Beaufort duct axis, and the 60 hydrophone DVLA spanned 50 to 600 m. The Beaufort Duct (BD; approximately 90 to 240-m depth) and the surface Duct (SD; approximately 0 to 90-m depth) form a coupled double-duct system. Previous work has described the statistics of the BD arrivals [J.Acoust. Soc. Am. 158, 38–50] so this analysis focuses on the SD. Because of lossy ice cover, the SD arrivals are only observed during open water and when the ice thickness does not exceed roughly 0.5 m. SD energy is detectable as an arrival coming in after the BD arrival but only on the shallowest hydrophones. The SD arrival is seen to be highly variable in both space and time. Mechanisms responsible for this variability will be evaluated.