Estimation of surface layer and Pacific summer water properties from acoustic transmissions in the Beaufort duct using a tomographic array during 2016–2017

Abstract

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 four hours 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 (approximately 90-m to 240-m depth) and the surface layer (approximately 0 to 90-m depth) form a coupled double-duct system. Observed arrivals in this system show reverse dispersion with the lowest Beaufort duct modes arriving first and higher double duct modes making up a transmission finale. In this talk, we investigate the oceanographic information content contained in the first and last arrivals which are the easiest to detect and track. The first arrival shows fluctuations from eddies, tides/inertial oscillations, and small seasonal heating/cooling. The last arrival shows a strong seasonal heating/cooling signal but is un-trackable during periods of significant ice cover due to enhanced transmission loss.