Prospects for acoustic remote sensing and acoustic system performance in the Beaufort Gyre region

Abstract

In the Beaufort Gyre region north of Alaska, the vertical interleaving of the near-surface temperature maximum, the warm Pacific Summer Water (PSW), the cool Pacific Winter Water, and the Atlantic layer make for unusual acoustic conditions. The dynamics of these upper ocean layers cause typical complex and turbulent-like oceanic flow that causes geographically variable heat content and acoustics. A sound duct in the PWW, below the PSW and above the Atlantic Layer, filling ∼75 to 225 m depth, is prominent but not universal. Erosion of the PSW warm layer by either vertical or horizontal mixing processes often breaks the duct, with an additional seasonal cycle of ducting effectiveness, and allows sound to escape to interact with the scattering and attenuating surface. The duct enables communication and navigation signaling, but with that interruption caveat. It also allows passive sensing, best for sound that enters the duct and moves through it. A challenge is to utilize sound that exists outside the duct. This includes sounds emitted outside the duct by mammals, fracturing ice, or anything else. This sound will either cycle through the duct at steep angle, or stay above the duct and repeatedly reflect from the top boundary. The combination of unducted sound being subject to strong attenuation by ice or wave interaction (the typical high-latitude situation) and high variability of the duct effectiveness, imposes limitations on the usefulness of the otherwise convenient duct.