KB-2-ACO: Investigating Kauaʻi Beacon receptions recorded at the ALOHA Cabled Observatory

Activation of the Kauai Beacon (KB) in 2023 opened the door to long-range acoustics applications (navigation and tomography). KB is seafloor-mounted (∼810 m depth) off the north shore of Kaua‘i. Recent studies demonstrated successful long-range reception of the signal at sites including Wake Island and Monterey Bay, with distances exceeding 4,000 km at the Ocean Observatories Initiative (OOI) sensor network. Prior work has shown that long-range propagation, particularly for bottom-mounted sources, is impacted by near-field interactions between the acoustic signal and the seafloor. To help improve long-range acoustic applications, we are working to betterunderstand the near-field of KB by analyzing KB signals recorded at the ALOHA Cabled Observatory (ACO). ACO is seafloor-mounted (∼4728 m depth), located 166 km downslope and east of KB, and is relatively “near-field” in the context of KB’s basin-scale propagation range. The hydrophone operates continuously; we present data from March 2023 to October 2025. This presentation will discuss our methods and preliminary findings, including observations of seasonal effects on the received signal. Evidence of 3D effects will be discussed, possibly from interaction with Ka’ena Ridge, which runs ∼140 km south of and roughly parallel to the KB-ACO transect. [Work supported by the Office of Naval Research Ocean Acoustics Program.]