A new approach to monitoring shipping noise variability with a recently developed energy-harvesting ocean-acoustic profiler

In early November 2024, an experimental energy-harvesting Persistent Smart Acoustic Profiler (PSAP) was deployed off the Kona coast of the Island of Hawaii to monitor the regional soundscape. In over 8 months, PSAP successfully conducted over 1000 dives to 700 m on a six-hourly cycle in a 5o-latitude by 5o-longitude box south of the Big Island. On each dive, the profiler collected conductivity, temperature, and depth data on its RBR CTD sensor and, while parked in the deep sound channel, it sampled the soundscape in the 0–2 kHz band with its Ocean Sonics icListen R9B smart hydrophone. Onboard data processing was used to convert the raw acoustic data to compressed statistical spectral probability density files. On each surfacing, the acoustic, oceanographic and engineering data were sent to shore over Iridium satellite. The 15–200-Hz band of the soundscape was primarily dominated by sounds of distant shipping, but over the monitored period, notable variation and trends in soundscape amplitude were observed at different temporal scales. This paper describes the observed variations, the likely origins driving them and explains how the new approach to monitoring using PSAP enabled these findings. Work supported by NPS CRUSER via ONR.