Passive Acoustic Measurements on Autonomous Profiling Floats

The Electromagnetic Autonomous Profiling Explorer (EM-APEX) float provides temperature, salinity, pressure, and ocean current measurements. We implemented a passive acoustic hydrophone system for the EM-APEX to measure the ambient sound of the ocean. Two EM-APEX acoustic floats were built, and five deployments were made in Puget Sound off the Washington Coast, and Hawaii. Time-averaged and frequency bin-averaged acoustic spectra were transmitted to the shore station in near real-time via the Iridium connection, and the raw acoustic data were recovered post-deployment for source classification and acoustic environment study using machine learning methods. The results confirmed that ambient noise levels from this platform could be used to derive sea surface processes such as wind speed, and the transient noise from ship traffic and calls of marine mammals can be detected when floats are in depth-holding mode.