Observational and Model-Based Assessment of a Self-Contained Receiver for Long-Range Underwater Acoustic Geolocalization

Abstract The RAFOS ocean acoustic monitoring (ROAM) tag is a miniature, low-cost, attachable device that is designed to augment oceanographic float instruments, autonomous vehicles, and marine wildlife with RAFOS-style subsurface acoustic geolocation. Equipped with an acoustic receiver, clock crystal, internal batteries, and temperature sensor, ROAM tags detect the arrival times of regularly scheduled signals from low-frequency underwater sound sources. Once the data are recovered, these records enable trilateration of subsurface positions over months to years. Tag success improves with proximity to the deep ocean sound channel (approximately 500–1300-m depth), where the range of sound sources can extend for hundreds of kilometers. Here, we analyze geolocation results from a pilot study using a tag-equipped glider in the vicinity of a moored sound source. We also evaluate predictions of transmission strength and positional uncertainty for different source configurations based on acoustic models. With this analysis and discussion, we aim to offer a comprehensive description of considerations for successful ROAM tag deployments, such as depth regime (shallow versus deep water), environmental characteristics of the water and sediments, and sound source arrangement. Significance Statement The RAFOS ocean acoustic monitoring (ROAM) tag is a miniature, low-cost, attachable device for long-range underwater positional tracking. The device makes use of a common oceanographic float method for subsurface positioning, featuring an embedded acoustic receiver that detects signals from active sound source moorings to estimate its position at programmed intervals. Here, we present the results of tag performance in a preliminary experiment and acoustic modeling of sound source propagations, both to investigate the performance of our deployed sound sources and to discuss tag applications in hypothetical study regions. Ultimately, the ROAM tag is a novel, attachable device to track the positions of float instruments, subsurface vehicles, and potentially marine wildlife below the ocean surface for deployments of up to 2 years.