Underwater Acoustic Signal Detection in the Ocean Using an Autonomous Surface Vehicle

Underwater acoustic target detection is crucial for various industries, including national defense, marine biology, and oceanography. As ocean ambient noise has increased, so has the need for target detection techniques that can resolve sounds with low signal-to-noise ratios. This challenge has two main aspects: identifying the signal of interest and determining its direction—both of which must be accomplished using low-frequency signals for long-range detection. Signal identification is hampered by our limited understanding of oceanic ambient background noise, which largely stems from physical processes like wind-wave interactions. Despite extensive research establishing empirical relationships between ocean processes and ambient noise, many studies fail to adequately explain the underlying physics governing the transfer of energy from ocean processes to acoustic energy. The primary obstacle in underwater signal localization of low-frequency signals is the requirement for large, complex arrays, typically towed by manned vessels. To address these issues, an autonomous surface vehicle platform—the Liquid Robotics Wave Glider—was developed for large-scale, long-term oceanographic and acoustic measurements. This vehicle is equipped with a compact three-dimensional hydrophone array capable of performing both low and mid-frequency source localization, as well as in situ time-synchronized ambient noise and oceanographic measurements. This setup allows for the creation of a physics-based relation between wind-wave parameters and acoustic energy. In two separate experiments, these vehicles were deployed in the northern Atlantic Ocean near the Atlantis II seamount. They conducted both active and passive acoustic experiments with frequencies between 200 Hz and 5 kHz and ranges between 1 km and 200 km. These experiments demonstrate that the Wave Glider is a compact, cost-effective tool capable of performing low and mid-frequency acoustic surveys and target detection.