The demonstration marks a significant milestone in transitioning NRL’s Skyfish sonar technology from controlled test environments into complex, real-world operational conditions. This effort builds upon decades of structural acoustics research at NRL and more than 10 years of development and testing supported by the Department of War and the Office of Naval Research.
“This was really about crossing that threshold from operating at a benign testing site to operating in a complex, real-world environment,” said David Raudales, Ph.D., an NRL researcher specializing in structural acoustics and signal processing. “Successfully executing this demonstration under live-site conditions build upon years of research and represents a major achievement for our team.”
Skyfish consists of a structural acoustic sonar payload integrated onto an autonomous underwater vehicle (AUV) with retractable wings. The sonar emits sound waves into the water column and collects acoustic echoes returning from the seafloor. Researchers analyze these echoes to map the seabed and distinguish potential unexploded ordnance from rocks, debris, and other clutter.
Conventional sonar systems generally operate at higher frequencies to produce images of the seafloor. Skyfish operates at lower frequencies, allowing acoustic energy to penetrate the seafloor and provide additional structural acoustic information researchers can use to detect and classify underwater UXO. The winged receivers onboard the vehicle permit the unique volumetric capability needed to locate objects beneath the seafloor.
The Vieques demonstration presented a considerably more challenging environment than previous Skyfish exercises. The seafloor featured rocky outcroppings, coral reef structures, and other complex features, while researchers had limited knowledge of what types of clutter they would encounter prior to beginning the survey.
“Think of it like going into a junkyard and trying to find specific objects in the midst of everything else,” Raudales said. “You have a complex bottom with diverse natural and man-made clutter, and you’re trying to determine which of these objects are unexploded ordnance.”
Underwater UXO presents a persistent environmental-remediation challenge. While significant progress has been made by addressing munitions on land, underwater sites remain more difficult to inspect and characterize. Munitions may rest visibly on the seafloor or may be partially or completely buried beneath the sediment. Skyfish was developed to address the difficult problem of buried ordnance.
The Vieques demonstration also served as a rigorous test of the system’s operational scalability.
The Vieques measurement field was considerably larger than the areas NRL typically surveys during ESTCP testing. For approximately two weeks, the data collection team deployed the system across the site and successfully completed the planned survey despite the size and complexity of the operating environment.
“The fact that the team could scale up what has scarcely been charted and successfully survey one of the most complex environments we’ve operated in was a great achievement for us,” Raudales said.
The demonstration represents the latest stage in a research path that began with fundamental target-scattering studies conducted at NRL. Researchers initially collected acoustic measurements in laboratory environments to better understand how sound interacts with potential targets in the structural acoustics domain. That research helped inform development of both the sonar payload and the algorithms used aboard the vehicle to distinguish potential UXO from clutter.
Over time, the research evolved from basic laboratory studies into a state-of-the-art sonar payload, integration onboard a Bluefin-21 autonomous underwater vehicle, and at-sea testing at increasingly realistic sites. Previous blind testing was performed in a comparatively benign environment before researchers progressed to the live Navy remediation site at Vieques.
“You can see the full chain of research beginning in the laboratory and going all the way out to sea,” Raudales said.
The autonomous platform also allows researchers to streamline the surveying process. The vehicle can follow pre-planned survey patterns while collecting acoustic measurements across the seafloor, providing a more efficient approach to inspecting large underwater areas.
The Vieques effort was conducted in coordination with Naval Facilities Engineering Systems Command personnel responsible for overseeing the site’s munitions-response activities and with support from ESTCP.
Because the demonstration was conducted as a blind test, the formal evaluation is not yet complete. NRL researchers will submit their results to ESTCP for independent assessment. The immediate accomplishment, however, was demonstrating that the Skyfish system could successfully operate and collect data at the much larger and more complicated live remediation site.
NRL and ESTCP are planning another live-site demonstration in the coming year as researchers continue working toward transitioning the technology from a research prototype into a capability that could support future Navy underwater munitions-response efforts.
“Our ultimate goal is to field a system that excels in the fleet, not just the laboratory,” Raudales said. “We want to show that it can actually be deployed in the real world.”
For Raudales, the Vieques demonstration also highlighted the personnel behind the technology.
“This milestone was made possible by the seamless, around-the-clock collaboration between the NRL data collection team, our partners at General Dynamics, and the crew of the Blue Manta,” Raudales said. “Seeing this joint team successfully manage the expanded scope is a major achievement that reflects the dedication of everyone involved.”
