Understanding how tectonic plates move on the deep seafloor is essential for improving models of earthquakes, tsunamis, and long-term geologic processes. Traditional methods for seafloor geodesy rely on expensive, crewed vessels and limited observation windows, making sustained measurements difficult.

Princeton University researchers collaborated with SeaTrac and DBV Technology to demonstrate a more economical and scalable approach: using an autonomous surface vehicle equipped with a GPS-Acoustic system to communicate with deep-ocean sensors deployed thousands of meters below the surface.

Base Platform and Operations

The team deployed SeaTrac’s SP-48, a 4.8-meter, solar-powered USV designed for offshore operations and complex sensor integration. The SP-48 executed pre-programmed survey transects while communicating acoustically with seafloor sensors and relaying data via satellite to shore-based operators located in Puerto Rico and Rhode Island.

The USV demonstrated excellent seakeeping in sea states reaching 10 feet, maintaining approximately ±3 meters of cross-track error over sustained survey legs. Deployment and recovery of the SP-48 and sensors were conducted from the research vessel RV Blue Manta, operated by Blue Tide Puerto Rico.

Subsurface Sensors and Acoustic Systems

The SP-48 was equipped with DBV Technology’s GPS-Acoustic (GPS-A) Surface System, integrated within the hull payload bay. The system communicated with Temporary Deep Ocean Geodetic Sensors (T-DOGs) deployed at depths of 3,500 and 5,500 meters.

Each T-DOG incorporated a chip-scale atomic clock for precise synchronization with GPS, enabling sub-centimeter positioning accuracy of the seafloor sensors. Acoustic transmissions supported synchronization, surveying, command and control, and data telemetry across horizontal distances of up to 11 km.

The project successfully demonstrated bi-directional acoustic communication from shore to the sea surface, down to the seafloor, and back again, validating the GPS-Acoustic approach in deep-ocean conditions. The SP-48 proved capable of supporting precision geodetic measurements while operating autonomously over long distances and durations.

Results exceeded system performance expectations and confirmed that autonomous surface vehicles can serve as reliable, cost-effective platforms for deep-ocean seafloor geodesy. The success of the demonstration laid the groundwork for future deployments using both temporary and long-duration geodetic sensors to monitor tectonic plate movement over years to decades.