AUV maps submerged blue holes off Florida
This story entered on 27th Jun, 2007 09:53:40 AM PST

A NOAA-sponsored Autonomous Undersea Vehicle (AUV), Eagle Ray, successfully mapped several “blue holes” at depths of 300 m or more off Florida's east coast during a cruise aboard the NOAA Research Vessel Nancy Foster. Blue holes are erosional sink holes or caves formed in limestone during past ice ages when lower sea levels put the shoreline of the southeastern U.S. out near the continental shelf edge.

The cruise was sponsored by the Gray’s Reef National Marine Sanctuary for the purpose of mapping seafloor habitats of interest to the South Atlantic Fisheries Management Council at accuracies not possible with shipboard mapping devices. During a seventeen hour deployment, the Eagle Ray traveled a linear distance of 85 km while mapping a priority area of 15 km2. The AUV reached a maximum depth of 792 meters, a new depth record for this vehicle.

This cruise followed a series of Eagle Ray test and evaluation exercises during which the vehicle’s behavior was fine-tuned and on-board sensor and control systems were calibrated. These systems include a Kongsberg Simrad EM2000 multibeam echosounder, a Seabird CTD (Conductivity, Temperature, Depth probe), and Doppler/inertial navigation system manufactured by Kearfott. The heart of this system is a 24 cm diameter laser ring gyroscope that is used to sense true north. Coupled with 3 precision accelerometers and a Doppler velocimeter, the Kearfott system is able to navigate the vehicle over the seafloor while maintaining position accuracies of a few meters several hours after deployment.

In the near future, the AUV will be on the NOAA Ships Ron Brown and Nancy Foster to map inner regions of the Hudson Canyon off New York and deep coral reefs, respectively. Advanced technologies in development for the Eagle Ray include installation of a phase-preserving sub-bottom profiler, a towed hydrophone array for geophysical surveys, and the installation of prototype sensors to allow the vehicle to survey the water column for biogeochemical parameters of interest, such as methane gas.

The Eagle Ray was acquired in 2006 by NOAA's National Institute for Undersea Science and Technology and is operated by the National Undersea Research Center at the University of North Carolina at Wilmington.

Contact information
Name: Raymond C Highsmith
Tel: (662) 915-6507
ray@olemiss.edu