ARLINGTON, Va., 26 Feb. 2013. U.S. Navy researchers needed improvements to a hovering unmanned underwater vehicle (UUV) to continue investigations in untethered inspection of ship hulls below the water line. They found their solution from unmanned vehicles specialist Bluefin Robotics Corp. in Quincy, Mass.
Officials of the Office of Naval Research (ONR) in Arlington, Va., are awarding a $3.1 million contract to Bluefin to make improvements to the company's Hovering Autonomous Underwater Vehicle 1 (HAUV1) for ONR's Autonomous Un-Tethered Inspection Of The Non-Complex Area Of A Ship Hull With The HAUV1 program.
The contract calls for Bluefin to make modifications to the company's Hull Unmanned Underwater Vehicle Localization System-3 (HULS3) UUV to support research efforts by the Massachusetts Institute of Technology (MIT) in Cambridge, Mass., and the University of Michigan in Ann Arbor, Mich.
Researchers at MIT and Michigan are conducting a variety of experiments with hovering UUVs involving command-and-control software, imaging sensors, imaging sonar, underwater navigation, and the ability for the UUV to compensate for drift and underwater currents.
Navy researchers ultimately want to develop capability for an untethered hovering UUV like the Bluefin HAUV to inspect the hulls of ships at anchor for terrorist-emplaced bombs or other suspicious and potential damaging objects.
The Bluefin HAUV has a Doppler velocity log (DVL), an imaging sonar, a ring laser gyro (internal), an optical camera and a light strobe. The sonar and DVL can be actuated independently to optimally align the sensors to the surface being inspected.
Bluefin Robotics and MIT have built a ship hull inspection vehicle, called the hovering autonomous underwater vehicle (HAUV), which is equipped with a Doppler velocity log (DVL) to measure velocity relative to a surface, a ring laser gyro for attitude measurements, and a dual frequency identification sonar (DIDSON) for imaging structures.
The HAUV uses its gyro and DVL sensors to estimate its position and heading, which unfortunately results in drift over time. Researchers cannot use a magnetic compass to compensate for drift because such a device performs poorly near the large metal structures of ship hulls.
The vehicle estimates its heading by integrating the rotation rates from the gyro, and estimates its position by dead reckoning using its heading estimate together with the velocities reported by the DVL. Using only onboard sensors for navigation, the UUV uses the ship hull for global positioning by using images of the ship's hull from the imaging sonar.
MIT researchers have used an approach to drift-free navigation that consists of sonar scan matching to obtain geometric alignment between sonar frames, and the actual pose estimation that solves the resulting SLAM problem.
When a ship hull has been mapped in a previous session, the recorded data can be used to detect changes on the hull, making it easier to identify potential targets in the ship inspection mode, MIT researchers say.