Defense Technology International - July 2007 - (Page 31)

JORIS JANSSEN LOK/DEFENSE TECHNOLOGY INTERNATIONAL The Double Eagle Mk II tethered UUV is equipped with mine-hunting sonar. Future generations will be autonomous in onboard intelligence, mother-ship communications and power supply. class of MCM vessel operates towed side-scan sonars to check that approaches to Brest, home port of the navy’s nuclear-powered Le Triomphant-class ballistic missile submarine ﬂeet, are not mined. Gesma, an acronym for Atlantic Underwater Studies Group (Groupe d’Etudes Sous-Marines de l’Atlantique), maintains its headquarters at the Brest naval base. “Gesma is in charge of research and technology programs that help prepare the DGA and the French navy for the future,” says Dabe. “A lot of our work focuses on enhancing the control of UUVs by optimizing utilization of the limited bandwidth of underwater acoustic communications.” The research agency is pursuing a number of AUV projects. In addition to improving underwater communications, these include: environmental assessment of littoral waters; detecting and classifying buried mines; mine countermeasures and neutralization; and improving underwater data communications. A basic challenge with any UUV is communications. Acoustics are the only practical way to communicate wirelessly underwater, but are inherently slow. Gesma is working www.aviationweek.com/dti the problem from two directions: increasing the speed of transmissions, and making the vehicles more autonomous so less trafﬁc is required. Gesma has conducted high-datarate acoustic communications trials with its Redermor AUV and the French navy’s research support ship Thetis. Redermor, equipped with two side-scan sonars to image the sea ﬂoor on both sides of its track, was ﬁtted with a high- and a low-data-rate acoustic communications transceiver as well as a modem and positioning system. “We were operating at data rates to 10 Kbps. in shallow water 20-30 meters deep, communicating between the Redermor and Thetis,” says Dabe. “Horizontal transmissions of acoustic data in such a thin layer of water are particularly difﬁcult.” One way to improve this, he says, is by transmitting snippets of information—data on targets that have been detected and classiﬁed by the processing software on board the UUV. “We want to deploy UUVs on covert and unsupervised missions into unknown or hostile environments. We’re looking at goal-driven mission planning and real-time performance-mapping techniques, with the initial planning being done on the mother ship and the UUV being able to adapt these plans during the mission.” Gesma is working with the Onera lab in Toulouse to develop path-planning algorithms that will enable a UUV to continue its mission if it senses obstacles blocking the route. Another capability is autonomous replanning, for use if a mine or other hazard is detected off the AUV’s track and an extra navigation pattern is required to obtain 3D imagery of the target. “We’re investigating sense-and-avoid concepts,” says Dabe. “Obviously, we don’t want the AUV to run into a tethered mine. But there are also objects like ﬁshing nets, and in the near future we are expecting UUV countermeasures.” For this purpose, the Redermor AUV has been ﬁtted with a forward-looking array of 10 echo sounders in the nose, which have undergone intense testing. But sense-andavoid is not a straightforward problem. “A school of ﬁsh will also show up as an obstacle, so just implementing an algorithm to make the UUV stop 20 meters in front of an obstacle isn’t the solution. The goal is to enable the UUV to classify what’s in front of 31 JULY/AUGUST 2007 DEFENSE TECHNOLOGY INTERNATIONAL http://www.aviationweek.com/dti

Table of Contents Feed for the Digital Edition of Defense Technology International - July 2007

Around the World Science Watch Tech Watch Parallax Ghost Ship Low Visibility Red Tape Sub Catcher Boom Time Broad Access Fight or Flight Cut Loose Loud and Clear Drone On Postmortem The Net Cutting Edge On the Record In Review Insight

Defense Technology International - July 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.