Tuesday, October 9, 2012

Undersea Vehicle Navigation and Autonomy

Changing operational and environmental factors will drive future unmanned naval systems away from remote operation and towards autonomy.  Today, a man-in-the loop is generally required to re-task platforms as the weather deteriorates, operational priorities shift, or maintenance problems occur.  Automation will allow dynamic retasking to take place without human intervention. Additionally, unmanned systems will increasingly operate beyond line-of-sight from their controllers and in areas prone to GPS or other electronic jamming, spoofing, and interference by adversary forces.   Moreover, as noted in the U.S. Air Force’s 2010 Science and Technology Roadmap, autonomous vehicles will enable “operational advantages over adversaries who are limited to human planning and decision speeds.”  Unmanned Underwater Vehicles (UUVs) require automation for the reasons mentioned above plus the simple fact that normal methods of navigation such as GPS do not work due to the limitations of electromagnetic propagation underwater. 

The most fundamental function of vehicle autonomy is the ability to safely navigate from point a to point b without human intervention.  Recognizing the need for non-GPS methods of navigation, the Office of Naval Research issued a Broad Area Announcement back in 2009, calling for research on "new and innovative navigation technologies that will provide more accurate, reliable, maintainable and affordable systems for Naval air, surface, subsurface, and ground platforms and forces." Last week, ONR awarded a $1.2 million contract to Pennsylvania State's Applied Research Laboratory to develop a bathymetric navigation system which could work on UUVs and submarines.  The basic concept of bathymetric navigation dates back hundreds of years to when mariners used a lead line to test the depth of a channel to ensure safe passage.  In modern terms, the technology is the underwater equivalent of the Tomahawk Land Attack Missile's Digital Scene Matching Area Correlation (DSMAC), which compares a stored image of a scene as the missile flies over the ground with a digital photo the missile snaps.  Bathymetric navigation will require detailed ocean floor maps and advanced imaging sonars such as those from Blueview (see above).

ONR is also exploring LIDAR for underwater navigation.  Blue/green lasers penetrate the water column best and can produce higher resolution than sonar, with some systems claiming to resolve details to 1mm.   LIDAR ocean mapping can even be performed from the air, although water clarity and depth can effect the laser's ability to reach the ocean floor.  One of the drawbacks of bathymetric navigation, regardless of sensor type, is that the surface of the ocean floor is dynamic and charts require constant updating due to seismic activity, marine growth, man-made construction, and debris.
Another navigation method, acoustic positioning, measures range and bearing to fixed sea floor transponders, similar to an underwater GPS system.  This technology (see Sonardyne video) has been successfully used for autonomous underwater vehicle navigation in the offshore oil industry and is another possibility for future naval AUVs. 

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