Thursday, October 23, 2014

Groping in the Dark - Unmanned Underwater Navigation

One of the more pressing technical challenges with today's unmanned underwater vehicles is maintaining an accurate navigational position.  Because GPS signals will not penetrate the water's surface, UUVs typically rely on inertial navigation systems and periodic trips to the surface to gain an accurate satellite fix.
Aquanauts with REMUS AUV - NPS Photograph
Bathymetric navigation, or finding one's ways through the contours of the sea floor, has been a tool used by mariners - both surface and subsurface - since the advent of sonar.  But accuracy was hampered due to inaccurate underwater charts and the processing limitations.

Advances in sensors and computing may change these dynamics as explored in Ensign Jacob T. Juriga's recent Naval Postgraduate School Thesis. Juriga's research
focused on terrain aided navigation (TAN) through a series of autonomous vehicle trials near the Aquarius Underwater Research Station located in Islamorada, Florida.  There, using two REMUS 100 AUVs and a SeaBotix vLBV300 Tethered, Hovering AUV (THAUS) contributed by the Naval Postgraduate School Center for Autonomous Vehicle Research, more than 3,046 sonar images were collected with a BlueView MBE 2250 micro-bathymetry sensor.  Then, the vehicles attempted to navigate using the previously created underwater map. The best run achieved a locational difference of only 2.846 meters from a GPS-aided fix.

Ensign Juriga's work isn't the only Navy effort to improve UUV positioning using TAN. But his thesis also emphasized the importance of autonomy, which "enables the vehicle, through exteroceptive sensing, to make intelligent navigational decisions such as obstacle avoidance and navigation in cluttered, dynamic environments."