Terrain matching localization for hybrid underwater vehicle in the Challenger Deep of the Mariana Trench

The maximum ocean depth so far reported is about 11000 m,and is located in the Mariana Trench in the Western Pacific Ocean.The hybrid unmanned underwater vehicle,Haidou,is developed to perform scientific survey at the deepest parts of the Earth oceans.For vehicles working at the full-ocean depth,acoustic positioning is the most effective and popular method.The 11000 m class acoustic positioning system is relatively massive and complex,and it requires specialized research vessels equipped with compatible acoustic instruments.As a compact testbed platform,it is impractical for Haidou to carry an LBL/USBL beacon with its large volume and weight.During the descent to about 11000 m,horizontal drift could not be eliminated because of the hydrodynamics and uncertain ocean currents in the sea trials.The maximum depth recorded by Haidou is 10905 m,and determining the precise location of the deepest point is challenging.With the bathymetric map produced by a multibeam sonar,the terrain contour matching(TERCOM)method is adopted for terrain matching localization.TERCOM is stable in providing an accurate position because of its insensitivity to the initial position errors.The final matching results show the best estimate of location in the reference terrain map.

Simulation research on a minimum root-mean-square error rotation-fitting algorithm for gravity matching navigation

Gravity/inertial combination navigation is a leading issue in realizing passive navigation onboard a submarine. A new rotation-fitting gravity matching algorithm, based on the Terrain Contour Matching (TERCOM) algorithm, is proposed in this paper. The algorithm is based on the principle of least mean-square-error criterion, and searches for a certain matched trajectory that runs parallel to a trace indicated by an inertial navigation system on a gravity base map. A rotation is then made clockwise or counterclockwise through a certain angle around the matched trajectory to look for an optimal matched trajectory within a certain angle span range, and through weighted fitting with another eight suboptimal matched trajectories, the endpoint of the fitted trajectory is considered the optimal matched position. In analysis of the algorithm reliability and matching error, the results from simulation indicate that the optimal position can be obtained effectively in real time, and the positioning accuracy improves by 35% and up to 1.05 nautical miles using the proposed algorithm compared with using the widely employed TERCOM and SITAN methods. Current gravity-aided navigation can benefit from implementation of this new algorithm in terms of better reliability and positioning accuracy.