Terrain-aided Navigation for an Underwater Glider

A terrain-aided navigation method for an underwater glider is proposed that is suitable for use in ice-covered regions or areas with heavy ship traffic where the glider may not be able to surface for GPS location updates. The algorithm is based on a jittered bootstrap algorithm, which is a type of particle filter that makes use of the vehicle's dead-reckoned navigation solution, onboard altimeter, and a local digital elevation model (DEM). An evaluation is performed through postprocessing offline location estimates from field trials that took place in Holyrood Arm, Newfoundland, overlapping a previously collected DEM. During the postprocessing of these trials, the number of particles, jittering variance, and DEM grid cell size were varied, showing that convergence is maintained for 1,000 particles, a jittering variance of 15 m2, and a range of DEM grid cell sizes from the base size of 2m up to 100m. Using nominal values, the algorithm is shown to maintain bounded error location estimates with root-mean-square (RMS) errors of 33 and 50m in two sets of trials. These errors are contrasted with dead-reckoned errors of 900m and 5.5 km in those same trials. Online open-loop field trials were performed for which RMS errors of 76 and 32 m- were obtained during 2-h-long trials. The dead-reckoned error for these same trials was 190 and 90m, respectively. The online open-loop trials validate the filter despite the large dead-reckoned errors, single-beam altitude measurements, and short test duration. (C) 2015 Wiley Periodicals, Inc.