Underwater localization and mapping: observability analysis and experimental results

Purpose We investigate the observability properties of the process of simultaneous localization and mapping of an Autonomous Underwater Vehicle (AUV), a challenging and important problem in marine robotics, and illustrate the derived results through computer simulations and experimental results with a real AUV. Design/methodology/approach We address the single/multiple beacon observability analysis of the process of simultaneous localization and mapping of an Autonomous Underwater Vehicle (AUV) by deriving the nonlinear mathematical model that describes the process; then applying a suitable coordinate transformation, and subsequently a time-scaling transformation to obtain a Linear Time Varying (LTV) system. The AUV considered is equipped with a set of inertial sensors, a depth sensor, and an acoustic ranging device that provides relative range measurements to a set of stationary beacons. The location of the beacons do not need to be necessarily known and in that case, we are also interested to localize them. Numerical tests and experimental results illustrate the derived theoretical results. Findings We show that, if either the position of one of the beacons or the initial position of the AUV is known, then the system is at least locally weakly observable, in the sense that the set of indistinguishable states from a given initial configuration contains a finite set of isolated points. The simulations and experiments results illustrate the findings. Originality/value In the single and multiple beacon case and for manoeuvres with constant linear and angular velocities both expressed in the body-frame, known as trimming or steady-state trajectories, we derive conditions under which it is possible to infer the state of the resulting system (and in particular the position of the AUV). We also describe implementation of an advanced continuous time constrained minimum energy observer combined with multiple model techniques. Numerical tests and experimental results illustrate the derived theoretical results.