Long-Baseline Ranging System for Acoustic Underwater Localization of the Seaglider Underwater Glider

This document describes a long-baseline underwater acoustic localization system that was developed to provide three-dimensional position information for the Seaglider underwater vehicle. The accurate inertial position of the glider can be used to estimate performance characteristics and to validate novel motion control and path planning strategies in future experiments. The system consists of three acoustic transponders that are placed at known locations at the surface of the water. Using the measured round-trip travel time of acoustic signals, slant ranges can be calculated between the surface units and the glider. The range measurements from the three transponders can be used to locate the position of the vehicle using geometrical methods or dynamic estimation algorithms. To provide smooth and accurate position estimates, the position information can be filtered using a hybrid extended Kalman filter. If data are available for post-processing, the estimation accuracy can be further improved by employing batch state estimation algorithms, such as the RTS smoothing method. Implementing such dynamic state estimators also allows to estimate the velocity components of prevailing ocean currents and the glider’s flow relative speed.