Twin autonomous glider formation: innovative navigation and sea current estimation using two acoustically connected underwater gliders

The knowledge of the position of underwater vehicles is fundametal to perform most of the missions. With the absence of the Global Positioning System (GPS) underwater, there is a need to find an alternative solution. This paper presents a methodology to improve the navigation of underwater gliders using a collaborative framework called Twin Autonomous Gliders (TAG). TAG, consists in deploying two preferably twin gliders (same manufacturer and external/internal configuration) that are bound by a possibly acoustic-based relative positioning system – e.g Ultra Short BaseLine (USBL). Thanks to the relative positioning system, the gliders are controlled in a leader follower formation. The main principle of the approach is that this setup can be used to estimate and track the sea current, which is one of the major sources of error in underwater glider navigation. Knowing the relative velocity between the two gliders (measured using the relative positioning system) and the velocity of each glider relative to the water (given by the hydrodynamic model of each vehicle), it is possible to measure the difference in sea current between the two locations of the gliders. This difference can be used to estimate the sea current. The paper shows simulation results using a realistic mediterranean sea model, realistic glider model and realistic sensor data based on Commercial Off The Shelf (COTS) equipment specifications and empirical properties.