Improving Slocum Glider dead reckoning using a Doppler Velocity Log

Abstract

The Slocum Electric Glider is a buoyancy driven Autonomous Underwater Vehicle (AUV) capable of long term deployments typically lasting four to six weeks. During missions execution, the vehicle makes use of the Global Positioning System (GPS) to navigate to its commanded waypoints. GPS, however, can only be used while the vehicle is at the surface. While underwater, the glider uses a simple dead reckoning (DR) algorithm to estimate its location and does not find its true position again until its next periodic surfacing. The Slocum Glider's dead reckoning algorithm estimates its position based on speed and heading calculations; they are derived from measurements from onboard sensors. Specifically, speed is determined by the depth rate change and pitch angle over a period of time. Since there is limited sensory input to the algorithm, the vehicle's estimated global position can differ significantly from its true position. Precise location information is important when collecting spatiotemporal sensitive sensor data and for vehicle navigation. In this paper, we will explore the benefits that can be gained if the dead reckoning algorithm makes use of a Doppler Velocity Log (DVL) to improve a vehicle's location estimates. Initial results based on a deployment equipped with the DVL on a Slocum Glider show promising results.