Acoustic localization of seagliders in the Philippine Sea using broadband transmissions from moored acoustic sources

Abstract

Seagliders obtain precise GPS positioning at surfacing events between dives, but can be underwater for several hours and travel several kilometers during a single dive, during which time less is known about the position of the glider. Four Seagliders deployed in the Philippine Sea from November 2010 to April 2011 were equipped with Acoustic Recorder Systems, enabling them to record over 2000 transmissions from five moored broadband acoustic sources at ranges up to 700 km and depths up to 1000 m. These sources sequentially transmitted linear FM sweeps from approximately 200 to 300 Hz at 9-min intervals. Source-receiver ranges, determined from travel-time offsets of the received pattern of acoustic arrival peaks, are combined for sets of source transmissions using the stochastic inverse method of least squares to estimate the position of the glider at the time of acoustic reception. Because the source transmissions are separated in time and because the glider is in constant motion, it can move appreciably between source receptions. A linear model of glider motion is incorporated into the least-squares analysis to account for this motion and to simultaneously estimate glider velocity. These acoustically derived estimates of glider position are compared with the positions estimated by a glider kinematic model.