USBL/DVL navigation through delayed position fixes

This paper proposes a navigation system for an Autonomous Underwater Vehicle (AUV) fusing dead reckoning navigation data, gathered on-board from a Doppler Velocity Log (DVL) and an Attitude Reference Heading System (AHRS), with absolute position fixes obtained from an Ultra-Short Base Line (USBL). The USBL is operated in a standard configuration, with the transponder onboard the AUV and the transceiver on the sea surface. Hence, position fixes are fed back to the AUV through an acoustic modem. An Extended Kalman Filter (EKF) is used for the Multi Sensor Data Fusion (MSDF). The clocks of the AUV and the USBL-computer are synchronized, and a bounded circular buffer of past vehicle poses is kept to project the received USBL position fix, to update the corresponding time step producing a delayed position fix. The method is validated using a data set gathered for a dam inspection task.