Estimation of constant ocean current velocity based on SINS/DVL integrated navigation with an augmented observable quantities filter

Ideally, navigation and positioning information for Autonomous Underwater Vehicles (AUVs) can be provided by a combined navigation system based on a velocity-matching Strap-down Inertial Navigation System (SINS) and Doppler velocity log (DVL). However, the velocity accuracy of DVL is affected by ocean currents when the DVL is operating in water track mode in deep ocean scenarios. The velocity of the currents remains stable over small areas of the ocean within a few hours and can be considered a constant value. Estimation and compensation of the ocean current velocity is a prerequisite for high-precision navigation performance and an important topic for oceanographic research. In this paper, we propose an Augmented Observable Quantities (AOQ)-based filter that constructs a new measurement equation from the difference between the velocities of the previous state and the current state to decouple the ocean current velocity from the velocity error of SINS, and without introducing other sources to provide any information on velocity or position. The simulation and lake test show that the AOQ filter can estimate the ocean current velocity and mitigate its effect on navigation accuracy.