A Modified Smoothing Scheme for Water Current-Aided SINS/DVL Integration System

Water current velocity-aided strapdown inertial navigation system (SINS)/Doppler velocity logs (DVLs) integration system has shown great performance in mid-water areas. Though the velocity error will converge once the DVL bottom track (DVL-BT) is obtained, the position error accumulated during the mid-water period should be further optimized by employing the updated velocity measurements. Thus, in this work, a novel smoothing scheme specified for water current-aided SINS/DVL mechanization is proposed. First, a state-of-the-art staggered grid-based water current-aided SINS/DVL architecture is presented to provide a continuous navigation solution in mid-water areas. Second, a modified forward Rauch–Tung–Striebel (RTS) smoothing method is proposed, where the observation equations are rebuilt in output correction mode. Then, a modified backward RTS smoother is also investigated to further enhance the smoothing performance. Finally, both the forward RTS and backward RTS smoothing results are combined, where the position and water current velocities are recalculated. Simulations are conducted to evaluate the effectiveness of the proposed smoothing scheme. The results show the functionality of the modified forward–backward (FB) RTS solution, where all the velocity, position, and grid water current estimation errors are alleviated, compared to the traditional SINS/DVL solution and RTS solution.