Abstract
Inertial navigation system (INS)/Doppler velocity log (DVL) integration is the most common navigation solution for underwater vehicles. Due to the complex underwater environment, the velocity information provided by DVL always contains some errors. To improve navigation accuracy, zero velocity update (ZUPT) technology is considered, which is an effective algorithm for land vehicles to mitigate the navigation error during the pure INS mode. However, in contrast to ground vehicles, the ZUPT solution cannot be used directly for underwater vehicles because of the existence of the water current. In order to leverage the strengths of the ZUPT method and the INS/DVL solution, an interactive multiple model (IMM)-aided ZUPT methodology for the INS/DVL-integrated underwater navigation system is proposed. Both the INS/DVL and INS/ZUPT models are constructed and operated in parallel, with weights calculated according to their innovations and innovation covariance matrices. Simulations are conducted to evaluate the proposed algorithm. The results indicate that the IMM-aided ZUPT solution outperforms both the INS/DVL solution and the INS/ZUPT solution in the underwater environment, which can properly distinguish between the ZUPT and non-ZUPT conditions. In addition, during DVL outage, the effectiveness of the proposed algorithm is also verified.
Highlights
Precise positioning and navigation technology still remains a challenge for underwater vehicles due to blockages of the global positioning system (GPS)
Define the coordinate frames employed in this work: i-frame: Earth-centered initially-fixed orthogonal reference frame; n-frame: Orthogonal reference frame aligned with the east–north–up (ENU) geodetic axes; b-frame: Orthogonal reference frame aligned with the inertial measurement unit (IMU) axes; n0 -frame: Calculated n-frame with small misalignment errors
It can be concluded that the inertial navigation system (INS)/zero velocity update (ZUPT) method can mitigate the velocity and position errors when the underwater vehicle travels with no water current, but fail to navigate when the water current exists
Summary
Precise positioning and navigation technology still remains a challenge for underwater vehicles due to blockages of the global positioning system (GPS). Compared to the traditional single INS/DVL model-based solution, the IMM-aided algorithm makes it possible to employ ZUPT methodology to deal with the zero velocity condition and the INS/DVL method to deal with the non-zero velocity condition, which may improve the navigation performance when the underwater vehicle travels under various patterns. The ZUPT model is integrated with the INS/DVL model by IMM for the first time to well utilize the dynamic ZUPT condition in an integrated navigation system, rather than in a pure INS This is the main contribution of the proposed method when compared to previous works. As the underwater vehicles are likely to be under simple motion for the most of the time, dynamic ZUPT is a very practical and effective method for reducing the accumulation of the lateral and vertical positioning errors. INS/ZUPT is integrated by KF, where zero velocity in lateral and vertical directions of the vehicle’s body frame is introduced to the integration mechanization
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