Applied Quaternion Optimization Method in Transfer Alignment for Airborne AHRS Under Large Misalignment Angle

The airborne attitude and heading reference system (AHRS) is an inertial system that provides the aircraft with navigation parameters in real time. A new coarse transfer alignment method is proposed for low-accuracy AHRS with a large misalignment angle between AHRS and master inertial navigation system (MINS). The new coarse alignment method is derived from the quaternion-optimization-based in-flight alignment (IFA) method. By resolving the alignment problem in body frame, the proposed method makes full use of the navigation information of MINS and transforms the alignment problem into a quaternion optimization problem. Its accuracy is improved by presenting a two-step iterative algorithm. Compared with the quaternion-optimization-based IFA method, the proposed method is more robust and accurate by introducing the attitude information of MINS. The simulation and experiment results show that the proposed method is applicable to both large and small misalignment angles, and it serves as a nice coarse alignment that permits the implementation of linear error model in fine alignment process.