A fine alignment method about Doppler-assisted SINS

In this paper, the issue of fine alignment method about Doppler-assisted Strapdown inertial navigation system is studied. The main errors of the typical fine alignment method are analysed. The problem of the typical fine alignment method is the speeds measured by Doppler velocity log have to be transformed from the body frame to the navigation frame. But the relationship between the body frame and the navigation frame have not be established exactly as the fine alignment is not completed. This brings large errors for the fine alignment. Then, an improved Doppler-assisted alignment method is proposed. The Kalman filter dynamic model in the body frame for Doppler-assisted SINS is deduced. Because the DVL speeds are used directly, it avoids the problem that the typical fine alignment method exists. Simulations show that the improved Doppler-assisted alignment method obtains higher alignment precision. As open-loop Kalman filter is used, the new method has a high project value.