In-Motion Alignment for Doppler Velocity Log-Aided SINS Based on Initial Velocity Error Estimation

Inertial frame alignment (IFA) for strapdown inertial navigation systems is widely considered to be a promising method due to its robustness to disturbances and noise. By using the velocity data from a Doppler velocity log (DVL), the IFA can be performed while the vehicle is in motion. However, this article reveals that the initial velocity error of the DVL at the startup continuously and considerably affects the precision of the in-motion IFA. Based on the formula derived with other sensor errors isolated, the azimuth error is proportional to the initial velocity error and is inversely proportional to the square of time, e.g., a 0.3 m/s measurement error in the initial velocity from the Doppler velocity log leading to a considerable azimuth error of more than 1.78° in five minutes. Moreover, the azimuth error becomes bulky if the latitude is high. The modified cost function with a constant vector is used to replace the cost function from the well-known Wahba's problem. Thus, an alignment result with a much higher precision and with the initial velocity error suppressed can be obtained in a short period of time. The vehicular experimental results further verify the error analysis and the improved method.