Vision-aided attitude error compensation for marine strapdown inertial navigation system

Attitude error compensation is difficult for marine strapdown inertial navigation system (SINS) because of the marine vehicle´s moving or rocking. This paper proposes a method that compensates the marine SINS attitude error based on vision measurement. The relation between the vision level attitude and the sea-sky-line is deduced based on the geometry of vision. The sea-sky-line is detected from images to measure the level attitude of the marine vision system. By tracking a far reference object in images the vision azimuth change can be calculated. Using the vision level attitude and azimuth change observations, an extended-kalman-filter (EKF) is designed to estimate and compensate the SINS attitude error. Simulations of error compensation for rocking SINS were performed. Results show that the proposed method works well and after compensation the SINS attitude comes to a high precision. The method in this paper gives a feasible way for marine SINS attitude error compensation in alignment or navigation.