Abstract:   This article described a new attitude measuring method of bit on the basis of the real operating condition of underwater mudpenetrator. The method which is based on a strapdown inertial system chooses the low frequency value of acceleration and angular rate as the observation and adopts extended Kalman filter to measure the attitude of bit. The results show that the new method is feasible and can improve the navigation accuracy of strapdown inertial system without additional sensor, the drift error decreases from 20°/h to 3°/h.  

Key words: underwater mudpenetrator, attitude measuring of bit, extended Kalman filter, strapdown inertial system