Strapdown gyrocompass algorithm for AUV attitude determination using a digital filter

The strapdown gyrocompass can provide attitude by measuring the Earth’s gravity vector. In practical applications, there usually exists unwanted disturbance accelerometers that will distort the accelerometer measurements, hence a filtering out procedure is essential. Current attitude determination method based on pendulum cutting off technology has the limitation for vehicle moving mode. This paper proposes a new strapdown gyrocompass algorithm via processing the accelerometer measurement with Butterworth low-pass filter (LPF) to remove the high frequency dynamic disturbance components. When the gravity variation in inertial frame is regulated, LPF can be applied to properly get the gravity even in the presence of acceleration disturbances, and subsequently can be applied to calculate the strapdown gyrocompass attitude. The proposed algorithm does not require declination information and inertial element biases estimation. The field test has been conducted and the results verified the effectiveness and reliability of the proposed AUV attitude determination method and have also shown that the gravity is proportional to the latitude and altitude of AUV.

► The gravity vector can be projected onto the Earth’s surface to determine attitude.
► The pendulum cutting off is used to shield the disturbed acceleration from AUV.
► The Butterworth LPF was introduced to filter out the disturbances from accelerometer.