An analysis of the effect of gravity anomaly to attitude estimation in high-precision GNSS/INS integrated navigation systems under overturning cases

In high-precision GNSS/INS integrated navigation systems, the effect of gravity disturbance to the position, velocity and attitude estimation should be considered. The velocity and position errors induced by gravity disturbance can be corrected directly by GNSS position and velocity through Kalman filtering. The horizontal components of gravity disturbance defined as DOV can affect the roll and pitch estimation and should be compensated by gravity map products, such as EGM2008 or other earth gravity models. While the effect of gravity anomaly to the attitude estimation is usually ignored, since it is much smaller than normal gravity and can be absorbed by the vertical accelerometer's bias. However, in some special cases, such as IMU rotating around one certain horizontal axis, the gravity anomaly can transfer to horizontal accelerometers, and introduce attitude estimation error. In this paper, we analyze the effect of gravity anomaly on attitude estimation in GNSS/INS integrated navigation systems under overturning cases. A theoretical analysis in the case that IMU rotate around east-axis and north-axis to the attitude estimation is derived based on IMU error propagation functions. It is indicated that the rotation around east-axis (north-axis) can introduce pitch (roll) estimation error proportional to gravity anomaly, the yaw estimation is also be affected due to the intercoupling characteristic of attitude errors, and which more sensitive to the rotation around east-axis while not north-axis. Then, the simulation is conducted and agrees well with the theoretical results. Finally, an RLG (Ring Laser Gyroscope) IMU, which has similar quality to Honeywell HG9900, is fixed on a dual-axis turntable to access the effect of gravity anomaly. The experimental result shows that the yaw error induced by gravity anomaly with magnitude 100mGal can reach 15 arcsecs when IMU rotation around a certain horizontal axis at an angle rate of 1.5°/s°.