SINS/GNSS Aided by Autonomous AHRS for a Small UAV

The paper is devoted to the development of a navigation system for an accurate attitude determination and high-precision positioning of a small-sized UAV. The navigation system consists of a single GNSS receiver and a MEMS inertial measurement system which includes gyroscopes and accelerometers, along with magnetometers and a pressure sensor. The three-axis-magnetometer is utilized to improve heading/yaw estimation. Since the magnetometer is strongly corrupted by time-varying distortions, it is proposed not to integrate it with the SINS/GNSS system, but to build an autonomous AHRS as an independent source of orientation based on accelerometers, gyroscopes, barometer and magnetic data. The proposed AHRS uses two spaced three-axis magnetometers which are continuously calibrated throughout the flight, performs compensation of the UAV's own dynamics and applies the barometer measurements to improve roll and pitch angles estimation. The SINS/GNSS system utilizes the AHRS data for heading estimation, fast alignment and validation of the navigation solution. Presented flight test results have shown that the developed navigation system, having a smaller weight and cost, provides comparable accuracy in terms of attitude determination including heading, as a SINS/GNSS compass system. At the same time, the proposed system has greater autonomy, interference immunity and reliability. In addition, the use of adaptive antenna array for protection of the GNSS receiver allows the navigation system to operate in strong radio frequency interference environments.