Single baseline GPS based attitude heading reference system (AHRS) for aircraft applications

Differential carrier phase GPS based attitude determination represents an alternative to expensive inertial measurement units (IMU) and attitude heading reference systems (AHRS) in aviation. Inertial systems rely on extremely accurate accelerometers and gyros to determine attitude. Ultra short baseline (less than 1 m between antennas) GPS systems have been shown to provide the integrity required in aviation. Previous work with three antenna, two baseline, ultra short baseline systems has shown sub degree accuracy in pitch, roll and yaw when coupled with automotive grade solid state rate sensors. For optimal performance, mapping of antenna phase errors is required. An alternative method of attitude determination based on GPS and accelerometers is presented. Roll and pitch are determined by using knowledge of acceleration. Yaw is determined using a single baseline oriented along the longitudinal axis. This approach, coupled with automotive grade inertial sensors, can provide equal or better accuracy to the two baseline techniques. The key advantage of GPS acceleration based attitude determination is that it provides for increased roll and pitch accuracy for cases in which there is a limitation on baseline length. In a three antenna configuration, roll angle accuracy is inversely related to the lateral distance between the antennas. In aircraft this distance may be quite small. In the acceleration based system, the accuracy is limited only by the quality of the accelerometers and accuracy of the acceleration determined from GPS measurements.