  In various applications of land vehicle navigation and automatic guidance
systems, Global Navigation Satellite System/Inertial Measurement Unit
(GNSS/IMU) positioning performance crucially depends on the attitude
determination accuracy affected by gyro and accelerometer bias instabilities.
Traditional bias estimation approaches based on the Kalman filter suffer from
implementation complexity and require non-intuitive tuning procedures. In this
paper we propose, as an alternative, a simple observer that estimates inertial
sensor biases exclusively in terms of quantities with obvious geometrical
meaning. By this, any multidimensional vector-matrix operations are avoided and
observer tuning is substantially simplified. The observer has been successfully
tested in a farming vehicle navigation system.
