We propose an attitude and gyro-bias estimation scheme for accelerated rigid
body systems using an inertial measurement unit (IMU) and a global positioning
system (GPS). The proposed scheme allows to obtain attitude estimates directly
on the Special Orthogonal group SO(3) while estimating the gyro bias and the
unknown apparent acceleration of the vehicle. We prove semi-global exponential
stability of the estimation errors. Furthermore, a new switching technique for
the attitude state is introduced which results in a velocity-aided hybrid
attitude observer with proven global exponential stability