  We propose a 12-dimensional, global, continuous, and exponentially convergent
observer for gyro bias and attitude of a rigid body. Any attitude observer
developed on the special orthogonal group suffers from the topological
restriction that prohibits global attractivity in continuous flow. In this
paper, the observer is designed in the set of 3 by 3 real matrices, thus making
the topological obstruction on the special orthogonal group irrelevant. The
efficacy of the proposed approach against other attitude observers is
illustrated by an indoor experiment utilizing visual landmarks.
