  This paper considers the problem of nonlinear attitude estimation for a rigid
body system using intermittent and multi-rate inertial vector measurements as
well as continuous (high-rate) angular velocity measurements. Two types of
hybrid attitude observers on Lie group $SO(3)$ are proposed. First, we propose
a hybrid attitude observer where almost global asymptotic stability is
guaranteed using the notion of almost global input-to-state stability on
manifolds. Thereafter, this hybrid attitude observer is extended by introducing
a switching mechanism to achieve global asymptotic stability. Both simulation
and experimental results are presented to illustrate the performance of the
proposed hybrid observers.
