I. Introduction
Robotic vehicles require accurate knowledge of their orientation to execute autonomous maneuvers. However, orientation, also referred to as attitude, cannot be directly measured. Instead, the attitude of a vehicle must be ascertained from a variety of available measurements, many of which may be of poor quality. This is the problem of attitude estimation. The attitude estimation of a miniature aerial vehicle, for example, can be a difficult task. Such vehicles are typically equipped with low-cost inertial measurement units (IMUs). These low-cost sensors are characterized by poor noise properties that can complicate attitude estimation [1]– [4].