Nonlinear Observers for GNSS- and Camera-Aided Inertial Navigation of a Fixed-Wing UAV

In this paper, exponentially stable nonlinear observers for the estimation of position, velocity, specific force, attitude, and gyro bias of a fixed-wing unmanned aerial vehicle (UAV) are proposed. The sensor suite consists of an inertial measurement unit, a global navigation satellite system receiver, a camera, an altimeter, and, possibly, auxiliary roll and pitch measurements. A first observer is designed making use of all the named sensors and is proved to be globally exponentially stable. Subsequently, the auxiliary roll and pitch measurements are removed and replaced by an additional feedback loop from the estimated attitude, and the new observer is analyzed and proved to be uniformly locally exponentially stable. An optical flow algorithm is used to calculate the UAV velocity based on the camera images, which is used as a measurement of the body-fixed velocity in the attitude observer. The performance of the observers is tested offline on simulated and experimental data.