Accuracy Analysis of INS/GNSS Integrated Navigation on a Straight Path with Constant Velocity for Airborne Synthetic Aperture Radar Application

Antenna positioning is very important in synthetic aperture radar systems and it is necessary in the design of a navigation subsystem to account for different sources of error and their effects on the accuracy of navigation results. According to the error behavior of inertial and satellite navigation systems, integration of inertial sensors with satellite positioning systems is a common method to achieve high accuracy navigation results. However, synthetic aperture radar considerations, lead to some problems in the utilization of integrated navigation results in the imaging period. Therefore, only the inertial navigation results are used in the imaging period, and integrated navigation results are used just as the initial conditions for the algorithm. This paper studies the estimation of these initial conditions and predicts the navigation error growth caused by them. Since the extended Kalman filter is the most common tool for the integration of inertial sensors and satellite data, the elements of the corresponding state covariance matrix represent the accuracy of integrated navigation results. In this study for a synthetic aperture radar flight scenario, in which the nominal path is a straight path with a constant velocity, the state covariance matrix is calculated analytically both in the steady-state conditions and after the GNSS data outage. These analytical results are verified with simulations. Specifically, the estimation accuracy of antenna position, velocity and attitude are calculated with respect to the noise level of inertial sensors and GNSS data. Results can be used in the design and/or selection of a proper navigation system in synthetic aperture radar applications.