Analysis and simulation of GPS/SINU integrated system for airborne SAR motion compensation

GPS/SINU integrated system for synthetic aperture radar motion compensation (SARMC) is studied. The mathematical model of the integrated system Kalman filter is described, the algorithm considers both long and short-term accuracy. Simulation results show that if the time interval of GPS updating SINU is smaller than the synthetic aperture time, the measurement error of the integrated system fluctuates rapidly, otherwise the measurement error is approximately linear increasing. While the former generates serious aberration, the latter mainly displaces the SAR cross-image. So the time interval of GPS updating SINU should be bigger than the synthetic aperture time in the practical SAR imaging phase. If the time interval of GPS updating SINU is bigger than the synthetic aperture time, the intentionally introduced sinusoidal position deviations on the magnitude of ten meters is estimated to linear increasing position errors whose relative variance in synthetic aperture time is within 5 cm. This will greatly facilitate the operation of SAR imaging processor.

1. Introduction

On-board a flight vehicle (airplane, satellite or space shuttle), synthetic aperture radar (SAR) is a kind of microwave imaging radar, which acquires high resolution in both range and azimuth direction by pulse compression technique and synthetic aperture principle [1]. The synthetic aperture principle is based on the knowledge of the relative motion between the vehicle (strictly is antenna phase center (APC)) and the target. In airborne SAR systems deviations of the trajectory from the nominal one as well as attitude and velocity variations frequently occur mainly due to atmospheric turbulence. These introduce motion errors on the received raw data that, besides the loss of geometrical accuracy, may strongly impair the final image quality if not properly accounted for during the processing [2].