<title>Synthetic aperture radar (SAR) image focus performance during maneuvers</title>

Abstract

Focus of a SAR image during maneuvers requires accurate estimates of the aircraft velocity vector. Velocity errors particularly along the radar line of sight (LOS) to the SAR map center cause LOS acceleration errors during an aircraft maneuver. This LOS acceleration results in defocused SAR images. Sensitivity to acceleration errors is greatest when mapping at small squint angles with respect to the aircraft velocity vector, i.e., at small angles with respect to the aircraft fore-aft axis. This paper shows the expected SAR map focus performance during maneuvers as a function of velocity errors. Simulation results showing expected focus performance using current and advanced processing techniques with background radar Doppler updates and with the use of Global Positioning System (GPS) are presented. With GPS aiding, velocity accuracy is improved by a factor of ten. The simulation results are compared to the flight test results performed with the APG-76 radar using both a gimbaled and a strapdown one nautical mile per hour class Inertial Navigation System with and without GPS aiding. The AN/APG-76 is a SAR radar with simultaneous Ground Moving Target Indication and is designed for `near the nose' imaging during aircraft maneuvers.