Transfer alignment from airplane GPS/MINS integrated system to SAR strapdown navigator

With the quick development of modern science and technology, higher resolution Image from an airborne Synthetic Aperture Radar (SAR) is required, so more accurate motion compensation should be applied to the radar returns to reduce image degradation which caused by spurious motion of antenna phase center (APC). This paper studies an improved SAR Motion Compensation System (SARMCS), which includes a "master" INS (Inertial Navigation System) and a GPS receiver located near the mass center of the aircraft, a "slaved" low cost strapdown IMU (Inertial Measurement Unit) mounted on the antenna structure. A Kalman filter is an integral part of the SARMCS; it acts to continuously transfer alignment from a high accuracy GPS/MINS integrated navigation system to the less stable strapdown navigator. The block diagram of SARMCS is described; the state equations and measurement equations are derived. Simulation results show the absolute velocity error of strapdown navigator is smaller than 0.3 m/s and the absolute attitude error of strapdown navigator is smaller than 180 arcsec. So this SARMCS is effective.