Implementation of an airborne SAR motion compensation system

The Canadian Department of National Defence has entered into the Phase 2 development of an airborne synthetic aperture radar motion compensation (SARMC) system, following a Phase 1 feasibility study which led to the specification of the SARMC sensor configuration and accuracy. This paper describes the hardware and software configurations of an airborne SARMC system implemented on board a Convair 580 research aircraft. The hardware configuration includes a gimballed LTN-51 inertial navigation system, a Decca Doppler radar, a baroaltimeter and a motion compensation inertial measurement subsystem (MCIMS). The MCIMS is a specially designed strapped-down inertial measurement unit mounted on the ring gear of the APS-506 radar antenna. Since motion compensation depends critically on knowledge of the MCIMS orientation with respect to the radar line-of-sight to the designated target, a laser alignment procedure was developed and performed to calibrate the azimuth encoder of the antenna ring gear. This procedure is discussed along with experimental results. Substantial effort was dedicated to streamlining the Kalman filter algorithms in the SARMC processing package to obtain a high degree of robustness and computational efficiency while optimally integrating the information from the motion compensation sensors. Preliminary flight trial data are presented and compared with simulation results to indicate the level of performance achievable with this optimized system.