Transfer alignment kalman filter of airborne synthetic aperture radar under structural deformation and vibration

Abstract

This paper proposes an integrated navigation system that compensates relative displacement error of Synthetic Aperture Radar (SAR) antenna on airborne platforms under structural deformation and vibration. SAR is a high-resolution microwave imaging sensor that can produce radar images even under extreme weather conditions. SAR functions in wide spectrum of applications as for geographical mapping, Earth monitoring, as well as reconnaissance and security-related applications. SAR can be implemented in satellite systems, airborne platforms, or in ground stations. A real-time SAR requires accurate relative displacement measurement of the motion of the radar antenna with minimal latency to produce well focused with minimal position error. While generation of high-resolution SAR images requires the elimination of antenna motion, airborne SAR system is under irregular wind turbulence and structural fluttering can cause deformation and vibration on the antenna, which leads to corruption in SAR images. SAR motion compensation system is required to suppress antenna motion induced phase distortion. The motion compensation system consists of the inertial measurement unit (IMU), embedded GPS inertial (EGI), and radar motion compensation software.

Antenna motion compensating Kalman filter is presented in this paper. Transfer Alignment Kalman Filter (TAKF) is employed to align the IMU’s computed local horizontal frame with the aircraft inertial navigator’s computed local horizontal frame. A three-dimensional initial misalignment angles and aircraft flexure angles that follow $2^{nd}$ order Markov process is established and transfer alignment through parameter identification is employed. The simulation results show that the TAKF based on parameter identification effectively improves the estimation accuracy.