Image-Domain Signal Modeling and Refocusing of Air Moving Targets for MEO Multichannel SAR

Air moving target indication (AMTI) is an important task of spaceborne radar. Medium-Earth-orbit (MEO) synthetic aperture radar (SAR) has the characteristics of large coverage, short revisit time, and high orbital altitude, and thus is an attractive tool for AMTI missions. However, due to air moving target's high-speed maneuvering and MEO SAR's long synthetic aperture time and significant curvature of trajectory, the signal of air moving target after imaging processing is very complex, which makes the design of AMTI method be challenging. In this article, a study on image-domain signal modeling and refocusing of air moving target for MEO multichannel SAR is presented. The range equation of an air moving target with 3-D velocities and accelerations is established. In addition, the target's signal models after range migration correction and azimuth compression with the stationary scene parameters are derived. Then, via dividing targets into three types based on their residual range migration and Doppler ambiguity, the image-domain signal models of air moving targets are developed. Furthermore, a refocusing method that can cope with large range migration and Doppler ambiguity is proposed. Finally, numerical experiments are conducted to validate the developed signal models and proposed refocusing method.