微多普勒通道间特性对SAR GMTI性能影响分析

现实环境中,地面目标在具有平动的同时常会叠加周期性的微动,如汽车的怠速抖动等.传统的合成孔径雷达地面运动目标检测技术(SAR-GMTI)主要集中于目标匀速、匀加速等平动形式,无法对微动造成的非线性相位历程进行处理.而目标微动产生的微多普勒会在SAR成像中使目标沿方位向出现等间隔的散焦点——"鬼影点".按照传统的GMTI理论,目标平动速度很小时,其多普勒很难与杂波区分,从而无法实现目标检测.通过对机载多通道SAR"一发多收"模式下地面振动目标运动建模,推衍出了地面振动目标在不同通道内的图像域回波表达式及通道间各鬼影点的干涉相位.通过仿真验证了该干涉相位的正确性,并量化分析了随载频、振动角频率、径向平动速度变化时,各鬼影点空域导向与杂波导向的正交区分度,从而证明即使目标的平动多普勒很小甚至为零时,利用微多普勒带来的空域信息检测地面运动目标仍具有充分的可靠性.

Analysis on the effect of multi channel micro doppler features on the performance of SAR GMTI

In real scene, the bulk motion is always combined with periodic micro-motion on a ground target, such as the idle speed of a car.Traditional synthetic aperture radar ground moving target detection(SAR-GMTI) mainly focus on constant velocity or uniform acceleration of a target,which is invalid for complicated nonlinear phase history coming from micro-motion.However, the micro-Doppler caused by micro-motion will produce equally spaced and symmetric defocusing points in azimuth in SAR image, which is named as "ghost points".In traditional SAR-GMTI technology, it's hard to distinguish the Doppler of a target in low bulk velocity and ever more harder for detection.In this paper, on the basis of setting up its airborne multi-channel SAR geometrical model, we derive the echo expression and the interferometric phase expression of the ground moving vibrating target, and it's derived in "single transmitter to multi-receiver " mode in image domain.The correlation coefficient of the spatial steering vectors between each ghost point and clutter are simulated, with the change of carrier frequency,vibrating angular frequency and target's radial bulk velocity, Thus demonstrating that the spatial information of ghost points is pretty useful in detecting low and even 0 bulk speed target.