复杂运动舰船目标SAR成像空/时变散焦特性研究

Study of space/time varying defocus characteristics of complex movingship targets in SAR imaging

合成孔径雷达(sythetic aperture radar,SAR)能够对海上舰船目标进行全天时、全天候成像,但是运动舰船在高分辨率SAR图像上的方位向散焦会严重影响后续对舰船目标的识别。由于舰船运动的非合作性,目前对复杂运动舰船在SAR图像中的散焦特性认识不足。本文首先从SAR成像原理出发,理论推导得出舰船复杂运动引起的SAR回波信号相位误差的空变性和时变性是导致其SAR图像质量下降的决定性因素。在此基础上,构建了一个复杂运动舰船目标SAR成像模拟器,通过对不同运动状态、不同合成孔径时间舰船点、线、面目标的SAR成像仿真,揭示了复杂运动舰船目标SAR成像空/时变散焦特性。其中,空变性会造成舰船在SAR图像上非均匀散焦;时变性使得舰船在SAR图像上变为一条方位向能量带。最后,结合空/时变散焦特性,探讨了未来SAR运动舰船重聚焦技术的发展方向。

Synthetic aperture radar(SAR)can take images of ship targets at sea all-day and all-weather.However,the azimuth defocus of moving ships in high resolution SAR images has seriously affected the subsequent recognition for ship targets.Due to the non-cooperative nature of ship motion,the defocus characteristics of complex moving ship in SAR images have not been well understood.In this paper,based on the principle of SAR imaging,it has been theoretically deduced that the spatial-variability and time-variability of SAR echo signal phase errors caused by complex ship motion are the decisive factors that lead to the degradation of SAR image quality.On this basis,a SAR imaging simulator for complex moving ship targets is constructed.By simulating SAR imaging of ship point,line,and surface targets at different motion states and synthetic aperture times,the spatial/temporal defocus characteristics of SAR imaging for complex moving ship targets are revealed.Among them,spatial variability can cause non-uniform defocus of ships in SAR images.Time variability causes the ship to transform into an azimuthal energy band in SAR images.Finally,based on the spatial/temporal defocus characteristics,the development direction of future SAR motion ship refocusing technology is discussed.