太赫兹合成孔径雷达成像运动补偿算法

摘要

合成孔径雷达(SAR)成像理论分析和工程经验表明当雷达平台的运动误差幅度达到亚波长量级时，会影响图像的聚焦质量。相对传统微波 SAR，太赫兹合成孔径雷达(THz-SAR)工作在波长更短的太赫兹频段，对搭载雷达平台的稳定性要求更苛刻，需要达到微米级的控制和测量精度，目前的平台控制和测量技术还不能满足要求。该文提出一种基于回波数据的THz-SAR成像运动补偿算法，通过惯性测量单元输出的姿态信息完成由运动误差引起的距离徙动的校正，结合天线方向图和粗聚焦图像中特显点的最大幅值估计最优位置并构建理想回波。利用实际回波和理想回波数据提取由平台运动误差引起回波的相位误差并进行补偿，有效地实现了THz-SAR高分辨率成像。采用中心频率0.2 THz的SAR系统进行室外车载实验，对目标进行2维高分辨成像，得到角反射器和金属条的SAR图像。实验结果验证了所提运动补偿算法的正确性和有效性。%Theoretical analysis and engineering experience of SAR imaging shows that radar platform’s motion error will affect the quality of the image if its amplitude is greater than sub wavelength. Compared with traditional SAR working in microwave frequency band, TeraHertz SAR (THz-SAR) works in a shorter wavelength as the TeraHertz band, the control and measure accuracy of radar platform’s motion should be micron dimension, but the current technology can not meet the requirements. A novel motion compensation algorithm for THz-SAR imaging based on echo data is proposed in this paper. The attitude information from the inertial measurement unit is used to calibrate the migration error caused by the motion. Firstly, an obvious point like object is found in the coarse focusing image and the optimal position of this point is estimated by combining the antenna pattern and the maximum echo’s amplitude. Then the ideal echo of this point object is generated using the above estimated position and the phase error caused by the motion error of the platform is extracted by comparing the actual echo and the ideal echo. The extracted phase error is used to compensate the motion error of platform. The SAR system with center frequency 0.2 THz is used to carry out the outdoor vehicle experiment. Two dimensional high resolutions of SAR images of the corner reflectors and the metal strips are achieved. The validity of the proposed motion compensation algorithm is proved by experimental results.