基于ADMM算法的机载太赫兹SAR成像高频振动补偿  

Vibration Compensation for Airborne Terahertz SAR Imaging Based on ADMM

作　　者：郝昭昕 张启明 孙进平[1] 王彦平 HAO Zhaoxin;ZHANG Qiming;SUN Jinping;WANG Yanping(School of Electronic and Information Engineering,Beihang University,Beijing 100191,China;School of Information Science and Technology,North China University of Technology,Beijing 100144,China)

机构地区：[1]北京航空航天大学电子信息工程学院,北京100191 [2]北方工业大学信息学院,北京100144

出　　处：《信号处理》2023年第11期1933-1942,共10页Journal of Signal Processing

基　　金：国防科技重点实验室基金项目(2021-JCJQ-LB-016-07-01)。

摘　　要：太赫兹波具有频率高、波长短的特点,因此相对于传统的工作在微波波段的合成孔径雷达(Synthetic Aperture Radar,SAR),太赫兹SAR具有高成像分辨率,并在视频SAR、慢动目标检测等方面具有显著的优势。但与此同时,太赫兹SAR也对雷达平台的高频振动非常敏感。对于机载太赫兹SAR,由于气流和载机自身飞行特性的影响,载机存在高频振动,会造成回波信号的相位误差,并使成像结果出现鬼影目标和散焦现象,严重恶化成像质量。为了实现聚焦成像,需要对机载太赫兹SAR的进行高频振动补偿。不同于现有的将高频振动建模为多个简谐运动之和形式的算法,本文提出了一种基于交替方向乘子法(Alternating Direction Method of Multipliers,ADMM)的高频误差补偿方法,无须对高频振动进行建模,可以补偿更复杂的高频振动相位误差。首先通过对接收到的回波信号使用方位向快速傅里叶变换(Fast Fourier Transform,FFT)得到粗聚焦的图像,然后将振动补偿问题转化为图像的l1范数最小化问题,引入辅助变量构造目标函数并使用ADMM算法求解。在ADMM算法迭代过程的每次循环中,利用图像熵最小化准则对相位误差进行更新。最后利用估计得到的相位误差构造相位补偿信号,用于补偿太赫兹SAR回波信号的相位误差。对点目标和分布式场景的仿真实验结果验证了该方法的有效性,且在低信噪比条件下也能获得聚焦良好的图像。Compared with the conventional microwave synthetic aperture radar(SAR),terahertz SAR have merits in many applications such as video SAR and slow-moving target detection due to the short wavelength.However,there is highfrequency vibration and flight path deviation for the radar platform due to the influence of air flow and the flight characteristics of the platform itself for airborne terahertz SAR,causing the phase error for the echo signal and ghost targets for imaging results.Therefore,the imaging quality of airborne terahertz SAR can be seriously deteriorated by the high-frequency vibration of radar platform.Thus,it is necessary to achieve high-frequency vibration compensation so as to obtain wellfocused image.Numerous vibration compensation methods approximate the high-frequency vibration as composition of simple harmonic vibrations at different frequencies.Different from those methods,alternating direction method of multipliers(ADMM)based vibration compensation method without vibration modeling was proposed in this paper to adapt to complex high-frequency vibration.Firstly,the azimuth fast Fourier transform(FFT)was used to obtain the coarsely focused image,and an auxiliary variable was used to construct the objective function which aims to minimize the l1-norm of the image.Then ADMM was used to solve the optimization problem,and the phase errors updating step was added to each iterative loop according to the principle of minimizing the image entropy.Finally,the phase compensation signal was constructed with the estimate of phase errors and was used to compensate the phase error of the terahertz SAR echo signal.Both simulations of point targets and distributed imaging scene were used to verify the validity of the proposed method.The results of simulations show that the defocus phenomenon can be well suppressed,and the well-focused image can be obtained under the condition of low signal-to-noise ratio.

关 键 词：太赫兹SAR 高频振动补偿 交替方向乘子法 图像熵最小化 

分 类 号：TN958[电子电信—信号与信息处理]