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Dual-channel Clutter Cancellation Processing Method Via Space-time Decoupling For Airborne BiSAR
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摘要: 杂波抑制是实现动目标指示的一项重要技术手段。然而，在机载双基合成孔径雷达(SAR)动目标指示中，受限于杂波的空时强耦合非线性和非平稳性，传统的空时自适应滤波、偏置相位中心方法不能获得期望的杂波抑制性能。为解决上述难题，该文提出了一种基于空时解耦的机载双基SAR双通道杂波对消处理方法。其核心在于建立空时解耦矩阵，将机载双基SAR强耦合非线性的空时谱解耦为空间频率保持一致的空时谱。所提方法主要分为以下3个步骤：(1)为提高目标信杂噪比，应用一阶Keystone变换和高阶距离徙动校正函数，使得目标信号能量集中在同一个距离单元；(2)为削弱双基平台运动造成的方位谱扩展效应，逐距离单元补偿多普勒调频率项；(3)为实现通道间杂波对消处理，引入空时解耦矩阵，在保持机载双基SAR同一距离单元内各杂波点归一化多普勒频率不变的情况下，将对应的空间频率均衡到零频，再利用通道间回波对消处理，实现杂波的有效抑制。通过仿真和实测数据处理，证明了所提方法进行机载双基SAR杂波抑制的有效性。Abstract: Clutter suppression is an important technology for moving target indication. However, for Bistatic Synthetic Aperture Radar (BiSAR) moving target indication, traditional space-time adaptive processing and displaced phase center antenna methods cannot achieve the expected clutter suppression because of the strong coupling nonlinearity and nonstationarity of clutter. To address the aforementioned challenge, this study proposes a dual-channel clutter cancellation processing method via space–time decoupling for airborne BiSAR. The core lies in establishing the space-time decoupling matrix, which converts the strongly coupled nonlinear two-dimensional space-time spectrum of airborne BiSAR into that with consistent spatial frequency. The proposed method mainly consists of the following steps: (1) To improve the signal-to-clutter-plus-noise ratio of moving targets, the first-order keystone transformation and high-order range migration correction function are applied to concentrate the energy of moving targets in the same range cell. (2) To weaken the azimuth spectrum expansion effect caused by the motion of bistatic platforms, the Doppler frequency rate term is compensated for each range cell. (3) To achieve clutter cancellation, the space-time decoupling matrix is introduced. The normalized Doppler frequency remains unchanged, and the clutter atoms on the airborne BiSAR space-time plane are linearly transformed into atomic positions with the same normalized spatial frequency. Then, the echo signals of dual channels are subtracted for effective clutter suppression. The effectiveness of the proposed method for airborne BiSAR clutter suppression is demonstrated through simulation and real data processing.
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图 1 机载双基SAR双通道几何构型
Figure 1. The geometry configuration of dual-channel airborne BiSAR
图 2 不同分布对机载双基SAR地海杂波幅度的拟合结果
Figure 2. Fitting results of different distributions for the ground/sea clutter amplitude of airborne BiSAR
图 3 机载双基SAR双通道杂波空时信号建模流程图
Figure 3. The clutter space-time signal modeling flowchart for dual-channel airborne BiSAR
图 4 机载双基SAR等效相位中心空时变特性分析
Figure 4. Analysis of space-time varying characteristic of equivalent phase center for airborne BiSAR
图 5 方位多普勒谱压缩前后空时分布曲线
Figure 5. The space-time distribution curve before and after azimuth Doppler spectrum compression
图 6 空时解耦前后机载双基SAR空时分布曲线
Figure 6. The airborne BiSAR space-time distribution curve before and after decoupling
图 7 机载双基SAR双通道杂波对消处理流程
Figure 7. The clutter cancellation processing flow for dual-channel airborne BiSAR
图 8 距离脉压后地面回波以及距离-多普勒谱
Figure 8. The ground echo after range compression and range-Doppler spectrum
图 9 距离徙动校正后的地面回波以及多普勒谱压缩后的距离-多普勒谱
Figure 9. The ground echo after range cell migration correction and range-Doppler spectrum after azimuth spectrum compression
图 10 地杂波空时解耦前后的空时谱
Figure 10. Space-time spectrum before and after decoupling of ground clutter
图 11 经过不同方法进行地杂波抑制前后的成像结果
Figure 11. Imaging results before and after ground clutter suppression with different methods
图 12 经过不同方法进行地面杂波抑制后动目标成像位置处剖面
Figure 12. Moving target imaging profile after ground clutter suppression using different methods
图 13 不同SCNR下经过3种方法进行地杂波抑制后的动目标检测概率
Figure 13. Detection probability after ground clutter suppression using three methods at different SCNRs
图 14 经过距离徙动校正和多普勒谱压缩后海面回波的距离-多普勒谱
Figure 14. Range-Doppler spectrum of sea echo after range cell migration correction and azimuth spectrum compression
图 15 海杂波空时解耦前后的空时谱
Figure 15. Space-time spectrum before and after decoupling of sea clutter
图 16 经过不同方法进行海杂波抑制前后的成像结果
Figure 16. Imaging results before and after sea clutter suppression with different methods
图 17 经过不同方法进行海面杂波抑制后动目标成像位置处剖面
Figure 17. Moving target imaging profile after sea clutter suppression using different methods
图 18 不同SCNR下经过3种方法进行海杂波抑制后的动目标检测概率
Figure 18. Detection probability after sea clutter suppression using three methods at different SCNRs
图 20 机载双基SAR飞行试验回波以及距离-多普勒谱
Figure 20. The ground echo of airborne BiSAR experiment and range-Doppler spectrum
图 21 距离徙动校正后的机载双基SAR飞行试验回波以及多普勒谱压缩后的距离-多普勒谱
Figure 21. The ground echo of airborne BiSAR experiment after range cell migration correction and range-Doppler spectrum after azimuth spectrum compression
图 22 经过不同方法进行实测数据回波抑制前后的成像结果
Figure 22. Imaging results before and after real data suppression with different methods
表 1 BiSAR系统参数
Table 1. The system parameters of BiSAR
参数 符号 数值 发射站位置 $ T $ (– 8000 , –1000 ,6000 ) m接收站位置 $ \boldsymbol{R} $ (0, – 8000 ,6000 ) m发射站速度 $ \boldsymbol{V}_{\mathrm{T}} $ (–50, 150, 0) m/s 接收站速度 $ \boldsymbol{V}_{\mathrm{R}} $ (0, 200, 0) m/s 载频 $ f_{{\mathrm{c}}} $ 10 GHz 带宽 $ B_{\mathrm{r}} $ 200 MHz 合成孔径时间 $ T_{{\mathrm{s}}} $ 1 s 脉冲重复频率 $ \text { PRF } $ 1200 Hz通道数量 $ N $ 2 脉冲数量 $ M $ 10 
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