相干场成像高精度目标重构技术研究

Coherent field imaging is an active imaging technique with high-resolution. As a core part, object reconstruction technique imposes significant influence on the imaging capability of the system. Based on thorough analysis on key factors related to the imaging process, comprehensive research is accomplished in this project. The research work is carried out from two aspects: enhance the imaging quality and reduce the imaging time in order to achieve the reconstructed image of the object precisely in the turbulence environment. The simulation study and experimental verification method are used. Firstly, a new global phase closure algorithm is designed to cancel out the random phase error and scintillation at the same time, from which the true phase is extracted with higher accuracy; then a combined processing model for the received signal is established to suppress noises and enhance SNR effectively. And an iterated all-phase FFT reconstruction method is presented to correct the practical frequency and measurement error, promoting the robustness of reconstruction process, eventually obtaining high-precision image. NUFT method and compressed sensing theory are introduced into the project’s research, which can bring major breakthrough in sparse design of transmitter array and reduction of the imaging time, hereby lowering the power of laser and cost of coherent field imaging system. Based on this project, the imaging capability of coherent field imaging system can be highly promoted, while providing valid technical reference for optimization design and realization of Fourier telescope. Therefore, the research work is of significant importance in theoretical and application aspects.

相干场成像是一种高分辨率激光主动成像技术，目标重构作为其核心关键技术直接影响系统的成像能力。本项目针对影响目标成像质量的关键因素：上行链路大气湍流扰动、回波噪声扰动、多种频率漂移及测量误差等，采用理论推导、数值模拟与实验验证的研究方法，系统开展提高成像质量、缩短成像时间的研究。在多光束发射阵列下，首先设计新的全局相位闭合算法，在消除大气随机相位误差同时抑制光强闪烁效应、提高真实相位的恢复精度；之后建立融合回波处理模型抑制噪声、提高信噪比；并提出新的迭代全相位谱目标重构算法，在湍流环境中校正多种误差、提高重构的鲁棒性及图像质量；同时将空域NUFT及压缩感知方法应用到相干场成像中，突破二维采样定理、实现发射阵列的稀疏设计，从而缩短成像时间、降低激光器功率需求。通过本项目研究将有力提升湍流环境中系统的成像能力，为傅里叶望远镜的优化设计与工程研制提供技术依据，具有重要的理论研究意义与应用价值。

为应对日益复杂的国际空间资源环境竞争、提高我国的空间态势感知能力， 探测和识别空间目标的能力需求不断增长。相干场成像技术，采用激光主动照明，作为一种非常规主动成像技术，具备对远距离暗弱目标超高分辨率成像能力，研究其核心的目标重构技术对提升相干场成像系统的成像能力具有重要意义。.本项目针对影响相干场成像目标成像质量的关键问题，从信号处理技术及重构算法的角度研究了提高目标成像质量、缩短系统成像时间的高精度目标重构技术；实现了消除大气湍流扰动影响、滤除回波信号噪声、抑制多种频率漂移及测量误差的多种算法和技术，主要研究内容包括：全局相位闭合算法、融合回波信号处理模型、成像系统发射阵列冗余度研究，压缩感知稀疏重构及空域非均匀采样技术研究、频率漂移校正技术研究。.全局相位闭合算法有效消除了大气随机相位误差、抑制了光强闪烁效应，提高相位闭合运算速度，针对室外实验数据获得了清晰的目标重构图像；建立的融合回波信号处理模型针对回波信号噪声特性融合了门限自适应算法、自适应陷波算法及小波分析去噪方法，针对室外实验实测回波信号有效抑制了单频扰动和杂散噪声，大幅提高了回波信噪比，提升了成像鲁棒性；频率漂移校正技术研究有效抑制了发射阵列中每束光在独立传输路径上存在的频率噪声、实时补偿了各拍频间独立的频率漂移由此提升了目标成像质量；压缩感知稀疏重构及空域非均匀采样技术研究，重构出目标真实频谱、实现了目标图像的高精度重构，能够缩短相干场成像的成像时间，为降低激光器功率需求提供了依据。.综上，本项目研究了影响相干场成像系统成像质量的核心信号处理技术及图像重构技术，所做研究促进了相干场成像技术进步，为推进傅里叶望远镜的优化设计与工程研制提供了技术支撑、奠定了重要的理论及技术基础。