基于合成孔径激光雷达相位补偿的大气湍流随机相位屏数值模拟方法

The laser beams' intensity and coherence is mainly affected by atmospheric turbulence which lower the imaging ability of practical synthetic aperture ladar (SAL). Because of the intermittency of turbulence, O-K statistical law is not suited for all cases，there also exists lots of Non-Oboukhov-kolmogorov（N-O-K）turbulence. Hence due to the relationship between atmospheric refractive index structure function and power spectrum, a generalized expression (both suited for O-K and Non-O-K cases) of the atmospheric turbulence power spectrum will be induced first in this project, then based on fractal theory, a formalism to model the atmospheric turbulence phase screen is introduced, with which the random midpoint motion(RMM) algorithm is developed and used to simulate both the O-K and N-O-K phase screens respectively. Simulation accuracy is examined by comparing its phase structure function with the theoretical value. Other simulation methods including phase structure function method (PSFM), power spectrum method (PSM) and polynomial expansion method (PEM) are also examined and compared. Because the laser beam coherence length has inverse proportion to the atmospheric turbulence intensity which highly affects the imaging ability of SAL, the critical proportion rate for SAL imaging need to be given which is another result of this project. Meanwhile, SAL back scatted signal of assumed Gaussian beam from assumed targets is simulated using the theory of Fourier propagation. The results show that phase distortion in atmospheric turbulence is severe that could reduce or eliminate SAL imaging ability, and fortunately, it is possible to be compensated. A corresponding algorithm based on phase compensation is developed and used to minimize these phase errors, and the simulation results that gives a better SAL solution will be examined and compared by some simulation experments. A parallel SAL simulation software including phase screen simulation and phase compensation function will be developed and opened to public that can be shared through web-service interface

激光大气传输湍流效应的存在会影响光束的强度和相干性，是制约合成孔径激光雷达高质量成像的重要因素之一。由于大气湍流存在间歇性，其统计规律与Oboukhov-Kolmogorov（O-K）湍流统计理论出现较大偏差，并且发现了大量的Non-O-K湍流。本课题拟根据大气折射率结构函数与功率谱的关系推导出大气湍流功率谱的也适用于Non-O-K湍流的普适表达式。依据其分性特征，建立随机相位屏的分形模型，开发随机中点位移算法进行模拟，对已有的谱反演法、多项式展开法和结构函数法进行了测试和改进，提高大气湍流畸变相位数值模拟的精度和速度。获取大气湍流参数与激光相干长度的关系，同时开发相位迭代补偿算法应用于机载SAL成像处理中，解决对流层大气湍流引入的相位畸变问题，成像结果通过模拟机载试验进行检验，并引入并行计算技术和Web-service技术搭建具有Web服务功能的SAL并行成像处理仿真平台，实现共享服务

合成孔径激光雷达（SAL）是一种主动式有源成像传感器，由于其工作频率远高于微波，因此与传统的微波合成孔径雷达（SAR）相比，对于相对运动速度相同的目标可以产生更大的多普勒频移，不仅克服了普通激光雷达波束窄、搜索目标困难等缺点，而且能提供比SAR更高的方位分辨率及更短的成像时间，并且具有对特定区域目标精确成像的能力。但是，在成像质量提高的同时，由于工作频率很高，SAL在成像过程中对于大气环境中的湍流效应以及被探测目标的不规则运动非常的敏感。对此，本课题针对SAL成像过程中所涉及到的传输介质、相位误差的补偿以及高性能计算平台的搭建等几个问题进行了研究，主要内容概括如下：提出了结构函数法生成大气湍流相位屏，并以之为基础构建大气湍流数值模型，分析传输介质中大气湍流对SAL探测信号的影响；针对SAL回波相位误差补偿问题提出秩一相位误差改进算法以获得最佳的误差补偿方案；引入并行计算技术和Web-service技术搭建具有Web服务功能的SAL并行成像处理仿真平台，实现共享服务。