基于差分光柱像运动的湍流廓线激光雷达优化技术研究

Real-time refractive index structure constant profile (also called turbulence profile) is important for laser propagation and analyzing adaptive optics compensation effects. Turbulence profile obtained from atmospheric coherent length profile has unique advantages due to atmospheric coherent length is not restricted by scintillation saturation. Atmospheric coherent length of different altitude can be obtained by differential column image motion (DCIM) Lidar simultaneously, so it has a good time resolution, which is the shortage of differential image motion (DIM) Lidar. But the real-time turbulence profile retrieved from atmosphere coherent length profile obtained by existing DCIM Lidar has a large error due to the lack of altitude range. In order to overcome this shortage, this work focuses on the method of extending altitude range by optimizing Lidarreceiving field of view. This work can be finished by studying the method of obtaining exact altitude of laser beacon, by studying the effects of distributed beacon and by studying the effects of imaging with SNR on measuring atmospheric coherent length. The method of obtain beacon altitude and the effects of distributed beacon can be accomplished by academic analysis and by carrying experiment observation.The effects of image with differential SNR can be accomplished by numerical analysis based on Lidar Equation. The fulfill of this work is benefit for optimizing DCIM Lidar system, and it can promote the study of retrieving turbulence profile from atmosphere coherent length profile obtained at real atmospheric conditions.

在激光大气传输及其校正评估应用中需要实时了解折射率结构常数的高度分布信息（以下称湍流廓线）。利用大气相干长度廓线得到湍流廓线不受闪烁饱和限制，有其独特的优势。差分光柱像运动（DCIM）雷达克服差分像运动雷达的不足，同时对不同高度激光成像测量大气相干长度廓线，实时性好。但现有DCIM雷达测量高度范围有限，实时反演的湍流廓线偏差较大。课题研究一种雷达优化技术，通过研究信标对应高度、信标扩展度和成像信噪比对测量大气相干长度廓线的影响，提供一种优化接收视场角来延伸廓线高度范围的方法。课题通过理论分析和近地面实验研究信标对应高度和信标扩展度变化的影响，利用雷达方程进行数值仿真研究成像信噪比的影响，结合接收视场角与系统参数的研究给出雷达优化方法。该研究有助于DCIM雷达的改进以延伸测量高度范围，对实际湍流条件下利用大气相干长度廓线实时得到湍流廓线的研究有促进作用。

本项目主要开展了优化差分光柱像运动雷达的技术和方法研究。按照项目计划，首先开展了信标长度较长时信标高度的准确获取方法研究，建立根据回波信号强度高度分布计算信标高度的方法，并根据相机门控功能验证了信标高度的计算方法。其次，按照当前激光雷达参数计算了成像信噪比随信标高度的变化、利用相位屏方法数值仿真了成像信噪比对大气相干长度测量的影响，搭建了成像信噪比对测量相干长度影响的近地面试验平台；数值计算表明，雷达系统在测量10千米高度时成像信噪比高于13，数值仿真和试验结果均支持成像信噪比高于10信噪比对大气相干长度测量影响小于5%的结论。然后，根据孔径滤波方法把扩展信标按照非相干扩展光源处理，分析了信标直径对大气相干长度测量的影响，搭建了验证信标扩展度对相干长度测量影响的试验平台；理论分析结果表明，信标尺度变大相干长度测量值变大、而试验结果表明在相同条件下信标扩展度对相干长度测量无影响；两者之间不一致的可能原因是孔径滤波方法没有考虑倾斜等晕角对扩展信标的影响；我们根据试验结果给出了通过保持信标相对于接收系统张角恒定实现信标扩展度随高度不变的方法。最后，根据以上研究给出优化雷达系统的方法，即：当前雷达系统可通过适当降低成像焦距来增大接收视场角，进而增大信标测量高度范围。在开展项目规定的研究同时，我们提出四孔差分光柱像运动激光雷达方法以研究正交方向上湍流强度的差异、差分光柱抖动与闪烁法测量湍流廓线的新思路。项目组所开展的工作对光学方法测量湍流廓线进展有促进作用。