中文摘要：

介绍了L625瑞利激光雷达系统结构以及基于瑞利散射理论探测大气分子数密度的原理．提出了反复迭代修正大气透过率的计算方法，并通过模拟仿真验证了该算法的可靠性．通过误差分析得到影响大气分子密度不确定度的主要因素为回波信号信噪比以及参考点处大气分子数密度值，给出了回波信号误差产生的主要来源以及参考点选取方法．最后，分析了激光雷达16年观测数据反演的结果，得到合肥地区大气分子数密度的月份以及年份分布状况，结果表明：中层大气分子数密度分布呈现明显的季节性分布特征，冬季分布稀疏，夏季分布密集，随年份分布则较为平稳．通过将统计平均得到的密度廓线与1976美国标准大气模式比对分析，发现由激光雷达观测反演得到的结果较模式值大，二者的比值在1．05～1．13之间．

英文摘要：

The structure of L625 Rayleigh lidar system, principles of atmospheric density measurement which is based on the Rayleigh scattering theory and iterative method to retrieve middle atmosphere density profiles were described respectively. In order to prove the effectiveness of iterative algorithm, simulation analysis was made. Error analysis indicated that contributions to the uncertainty of the retrieved molecular number density mainly derived from signal to noise ratio of the return signals and molecular number density at the reference point. Meanwhile, main error sources of the return signals and method to determine the reference point were given. Finally, according to 16 years＇ routine observations of L625 Rayleigh lidar, monthly distribution and annual average of molecular number density from 1997 to 2004 and 2006 to 2012 in the middle atmosphere were presented. Results show that molecule number density distribution is sparse in winter and it becomes thick in summer. The yearly distribution ofmolecular number density seems to be relatively stable. Comparison with the model density which is obtained from 1976 USA standard atmospheric model indicates that density ratio profile of L625 Rayleigh lidar to the model density fluctuates between 1.05 and 1.13.