基于星载激光雷达双通道信息的气溶胶消光系数廓线反演算法研究

An Algorithm of Aerosol Extinction Coefficient Retrieval from Dual-Wavelength Mie Lidar Observations

星载Mie散射激光雷达是当前应用最为广泛的获取全球尺度气溶胶剖面信息的探测设备。然而,大气气溶胶类型多样,通常假定气溶胶遵循特定模式并以此为先验,从而实现从激光雷达信号反演气溶胶消光系数廓线,但这一定程度上会影响反演精度的进一步提升。鉴于此,提出了一种基于星载激光雷达双通道信息的气溶胶消光系数廓线的迭代反演优化算法。该方法首先在给定的先验气溶胶模式下获得初始消光-后向散射比(即激光雷达比),并基于此分别反演两个通道的气溶胶消光系数和光学厚度。同时借助构建的气溶胶光学厚度与气溶胶质量柱总量之间的关系,得到两通道独立估计的大气气溶胶质量柱总量。最后以两通道大气气溶胶质量柱总量相同为约束,实现仅依赖激光雷达数据的激光雷达比及气溶胶相关光学参数的迭代优化。由于双通道激光雷达观测的限制,该方法适用于两种类型气溶胶混合下的反演,利用内蒙古包头地区的多年气溶胶背景场,对反演模型的精度和适用性进行了评估。与采用经验估算激光雷达比的Fernald方法反演结果相比,所提算法反演的气溶胶消光系数廓线在532 nm和1064 nm通道的平均精度分别提高了21.16%和3.00%。此外,还将该方法应用在CALIOP数据中,进一步验证了该反演模型的应用潜力。

Space-borne Mie lidar is the most widely used instrument to profile aerosols in the global scale.However,due to the variation of atmospheric aerosol types,the retrieval model for aerosol extinction coefficients from lidar signals assumes a prior aerosol model,which impedes the further improvement of retrieval accuracy.As such,an iteration algorithm for aerosol extinction coefficient profiling from space-board dual-wavelength lidar observation is proposed.First,the initial extinction-to-backscatter ratio(i.e.,lidar ratio)is obtained based on a prior aerosol mode and the aerosol extinction coefficient and optical depth at two channels are then retrieved.Moreover,with the relationship built between aerosol optical depth and aerosol mass column,the total aerosol mass columns at two channels are estimated.Finally,by applying the constraints that the two-channel observations correspond to the same aerosol mass column,the lidar ratio and the optical parameters are optimized iteratively based on lidar observation extensively.Due to the limitation of the channel number of the dual-wavelength lidar,the method is only applicable to the two-type mixed aerosol model.The accuracy and the applicability of the method are evaluated based on the background information of aerosol profiles in Baotou,Inner Mongolia,China.The retrieval results from the empirically estimated lidar ratio are taken as the control group.The results show that the proposed method yields mean accuracy improvement of extinction coefficient at 532 nm and 1064 nm channels by 21.16%and 3.00%,respectively.The method is also applied to CALIOP data to further validate the application potential of the proposed retrieval model.