利用飞机观测订正激光雷达反演消光廓线算法及其应用

Aerosol vertical distribution in troposphere is the basis of estimating radiative forcing as well as climate studies. MPL (Micro Pulse Lidar) which can provide continuously quantitative aerosol information with high temporal and spatial resolution is a useful remote sensing method. The parameter of lidar ratio (aerosol extinction-to-backscatter ratio) plays a principal part in the retrieval method of lidar for aerosol extinction coefficient by accepted signal echo, so how to determine lidar ratio is important. Previous processing technique for determining Lidar ratio is to set a fixed value, but it will produce large error because lidar ratio correlating with particle size distribution, particle shape, particle component and so on show complex spatial and temporal change,which neglect the characteristic of each vertical layer in a certain extent. So we will determine more meticulous lidar ratio of each vertical layer using aircraft measurement to improve the retrieval method of lidar for aerosol extinction coefficient, which is suited for Beijing in different seasons, airflows and skies(e.g. clear,haze and dust).This retrieval method can provide more accurate real-time aerosol extinction coefficient profile which is related with the mass concentration of PM2.5. So the ralationship between extinction coefficient profile and the mass concentration of PM2.5 is established, and then the vertical characteristic of extinction coefficient and the mass concentration of PM2.5 are analysed in Beijing.

气溶胶垂直分布特征是估计气溶胶辐射强迫和相关气候效应的重要基础，地基激光雷达是观测气溶胶垂直分布的有效遥感方法，可提供连续的高时空分辨率的气溶胶定量化信息。激光雷达反演气溶胶垂直消光系数算法中的参数雷达比是影响反演精度的主要因素，之前多采用柱平均固定雷达比值，但由于雷达比与气溶胶谱分布、形状和成份等参量有关，存在显著时空变化，固定值将带来较大的误差，一定程度上弱化了各垂直分层的特征。为此本项目拟利用飞机观测的气溶胶信息订正激光雷达算法，确定各垂直分层的雷达比，建立起适用于北京地区基于季节、天气条件（晴空，灰霾和沙尘等）和气团来源的垂直分层的雷达比廓线查算表。此改进算法应用于激光雷达可提供更加精确的实时连续的气溶胶垂直消光系数，气溶胶垂直消光廓线信息进一步与污染物浓度建立关系模型，建立基于激光雷达的PM2.5质量浓度反演算法，分析北京地区气溶胶消光和污染物浓度的垂直分布特征。

气溶胶垂直分布特征是估计气溶胶辐射强迫和相关气候效应以及气溶胶和云相互作用的重要基础。地基激光雷达是观测气溶胶垂直分布的有效遥感手段，可提供实时连续的高时空分辨率气溶胶信息。在利用激光雷达反演气溶胶垂直消光系数算法中，参数雷达比是影响反演精度的主要因素。以往的研究多假设雷达比为固定常数，并且垂直无变化，带来较大的误差。(1)本研究发现雷达比受气溶胶粒径谱分布和环境相对湿度的影响，呈现一定的吸湿增长特性，吸湿增长因子随相对湿度指数递增，相对湿度高于70%，雷达比值迅速增长。分析得到雷达比吸湿增长因子的参数化模型。而气溶胶有效粒径与雷达比变化趋势一致，能较好的代表雷达比的垂直变化趋势。雷达比值分布于40—70sr的频数较大。(2)研究发现边界层内外雷达比存在显著差异，边界层顶雷达比值突变，边界层顶的识别对于雷达比值的确定至关重要。基于激光雷达本身能较好的给出边界层高度及其变化趋势。（3）分析研究给出不同季节、天气条件和边界层顶的雷达比值的垂直分布，霾天整层雷达比高于晴空。并将雷达比值应用于激光雷达的反演中，得到较为精确的气溶胶垂直消光廓线。（4）建立的消光系数与PM2.5的关系，还可以直观地了解PM2.5的垂直分布情况。未来可以根据垂直气溶胶消光系数进一步获得PM2.5的垂直分布，对于进一步认识污染的垂直分布特点意义重大。