青藏高原卫星臭氧遥感产品精度定量评估

The Tibetan Plateau is a key area not only for ozone depletion in the mid-latitude regions of the Northern Hemisphere, but also for research on global ozone and climate change. The ozone change monitoring and trend analysis on the Tibetan Plateau are mainly based on satellite remote sensing data. However, in the Tibetan Plateau, ozone remote sensing is impressionable by some effecting factors. These factors are: (1) the ozone prior information of present ozone retrieval algorithms mainly comes from American standard atmosphere datasets, which is quite different of the real ozone distribution over the Tibetan Plateau, and the difference will result in retrieval errors in ozone remote sensing products; (2) the flexibility of underlying surfaces over the Tibetan including clouds, land covers, grades of slope and orientations of slope result in the flexibility of surface reflectivity and affect the precision of radiation calculation and retrieval results. In this project, to solve the first question, we will check and modify ozone prior information with surface ozone observing and ozone sonde datasets over the Tibetan. We will then carry out comparative retrieval experiments with the ozone retrieval simulation system OZPTOPGSS to evaluate the retrieval precision. The OZPTOPGSS (Ozone Vertical Profile and Total Ozone Products Generating Simulation System) has been built in the FY-3 satellite surface data processing system construction. To solve the second question, we will carry out ultraviolet radiation forward simulating calculation with the forward calculation system SBURFCSS to evaluate the effects of underlying surfaces on satellite ultraviolet radiation observing data, and then carry out the simulating retrieval calculation with OZPTOPGSS to evaluate its effects on retrieval results. With the basis of these calculations, we will carry out quantitative evaluation of ozone remote sensing data precision by comparisons of ozone data from both Chinese and foreign satellites with surface observation and ozone sonde data over the Tibetan.

青藏高原是北半球中纬度臭氧损耗的重点地区，也是全球臭氧和气候变化研究的关键地区。青藏高原臭氧变化监测主要依赖卫星臭氧遥感数据。在高原特殊条件下，卫星臭氧遥感数据精度容易受到一些因素的影响。这些因素主要包括两个方面：一是现有的反演算法使用的臭氧先验信息，主要来自美国标准大气数据库，与高原实际状况存在较大差异，这种差异通过反演迭代计算产生反演误差；二是高原云多变化、地表覆盖高度破碎化、坡度坡向各异等造成下垫面反射率多变，影响辐射计算和反演结果精度。本项目针对第一个问题，利用高原地基观测和臭氧探空资料，改进先验信息，使之更符合高原实际状况，通过对比反演，考察先验信息对反演结果的影响；针对第二个问题，首先利用正演仿真计算，考察下垫面反射率变化对卫星观测值的影响，然后与反演计算相结合，考察对反演结果的影响。在此基础上，通过国内外不同卫星遥感数据与地基观测和臭氧探空的对比，定量评估卫星反演产品的精度。

青藏高原是全球臭氧和气候变化研究的关键地区。高原臭氧变化监测和研究主要依赖卫星臭氧遥感数据，然而，卫星臭氧遥感精度容易受高原下垫面等因素影响。本项目基于我国风云三号卫星臭氧垂直探测仪算法研发过程建立的正演和反演仿真计算系统，通过提取青藏高原卫星紫外臭氧垂直探测仪像元下垫面参数，开展正演和反演模拟计算，定量评估高原下垫面等因素对卫星臭氧反演精度的影响作用。同时，利用长时间序列卫星遥感数据，结合欧洲和美国再分析资料，综合考察了高原自2008年以来春季臭氧逆转的增加趋势，以及与之相伴的平流层下部增温、对流层上部降温趋势，表明青藏高原春季大气臭氧恢复与大气温度变化趋势紧密相关。主要内容和成果：一正演计算，揭示高原下垫面反射率对卫星臭氧垂直探测仪第7-12通道辐亮度观测值产生显著影响，观测值随着反射率增大而增大，而且增加率随波长增大而增大；下垫面气压对卫星臭氧垂直探测仪第9-12通道辐亮度观测值产生显著影响，辐射值随着气压减小而增大，而且增大率随波长增大而增大。计算表明：下垫面高反射率和低气压显著影响长波长通道的辐射观测值。二模拟反演计算，揭示青藏高原下垫面反射率、气压等要素对臭氧垂直廓线反演精度的影响在对流层上部到平流层可以达到10-18%。表明高原下垫面多变性对对流层上部到平流层各层卫星臭氧廓线反演精度产生显著影响；三是通过对不同来源长时间序列卫星臭氧遥感数据综合分析，揭示2008年以来高原春季月份、尤其是5月臭氧成像显著增加趋势。与此同时，春季高原上空平流层下部150-50hPa呈现明显的增温趋势，对流层上部300-175hPa则呈现明显的降温趋势。表明高原春季臭氧已经由过去减少趋势逆转为增加，同时平流层下部到对流层上部大气温度也呈现相应的逆转趋势。这些结果与前人研究的结果完全相反，这是一个具有重要意义的发现，对深化高原大气臭氧和气候变化认识具有重要价值。