中国3个典型城市气溶胶光学厚度地基观测及其MODIS气溶胶产品精度分析

利用中国太阳分光观测网的观测资料结合MODIS(中分辨率成像光谱仪)的气溶胶产品分析了北京、兰州、上海3个典型区域城市的气溶胶光学特性。结果表明:北京AOD(气溶胶光学厚度)年平均为0.41±0.35,春夏高,秋冬低,Angstrm波长指数α年平均为1.40±0.85表现为细模态粒子,MODIS的光学厚度为0.52±0.39与地面观测相关系数为0.91,存在系统性高估;兰州AOD年平均为0.55±0.21,夏季最低,秋冬较高,α年平均为0.95±0.20表现为粗模态粒子,MODIS光学厚度为0.43±0.21与地面观测相关系数仅为0.07,存在系统性低估;上海AOD年平均为0.55±0.21,无明显季节变化,α平均为1.03±0.25,MODIS光学厚度为0.74±0.30与地面观测相关系数为0.75,存在系统性高估。城市地理位置和复杂地表等原因造成反照率的不确定,MODIS气溶胶产品在这3个城市的反演效果仍有很大提升空间。

Aerosol Optical Depth Observed by Chinese Sun Hazemeter Network and Comparison with MODIS Products in Three Typical Cities in China

The CSHNET(Chinese Sun Hazemeter Network) data and MODIS(Moderate Resolution Imaging Spectroradiometer) aerosol products are used to analyze the aerosol optical characteristics in three typical Chinese cities:Beijing,Lanzhou,and Shanghai.The results showed that the annual mean AOD(Aerosol Optical Depth) were 0.41±0.35,0.55±0.21,0.55±0.21 in Beijing,Lanzhou,and Shanghai,respectively.The seasonal mean AOD generally exhibited a maximum in summer and aminimum in winter in Beijing but in the opposite trend in Lanzhou and no distinct seasonal cycles in Shanghai.Angstrm index(α) which conveys aerosol size distributions characteristics were 1.40±0.85,0.95±0.20,1.03±0.25 in Beijing,Lanzhou,and Shanghai,respectively,suggesting fine mode particles in Beijing and coarse mode particles in Lanzhou.MODIS AOD reveal satisfactory validations against surface measurements with correlation coefficients 0.91 in Beijng and 0.75 in Shanghai while poor validation is found in Lanzhou with correlation coefficients 0.07.Overestimations of MODIS AOD are noted in Beijing and Shanghai with annual mean 0.52±0.39 and 0.74±0.30 comparing to the underestimation in Lanzhou with annual mean 0.43±0.21.Considering the uncertainty of reflectance result from geographical positions and complicated coverage of urban area,the results are not well enough and the MODIS aerosol products shall be improved in future studies.