利用MODIS卫星资料反演北京地区气溶胶光学厚度

大气气溶胶是影响城市环境空气质量的重要因素，同时对人类健康具有重要影响。传统的气溶胶遥感反演方法多适用于海洋及植被等地表反射率较低的区域，对于城市等高亮地表区域，地表反射率较高且难以确定，气溶胶反演面临巨大挑战。针对该问题，提出一种新的地表反射率的确定方法，将下垫面划分为暗地表和亮地表两种类型，分别使用可见光与短波红外的线性关系和利用长时间序列MODIS表现反射率数据使用最小值合成技术构建先验数据集的方法，确定其地表反射率，然后基于辐射传输方程理论利用查找表方法，进行气溶胶光学厚度反演。选择下垫面复杂、空气污染问题严重的北京市作为研究区，应用MODIS数据进行气溶胶反演实验，最后使用北京站、香河站、北京CAMS站和北京RADI站4个AERONET气溶胶地基观测数据和MODIS气溶胶产品对反演结果进行对比验证。结果表明该算法气溶胶反演结果与地基观测数据具有较高的一致性（R2=0.902），能以较高精度实现城市等高反射率地区的气溶胶反演，反演精度与空间连续性上较MOD04有显著提高。

Aerosol Optical Depth Retrieval over Beijing Using MODIS Satellite Images

Atmospheric aerosol is one of the most important factors that affect air quality of urban environment, meanwhile, it has important effects on human health. Traditional aerosol optical depth (AOD) retrieval algorithms are always suitable for dark areas with low surface reflectance including ocean and densely vegetated areas, however, for bright urban areas, surface reflectance is high and difficult to be determined, leading to great challenges. Aiming at this problem, a new improved approach of surface reflectance estimation is proposed and the underlying surfaces are divided into dark and bright areas. Surface reflectance is determined using the simulated relationships between the surface reflectance between visible and short-wave infrared channels and a priori surface reflectance dataset constructed with long time series of MODIS apparent reflectance images using the minimum value synthesis technology. Then aerosol retrieval is performed based on the radiative transfer theory with pre-calculated Look-up Tables. Beijing, which features complex surfaces and serious air pollution, is selected as the study area and the proposed algorithm is applied to the MODIS data for aerosol retrieval experiments. Four AErosol RObotic NETwork (AERONET) AOD ground-measured stations, Beijing, Xianghe, Beijing_CAMS and Beijing_RADI, and operational MODIS aerosol product (MOD04) are selected for validation and comparison purposes. Results showed that AOD retrievals are highly consistent with AERONET AOD ground measurements (R2=0.902) and showed overall higher accuracy with more detailed spatial distribution compared to MOD04 AOD products over bright urban areas.