Development and Validation of a Robust Algorithm for Retrieving Aerosol Optical Depth Over Land From MODIS Data
Development and Validation of a Robust Algorithm for Retrieving Aerosol Optical Depth Over Land From MODIS Data
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DOI：
10.1109/jstars.2015.2396491
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发表时间：
2015-02
影响因子：
5.5
通讯作者：
Guanghui Huang;Chunlin Huang;Zhengqiang Li;Hao Chen
中科院分区：
文献类型：
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作者：
Guanghui Huang;Chunlin Huang;Zhengqiang Li;Hao Chen
由于地表暗目标的限制，在某些区域和某些地表类型上，中分辨率成像光谱仪(MODIS)标准气溶胶算法不能很好地工作。在本文中，我们开发并验证了一种稳健的算法，该算法结合了修正的最小反射比技术以及Terra和Aqua MODIS的协同技术，消除了对地表条件的依赖。该算法的基本思想是首先识别出某一时间窗内的“最清晰”日观测，然后假设在这一天从Terra到Aqua立交桥之间的有限时段(0-3h)内气溶胶光学厚度不变，然后得到可见光波段与2.1μm波段地表反射率之间的关系，最后在该时间窗内反演所有观测的气溶胶光学厚度。该算法使用2006年分布在北中国、中亚、美国东部和西欧的13个气溶胶机器人网络(AERONET)站点的测量数据进行了验证。对于AOD，在MOD04内，对于所有级别的质量保证置信度(QAC)和QAC=3，分别有65.5%和72.7%的检索预期误差包络，R2为0.87，并且发现更少的差距。与MODIS气溶胶产品相比，新算法在较暗的地表上总体上表现出与MODIS气溶胶产品相似的精度，但在较亮的地表上提供了更多的反演量。这表明新算法可以为多种地表类型提供更稳定的反演结果。特别是在城市地表，如北京的中国，反演的气溶胶光学厚度明显好于MODIS气溶胶产品。因此，新算法可以为在标准暗目标算法不能很好地工作或需要更高空间分辨率的区域上进行AOD反演提供一种替代方法。
Due to the limitation of surface “dark-target,” in some regions and over certain surface types, Moderate Resolution Imaging Spectroradiometer (MODIS) standard aerosol algorithm does not work very well. In this paper, we developed and validated a robust algorithm, which combines the revised minimum reflectance technique and the technique of the synergy of Terra and Aqua MODIS to eliminate the dependence on surface conditions. The rationale of our algorithm is to first identify the “clearest” day observations in certain temporal window, assume that the aerosol optical depth (AOD) does not change during the limited period (0-3 h) between Terra and Aqua overpass in this day, subsequently obtain the relationships between visible bands and 2.1 μm band surface reflectance, and finally retrieve the AOD of all observations in the temporal window. The algorithm was validated using year 2006 measurements from 13 Aerosol Robotic Network (AERONET) sites distributed in North China, Central Asia, eastern United States, and Western Europe. For AOD, 65.5% and 72.7% of retrievals within MOD04 expected error envelope for all levels of quality assurance confidence (QAC) and QAC = 3, respectively, R2 of 0.87 and a less amount of gaps are found. In comparison to the MODIS aerosol products, the new algorithm on the whole shows similar accuracy over dark land surface, but gives a larger amount of retrievals over bright land surface. This indicates that the new algorithm can provide a more steady inversion for a variety of surface types. Especially over urban surface, such as Beijing in China, the inverted AOD is clearly better than that from MODIS aerosol products. Therefore, the new algorithm can provide an alternative way for AOD retrieving over regions where the standard dark target algorithm does not work well or higher spatial resolution is imperative.