Validation of MODIS C6 AOD Products Retrieved by the Dark Target Method in the Beijing–Tianjin–Hebei Urban Agglomeration, China

The quality of the MODIS C6 3-km and 10-km aerosol optical depth（AOD） products retrieved by the Dark Target（DT）method is discussed using ground-based observations in the Beijing–Tianjin–Hebei region from 1 August 2007 to 31 July2008. Good consistency exists between the 3-km and 10-km products and ground-based observations. The retrieval accuracy of the two products both show distinctive seasonality. The percentage falling within the expected error（EE） is largest in the winter, moderate in the spring and autumn, and smallest in the summer. A worse overestimation appears in the spring and summer（27%–66%）. However, the 3-km and 10-km products over different surfaces still exhibit obvious deviations. The 10-km product performs better in the large cities, while the 3-km product has advantages in the suburbs. In urban areas, the percentage falling within EE of the 3-km AOD product（18%–59%） is lower than that for the 10-km AOD product（31%–69%）. However, in suburban areas, the percentage falling within EE of the 3-km AOD product（61%–84%） is higher than for the 10 km AOD product（54%–83%）.The percentages falling within EE differ considerably when the AOD is greater than1.5（73% and 63% for the 3-km and 10-km products, respectively）. On the whole, the 3-km（10-km） AOD product performs better in suburban（urban） areas.