Monday, 11 January 2016
The MODIS C4, C5 and C6 versions aerosol products AODs were analyzed over Chinese terrestrial regions using the Chinese Sun Hazemeter Network (CSHNET) from 2004 to 2007. The valid data of the three versions had very large difference over the different eco-geographical systems in China. In view of the C6 products, DB algorithm had the most effective days, and the ratio of the effective days reduced gradually from the north (55%~85%) to the south (45%). The second is the C6 merge products, in the north-central of China (except for the Qinghai-Tibet plateau, the northeast), the ratio of available days merge products was 55% between DB and DT products. The merge and DT products had the same available days in the south, less than the north-central region, and the ratio was about 35%. DT products had the least available days, which the ratio was slightly more in the Middle East and south (about 35%), while in the northeast, the northwest and the Tibetan plateau area, the ratio of available days was the least (about 20%). Due to improving of DT algorithm, the available days were reducing gradually from C4 to C6. This phenomenon was much more obvious in the northeast, in the northwest desert, in the Tibetan plateau, in the lakes and especially in the urban areas, but there is no significant decline in the east-central farmland and the forest regions. From the national scale, the accuracy of C6 products given by DT algorithm was much better than C4 and C5, especially in the northeast, in the northwest desert and in the Qinghai-Tibet plateau areas. C6 products contributed by these algorithms underestimated AODs over the national region. DB and Merge products underestimated about 20%. DT products underestimated about 14%. In the central east area, AOD is the highest, but in the northwest desert and northeast Qinghai-Tibet plateau region, AOD is low. Using the same DT algorithm, C5 underestimated an average of 11% across the country; however, the C4 overestimated 7%. Although the C6 underestimated a little more, but in terms of different areas, C6 products were much more accurate in the central and eastern regions. The VIIRS IP aerosol retrievals that falling within the expected uncertainty range defined for MODIS was from 59.2% to 62.1%, and having similar magnitudes of correlation 0.88 to 0.91. But the VIIRS over the urban exhibits more scatter and therefore less precision than over the marine and the rural area. Besides, Chinese FY satellite's AOD products showed large errors in the region.
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