Abstract
The visible infrared imaging radiometer suite (VIIRS) environmental data record aerosol product (VIIRS_EDR) and the aqua-moderate resolution imaging spectroradiometer (MYD04) collection 6 (C6) aerosol optical depth (AOD) products are validated against the Cimel sun–photometer (CE318) AOD measurements during different air quality conditions over the Yangtze river basin (YRB) from 2 May 2012 to 31 December 2016. For VIIRS_EDR, the AOD observations are obtained from the scientific data set (SDS) “aerosol optical depth at 550 nm” at 6 km resolution, and for aqua-MODIS, the AOD observations are obtained from the SDS “image optical depth land and ocean” at 3 km (DT3K) and 10 km (DT10K) resolutions, “deep blue aerosol optical depth 550 land” at 10 km resolution (DB10K), and “AOD 550 dark target deep blue combined” at 10 km resolution (DTB10K). Results show that the high-quality (QF = 3) DTB10K performs the best against the CE318 AOD observations, along with a higher R (0.85) and more retrievals within the expected error (EE) ± (0.05 + 15%) (55%). Besides, there is a 10% overestimation, but the positive bias does not exhibit obvious seasonal variations. Similarly, the DT3K and DT10K products overestimate AOD retrievals by 23% and 15%, respectively, all over the year, but the positive biases become larger in spring and summer. For the DB10K AOD retrievals, there is an overestimation (underestimation) in autumn and winter (spring and summer). Compared to the aqua-MODIS AOD products, the VIIRS_EDR AOD retrievals are less correlated (R = 0.73) and only 44% of the retrievals fall within EE. Meanwhile, the VIIRS_EDR shows larger bias than the aqua-MODIS C6 retrievals, and tends to overestimate AOD retrievals in summer and underestimate in winter. Additionally, there is an underestimation for the VIIRS_EDR AOD retrievals over the regions during high aerosol loadings. These indicate that the VIIRS_EDR retrieval algorithm needs to be improved in further applications over the YRB.
Highlights
Aerosols are small suspended particles in the atmosphere of the earth, which have a significant effect on climate change, air quality, visibility and human health [1]
Overall, filtering by quality flags (QF > 1), the comparison has been improved for all statistics, i.e., RMSE is decreased by 11%, the R and the percentage of retrievals within the expected error (EE) are increased up to 3% and 5%, respectively
The correlation coefficient (R) is in the range of 0.78–0.81, along with 43–46% of depth land and ocean” at 3 km (DT3K) aerosol optical depth (AOD) retrievals falling into the expected error (EE) envelope. This indicates that the correlation is good, the DT3K still does not meet the requirements of the EE as the percentage within the EE is less than one standard deviation (i.e., 68%)
Summary
Aerosols are small suspended particles in the atmosphere of the earth, which have a significant effect on climate change, air quality, visibility and human health [1]. In order to meet the requirements of air quality monitoring and climate change assessment, long-term continuous aerosol observations over regional scales are necessary and critical. With the improvement of satellites resolution, satellite remote sensing is expected as an ideal technology for retrieving aerosol optical and radiative properties at global and regional scales. VIIRS is the next-generation polar-orbiting operational environment sensor launched in October 2011, which is expected to continue to provide, in the long run, global aerosol retrievals after MODIS. Compared with MODIS C6 aerosol products, the VIIRS_EDR AOD retrievals showed lower accuracy (−0.009 vs −0.005) and larger uncertainty (0.130 vs 0.106) over global land [6,7]. The robustness of the VIIRS_EDR retrieval algorithm needs to be improved
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