VIIRS Environmental Data Record and Deep Blue aerosol products: validation, comparison, and spatiotemporal variations from 2013 to 2018 in China

摘要

Recently, the Deep Blue (DB) algorithm has been successfully applied to the Visible Infrared Imaging Radiometer Suite (VIIRS) to expend the long-term aerosol records over land in conjunction with the Environmental Data Record (EDR) product. However, the overall accuracy and uncertainty of VIIRS DB and EDR Aerosol Optical Depth (AOD) products are still unclear in China, in particular, due to the sparse distribution of ground observation stations. Therefore, the objective of this study is to evaluate and compare VIIRS EDR and DB AOD retrievals against ground measurements collected from both Aerosol Robotic Network (AERONET) and Chinese Sun-sky radiometer Observation Network (SONET) in China from 2013 to 2018. Results suggest that both EDR and DB products have a significant refinement after quality assurance (QA) controlling. DB (QA = Best) performs best with high correction (R = 0.92), and up to 80.32% of AOD matches falling within the expected error (EE), while approximately 46% of EDR (QA = Best) AOD retrievals are overestimated. However, EDR has a higher retrieval frequency than DB over most regions of China, except for the arid and semi-arid areas such as the Northwest. Generally, despite some exceptions, both EDR and DB products perform relatively poorly in summer for all statistics. Furthermore, the error analysis explains that DB is less sensitive to varying air pollution levels, diverse aerosol types, and different surface conditions, while the pattern of EDR is complicated. In addition, due to the common algorithmic heritage, both VIIRS EDR and MODIS DT products only show good matching over dark surfaces, while VIIRS DB and MODIS DB algorithms have good performance over both dark and bright surfaces. Finally, both EDR and DB products have shown significant downward AOD trends equal to-0.0008 per year (p 0.01) in China during the last past six years, especially for three typical urban agglomerations. These evaluation results are expected to provide appropriate guidance for the application of VIIRS aerosol products in China.