Validation of MODIS C6 dark target aerosol products at 3 km and 10 km spatial resolutions over the China seas and the Eastern Indian Ocean

In this study, MODerate resolution Imaging Spectroradiometer (MODIS) Collection 6 (C6) level-2 Dark Target (DT) Aerosol Optical Depth (AOD) products at 3 km (DT3K) and 10 km (DT10K) spatial resolutions were validated over the China seas and the eastern Indian Ocean against Maritime Aerosol Network (MAN) Level 1.5 AOD measurements collected through 13 cruises from 2010 to 2014. For this, DT3K and DT10K AOD observations were obtained from four Scientific Data Sets (SDS), i.e., "Effective_Optical_Depth_Average_Ocean" (EODAO_AOD), "Effective_Optical_Depth_Best_Ocean" (EODBO_AOD), "Image_Optical_Depth_Land_And_Ocean" (IODLAO_AOD) and "Optical_Depth_Land_And_Ocean" (ODLAO_AOD). The MAN AOD measurements were filtered within (i) ±2 h, (ii) ±4 h, (iii) ±6 h, and (iv) ±12 h of MODIS overpass time. Results showed that the DT10K and DT3K performed equally over the China seas and the eastern Indian Ocean in terms of retrievals quality and agreement with the MAN AOD measurements, whereas the DT3K has less coincident observations than the DT10K. For seasonal analysis, larger underestimation in the DT algorithm was observed in autumn followed by spring, whereas retrievals were well correlated with the MAN AOD data in summer. Overall, this study found that ODLAO_AOD observations for the DT3K and DT10K were much better than EODAO_AOD, EODBO_AOD and IODLAO_AOD in terms of high correlation and a large percentage of the AOD retrievals within the Expected Error (EE = +(0.04 + 10%), -(0.02 + 10%)).