Tuygun, GT; Ozdemir, E; Elbir, T (2020). Evaluation of MODIS C6 and C6.1 Dark Target AOD products over Turkey based on NDVI and aerosol type. ATMOSPHERIC POLLUTION RESEARCH, 11(12), 2335-2349.

This study aims to evaluate the accuracy of the MODIS C6 and C6.1 Aerosol Optical Depths (AOD) from Terra and Aqua satellites over the two sites located in the urban and coastal regions of Turkey. This is the first study in Turkey focusing on comparison of MODIS Dark Target (DT) C6 and C6.1 AOD against AERONET AOD to provide a better understanding of applicability and suitability of MODIS products under different surfaces and aerosol loadings. Analysis was performed with direct comparisons between MODIS DT AOD retrievals with 3 km and 10 km resolutions and Aerosol Robotic Network (AERONET) Version 3 Level 2 ground-based observations at site scale. Meanwhile, the spatial and temporal variations were also compared and discussed. Accuracy of the spatially and temporally collocated AOD retrievals was analyzed with the correlation coefficient (R), normalized mean bias (NMB), the root mean square error (RMSE), and the expected error (EE) (0.05% + 20%) and (0.05% + 15%) of the DT 3 km and 10 km algorithm over land, respectively. The C6.1 showed better accuracy than the C6 with the higher number of the retrievals falling within the expected error (EE). The C6.1 DT exhibited more significant improvements over the urban site than the coastal site, but both the DT 3 km and 10 km products did not show satisfactory performance with the lower percentages of the retrievals falling within EE (ranging from 36.7% to 50.6%), that was less than one standard deviation confidence interval over the urban site. Moreover, C6.1 DT had a little effect on improvements over the coastal site. Higher percentages of the retrievals falling within EE (ranging from 80.2% to 90.7%) were found at the coastal site. The effects of the surface reflectance based on NDVI and SSA parameter for understanding the aerosol type effect on aerosol retrievals were also discussed. Underestimation of the AOD over the coastal site indicated an inaccurate assumption in the aerosol model. Highly absorbing aerosols also caused overestimation over the urban site. This study suggests that further improvements are required to provide better estimates of satellite-based AOD over urban areas of Turkey.