Evaluation of MODIS C6 and C6.1 Dark Target AOD products over Turkeybased on NDVI and aerosol type

Özet

This study aimstoevaluate the accuracyof theMODIS C6and C6.1Aerosol Optical Depths(AOD) fromTerraandAquasatellitesoverthetwositeslocatedintheurbanandcoastalregionsofTurkey.ThisisthefirststudyinTurkeyfocusingoncomparisonofMODISDarkTarget(DT)C6andC6.1AODagainstAERONETAODtoprovidea better understanding of applicability and suitability of MODIS products under different surfaces and aerosolloadings. Analysis was performed with direct comparisons between MODIS DT AOD retrievals with 3 km and10kmresolutionsandAerosolRoboticNetwork(AERONET)Version3Level2ground-basedobservationsatsitescale. Meanwhile, thespatial and temporal variations were also compared anddiscussed. Accuracy of the spa-tially and temporally collocated AOD retrievals was analyzed with the correlation coefficient (R), normalizedmean bias (NMB), the root mean square error (RMSE), and the expected error (EE) (0.05% + 20%) and(0.05%+15%)oftheDT3kmand10kmalgorithmoverland,respectively.TheC6.1showedbetteraccuracythan the C6 with the higher number of the retrievals falling within the expected error (EE). The C6.1 DT ex-hibitedmoresignificantimprovementsovertheurbansitethanthecoastalsite,butboththeDT3kmand10kmproducts 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 urbansite. Moreover, C6.1 DT had a little effect on improvements over the coastal site. Higher percentages of theretrievals falling within EE (ranging from 80.2% to 90.7%) were found at the coastal site. The effects of thesurface reflectance based on NDVI and SSA parameter for understanding the aerosol type effect on aerosolretrievals were also discussed. Underestimation of the AOD over the coastal site indicated an inaccurate as-sumption in theaerosol model. Highly absorbingaerosols also caused overestimationover the urbansite. Thisstudy suggests that further improvements are required to provide better estimates of satellite-based AOD overurban areas of Turkey.