Validation of MODIS and VIIRS derived aerosol optical depth over complex coastal waters

� 2016 Elsevier B.V. In this study, the Simplified Aerosol Retrieval Algorithm (SARA) was applied to both MODIS and Visible Infrared Imaging Radiometer Suits (VIIRS) images to retrieve aerosol optical depth (AOD) over water for blue, green and red wavelengths at 500�m (MODISSARA)and 750�m (VIIRSSARA) resolutions, respectively. Retrievals were compared with the Terra–MODIS Dark Target (DT) AOD at 3�km resolution (MODIS3K) and the VIIRS Environmental Data Record (VIIRSEDR) AOD at 6�km resolution. Validation was conducted using 86 Microtops II Sun photometer AOD measurements collected over different classes of water quality (low to high sediment levels) for seven days (6, 8, 9, 13, and 15, 16 and 17 October 2014) between 10:00 to 15:00 local time. Thirty-eight to fifty percent and 44–54% of the MODIS3Kand the VIIRSEDRAOD retrievals respectively, fall within the expected error (EE) with root mean square error from 0.12 to 0.14 and mean absolute error from 0.10 to 0.11. The MODISSARAand the VIIRSSARAAOD retrievals are well correlated with the ground–based measurements (R: MODISSARA�=�0.86–0.89 and VIIRSSARA�=�0.85–0.94), with a larger number of retrievals falling within the EE MODISSARA�=�73–77% and VIIRSSARA�=�71–82%) than MODIS3Kand VIIRSEDR. The results indicate that the SARA algorithm is more robust than MODIS3Kand VIIRSEDRglobal AOD products, and can retrieve accurate AOD over low to highly sedimented water surfaces, similar to good AOD retrievals over land.