Abstract
This study validated MODIS (Moderate Resolution Imaging Spectroradiometer) of the National Aeronautics and Space Agency, USA, Aqua and Terra Collection 6.1, and MERRA-2 (Modern-ERA Retrospective Analysis for Research and Application) Version 2 of aerosol optical depth (AOD) at 550 nm against AERONET (Aerosol Robotic Network) ground-based sunphotometer observations over Turkey. AERONET AOD data were collected from three sites during the period between 2013 and 2017. Regression analysis showed that overall, seasonally and daily statistics of MODIS are better than MERRA-2 by the mean of coefficient of determination (R2), mean absolute error (MAE), and relative root mean square deviation (RMSDrel). MODIS combined Terra/Aqua AOD and MERRA-2 AOD corresponding to morning and noon hours resulted in better results than individual sub datasets. A clear annual cycle in AOD was detected by the three platforms. However, overall, MODIS and MERRA-2 tend to overestimate and underestimate AOD, respectively, in comparison with AERONET. MODIS showed higher efficiency in detecting extreme events than MERRA-2. There was no clear relation found between the accuracy in MODIS/MERRA-2 AOD and surface relative humidity (RH).
Highlights
Anthropogenic aerosols influence the Earth’s radiation budget and climate directly by scattering solar light in the cloud-free atmosphere and indirectly by changing the cloud properties [1,2].Anthropogenic aerosols on the whole cool the climate, while black carbon and mineral dust absorb solar radiation
(i) aerosol optical depth (AOD) Deep Blue (DB)/DT retrievals were obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua scientific datasets of “Dark_Target_Deep_Blue_AOD_550_Combined” by extraction and georeferencing against corresponding geolocation files using ENVI IDL iterative script. (ii) Mosaicking was conducted to merge the adjacent layers in each dataset over the study area to produce daily layers using an ArcGIS automated model. (iii) MODIS Aqua and Terra AOD collocated pixels values were averaged separately and combined. (iv) MERRA-2 AOD hourly values were averaged over the morning and noon hours (7:00–11:00 and 11:00–14:00, respectively) as well as over these two periods and extracted over the three Aerosol Robotic Network (AERONET) sites. (v) The mean wind speed in the study area is about 4.4 m s−1 [40], which means that aerosol particles can be transported approximately
MODIS and MERRA-2 daily AOD are compared to the AERONET measurements in Figure 1, MODIS
Summary
Anthropogenic aerosols influence the Earth’s radiation budget and climate directly by scattering solar light in the cloud-free atmosphere and indirectly by changing the cloud properties [1,2].Anthropogenic aerosols on the whole cool the climate, while black carbon and mineral dust absorb solar radiation. Anthropogenic aerosols influence the Earth’s radiation budget and climate directly by scattering solar light in the cloud-free atmosphere and indirectly by changing the cloud properties [1,2]. Since aerosol optical depth (AOD) is related to aerosol loads in the atmosphere, it is a widely used parameter to study and monitor anthropogenic aerosols. Aerosol Robotic Network (AERONET) provides high-quality sunphotometer measurements of AOD at multiple wavelengths, where computerized procedures for cloud-screening and pre- and post-field calibration generalization are used [5]. These measurements are associated with sparse coverage over the Earth and a lack of long-term observations at many of the ground-based sites
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