چکيده

The atmospheric Aerosol Optical Depth (AOD) is one of the major uncertainties in retrieving Downward Surface Shortwave Radiation (DSSR). In the current study, Yang’s model, which determines the effect of each component of atmosphere separately, was used to estimate DSSR under cloud-free conditions. Recent studies have used MODIS AOD data to calculate DSSR, while in this article the retrieved AOD from the Simplified Aerosol Retrieval Algorithm (SARA) was used to estimate DSSR over the Chitgar site in Tehran, Iran. For comparison purpose, MODIS AOD products were also used to estimate DSSR over the studied region. Estimated DSSR based on SARA AOD, MODIS Level 2 (L2) AOD, and MODIS Level 3 (L3) AOD were evaluated with ground-based measurements of DSSR at the Chitgar site during summer of 2013. Results show R2 = 0.88, RMSE = 25.09 W/m2, and Bias = 2.05 W/m2 for SARA-based DSSR, and R2 = 0.61, RMSE = 41.75 W/m2, and Bias = 15.93 W/m2 for MODIS-L2 based DSSR, and R2 = 0.82, RMSE = 60.73 W/m2, and Bias = 53.77 W/m2 for MODIS L3-based DSSR. The results showed higher accuracy of estimated DSSR based on the SARA AOD than the estimated DSSR based on MODIS products. As RMSE of SARA-based DSSR is 1.6 and 2 times MODIS-L2 based DSSR and MODIS-L3 based DSSR, respectively. In the proposed method, Bias reached close to zero. These results also showed that our modeling scheme of combining Yang’s model with the SARA algorithm can be used from the regional to global scale under the assumption of future access to spatially distributed AERONET sites.