A MODIS-based modeling scheme for the estimation of downward surface shortwave radiation under cloud-free conditions

Abstract

Atmospheric aerosol optical depth (AOD) plays an important role in radiation modeling and partly determines the accuracy of estimated downward surface shortwave radiation (DSSR). In this study, Iqbal's model C was used to estimate DSSR under cloud-free conditions over the Koohin and Chitgar sites in Tehran, Iran; the estimated DSSR was based on (1) our proposed hybrid modeling scheme where the AOD is retrieved using the Simplified Aerosol Retrieval Algorithm (SARA), ground-based measurements at the AERONET site in Zanjan and (2) the AOD from the Terra MODerateresolution Imaging Spectroradiometer (MODIS) sensor. Several other Terra MODIS land and atmospheric products were also used as input data, including geolocation properties, water vapor, total ozone, surface reflectance, and top-ofatmosphere (TOA) radiance. SARA-based DSSR and MODIS-based DSSR were evaluated with ground-based DSSR measurements at the Koohin and Chitgar sites in 2011 and 2013, respectively; the averaged statistics for SARA-based DSSR [R 2 ≈ 0.95, RMSE ≈ 22 W/m 2 (2.5% mean value), and bias ≈ 3 W/m 2 ] were stronger than those for MODIS-based DSSR [R 2 ≈ 0.79, RMSE ≈ 51 W/m 2 (5.8% mean value), and bias ≈ 34 W/m 2 ]. These results show that the proposed hybrid scheme can be used at regional to global scales under the assumption of future access to spatially distributed AERONET sites. Additionally, the robustness of this modeling scheme was exemplified by estimating the aerosol radiative forcing (ARF) during a dust storm in Southwest Asia. The results were comparable to those of previous studies and showed the strength of our modeling scheme.

Estimation of Net Surface Shortwave Radiation From Remotely Sensed Data Under Dust Aerosol Conditions

“…For instance, Ceamanos et al introduced a method of estimating surface radiation (SIRAMix) for aerosol parameters by dynamically estimating the content and type of aerosols, which improved the retrieval accuracy of the downward radiant flux (DSSR) [22]. Generally, the aerosol radiative forcing (ARF) under the complicated atmospheric conditions is higher than the clear skies [23], [24]. Specifically, during super dust storm weather, the surface shortwave net aerosol radiative forcing (ASRF) could result in 144 W/m 2 reduction than non-dusty days [25].…”