Uncertainty and variability in satellite-based water vapor column, aerosol optical depth and Angström exponent, and its effect on radiative transfer simulations in the Iberian Peninsula

The water vapor column product from the MODIS instrument onboard the Terra satellite is compared with ground-based measurements at six Spanish locations (AERONET stations) in the Iberian Peninsula. In addition, aerosol optical depth (AOD) at 443 nm and at 675 nm retrievals from the MISR instrument onboard the Terra satellite is also compared with ground-based measurements at the same locations to determine their uncertainties. Remote sensing data of water vapor and aerosol optical properties are averaged each month to obtain climatology tables and to characterize atmospheric properties at nine locations in the Iberian Peninsula. These tables are used as input in a radiative transfer model to calculate total shortwave (SW) and ultraviolet erythemal (UVER) irradiance at the nine locations. SW and UVER simulations are recalculated considering the uncertainties and the climatological variability of the input datasets. AOD uncertainty provides changes lower than 6% in most cases for both SW and UVER simulations. The propagation of water vapor uncertainty causes variations in SW simulations less than 4% for solar zenith angles below 75°.