Development of empirical angular distribution models for smoke aerosols: Methods

摘要

Using broadband shortwave radiance measurements from the Clouds and Earth Radiant Energy System (CERES) sensors onboard the Terra and Aqua satellites, empirical angular distribution models (EADM) are constructed for smoke aerosols. These EADMs are constructed for smoke aerosols emitted during the biomass burning season (August-October), in South America. All available years (2000-2008) of both rotating azimuth plane and cross-track radiance data from CERES have been utilized. Aerosol scenes are identified using coincident aerosol optical thickness retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS). The new EADMs are used to estimate top-of-atmosphere (TOA) shortwave flux for cloud free scenes. The CERES clearly shows the angular dependence of shortwave radiance on smoke aerosol optical thickness. A comparison of TOA shortwave fluxes estimated from the new smoke EADM with the existing CERES TOA shortwave fluxes shows that the CERES fluxes are higher (lower) for aerosol optical thickness less (greater) than 0.3, largely due to the use of aerosol optical thickness in characterizing the new EADMs developed in this study. Empirical ADMs for smoke aerosols over land are developed for the first time in this study, and our results demonstrate that large amounts of aerosols emitted during biomass burning activities contribute to the anisotropy of the radiance distribution at the TOA. Therefore, it is imperative to include aerosol information in the angular distribution models, especially now that more than a 10 year record of Terra data is available