Retrieving aerosols single scattering albedo from MODIS reflectances

Abstract

Single scattering albedo (SSA) is a key parameter to estimate aerosol direct radiative forcing. However, retrieving SSA from satellite observations is still challenging. In this study, a new method optimizing the aerosol optical model based on four basic aerosol components is developed for retrieving SSA from Moderate Resolution Imaging Spectroradiometer (MODIS) data. The new method takes advantage of the relationship between aerosol composition and reflectance at multiple wavelengths to derive SSA, which considers the variation of aerosol species with time and location. A sensitivity study considering the uncertainties from the top of the atmosphere (TOA) apparent reflectance, aerosol optical depth (AOD) at 550 nm and land surface bidirectional reflectance distribution function (BRDF) parameters is performed to test the stability of the proposed method. The results demonstrate the high accuracy and robustness of the new method. The root mean square error (RMSE) is within 0.03 at 470 and 550 nm based on the sensitivity study. The aerosol components used in our method show better representativeness of real aerosol components than that used in the Second Simulation of a Satellite Signal in the Solar Spectrum - Vector (6SV) model. The aerosols SSA values are retrieved from real MODIS observations with the new method and compared with the AERONET SSA product at two polluted AERONET sites in Asia. A better consistency with the correlation coefficient (R) of 0.27– 0.55 and the RMSE within 0.04 at 470 and 550 nm wavelengths between MODIS SSA retrievals and the AERONET SSA product is obtained with the new method compared with that of deep blue (DB) SSA. The new method can help to better understand aerosol radiative forcing regionally and globally.