An efficient approach to estimate the transmittance and reflectance of a mixture of aerosol components

Abstract

Atmospheric aerosols are formed by a mixture of different chemical components that changes rapidly with time and space. The refined characterization of this mixture is crucial to meet the accuracy requirements of satellite products derived from passive sensor data in the shortwave wavelengths. This article proposes an efficient analytical approach to estimate two key radiative terms in aerosol remote sensing: the transmittance and reflectance of an aerosol mixture. This study demonstrates that these terms can be approximated by a simple weighted average of the individual radiative counterparts related to each aerosol component. Weights are the optical depths resulting from each aerosol component separately. The proposed approach is very fast and is exact for the first order of scattering. Its accuracy is assessed against exact radiative transfer calculations for a broad range of aerosol scenarios. For typical aerosol conditions (optical depth lower than 1.0 and solar zenith angle lower than 70°), the average error of estimated transmittances is 0.6%. Reflectances are affected by a higher average error of 7.6% due to their higher sensitivity to multiple scattering orders. The proposed approach may advantageously replace the use of sophisticated radiative transfer codes at the cost of a slight accuracy decrease to better answer the needs of the near real time constraint required by the remote sensing community.