The column optical thickness of the atmospheric aerosol load is routinely retrieved using space borne measurements of the natural levels of upwelling shortwave radiation at the top of the atmosphere. The information content of the measurements includes contributions from several components of the earth-atmosphere system: the scattering and absorption processes of the molecular atmosphere (i.e., Rayleigh scattering and gas absorption), the scattering and absorption of aerosol particles, as well as the reflection from clouds and the underlying surface. The relative contribution from each component is a strong function of the wavelength of the incident radiation. Generally, the aerosol contribution is a very small fraction of the measurement. Therefore, as a part of the retrieval process, corrections for non-aerosol effects need to be applied to isolate the net aerosol effect.
"Use of satellite measurements in the retrieval of aerosol properties", Proc. SPIE 5103, Intelligent Computing: Theory and Applications, (4 August 2003); doi: 10.1117/12.512856; https://doi.org/10.1117/12.512856