Direct observation of the sun for aerosol retrieval

The simplest remote sensing methods rely on the observation of the extinction of radiation, as it is defined in Chapter 2, in Eqs 2.4 and 2.5 (Beer exponential extinction law), which we recall here as Eqs 4.1 and 4.2: $$I(S_2)=I(S_1)\, {\rm exp}(-\tau_e),$$ (4.1) where $${\tau_e}={\int\limits_{s_1}^{s_2}}{\sigma_e}(s)ds.$$ (4.2)