Angular discretization

In the DOM, the calculation of a radiative source term at a given point is based on the discretization of the Radiative Transfer Equation (Eq.) according to a chosen number $N_{dir}$ of discrete directions $\textbf{s}_i (\mu_i, \eta_i, \xi_i)$ , associated to the corresponding weights $w_i$ , contained in the solid angle $4\pi$ , and where ( $\mu_i, \eta_i, \xi_i$ ) are directional cosines. Different angular discretizations may be used. In a recent study, Koch and Becker [#!Koc03!#] compare the efficiency of several types of angular quadratures. They recommend the $LC_{11}$ quadrature for its better accuracy. However calculations performed with the $S_4$ quadrature satisfy a good compromise between accuracy and rapidity as shown in [#!Stanford!#], and may also be used.