How to configure the empirical BRDF terrain correction?

[rese_support]

For the combined atmospheric / topographic processing ATCOR offers an empirical BRDF correction that depends on the illumination and viewing geometry. In its simplest form it reads : rho(corrected) = rho(isotropic) * cos(beta) / cos(beta_t) where beta is the local solar incidence angle on a surface element, and beta_t is a threshold angle to be specified by the user.