Left panel: mean intensity versus optical depth τ normalized to the incident specific intensity I₀. The solid black curve shows the depth dependence of the mean intensity assuming dust parameters ω = 0.4, g = 0.7, approximately describing the WD01-7 dust sort. The dashed and dotted curves denote mean intensities using the same albedo ω, but assuming isotropic and pure forward-scattering, respectively. Right panel: absolute error  | log (J_i/I₀) − log (J_k/I₀) |  of assuming isotropic g = 0 and pure forward-scattering g = 1 with respect to more realistic values ω = 0.4, g = 0.7 (dashed and dotted lines, respectively).