Normalized reflected flux (top) and degree of linear polarization (bottom) as a function of the phase angle α for various atmospheric models τ_g = 5, 0, 0.097; ω_s = 1, 0.5, 0; f_c = 0, 0.3, 0.7). Shown are the cloud-free homogeneous atmosphere (model I; orange and light blue lines), the Lambertian reflecting sphere without an atmosphere τ_g = 0; green line), and the cloudy inhomogeneous atmosphere (model II; yellow and dark blue lines) with various cloud fractions f_c. Our numerical calculations (plus symbols) are compared with results by Buenzli & Schmid (2009) for the homogeneous atmosphere, with the analytical solution by Russell (1916) for the Lambertian reflecting sphere, and with the results by Karalidi et al. (2012) for the inhomogeneous atmosphere. The color-coding applies to both panels. See Sects. 3.1 and 3.2 for details.