Total flux (left column) and polarized flux (right column) phase functions of horizontally homogeneous model planets covered by ocean (first row), sandy desert (second row), vegetation (third row), or clouds (fourth row), from 400 to 800 nm. The total fluxes have been computed for Lambertian reflecting (dotted lines) and bidirectionally reflecting planets (solid lines), and the polarized fluxes only for bidirectionally reflecting planets. The curves are normalized such that a white Lambertian reflecting planet at α = 0° has a total flux of one. Near α = 180°, the approximation that the surface and atmosphere are locally plane-parallel breaks down (because of the very low fluxes, this is not visible in the curves).