Albedo at high angles of incident light such as those that occur on the illuminated side of Earth near the terminator (early morning, late afternoon, and near the poles). However, as mentioned above, waviness causes an appreciable reduction. Because light specularly reflected from water does not usually reach the viewer, water is usually considered to have a very low albedo in spite of its high reflectivity at high angles of incident light. Note that white caps on waves look white (and have high albedo) because the water is foamed up, so there are many superimposed bubble surfaces which reflect, adding up
Incompressible surface ∂"D". If "D" were to bound a disk inside "S" (which is always the case if "S" is incompressible, for example), then compressing "S" along "D" would result in a disjoint union of a sphere and a surface homeomorphic to "S". The resulting surface without the sphere might or might not be isotopic to "S". There is also an algebraic version of incompressibility. Suppose formula_4 is a proper embedding of a compact surface in a 3-manifold. Then "S" is "π"-injective (or algebraically incompressible) if the induced map on fundamental groups is injective. In general, every "π"-injective surface is incompressible, but