Editing Albedo (section)

===Water===
[[File:water reflectivity.jpg|thumb|upright=1.3|Reflectivity of smooth water at {{convert|20|C|F}} (refractive index=1.333)]]
Water reflects light very differently from typical terrestrial materials. The reflectivity of a water surface is calculated using the [[Fresnel equations]].

At the scale of the wavelength of light even wavy water is always smooth so the light is reflected in a locally [[specular reflection|specular manner]] (not [[Diffuse reflection|diffusely]]). The glint of light off water is a commonplace effect of this. At small [[angle of incidence (optics)|angles of incident]] light, [[waviness]] results in reduced reflectivity because of the steepness of the reflectivity-vs.-incident-angle curve and a locally increased average incident angle.<ref name="Fresnel" />

Although the reflectivity of water is very low at low and medium angles of incident light, it becomes very high at high angles of incident light such as those that occur on the illuminated side of Earth near the [[terminator (solar)|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 their reflectivities. Fresh 'black' ice exhibits Fresnel reflection.
Snow on top of this sea ice increases the albedo to 0.9.<ref>{{Cite web |date=2007-01-31 |title=Arctic Reflection: Clouds Replace Snow and Ice as Solar Reflector |url=https://earthobservatory.nasa.gov/features/ArcticReflector/arctic_reflector4.php |access-date=2022-04-28 |website=earthobservatory.nasa.gov |language=en}}</ref>