Reflectivity

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In optics, reflectivity is the reflectance (the ratio of reflected power to incident power, generally expressed in decibels or percentage) at the surface of a material so thick that the reflectance does not change with increasing thickness; i.e., the intrinsic reflectance of the surface, irrespective of other parameters such as the reflectance of the rear surface. The concept is of some importance in telecommunications and in radars.

[edit] Explanation

Surface reflectance may be subdivided into diffuse or Lambertian reflectance and specular reflectance. The apparent reflectance for an ideal Lambertian surface is independent of the observer's angle of view. This contrasts with a shiny (specular) surface, where the apparent brightness is highest when the observing angle is equal and opposite to the source angle. Most real objects have some mixture of diffuse and specular qualities.

Source: from Federal Standard 1037C

Fresnel reflection occurs when light moves from a medium with one index of refraction into a second medium with a different index of refraction.

Note: In climatology, reflectivity is called albedo.

[edit] Water reflectance

That part of incident light that is reflected from a body of water is specular and is calculated by the Fresnel equations. Fresnel reflection is directional and therefore does not contribute significantly to albedo which is primarily diffuse reflection.

A real water surface may be wavy. Reflectance assuming a flat surface as given by the Fresnel equations can be adjusted to account for waviness. A formula and graph for correction for waviness for two different wave energy spectrum definitions exists. [1]