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While directional-hemispherical reflectance factor is calculated for a single angle of incidence (i.e., for a given position of the Sun), albedo is the directional integration of reflectance over all solar angles in a given period. The temporal resolution may range from seconds (as obtained from flux measurements) to daily, monthly, or annual ...
Another measure of reflectance, depending only on the outgoing direction, is I/F, where I is the radiance reflected in a given direction and F is the incoming radiance averaged over all directions, in other words, the total flux of radiation hitting the surface per unit area, divided by π. [2]
For a partially reflective surface, the second term must be multiplied by the reflectivity (also known as reflection coefficient of intensity), so that the increase is less than double. For a diffusely reflective surface, the details of the reflection and geometry must be taken into account, again resulting in an increased net radiation ...
The ratio of waves' electric field (or magnetic field) amplitudes are obtained, but in practice one is more often interested in formulae which determine power coefficients, since power (or irradiance) is what can be directly measured at optical frequencies. The power of a wave is generally proportional to the square of the electric (or magnetic ...
Radiative flux, also known as radiative flux density or radiation flux (or sometimes power flux density [1]), is the amount of power radiated through a given area, in the form of photons or other elementary particles, typically measured in W/m 2. [2]
Planetlight is the diffuse reflection of sunlight from a planet, whose albedo can be measured. The most observed and familiar example of planetshine is earthshine on the Moon , which is most visible from the night side of Earth when the lunar phase is crescent or nearly new , [ 1 ] without the atmospheric brightness of the daytime sky.
Diagram of Lambertian diffuse reflection. The black arrow shows incident radiance, and the red arrows show the reflected radiant intensity in each direction. When viewed from various angles, the reflected radiant intensity and the apparent area of the surface both vary with the cosine of the viewing angle, so the reflected radiance (intensity per unit area) is the same from all viewing angles.
A measure of the proportion of the total solar radiation received by an astronomical body, such as a planet, that is diffusely reflected away from the body. It is a dimensionless quantity typically measured on a scale from 0 (indicating total absorption of all incident radiation, as by a black body ) to 1 (indicating total reflection).