Reflectivity

The reflectance (also reflectivity, reflectivity or reflectance ) ρ (also R ) is the ratio between reflected and incident intensity sound energy quantity, eg electromagnetic waves (light current) or sound waves (sound pressure, sound field size). Is a disturbed propagation of the wave.

• : Reflectance
• P0: incident power

What is meant is generally also the scattered throwing back a quantity, such as the diffuse reflection of light from rough ( " non-specular " ) surfaces. In astronomy and geography, the term albedo is used for the diffuse reflected light flux.

Correlations with other physical quantities

In reflection of a wave energy losses also occur always reflected with respect to the incident wave in the form of absorption and transmission. For the respective energy terms is generally:

In which

• Of the absorption coefficient α is a measure of the power absorbed,
• The transmittance τ is a measure of the transmitted,
• Of dissipation of δ is a measure of the " lost" intensity.

Electromagnetic wave, the reflectance and the transmittance of the Fresnel equations using the refractive indices of the materials involved can be calculated in the case of specular reflection.

In contrast to the reflectance of the reflection coefficient ( and reflectance ) r refers to the amplitude size. The reflectance corresponds to the square of the reflection coefficient r:

Complex variables, such as occur in the reflection of light with absorbent media, corresponding to the reflectance of the product of the reflectance factor R, with its complex conjugate r *:

Reflectances in the remote sensing

In the graphic besides the reflectances of the six surfaces are shown. The spectra were measured with a hyperspectral remote sensing sensor.

The upper figure shows three vegetation spectra. These each have similar profiles, but differ in their albedo. In the visible region of the spectrum ( 0.4 to 0.7 micron ) is to detect the so-called Green peak generated by the intense light absorption of chlorophyll in the blue and red spectral range and weaker absorption in the green region ( about 0.55 microns ) will. Through the Green Peak vegetation appears green to the human eye. The sharp increase in reflectance at 0.7 microns is called Red Edge. The high reflection in the near infrared spectral range (up to 1.3 microns ) is caused by multiple scattering of the sheet structure, said absorbent material is missing in this spectral range. Weak water absorption bands can be seen at 0.95 and 1.2 microns. The middle infrared spectral range ( 1.3 to 2.5 microns ) is dominated by strong water absorption bands at 1.45, 1.95 and 2.6 microns.

The lower figure shows the reflection of the floor with straw, grain just before harvest maturity and turbid water.

Others

The material with the previously smallest reflectance of visible light ( .045 %) is a kind of mat with vertical carbon nanotubes, and was developed at Rensselaer Polytechnic Institute. The thickness of the mat is 10 to 800 micrometers.