The refractive index

Refractive index

In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....

 of water at 20°C is 1.332986. The refractive index of normal ice is 1.31. (From List of refractive indices.)
In general, an index of refraction is a complex number with both a real and imaginary part, where the latter indicates the strength of absorption loss at a particular wavelength. In the visible part of electromagnetic spectrum the imaginary part of the refractive index is very small. However, water and ice absorb in infrared and close the atmospheric window

Atmospheric window

The infrared atmospheric window is the overall dynamic property of the earth's atmosphere, taken as a whole at each place and occasion of interest, that lets some infrared radiation from the cloud tops and land-sea surface pass directly to space without intermediate absorption and re-emission, and...

 thereby contributing to the greenhouse effect

Greenhouse effect

The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...

The absorption spectrum of pure water is used in numerous applications, including light scattering and absorption by ice crystals

Ice

Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

 and cloud water droplets

Cloud physics

Cloud physics is the study of the physical processes that lead to the formation, growth and precipitation of clouds. Cloud formations are composed of microscopic droplets of liquid water , tiny crystals of ice , or both...

, theories of the rainbow

Rainbow

A rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines on to droplets of moisture in the Earth's atmosphere. It takes the form of a multicoloured arc...

, determination of the single scattering albedo

Single scattering albedo

Single scattering albedo - the ratio of scattering efficiency to total extinction efficiency . Most often it is defined for small-particle scattering of electromagnetic waves...

, ocean color

Ocean color

The "color" of the ocean is determined by the interactions of incident light with substances or particles present in the water.For pure ocean water, such like the open ocean water, it appears as a very dark navy blue. The reason the ocean is blue is due to the absorption and scattering of light...

, and many others.

Quantitative description of the refraction index

The real part of the index of refraction is described by the following expression:



Where:

K	kg/m3	nm

And T is the absolute temperature of water (in K), is the wavelength, is the density of the water and n is the refraction index

See also

• List of refractive indices
• Absorption (electromagnetic radiation)
  Absorption (electromagnetic radiation)
  In physics, absorption of electromagnetic radiation is the way by which the energy of a photon is taken up by matter, typically the electrons of an atom. Thus, the electromagnetic energy is transformed to other forms of energy for example, to heat. The absorption of light during wave propagation is...
  
  
• Atmospheric radiative transfer codes
  Atmospheric radiative transfer codes
  An Atmospheric radiative transfer model, code or simulator calculates radiative transfer of electromagnetic radiation through a planetary atmosphere, such as the Earth's.- Methods :...
  
  
• Color of water
  Color of water
  The color of water is a subject of both scientific study and popular misconception. While relatively small quantities of water are observed by humans to be colorless, pure water has a slight blue color that becomes a deeper blue as the thickness of the observed sample increases...