Optical properties of water and ice

Main article: Properties of water

The refractive index 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 thereby contributing to the greenhouse effect

The absorption spectrum of pure water is used in numerous applications, including light scattering and absorption by ice crystals and cloud water droplets, theories of the rainbow, determination of the single scattering albedo, ocean color, and many others.

Quantitative description of the refraction index

The real part of the index of refraction is described by the following expression: ^[1]

$\frac{n^{2}-1}{n^{2}+2}(1/\overline{\rho })=a_{0}+a_{1}\overline{\rho}+a_{2}\overline{T}+a_{3}{\overline{\lambda}}^{2}\overline{T}+\frac{a_{4}}{{\overline{\lambda}}^{2}}+\frac{a_{5}}{{\overline{\lambda }}^{2}-{\overline{\lambda}}_{\mathit{UV}}^{2}}+\frac{a_{6}}{{\overline{\lambda}}^{2}-{\overline{\lambda }}_{\mathit{IR}}^{2}}+a_{7}{\overline{\rho}}^{2}$

Where:

a0 = 0.244257733	a1 = 0.00974634476	a2 = − 0.00373234996
a3 = 0.000268678472	a4 = 0.0015892057	a5 = 0.00245934259
a6 = 0.90070492	a7 = − 0.0166626219
$\overline T = \frac{T}{T^{\text{*}}}$	$\overline \rho = \frac{\rho}{\rho^{\text{*}}}$	$\overline \lambda = \frac{\lambda}{\lambda^{\text{*}}}$
T* = 273.15 K	ρ* = 1000 kg/m3	λ* = 589 nm
$\overline\lambda_{\text{IR}}=5.432937$	$\overline\lambda_{\text{UV}}=0.229202$

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

See also

• List of refractive indices
• Absorption (electromagnetic radiation)
• Atmospheric radiative transfer codes
• Color of water

Notes

1. ^ The International Association for the Properties of Water and Steam (1997) (PDF). Release on the Refractive Index of Ordinary Water Substance as a Function of Wavelength, Temperature and Pressure. http://www.iapws.org/relguide/rindex.pdf. Retrieved 2008-10-08. 

References

• R. M. Pope and E. S. Fry, Absorption spectrum (380-700 nm) of pure water. II. Integrating cavity measurements, Appl. Opt., 36, 8710-8723, 1997.
• Mobley, Curtis D., Light and water : radiative transfer in natural waters; based in part on collaborations with Rudolph W. Preisendorfer, San Diego, Academic Press, 1994, 592 p., ISBN 0125027508