n_water: Dispersion formula for the refractive index of liquid water
In AlexCast/rho: R Hydrology Optics

Description Usage Arguments Details Value References See Also Examples

This function calculates the real part of the refractive index of pure water relative to vaccum. The complex refractive index can also be returned. See details.

1	n_water(lambda, Tc = 20, S = 0, P = 0, type = c("real", "complex"))

`lambda`	Wavelength in vacuum (nm).
`Tc`	Temperature (ºC).
`S`	Salinity (parts per thousand).
`P`	Pressure (bar in excess of 1 ATM).
`type`	One of: "real" or "complex". See details.

The temperature and salinity dependent spectral refractive index of (saline) water is based on the empirical dispersion equation parametrized by Quan & Fry (1995) for the visible range. Huibers (1997) analyzed the available data and models and attested that the model could be extrapolated to the UV and NIR (220 to 1100 nm).

The Quan & Fry (1995) formulation is for standard atmosphere pressure. It can be converted to any desired pressure with the isothermic density derivative of the refractive index of liquids parametrized by Proutiere et al. (1992). That pressure, in bar, should be in excess of surface pressure, i.e., to retrieve surface values, P = 0.

The imaginary part of the refractive index of pure water is calculated from the temperature and salinity dependent absorption of pure (saline) water ( function a_water).

The original parametrization of Quan & Fry (1995) is based on refractive index relative to air measured by Austin & Halikas (1976), and the function will return the values relative to vacuum by using the refractive index of standard dry air (n_air), as recommended by Zhang et al. (2009).

Another parametrization with comparable to that of Quan & Fry (1995) in the visible range Huibers, 1997) is that of Schiebener et al. (1990). This model has an extended range (200 to 2500 nm) and could be added as an option in a future version.

A numeric (or complex) vector of the refractive index (unitless) of pure (saline) water relative to vacuum .

Austin, R. W.; Halikas, G. 1976. The index of refraction of seawater. SIO Ref. 76-1, Scripps Institution of Oceanography, La Jolla, California.

Huibers, P. D. T. 1997. Models for the wavelength dependence of the index of refraction of water. Applied Optics 36, 16, 3785-3787. DOI: 10.1364/ao.36.003785

Jonasz, M.; Fournier, G. R. 2007. Light Scattering by Particles in Water - Theoretical and Experimental Foundations. Academic Press, 715 pp.

Proutiere, A.; Megnassan, E.; Hucteau, H. 1992. Refractive index and density variations in pure liquids: A new theoretical relation. The Journal of Physical Chemistry 96, 3485-3489. DOI: 10.1021/j100187a058

Quan, X.; Fry, E. S. 1995. Empirical equation for the index of refraction of seawater. Applied Optics 34, 3477–3480. DOI: 10.1364/AO.34.003477

Schiebener, P.; Straub, J.; Levelt Sengers, J. M. H.; Gallagher, J. S. 1990. Refractive index of water and steam as a function of wavelength, temperature and density. Journal of Physical and Chemical Reference Data 19, 677–717. DOI: 10.1063/1.555859

Zhang, X. Hu, L. 2009. Estimating scattering of pure water from density fluctuation of the refractive index. Optics Express 17, 3, 1671-1678. DOI: 10.1364/OE.17.001671

n_air, n_cellulose, n_calcite, n_quartz, snell, fresnel

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# Real part of the refractive index of average seawater at 1 atmospheric 
# pressure and in the visible range:
n_water(lambda = 400:700, S = 34.72, Tc = 3.5, P = 0)