fresnel: Calculate the reflectance at a flat interface
In AlexCast/rho: R Hydrology Optics

Description Usage Arguments Details Value References See Also Examples

The function calculates the reflectance, i.e., the squared modulus of the (complex) amplitude reflection coefficient, of (polarized) electromagnetic radiation incident at a flat interface.

1	fresnel(thetai, thetar, ni, nr, fp = 0.5, ave = FALSE)

`thetai`	Incidence angle relative to the normal of the interface between the two mediums (radians).
`thetar`	Refracted angle relative to the normal of the interface between the two mediums (radians). If missing, function `snell` will be called internally.
`ni`	Refractive index of the medium of incidence (unitless).
`nr`	Refractive index of the medium of refraction (unitless).
`fp`	Fraction of parallel polarization (unitless).
`ave`	Logical. Should the reflections for S and P polarizations be returned separately?

Uses Fresnel's formulations to calculate the reflectance based on the incident and (complex) refracted angles and the (complex) indexes of refraction. NAs allowed in all arguments.

If ave is set to TRUE, the weighted average reflectance will be calculated, with the weights of each polarization given by fp.

A numeric vector if average reflectance is desired or a matrix with the reflectance for parallel (R_p) and perpendicular polarizations (R_s).

Bohren, C. F.; Huffman, D. R. 1983. Absorption and Scattering of Light by Small Particles. Wiley, New York.

snell, snell_decomp

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# Reflection from standard dry air to average seawater at 550 nm:
fresnel(thetai = c(0, pi/4, pi/2), ni = 1.000278, nr = 
complex(real = 1.342033, imaginary = 2.442E-09), ave = TRUE)