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Fresnel reflectance at the air-water interface.

Source: R/optical_properties.R
fresnel_reflectance.Rd

Unpolarised Fresnel reflectance for light crossing a flat air-water boundary, as a function of incidence angle (Johnsen 2012, ch. 5). At normal incidence about 2% of downwelling light is reflected (\(R = ((n-1)/(n+1))^2\)). Going from water to air, total internal reflection (\(R = 1\)) occurs beyond the critical angle (the edge of snells_window).

Usage

fresnel_reflectance(
  angle = 0,
  n = 1.333,
  from = c("air", "water"),
  component = c("unpolarized", "s", "p")
)

Arguments

angle

Angle of incidence from the surface normal, in degrees (0-90). Vectorised.

n

Refractive index of water relative to air. Default 1.333.

from

Incident medium: "air" (default) or "water".

component

Which polarization component to return: "unpolarized" (default; the mean of the two), "s" (perpendicular / TE), or "p" (parallel / TM). The difference between the s- and p-components is why reflection off water partially polarizes light (vanishing for the p-component at Brewster's angle).

Value

Reflectance (0-1); the transmitted fraction is \(1 - R\).

References

Johnsen S (2012) The Optics of Life. Princeton University Press, ch. 5.

See also

snells_window, underwater_polarization

Examples

fresnel_reflectance(0)                       # ~0.02 at normal incidence
#> [1] 0.02037319
fresnel_reflectance(60, from = "water")      # total internal reflection -> 1
#> [1] 1
fresnel_reflectance(53.1, component = "p")   # ~0 near Brewster's angle
#> [1] 3.403873e-08