propagate_r: Propagates reflectance across air-water interface
In AlexCast/rho: R Hydrology Optics

Description Usage Arguments Details References See Also

This function propagates the reflectance across the air-water interface.

1	propagate_r(r, to = c("air", "water"), aop = c("rrs", "rho"))

`r`	Reflectance (unitless or 1/sr).
`to`	One of: "air" or "water".

This function applies the average coefficients for water transmittance and refractive index of water relative to air to calculate the scaling of the reflectance signal just above or just below the water surface. The base equation and data is described in Gordon et al. (1988).

Irradiance reflectance just above the water surface (R(+)) is related to the irradiance reflectance just below the water surface (R(-)) by:

R(+) = t(Lu) * (na/nw)^2 * t(Ed) * R(-) / (1 - r(Eu) * R(-)),

where t(Lu) is the transmittance of in water upwelling radiance to air, (na/nw)^2 takes in account the radiance invariance law, t(Ed) in the transmittance of the in air downwelling irradiance to water and r(Eu) is the reflectance of the in water upwelling radiance by the interface. A similar relation is found for Rrs(+) and rrs(-) by including the factor 1/Q, where Q is the relation Eu/Lu. The interface transmittance and reflection coefficients depend on its roughness and the directional irradiance distribution (Gordon 2005) and on the wavelength dependent refractive indexes of air and water (Voss & Flora, 2017).

Voss, K. J.; Flora, S. 2017. Spectral dependence of the seawater-air radiance transmission coefficient. Journal of Atmospheric and Oceanic Technology 34, 6, 1203-1205. DOI: 10.1175/JTECH-D-17-0040.1

Gordon, H. R.. 2005. Normalized water-leaving radiance: Revisiting the influence of surface roughness. Applied Optics, 44, 241-248. DOI: 10.1364/AO.44.000241

Gordon, H. R.; Brown, O. B.; Evans, R. H.; Brown, J. W.; Smith, R. C.; Baker, K. S.; Clark, D. K. 1988. A semianalytic radiance model ofocean color. Journal of Geophysical Research 93, 10, 909-10.924. DOI: 10.1029/JD093iD09p10909

Lee, Z.-P.; Carder, K. L.; Mobley, C. D.; Steward, R. G.; Patch, J. S. 1998. Hyperspectral remote sensing for shallow waters. I. A semianalytical model. Applied Optics 37, 27, 6329-6338. DOI: 10.1364/AO.37.006329

Lee, Z.-P.; Carder, K. L.; Arnone, R. A. 2002. Deriving inherent optical properties from water color: a multiband quasi-analytical algorithm for optically deep waters. Applied Optics 41, 27, 5755-5772. DOI: 10.1364/AO.41.005755

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AlexCast/rho documentation built on Dec. 14, 2021, 9:47 a.m.