light_advanced: Advanced radiation transfer functions
In medfate: Mediterranean Forest Simulation

light_advanced

R Documentation

Advanced radiation transfer functions

Description

Functions light_layerDirectIrradianceFraction and light_layerDiffuseIrradianceFraction calculate the fraction of above-canopy direct and diffuse radiation reaching each vegetation layer. Function light_layerSunlitFraction calculates the proportion of sunlit leaves in each vegetation layer. Function light_cohortSunlitShadeAbsorbedRadiation calculates the amount of radiation absorbed by cohort and vegetation layers, while differentiating between sunlit and shade leaves.

Usage

light_leafAngleCDF(leafAngle, p, q)

light_leafAngleBetaParameters(leafAngle, leafAngleSD)

light_directionalExtinctionCoefficient(p, q, solarElevation)

light_layerDirectIrradianceFraction(
  LAIme,
  LAImd,
  LAImx,
  kb,
  ClumpingIndex,
  alpha,
  gamma,
  trunkExtinctionFraction = 0.1
)

light_layerDiffuseIrradianceFraction(
  LAIme,
  LAImd,
  LAImx,
  K,
  ClumpingIndex,
  ZF,
  alpha,
  gamma,
  trunkExtinctionFraction = 0.1
)

light_cohortSunlitShadeAbsorbedRadiation(
  Ib0,
  Id0,
  LAIme,
  LAImd,
  LAImx,
  kb,
  K,
  ClumpingIndex,
  ZF,
  alpha,
  gamma,
  trunkExtinctionFraction = 0.1
)

light_layerSunlitFraction(LAIme, LAImd, kb, ClumpingIndex)

light_instantaneousLightExtinctionAbsortion(
  LAIme,
  LAImd,
  LAImx,
  p,
  q,
  ClumpingIndex,
  alphaSWR,
  gammaSWR,
  ddd,
  ntimesteps = 24L,
  trunkExtinctionFraction = 0.1
)

light_longwaveRadiationSHAW(
  LAIme,
  LAImd,
  LAImx,
  LWRatm,
  Tsoil,
  Tair,
  trunkExtinctionFraction = 0.1
)

Arguments

`leafAngle`	Average leaf inclination angle (in radians).
`p`, `q`	Parameters of the beta distribution for leaf angles
`leafAngleSD`	Standard deviation of leaf inclination angle (in radians).
`solarElevation`	Solar elevation (in radians).
`LAIme`	A numeric matrix of live expanded LAI values per vegetation layer (row) and cohort (column).
`LAImd`	A numeric matrix of dead LAI values per vegetation layer (row) and cohort (column).
`LAImx`	A numeric matrix of maximum LAI values per vegetation layer (row) and cohort (column).
`kb`	A vector of direct light extinction coefficients.
`ClumpingIndex`	The extent to which foliage has a nonrandom spatial distribution.
`alpha`	A vector of leaf absorbance by species.
`gamma`	A vector of leaf reflectance values.
`trunkExtinctionFraction`	Fraction of extinction due to trunks (for winter deciduous forests).
`K`	A vector of light extinction coefficients.
`ZF`	Fraction of sky angles.
`Ib0`	Above-canopy direct incident radiation.
`Id0`	Above-canopy diffuse incident radiation.
`alphaSWR`	A vecfor of hort-wave absorbance coefficients for each cohort.
`gammaSWR`	A vector of short-wave reflectance coefficients (albedo) for each cohort.
`ddd`	A dataframe with direct and diffuse radiation for different subdaily time steps (see function `radiation_directDiffuseDay` in package meteoland).
`ntimesteps`	Number of subdaily time steps.
`LWRatm`	Atmospheric downward long-wave radiation (W/m2).
`Tsoil`	Soil temperature (Celsius).
`Tair`	Canopy layer air temperature vector (Celsius).

Details

Functions for short-wave radiation are adapted from Anten & Bastiaans (2016), whereas long-wave radiation balance follows Flerchinger et al. (2009). Vegetation layers are assumed to be ordered from bottom to top.

Value

Functions light_layerDirectIrradianceFraction, light_layerDiffuseIrradianceFraction and light_layerSunlitFraction return a numeric vector of length equal to the number of vegetation layers.

Function light_cohortSunlitShadeAbsorbedRadiation returns a list with two elements (matrices): I_sunlit and I_shade.

Author(s)

Miquel De Cáceres Ainsa, CREAF

References

Anten, N.P.R., Bastiaans, L., 2016. The use of canopy models to analyze light competition among plants, in: Hikosaka, K., Niinemets, U., Anten, N.P.R. (Eds.), Canopy Photosynthesis: From Basics to Application. Springer, pp. 379–398.

Flerchinger, G. N., Xiao, W., Sauer, T. J., Yu, Q. 2009. Simulation of within-canopy radiation exchange. NJAS - Wageningen Journal of Life Sciences 57 (1): 5–15. https://doi.org/10.1016/j.njas.2009.07.004.

Examples

solarElevation <- 0.67 # in radians
SWR_direct <- 1100
SWR_diffuse <- 300
PAR_direct <- 550
PAR_diffuse <- 150

LAI <- 2
nlayer <- 10
LAIlayerlive <- matrix(rep(LAI/nlayer,nlayer),nlayer,1)
LAIlayerdead <- matrix(0,nlayer,1)
meanLeafAngle <- 60 # in degrees
sdLeafAngle <- 20

beta <- light_leafAngleBetaParameters(meanLeafAngle*(pi/180), sdLeafAngle*(pi/180))

## Extinction coefficients
kb <- light_directionalExtinctionCoefficient(beta["p"], beta["q"], solarElevation)
kd_PAR <- 0.5
kd_SWR <- kd_PAR/1.35

medfate documentation built on April 4, 2025, 2:01 a.m.