Advanced radiation transfer functions

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).

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.

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.

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.

See also

spwb, light_basic

Author

Miquel De Cáceres Ainsa, CREAF

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