cansw: Calculates radiation received under vegetated canopies

In ilyamaclean/microctools: Various worker functions for microclimc package

Calculates radiation received under vegetated canopies

Description

cansw calculates the flux density of incoming shortwave radiation underneath vegetation canopies

Usage

cansw(
  globrad,
  dp = NA,
  jd,
  localtime,
  lat,
  long,
  l,
  x,
  ref = 0.2,
  hourly = FALSE,
  watts = TRUE,
  merid = round(long/15, 0) * 15,
  dst = 0,
  corr = 1,
  tme = NA,
  clump = 0
)

Arguments

globrad	a vector of incoming shortwave radiation values (either MJ m-2 hr-1 or W m-2)
dp	optional numeric value or vector of values indicating the proportion of globarad that is diffuse. If no value is provided, calculated using difprop()
jd	the Julian day as returned by jday()
localtime	a single numeric value representing local time (decimal hour, 24 hour clock)
lat	latitude of location (decimal degrees, -ve south of equator).
long	longitude of location (decimal degrees, -ve west of Greenwich meridian).
l	leaf area index (total one-sided area of leaf per unit ground area)
x	leaf distribution angle coefficient
ref	average reflectivity of leaves in shortwave spectrum.
hourly	Used if dp = NA. Specifies whether values of rad are hourly (see details).
watts	Used if dp = NA. A logical value indicating whether the units of rad are W m-2 (TRUE) or MJ m-2 hr-1 (FALSE).
merid	an optional numeric value representing the longitude (decimal degrees) of the local time zone meridian (0 for GMT). Default is round(long / 15, 0) * 15
dst	an optional numeric value representing the time difference from the timezone meridian (hours, e.g. +1 for BST if merid = 0).
corr	Used if dp = NA. An optional numeric value representing a correction to account for over- or under-estimated diffuse proportions. Values > 1 will apportion a greater ammount of total radiation as diffuse than originally calculated by the formula.
tme	object of POSIXlt indicating times in UTC. Can be used in place of specifying jd, localtime, dst and merid
clump	clumpiness factor for canopy (0-1, see details)

Details

Calculated the flux density of radiation received below leaf area l, not absorbed. I.e. ground albedo not accounted for. if clump = 0 the canopy is assumed entirely uniform and radiation transmission is as for a turbid medium. As clump approaches 1, the canopy is assumed to be increasingly patchy, such that a greater proportion of reaches the ground without being obscured by leaves.

Value

shortwave radiation received underneath vegetated canopies. Units as for globrad.

See Also

cantransdir(), cantransdif() and canlw()

Examples

l <- c(0:1000)/100
sw <- cansw(500, dp = 0.5, jday(2020, 6, 21), 12, 50, -5, l, 1)
plot(sw ~ l, type = "l")

ilyamaclean/microctools documentation built on Jan. 25, 2023, 5:29 a.m.