Convert transmittance into absorptance.

Function that converts transmittance (fraction) into absorptance (fraction). If reflectance (fraction) is available, it also allows conversions between internal and total absorptance.

Usage

T2Afr(x, action, byref, clean, ...)

# Default S3 method
T2Afr(x, action = NULL, byref = FALSE, clean = FALSE, ...)

# S3 method for class 'numeric'
T2Afr(x, action = NULL, byref = FALSE, clean = FALSE, Rfr = NA_real_, ...)

# S3 method for class 'filter_spct'
T2Afr(x, action = "add", byref = FALSE, clean = FALSE, ...)

# S3 method for class 'object_spct'
T2Afr(x, action = "add", byref = FALSE, clean = FALSE, ...)

# S3 method for class 'filter_mspct'
T2Afr(
  x,
  action = "add",
  byref = FALSE,
  clean = FALSE,
  ...,
  .parallel = FALSE,
  .paropts = NULL
)

# S3 method for class 'object_mspct'
T2Afr(
  x,
  action = "add",
  byref = FALSE,
  clean = FALSE,
  ...,
  .parallel = FALSE,
  .paropts = NULL
)

Arguments

x

an R object.

action

character Allowed values "replace" and "add".

byref

logical indicating if new object will be created by reference or by copy of x.

clean

logical replace off-boundary values before conversion.

...

not used in current version.

Rfr

numeric vector. Spectral reflectance o reflectance factor. Set to zero if x is internal reflectance,

.parallel

if TRUE, apply function in parallel, using parallel backend provided by foreach

.paropts

a list of additional options passed into the foreach function when parallel computation is enabled. This is important if (for example) your code relies on external data or packages: use the .export and .packages arguments to supply them so that all cluster nodes have the correct environment set up for computing.

Value

A copy of x with a column Afr added and other columns possibly deleted except for w.length. If action = "replace", in all cases, the redundant columns are removed, even when column Afr was present in the argument passed to x.

Details

Absorptance, internal transmittance and total reflectance when expressed as fractions, add up to one:

$$1 = \alpha + \tau + \rho$$

where, \(\alpha\) is absorptance, \(\tau\) is internal transmittance and \(\rho\) is total reflectance. If any two of these quantities are known, the third one can be computed from them.

On the other hand:

$$1 = \alpha\prime + T$$

where, \(\alpha\prime = \alpha + \rho\), measured together. In this case, there is not enough information available to compute \(\alpha\).

Thus, method T2Afr() computes either \(\alpha\) or \(\alpha\prime\), depending on whether \(\tau\) or \(T\) are contained in the argument passed to x, but neither of them when only \(\tau\) is known. To know which quantity has been computed, use getTfrType() to query whether the computations were based on \(\tau\) or \(T\).

The R names used are: Tfr for \(\tau\) and \(T\) are Tfr, Afr for \(\alpha\) and \(\alpha\prime\), and Rfr for \(rho\). The distinction between \(\tau\) and \(T\) and between \(\alpha\) and \(\alpha\prime\) is made based on metadata attributes.

Methods (by class)

• T2Afr(default): Default method for generic function

• T2Afr(numeric): Default method for generic function

• T2Afr(filter_spct): Method for filter spectra

• T2Afr(object_spct): Method for object spectra

• T2Afr(filter_mspct): Method for collections of filter spectra

• T2Afr(object_mspct): Method for collections of object spectra

See also

Other quantity conversion functions: A2T(), Afr2T(), T2A(), any2T(), as_quantum(), e2q(), e2qmol_multipliers(), e2quantum_multipliers(), q2e()

Examples

T2Afr(Ler_leaf.spct)
#> Object: object_spct [2,401 x 4]
#> Wavelength range 250-850 nm, step 0.25 nm 
#> Label: Ler_06_black.spct 
#> Measured on 2017-07-03 13:17:09.548817 UTC 
#> Variables:
#>  w.length: Wavelength [nm]
#>  Tfr: Total spectral transmittance [/1]
#>  Rfr: Total spectral reflectance [/1]
#>  Afr: Spectral absorptance [/1] 
#> --
#> # A tibble: 2,401 × 4
#>    w.length   Tfr    Rfr   Afr
#>       <dbl> <dbl>  <dbl> <dbl>
#>  1     250      0 0.0467 0.953
#>  2     250.     0 0.0467 0.953
#>  3     250.     0 0.0467 0.953
#>  4     251.     0 0.0467 0.953
#>  5     251      0 0.0467 0.953
#>  6     251.     0 0.0467 0.953
#>  7     252.     0 0.0467 0.953
#>  8     252.     0 0.0467 0.953
#>  9     252      0 0.0467 0.953
#> 10     252.     0 0.0467 0.953
#> # ℹ 2,391 more rows