Convert a broadband scalar reading into a plausible spectrum.

Given a single measured value and a reference spectral shape, returns a rescaled spectrum whose forward operator reproduces the input. The shape assumption must be provided by the caller (e.g. from solar_irradiance()).

Usage

broadband2spectrum(
  value,
  unit = c("lx", "W", "kW", "umol", "radiance_W", "cd"),
  spectrum,
  water_type = NULL,
  depth = 0,
  wavelength_policy = c("error", "trim", "constant")
)

Arguments

value

The measured scalar (e.g. 18200 lux, 480 W, 1.2 kW).

unit

One of "lx", "W", "kW", "umol", "radiance_W", "cd".

spectrum

Reference spectral shape as a data frame with columns wavelength and irradiance.

water_type

Optional Jerlov water type string (e.g. "IA"). If supplied, the reference shape is pre-attenuated to depth before rescaling — use when the measurement was taken at depth.

depth

Depth in metres at which the measurement was taken. Only used when water_type is not NULL. Default 0.

wavelength_policy

Policy for wavelengths outside the bundled Jerlov domain when attenuation is requested: "error" (default), explicit restriction to the supported intersection with "trim", or explicit constant endpoint extension with "constant".

Value

A data frame with columns wavelength and irradiance, with a luxR.assumption attribute recording the provenance.

Details

Supported units and their forward operators:

"lx"

photopic integral via irradiance2lux()

"W"

broadband integral \(\sum E \cdot \Delta\lambda\)

"kW"

same as "W" divided by 1000

"umol"

PAR-band photon flux (400–700 nm) in \(\mu\)mol/s/m^2

"radiance_W"

Lambertian radiance: \(E = \pi L\), then integrate

"cd"

photometric radiance: \(L = \text{lux} / \pi\)

Examples

lam  <- seq(400, 700, by = 10)
spec <- data.frame(wavelength = lam, irradiance = rep(1, length(lam)))
broadband2spectrum(480, unit = "W", spectrum = spec)
#>    wavelength irradiance
#> 1         400   1.548387
#> 2         410   1.548387
#> 3         420   1.548387
#> 4         430   1.548387
#> 5         440   1.548387
#> 6         450   1.548387
#> 7         460   1.548387
#> 8         470   1.548387
#> 9         480   1.548387
#> 10        490   1.548387
#> 11        500   1.548387
#> 12        510   1.548387
#> 13        520   1.548387
#> 14        530   1.548387
#> 15        540   1.548387
#> 16        550   1.548387
#> 17        560   1.548387
#> 18        570   1.548387
#> 19        580   1.548387
#> 20        590   1.548387
#> 21        600   1.548387
#> 22        610   1.548387
#> 23        620   1.548387
#> 24        630   1.548387
#> 25        640   1.548387
#> 26        650   1.548387
#> 27        660   1.548387
#> 28        670   1.548387
#> 29        680   1.548387
#> 30        690   1.548387
#> 31        700   1.548387