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Resample a spectrum to a new wavelength grid

Source: R/resample_spectrum.R
resample_spectrum.Rd

Interpolates spectral values onto a target wavelength grid using approx (linear, default) or spline (cubic). The most common use case is harmonising spectra from two instruments before arithmetic or comparison (e.g. aligning a TriOS RAMSES spectrum at 3.3 nm resolution with a Jerlov-based Kd vector at 25 nm steps).

Usage

resample_spectrum(
  x,
  lambda,
  from = NULL,
  method = c("linear", "cubic"),
  rule = 1
)

# S3 method for class 'lux_spectrum'
resample_spectrum(
  x,
  lambda,
  from = NULL,
  method = c("linear", "cubic"),
  rule = 1
)

# S3 method for class 'numeric'
resample_spectrum(
  x,
  lambda,
  from = NULL,
  method = c("linear", "cubic"),
  rule = 1
)

Arguments

x

A lux_spectrum object or numeric spectral-value vector.

lambda

Target wavelength grid in nm (numeric vector). When x is a lux_spectrum this argument is required.

from

Source wavelength grid in nm. Required when x is a numeric vector; ignored when x is a lux_spectrum (wavelengths are taken from x$lambda).

method

Interpolation method: "linear" (default) or "cubic".

rule

Integer passed to approx controlling out-of-range behaviour. Default 1 (return NA); use 2 to extend with boundary values.

Value

A lux_spectrum (when x is a lux_spectrum) or a named numeric vector, resampled onto lambda.

Details

Values are not extrapolated beyond the source wavelength range. By default (rule = 1) wavelengths outside that range receive NA; set rule = 2 to extend using the nearest boundary value instead. Because a lux_spectrum cannot contain non-finite values, its method raises a validation error when rule = 1 produces NA. The target grid for a lux_spectrum must also be strictly increasing and regular. The numeric method can be used to resample raw values from an irregular source grid before constructing a lux_spectrum.

See also

lux_spectrum, as_lux_spectrum

Examples

# Resample a solar spectrum from 10 nm to 5 nm bins
sp  <- solar_irradiance("clear_noon")
x   <- as_lux_spectrum(sp)
x5  <- resample_spectrum(x, lambda = seq(300, 800, by = 5))
x5
#> <lux_spectrum> irradiance [W/m2/nm] | 300-800 nm, 5 nm bins (101 pts)

# Align a Jerlov Kd vector to the Naples wavelength grid
lam_naples <- from_naples("0m")$lambda
lam_naples <- lam_naples[lam_naples >= 350 & lam_naples <= 700]
lam_jerlov <- seq(350, 700, by = 25)
Kd_coarse  <- jerlov_Kd("II", lam_jerlov)
Kd_fine    <- resample_spectrum(Kd_coarse, lambda = lam_naples,
                                 from = lam_jerlov, rule = 1)