continuumRemoval: Continuum Removal

In prospectr: Miscellaneous Functions for Processing and Sample Selection of Spectroscopic Data

Continuum Removal

Description

Compute the continuum removed values of a data matrix or vector

Usage

continuumRemoval(X, wav, type = c("R", "A"),
                 interpol = c("linear", "spline"),
                 method = c("division", "substraction"))

Arguments

X	a numeric matrix or vector to process (optionally a data frame that can be coerced to a numerical matrix).
wav	optional. A numeric vector of band positions.
type	the type of data: 'R' for reflectance (default), 'A' for absorbance.
interpol	the interpolation method between points on the convex hull: 'linear' (default) or 'spline'.
method	normalization method: 'division' (default) or 'subtraction' (see details section).

Details

The continuum removal technique was introduced by Clark and Roush (1984) as a method to highlight energy absorption features of minerals. It can be viewed as a way to perform albedo normalization. The algorithm find points lying on the convex hull (local maxima or envelope) of a spectrum, connects the points by linear or spline interpolation and normalizes the spectrum by dividing (or subtracting) the input data by the interpolated line.

Value

a matrix or vector with the filtered spectra.

Author(s)

Antoine Stevens & Leonardo Ramirez-Lopez

References

Clark, R.N., and Roush, T.L., 1984. Reflectance Spectroscopy: Quantitative Analysis Techniques for Remote Sensing Applications. J. Geophys. Res. 89, 6329-6340.

See Also

savitzkyGolay, movav, gapDer, binning

Examples

data(NIRsoil)
wav <- as.numeric(colnames(NIRsoil$spc))
# plot of the 10 first abs spectra
matplot(wav,
  t(NIRsoil$spc[1:10, ]),
  type = "l",
  ylim = c(0, .6),
  xlab = "Wavelength /nm",
  ylab = "Abs"
)
#  # type = 'A' is used for absorbance spectra
cr <- continuumRemoval(NIRsoil$spc, wav, type = "A")
matlines(wav, t(cr[1:10, ]))

prospectr documentation built on Aug. 31, 2022, 5:05 p.m.