rad.corr: Radiometric correction

In edwardpmorris/FASTSpectra: Parse and radiometrically correct Ocean Optics spectra files

Description

Convert instrument values, called digital number (DN) counts, to radiometric units using instrument specific metadata and calibration values (instrument response functions).

Usage

rad.corr(dn, type = c("norm.DN", "radiant.energy", "spectral.flux",
  "spectral.intensity", "spectral.radiance", "spectral.irradiance"),
  cal.DN2RadiantEnergy = NULL, is.REF = FALSE, cal.RRefPanel = NULL,
  instrument.metadata = list())

Arguments

dn	A hyperSpec object that includes a matrix of hyperspectral digital number values [counts] and a dataframe that includes the 'integration time' of each spectrum
type	The type of conversion to be calculated. See details
cal.DN2RadiantEnergy	Path to a file that contains the instrument specific calibration for conversion from counts to radiant energy [uJ/count] and other radiometric units
is.REF	Is the spectra of a 'reference panel'. If true the spectra is multiplied by panel-specific reflectance (must be supplied)
cal.RRefPanel	Path to a file that contains the reference panel specific calibration of reflectance [-]
instrument.metadata	A named list with instrument metadata. See details.

Details

Radiometry terminology and units from https://en.wikipedia.org/wiki/Template:SI_radiometry_units.

Various unit conversions can be applied: Options include normalised DN [counts/s nm], radiant energy [J], spectral flux [W/nm], spectral intensity [W/sr nm], spectral radiance [W/sr m2 nm], spectral irradiance [W/m2 nm] and spectral irradiance of a reference panel relative to a 'lambertian' surface with a reflectance factor of 1 throughout the wavelength range of interest [W/m2 nm].

These only make sense if the 'measurement geometry', 'integration time' [s] of a measurement, 'surface area of the instrument light apature' [m], and 'instrument-specific response function' in radiant energy (e.g., J/count or other units; FIXME: are there options for specifying other units?) is known and supplied to the function.

Reference panel-specific reflectance over the wavelngth range of the measurement to be converted must be supplied to for reference panel values.

Value

A hyperSpec object including a matrix of radiometrically corrected spectra, metadata extracted from the spectra headers and file information.

Examples

# set path to data files
file.path <- system.file("extdata", package = "FASTSpectra")

# parse spectra into hyperSpec object
dn <- read.txt.OceanOptics(files=paste0(file.path,"/*.txt"))

# assign measurement id and type using fieldlog file
logfile <- paste0(file.path,"/fieldlog.csv")
dn <- assign.type(dn, logfile=logfile)

# split into sample and reference
type <- slot(dn,"data")[["type"]]
dn <- split(x=dn, f=type)

# convert samples to spectral radiance [W / sr m2 nm]
cal.rad <- paste0(file.path,"/*.IrradCal")
rad <- rad.corr(dn$SAMP, type="spectral.radiance", cal.DN2RadiantEnergy = cal.rad)
require(hyperSpec)
plot(rad, wl.range=380:850)

# convert references to spectral irradiance relative to 100% reference panel [W / m2 nm]
cal.ref <- paste0(file.path,"/*.ReflCal")
ref <- rad.corr(dn$REF, type="spectral.radiance", is.REF=TRUE, cal.DN2RadiantEnergy = cal.rad, cal.RRefPanel = cal.ref)
plot(ref, wl.range=380:850)

edwardpmorris/FASTSpectra documentation built on May 15, 2019, 11:03 p.m.