R/mssdn2refl.r

In jdbcode/LandsatLinkr: Tools to spectrally link Landsat data

#' Convert DN values to toa reflectance
#'
#' Convert DN values to toa reflectance
#' @param file The full path name of the *archv file
#' @import raster
#' @import rgdal
#' @export


mssdn2refl = function(file, overwrite=F){
  
  check = file_check(file,"reflectance.tif",overwrite)
  if(check == 0){return(0)}
  
  #link to the equations to convert DN to TOA and TOA to SR
  #http://landsathandbook.gsfc.nasa.gov/data_prod/prog_sect11_3.html
  
  #define the reflectance function
  refl = function(file, band, gain, bias, sunzen, d, esun){
    orig = raster(file, band)
    img = as.matrix(orig)   
    img = ((gain*img)+bias)
    img[img < 0] = 0
    img = (pi * img * (d^2))/(esun * cos(sunzenith))
    img = round(img * 10000)
    img = setValues(orig,img)
    return(img)
  }
  
  #read in the image metadata  
  info = get_metadata(file)
  
  #define esun values for mss (chander et al 2009 summary of current radiometric calibration coefficients... RSE 113)
  if(info$sensor == "LANDSAT_1"){esun = c(1823,1559,1276,880.1)}
  if(info$sensor == "LANDSAT_2"){esun = c(1829,1539,1268,886.6)}
  if(info$sensor == "LANDSAT_3"){esun = c(1839,1555,1291,887.9)}
  if(info$sensor == "LANDSAT_4"){esun = c(1827,1569,1260,866.4)}
  if(info$sensor == "LANDSAT_5"){esun = c(1824,1570,1249,853.4)}
  
  #define the earth sun distance 
  doy = as.numeric(substr(basename(file),14,16))
  d = eudist(doy)
  sunzenith = info$sunzen/57.2958 
  
  #apply the conversion to reflectance
  b1 = refl(file,1,info$b1gain, info$b1bias, sunzen, d, esun[1]) 
  b2 = refl(file,2,info$b2gain, info$b2bias, sunzen, d, esun[2])
  b3 = refl(file,3,info$b3gain, info$b3bias, sunzen, d, esun[3])
  b4 = refl(file,4,info$b4gain, info$b4bias, sunzen, d, esun[4])
  
  #stack the bands
  img = stack(b1,b2,b3,b4)
  
  #write it out
  projection(img) = set_projection(file)
  img = as(img, "SpatialGridDataFrame")         #convert the raster to SGHF so it can be written using GDAL (faster than writing it with the raster package)
  outfile = sub("archv", "reflectance", file)
  writeGDAL(img, outfile, drivername = "GTiff", type = "Int16", mvFlag = -32768, options="INTERLEAVE=BAND")
  return(1)
}