Automatic computation of cold pixel Radiometric Surface Temperature

This function computes temperature of a cold pixel based on NDVI, Surface Temperature, DEM and albedo. It plots histograms indicating the selected values. The main difference with coldTs2 is that preference is given to temperature selection before considering NDVI and albedo selection.

Usage

coldTs(
  Ts,
  NDVI,
  albedo = NULL,
  sunangle = NULL,
  DEM = NULL,
  cluster = 8,
  extent = "interactive",
  upper = 0.95,
  lower = 0.2,
  plot = TRUE,
  layout = "portrait",
  draw = "poly",
  folder = NULL,
  welev = NULL,
  clip = NULL,
  iter.max = 100,
  seed = NULL
)

# Default S3 method
coldTs(
  Ts = NULL,
  NDVI,
  albedo = NULL,
  sunangle = NULL,
  DEM = NULL,
  cluster = 8,
  extent = "interactive",
  upper = 0.95,
  lower = 0.2,
  plot = TRUE,
  layout = "portrait",
  draw = "poly",
  folder = NULL,
  welev = NULL,
  clip = NULL,
  iter.max = 100,
  seed = NULL
)

Arguments

Ts: A RasterLayer data that indicates radiometric surface temperature values from remote sensing image, preferably in Kelvin (K). You can also point to raster file on your computer.
NDVI: A RasterLayer data that indicates NDVI (Normalized Difference Vegetation Index) values. You can also point to a file on your computer.
albedo: A RasterLayer data that has albedo values. You can also provide file path or location on your computer
sunangle: sun angle (degree) above the horizon.
DEM: A digital elevation model[m]
cluster: numeric, a value indicating the number of clusters.
extent: A subset of the raster file than include c(xmin, xmax, ymin, ymax). You can set it to "interactive" where you can digitise polygon. You can set to "auto" where it will be automatically generated. You can set it to "full" where all the image dimension will be used. See layout parameter below for more details. see extent
upper: The quantile probability at which NDVI should be included in the selection project. It ranges from 0-1. The default is 0.95
lower: The quantile probability at which Ts should be included in the slection project.The default is 0.2
plot: logical:TRUE or FALSE. To indicate if histograms or triangle should be plotted
layout: character. It takes "portrait" or "landscape". If extent is set to "auto" the middle part of the image will be used so that NAs can be avoided. You indicate whether the automatic slection should indicate west-east (landscape) or north-south direction (portraite)
draw: interactive. The method of digitisation if extent is set "auto". It takes "poly" or "rect"
folder: An original directory of the images that contains all landsat 5,7 or 8 bands and metadata. At the moment only Landsat folder is supported
welev: Weather station elevation in meters
clip: extent object or raster object or polygon from which an Extent object can be extracted. A polygon or raster will be reprojected to conform the data to be cropped. for example clip can take the form of c(xmin, xmax, ymin, ymax)
iter.max: The number iterations that kmeans cluster should use.
seed: optional single number. Passed to set.seed before the k-means clustering so the pixel selection is reproducible. The default NULL leaves the random-number stream untouched.

Value

Ts:: The selected or input Ts [K]
Tscold:: The Temperature of cold pixe [K]
TC:: The average temperature of the cold pixels [K]
x:: The x cordinate of the cold pixel
y:: The y cordinate of the cold pixel
xycold:: combined x and y coordinates
candidates:: The similiar candidates' pixels that can be used

Details

The function first divides the selected area into a number of clusters. The mean and standard devaitions are computed. The cluster means with the lowest standard devaitions and qualifying for upper (NDVI) and lower (Ts) limits (see above) are slected. The provided upper and lower probabilities are also used to select the final Ts.

References

Allen, R. G., Burnett, B., Kramber, W., Huntington, J., Kjaersgaard, J., Kilic, A., Kelly, C., & Trezza, R. 2013. Automated Calibration of the METRIC-Landsat Evapotranspiration Process. JAWRA Journal of the American Water Resources Association, 49(3): 563-576.

Author

George Owusu

Examples

if (FALSE) { # \dontrun{
#using landsat folder
folder=system.file("extdata","stack",package="sebkc")
modcold=coldTs(folder=folder,welev=170,extent="auto")

#use object of  
folder=system.file("extdata","stack",package="sebkc")
data=landsat578(data=folder, welev=362)
modcold=coldTs(folder=data,welev=170,extent="auto",cluster=3)

modcoldTs=coldTs(data,welev=170,extent="auto",cluster=3)

#using input different input data
albedo=raster(system.file("extdata","albedo.grd",package="sebkc"))
Ts=raster(system.file("extdata","Ts.grd",package="sebkc"))
NDVI=raster(system.file("extdata","NDVI.grd",package="sebkc"))
#simulate with default parameters without albedo
modcold=coldTs(Ts=Ts,NDVI=NDVI,sunangle=50.7)
#simulate with albedo but set extent to "auto" and cluster to 7
modcold=coldTs(Ts=Ts,NDVI=NDVI,albedo=albedo,sunangle=50,cluster=7,
extent="auto")
} # }