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Water Deficit Index (WDI)

Source: R/WDI.R
wdi.Rd

Moran et. al (1994) Estimation of crop water deficit using surface-air temperature and spectral vegetation index.

Usage

wdi(
  Ts = NULL,
  Ta,
  NDVI,
  albedo = NULL,
  Tsmax = "auto",
  Tsmin = "auto",
  sunelev = NULL,
  folder = NULL,
  welev = NULL,
  Rn24 = NULL
)

wdi(
  Ts = NULL,
  Ta,
  NDVI,
  albedo = NULL,
  Tsmax = "auto",
  Tsmin = "auto",
  sunelev = NULL,
  folder = NULL,
  welev = NULL,
  Rn24 = 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.

Ta

numeric. Air temperature. If not available you can use

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

Tsmax

numeric. Maximum sensor surface temperature [K]

Tsmin

numeric. Minimum sensor surface temperature [K] sebal to get pixel based Ta.

sunelev

Angle of Sun elevation in degrees, as found in the meta data of the satellite image

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

Rn24

A 24 hour net radiation [W/m2]. It is needed to estimate daily ET. It can be computed with ETo with even a minimal data of Tmax and Tmin. You can also point to raster file on your computer

Value

EF:

standardised wdi excluding negatives and one plus

index:

raw wdi including negatives and more than one

Details

Note that surface temperature (Tsmin and Tsmax) are different from air temperature (Tmin and Tmax) in ETo, sseb, sebs

You can get Ta from sebal Ta

References

Moran, M. S., Clarke, T. R., Inoue, Y., & Vidal, A. 1994. Estimating crop water deficit using the relation between surface-air temperature and spectral vegetation index. Remote Sensing of Environment, 49(3): 246-263.

See also

sseb and sebi

Author

George Owusu

Examples

 if (FALSE) { # \dontrun{
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"))
modWDI=wdi(Ts=Ts,Ta=299,NDVI=NDVI,albedo=NULL,Tsmax="auto",
Tsmin="auto",sunelev=50)
plot(modWDI$EF)

#Using folder parameter
folder=system.file("extdata","stack",package="sebkc")
wdiauto=wdi(folder=folder,welev=317,Tsmax=31,Tsmin=28,Ta=290)

#' #Another interactive example
#get Ts, Albedo, NDVI, SAVI, sunelev, DOY from landsat data 
welev=278
data=landsat578(rawdata,welev=welev)
#perform semi-auto simulation 
#Determine xyhot. Digitize polygon on the Ts map
modhot=hotTs(data,welev=300,extent="auto",cluster=2)
#determine the cold. Digitize polygon on the Ts map
modcold=coldTs(data,welev=275,extent="auto",cluster=2)
Tsmax=modhot$Tshot
Tsmin=modcold$Tscold
#use object of \code{\link{coldTs}} or \code{\link{hotTs}} in different ways
modWDI2=wdi(data,Ta=299,Tsmax=Tsmax,Tsmin=modcold,sunelev=50)
plot(modWDI2$EF)
} # }