sebs: SEBS Estimation of Evapotranspiration Fraction

In gowusu/sebkc: The Surface Energy Balance and Crop Coefficient Estimation with R

SEBS Estimation of Evapotranspiration Fraction

Description

sebs computes Su (2002) Surface Energy Balance System (SEBS) for estimation of turbulent heat fluxes

Usage

sebs(albedo, Ts, Tmax, Tmin, RHmax = NULL, RHmin = NULL, n = NULL, NDVI,
  SAVI, iter.max = 7, xyhot, xycold, DOY, sunelev, welev, zx, u, zomw,
  zom = NULL, LAI = NULL, DEM = NULL, lapse = 0.0065, Rn24 = NULL,
  wmo = NULL, airport = NULL, Krs = 0.16, surface = "grass",
  latitude = NULL, model = "SEBS", clip = NULL, folder = NULL)

## Default S3 method:
sebs(albedo = NULL, Ts, Tmax, Tmin, RHmax = NULL,
  RHmin = NULL, n = NULL, NDVI, SAVI, iter.max = 7, xyhot = "auto",
  xycold = "auto", DOY = NULL, sunelev, welev, zx = 10, u = 2,
  zomw = 2, zom = NULL, LAI = NULL, DEM = NULL, lapse = 0.0065,
  Rn24 = NULL, wmo = NULL, airport = NULL, Krs = 0.16,
  surface = "grass", latitude = NULL, model = "SEBS", clip = NULL,
  folder = NULL)

Arguments

albedo	A RasterLayer data that has albedo values. You can also provide file path or location on your computer
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.
Tmax	Numeric. Maximum air Temperature in degree Celsius
Tmin	Numeric. Minimum air Temperature in degree Celsius
RHmax	Maximum Relative Humidity in percent
RHmin	Minimum Relative Humidity in percent
n	Sunshine hours
NDVI	A RasterLayer data that indicates NDVI (Normalized Difference Vegetation Index) values. You can also point to a file on your computer.
SAVI	A RasterLayer data that indicates SAVI(Soil-adjusted Vegetation Index) values. You can also point to file on your computer.
iter.max	maximum iterations of sensible heat calculation.
xyhot	numeric or "auto". A list of x and y coordinates of a hot pixel in the form c(x,y). If it is set to "auto", hotTs will be used to compute it.
xycold	numeric or "auto". A list of x and y coordinates of a cold pixel in the form of c(x,y). If it set to "auto", coldTs will be used to compute it.
DOY	Numeric or Date [YYYY-mm-dd]. Day of the Year. If you give data in the form of date [YYYY-mm-dd], it will be converted to DOY
sunelev	Angle of Sun elevation in degrees, as found in the meta data of the satellite image
welev	Weather station elevation in meters
zx	The height above the weather station where the wind speed is measured [m]
u	The satellites overpass time wind speed at the weather station [m/s]
zomw	the roughness length for the weather station surface [m]
zom	the momentum roughness length for each pixel [m]. You can also point to a raster file on your computer
LAI	Leaf Area Index, dimensionless
DEM	A digital elevation model[m]
lapse	A local lapse rate that is applied to correct DEM [K/m]. Default value is 0.0065
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
wmo	numeric. World Meteorological Organization weather station code. You can use the Worldwide Station List at https://www.wunderground.com/about/faq/international_cities.asp [Accessed on 2016-5-6] or http://www.wetterzentrale.de/klima/stnlst.html [Accessed on 2016-5-6]
airport	numeric. IATA or ICAO code. They are alphabetically listed at https://en.wikipedia.org/wiki/List_of_airports_by_IATA_code:_A [Accessed on 2016-5-6]
Krs	Relationship between the fraction of extraterrestrial radiation that reaches the earth's surface, Rs/Ra, and the air temperature difference Tmax - Tmin for interior (Krs = 0.16) and coastal (Krs = 0.19) regions
surface	character. It is either "grass" or "alfalfa"
latitude	geographical coordinates in decimal degrees. It should be negative for southern hemisphere
model	character. The type of model. It takes either "SEBAL" or "METRIC"
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)
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

Details

Function ETo will be automatically used to estimate parameters y (psychrometric constant), slope (slope of saturation vapour pressure curve) and vpd (Vapour pressure deficit). For information on data input procedure see 'details' at sebal

Value

EF Evapotranspiration Fraction

Author(s)

George Owusu

References

Su, Z. 2002. The Surface Energy Balance System (SEBS) for estimation of turbulent heat fluxes. Hydrol. Earth Syst. Sci., 6(1): 85-100.

See Also

sebal , ETo, sebi

Examples

## Not run: 
#define 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"))
LAI=raster(system.file("extdata","LAI.grd",package="sebkc"))
Tmax=31
Tmin=28
RHmax=84,
RHmin=63
#perform simulation
modsebs=sebs(albedo=albedo,Ts=Ts,Tmax=Tmax,Tmin=Tmin,RHmax=RHmax,
RHmin=RHmin,NDVI=NDVI,SAVI=NULL,iter.max=7,xyhot="full",
xycold="full",DOY=37,sunelev=50.71154048,welev=317.1,zx=10,
u=2,zomw=2,zom=NULL,LAI=LAI,Rn24=NULL,model="SEBS")


#use original landsat 7 data by specifying folder path
folder=system.file("extdata","stack",package="sebkc")
modauto=sebs(folder = folder,welev = 380,Tmax=Tmax,
Tmin=Tmin,RHmax=RHmax,RHmin=RHmin)
#plot ET fraction
plot(modauto$EF)

#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="digitize",cluster=2)
#determine the cold. Digitize polygon on the Ts map
modcold=coldTs(data,welev=275,extent="digitize",cluster=2)
xyhot=modhot$xyhot
xycold=modcold$xycold
#use object of \code{\link{coldTs}} or \code{\link{hotTs}} in different ways
modsebs=sebs(data,xyhot=modhot,xycold=xycold,welev=welev,
Tmax=Tmax,Tmin=Tmin,RHmax=RHmax,RHmin=RHmin)
 
## End(Not run)

gowusu/sebkc documentation built on July 28, 2023, 11:44 a.m.