kc_s2 function

Crop coefficient (ETa / ET0) using Sentinel-2 images with single agrometeorological data.

kc_s2(doy, RG, Ta, a, b)

Arguments

• doy: is the Day of Year (DOY)
• RG: is the global solar radiation
• Ta: is the average air temperature
• a: is one of the regression coefficients of SAFER algorithm
• b: is one of the regression coefficients of SAFER algorithm

Returns

It returns in raster format (.tif) the Surface Albedo at 24h scale ("Alb_24"), NDVI, Surface Temperature ("LST"), Crop Coefficient ("kc") and net radiation ("Rn_MJ").

Examples

library(agriwater)

# dependencies of package 'agriwater'
library(terra)

# Using a temporary folder to run example
wd <- tempdir()
initial = getwd()
setwd(wd)

# creating raster which simulate Sentinel-2 reflectances - for using
# real data, please download:
# https://drive.google.com/open?id=14E1wHNLxG7_Dh4I-GqNYakj8YJDgKLzk

xy <- matrix(rnorm(4, mean = 0.07, sd = 0.01), 2, 2)
rast <- rast(xy, crs="+proj=longlat +datum=WGS84")
ext(rast) <- c(-40.5,-40.45,-9.5,-9.45)
writeRaster(rast, file.path(wd, "B2.tif"),filetype = "GTiff", overwrite=TRUE)
xy <- matrix(rnorm(4, mean = 0.05, sd = 0.015),2, 2)
rast <- rast(xy, crs="+proj=longlat +datum=WGS84")
ext(rast) <- c(-40.5,-40.45,-9.5,-9.45)
writeRaster(rast, file.path(wd, "B3.tif"),filetype = "GTiff", overwrite=TRUE)
xy <- matrix(rnorm(4, mean = 0.03, sd = 0.018),2, 2)
rast <- rast(xy, crs="+proj=longlat +datum=WGS84")
ext(rast) <- c(-40.5,-40.45,-9.5,-9.45)
writeRaster(rast, file.path(wd, "B4.tif"),filetype = "GTiff", overwrite=TRUE)
xy <- matrix(rnorm(4, mean = 0.05, sd = 0.015),2, 2)
rast <- rast(xy, crs="+proj=longlat +datum=WGS84")
ext(rast) <- c(-40.5,-40.45,-9.5,-9.45)
writeRaster(rast, file.path(wd, "B8.tif"),filetype = "GTiff", overwrite=TRUE)
mask <- as.polygons(rast)
writeVector(mask, file.path(getwd(),"mask.shp"), overwrite=TRUE)

# using "agriwater"
kc_s2(doy = 134, RG = 17.6, Ta = 27.9, a = 1.8, b = -0.008)

#Exiting temporary folder and returning to previous workspace
setwd(initial)