Calculate Vegetation Index from Bottom of Atmosphere Image Bands

Use this function to prepare vegetation index from SAFE imagery when you have already downloaded Sentinel 2 image files in advance

Usage

calculate_vi(
  img_stk,
  redband = 4,
  greenband = 3,
  blueband = 2,
  nirband = 5,
  scale_factor = 2^15
)

Arguments

img_stk,

terra SpatRaster, multiband stack of images, already clipped to aoi

redband,

integer, number of red band

greenband,

integer, number of green band

blueband,

integer, number of blue band

nirband,

integer, number of NIR band

scale_factor,

numeric, scales Sentinel-2 15 bit values down to range (0,255) as expected for vegetation indices default 32768 (2^15)

Value

vi_rast, SpatRaster of vegetation index

Note

The scale_factor parameter reduces numeric range "digital number", (DN) of Sentinel-2 images from 15 bit integer to 8 bit. Vegetation indices such as SAVI expect values in the range (0, 255). This scale_factor produces values in that range. When using Landsat 8 images (DN already in range of (0, 255)) then set scale_factor to 255.

Examples

img_stk <- terra::rast(system.file("extdata", "BOA",
         "BOA_2023-01-20_T36RXV.tif", package = "rOPTRAM"))
vi <- calculate_vi(img_stk)