Compute the NDVI from spectral reflectance according to waveband definitions from standards or corresponding to satellite imagers.
Value
A numeric vector. When the wavelength range of spct
does not
fully overlap with both wavebands NA
is silently returned.
Details
NDVI is used in remote sensing to the diagnose the condition of vegetation, including crops. It is used for Landsat imagery but also at the farm or plot scale using cameras on drones. It is computed as:
NDVI = (NIR - Red) / (NIR + Red)
The waveband ranges used to compute reflectance vary. Even the imagers
in the different Landsat satellites 1 to 8 have had somehow different
wavelength sensitivities. The NDVI()
function uses the waveband
constructors Red
and NIR
defined in this
package. Reflectance is averaged over the wavebands using function
reflectance
.