Convert Nanometers to Wavenumbers

 All we know that the wavelength scale (X axis) is different for a dispersive NIR or a FTNIR. Sometimes, for some reasons we want to convert the wavelength scale of a NIR spectra database,  to the wavenumber scale or vice versa. 

In this case I apply with R the conversion of the NIRsoil$spc data (from the "prospectr" package) from nanometers :

to wavenumbers (cm-1)

We just have to apply the formula:

wn <- 1/(x*10^-7)

Where x is the value in "nm" of every element for the range of our NIR spectrum, in this case 1100 to 2498 with an interval of 2 nm.