Quadratic trendlines

In the last post, I talk about the use of the function "detrend" in the package "prospectr" to remove the quadratic trend lines in the soil NIR spectra. We can see these trendlines overplotted to the spectra (I do it just for five of the soil spectra from the Spanish soil LUCAS database).

In red is the spectra treated with SNV and in blue the quadratic trend lines to apply to the SNV treated spectra, to remove them and convert them in a SNV + Detrend spectra.