Method of comparison object / library

The principle of the method is very simple : once the spectrum of an unknown object is cleaned of instrumental effects, and spurious pixels or lines, it can be adjusted, order by order, pixel by pixel, against several reference spectra by a least square method. The reduced $\chi^2$ of the fit is taken as a measure of resemblance between the target spectrum and a reference spectrum. There are two steps for this : wavelength adjustment and signal amplitude adjustment.