To correctly reconstruct the original fluxes, our proposed method utilises models of the intermediate spectra (see Eqs. (42) and (43)). Appropriate windows around the spectral lines must be set as one is interested in the continuum contribution only. The left panel shows the results for the simpler case using second-order polynomials that are able to describe the baseline. For the standing-wave case (right panel), a more complicated fitting model m(ν) had to be applied (see Eq. (44)).