FIGURE 4.

Preprocessing of Raman spectra. The raw Raman spectra, used for regression modeling, are shown over the recorded wavenumber range from yellow to red to visualize the different samples of all experiments (A). The black line represents one specific spectrum to better visualize the preprocessing effects. Preprocessing techniques, such as the baseline correction (C) and the SG filter, are applied to the spectra with a KS (B) or manual data split (D) to enhance spectral differences. The gray boxes in (C, D) depict the Raman shift ranges that are used for the PLS model development.