Fig. 4
(a) Original spectrogram. (b) Comparison of spectral pre-processing. Spectrum acquired at point 10 (BaiYuKou). The blue line represents the original spectrum, the orange line represents the spectrum after SG smoothing, the red line represents the spectrum after SNV transformation based on the orange line, the green line represents the spectrum after MSC transformation based on the orange line; (c) Spectral derivative and logarithmic transformations. The spectral changes from top to bottom are first-order derivative, second-order derivative, third-order derivative, logarithmic first-order derivative, logarithmic second-order derivative, and logarithmic third-order derivative. All six spectral variations are based on preprocessed spectra at point 10.
