Fig. 1. Architecture of the broad learning system

Fig. 2. Average spectral curves with standard deviation

Fig. 3. Visualization analysis
(a), (b), (c), (d): Spectral curves by using different preprocessing methods; (e), (f), (g), (h): Visualization using t-SNE

Fig. 4. Analysis of the importance of wavelength variables by RF

Fig. 5. Analysis of effective PC scores and loading
(a): PCA score plot of PC₁vs. PC₂; (b): Wavelength selection on PC₁ and PC₂ loading lines

Fig. 6. The 2D-COS spectrum of samples with different days of refrigeration
(a): Synchronous contourmap plot; (b): Autocorrelation peak intensity curve