Fig. 1. Schematic diagram of experimental procedure

Fig. 2. Fluorescence spectrum and microscopic image of algal solution. (a) Fluorescence spectrum; (b) microscopic image

Fig. 3. Structural similarity index of spectra corresponding to algal suspension with different cell density of spectral data under different embedding dimensions and delay times

Fig. 4. Correspondence of full-spectrum spectral transformations

Fig. 5. Comparison of the effect of traditional recursive graphs and no-threshold recursive graphs. (a) Traditional recursive graph of spectral sequence of algae suspension with different cell density; (b) no-threshold recursive graph of spectral sequence of algae suspension with different cell density

Fig. 6. Schematic diagram of 2D-BLS

Fig. 7. 2D-ENBLS module

Fig. 8. Weights and heat visualization map. (a)(d) Lasso regression; (b)(e) Ridge regression; (c)(f) Elastic Net regression

Fig. 9. Scatterplot of measured and predicted values. (a) CNN-BLS; (b) 2D-BLS; (c) bias plots of true values and predicted values for two models

Fig. 10. Model prediction effect diagram. (a) 2D-BLS; (b) 2D-L2BLS; (c) 2D-ENBLS; (d) bias plots of true values and predicted values for three models