Fig. 1. The reflectance spectrum curves of samples

Fig. 2. The contribution rate of the first 10 principal components

Fig. 3. The structure of ELM

Fig. 4. The structure of MELM

Fig. 5. The flow chart of the model

Fig. 6. The flow chart of the model

Fig. 7. The graph of salt content

Fig. 8. The different data of reflectance spectroscopy corresponds to the different salt content

Fig. 9. Iteration of the model

Fig. 10. The accuracy in the case of random value

Fig. 11. The operation time comparison chart

Fig. 12. The comparison of accuracy with two hidden layers