Fig. 1. Spectral pretreating
(a): Original spectra; (b): Smoothing+MSC

Fig. 2. Flowchart of data processing

Fig. 3. The flowchart of the ELM algorithm optimized with SOA

Fig. 4. Results of principal component analysis

Fig. 5. Preferred characteristic wavelength distribution

Fig. 6. Full spectroscopy and ELM detection results

Fig. 7. PCA+ELM detection results

Fig. 8. SPA+-ELM test results

Fig. 9. SPA+PSO-ELM test results

Fig. 10. SPA+SOA-ELM test results