Fig. 1. Original near infrared spectra of soil

Fig. 2. Preprocessed near infrared spectra of soil
(a): Preprocessed by MSC; (b): Preprocessed by SNV;(c): Preprocessed by first derivative; (d): Preprocessed by second derivative;(e): Preprocessed by smoothing

Fig. 3. The best training effects based on different algorithms
(a): S_G-BP model; (b): SNV-SVM model; (c): S_G-GP model

Fig. 4. The best prediction fitting effects based on different algorithms
(a): S_G-SVM model; (b): BP model; (c): MSC-GP model

Fig. 5. Comparison of prediction results
(a): Based on original data; (b): Based on MSC preprocessing;(c): Based on SNV preprocessing; (d): Based on first derivative preprocessing;(e): Based on the preprocessing of second derivative; (f): Based on smoothing preprocessing