Fig. 1. Surface states of four types of features. (a) Soybean; (b) corn; (c) rice; (d) bare soil

Fig. 2. Average reflectance spectral curves of four types of features in the range of 350-2500 nm

Fig. 3. Spectral curves of some samples of four types of features from 350-1800 nm (20 bars). (a) Soybean; (b) corn; (c) rice; (d) bare soil

Fig. 4. SPA feature band selection results. (a) RMSE; (b) average spectral reflectance

Fig. 5. Distribution of feature sample points. (a) 410 nm and 542 nm; (b) 410 nm and 714 nm; (c) 410 nm and 856 nm; (d) 410 nm and 1423 nm; (e) 410 nm and 1475 nm; (f) 410 nm and 1712 nm

Fig. 6. Structure diagrams. (a) 1DCNN; (b) 1DCNN-SPA

Fig. 7. 1DCNN model training results. (a) Loss; (b) classification accuracy

Fig. 8. 1DCNN-SPA model training results. (a) Loss; (b) classification accuracy

Fig. 9. LSTM architecture

Fig. 10. Structure diagrams. (a) LSTM; (b) LSTM-SPA

Fig. 11. LSTM model training results. (a) Loss; (b) classification accuracy

Fig. 12. LSTM-SPA model training results. (a) Loss; (b) classification accuracy

Fig. 13. Overall classification accuracy of different models with different wave sets

Fig. 14. Different model accuracy metrics

Fig. 15. Confusion matrix for different model classifications. (a) BP; (b) KNN; (c) 1DCNN; (d) LSTM

Fig. 16. BP Spectral curves. (a) Soybeans classified correctly, soybeans misclassified into corn samples; (b) corns classified correctly, soybeans misclassified into corn samples

Fig. 17. KNN Spectral curves. (a) Corns classified correctly, corns misclassified into soybean samples; (b) soybeans classified correctly, corns misclassified into soybean samples

Fig. 18. Comparison of soybean misclassification into corn samples at different stages of BP with correct soybean and corn classification samples.(a) Stage 1(16); (b) stage 2(11); (c) stage 3(6); (d) stage 4(5)

Fig. 19. Comparison of corn misclassification into soybean samples at different stages of KNN with correct corn and soybean classification samples(No change in the fourth stage).(a) Stage 1(8); (b) stage 2(6); (c) stage 3(3)

Fig. 20. Overall classification accuracy of soybean and corn for four methods under different stage feature band sets