Fig. 1. Correlation analysis between different spectral transformations and Cd content

Fig. 2. Flow chart of CARS-GA band selection

Fig. 3. Key variables selected by CARS method. (a) Change in number of waveband variables; (b) variation of RMSECV

Fig. 4. RMSECV changes with the number of iterations

Fig. 5. Comparison of PLSR model results based on different band selection methods. (a) Comparison chart of R²; (b) comparison chart of RMSE; (c)^{comparison chart of number of characteristic bands}

Fig. 6. Scatter diagram of model verification under transformed spectra by SNV. (a) CC-PLSR; (b) CARS-PLSR; (c) CARS-GA-PLSR

Fig. 7. Scatter diagram of model verification under transformed spectra by FD. (a) CC-PLSR; (b) CARS-PLSR; (c) CARS-GA-PLSR

Fig. 8. Importance diagram of characteristic bands of Cd element

Fig. 9. Distribution map of Cd content in bare area of Tongguan County