Table 3.
Determination accuracies of Cr concentrations based on Vis–NIR spectral bands.
| Preprocessing | PLSR | PCR | SVMR | |||
|---|---|---|---|---|---|---|
| RMSE | R2 | RMSE | R2 | RMSE | R2 | |
| SG + CR | 3.3 | 0.19 | 3.61 | 0.04 | 2.73 | 0.55 |
| SG + CR + NOR | 3.3 | 0.2 | 3.67 | 0.002 | 3 | 0.47 |
| SG + CR + MSC | 3.3 | 0.2 | 3.61 | 0.04 | 2.73 | 0.55 |
| SG + CR + SNV | 3.3 | 0.19 | 3.61 | 0.04 | 2.73 | 0.55 |
| SG + CR + FD | 1.25 | 0.88 | 3.5 | 0.09 | 2.44 | 0.71 |
| SG + CR + NOR + FD | 3.03 | 0.32 | 3.67 | 0.004 | 2.49 | 0.72 |
| SG + CR + MSC + FD | 1.17 | 0.9 | 3.68 | 0.0002 | 2.41 | 0.76 |
| SG + CR + SNV + FD | 0.25 | 0.99 | 3.68 | 0.002 | 2.28 | 0.8 |
| SG + CR + SD | 0.45 | 0.98 | 3.36 | 0.16 | 2.19 | 0.82 |
| SG + CR + NOR + SD | 1.64 | 0.8 | 3.31 | 0.19 | 2.33 | 0.77 |
| SG + CR + MSC + SD | 0.34 | 0.99 | 3.43 | 0.13 | 2.28 | 0.78 |
| SG + CR + SNV + SD | 2.76 | 0.44 | 3.42 | 0.13 | 2.15 | 0.84 |
| SG + CR + LOG | 3.3 | 0.19 | 3.52 | 0.08 | 2.73 | 0.55 |
| SG + CR + NOR + LOG | 1.09 | 0.91 | 3.67 | 0.006 | 2.9 | 0.62 |
| SG + CR + MSC + LOG | 3.3 | 0.19 | 3.59 | 0.04 | 2.72 | 0.56 |
| SG + CR + SNV + LOG | 1.43 | 0.85 | 3.67 | 0.001 | 2.22 | 0.82 |
PLSR: partial least squares regression, PCR: principal component regression, SVMR: support vector machine regression, RMSE: root-mean-square error, R2: coefficient of determination, SG: Savitzky–Golay, CR: continuum-removal, NOR: normalization, MSC: multiplicative scatter correction, SNV: standard normal variate, FD: first derivative, SD: second derivative, LOG: reciprocal logarithm.