Table 2.
The optimal wavelengths selected by the PCA loadings, second derivative spectra, successive projections algorithm (SPA), and competitive adaptive reweighted sampling (CARS) for the three sample sets.
| Sample | Methods | No. * | Wavelengths (nm) |
|---|---|---|---|
| Set 1 | Second derivative | 7 | 636, 649, 676, 696, 710, 732, 764 |
| PCA loading | 5 | 553, 657, 714, 723, 924 | |
| SPA | 14 | 668, 673, 550, 570, 681, 831, 521, 770, 663, 690, 932, 638, 650, 511 | |
| CARS | 16 | 550, 554, 559, 580, 589, 621, 628, 643, 663, 664, 852, 871, 901, 916, 945, 950 | |
| Set 2 | Second derivative | 12 | 533, 560, 608, 636, 650, 668, 674, 693, 707, 734, 764, 773 |
| PCA loading | 6 | 557, 673, 707, 714, 739, 770 | |
| SPA | 5 | 730, 782, 702, 558, 950 | |
| CARS | 16 | 629, 634, 636, 649, 762, 771, 798, 828, 837, 870, 875, 900, 908, 926, 940, 950 | |
| Set 3 | Second derivative | 13 | 533, 562, 609, 636, 650, 658, 667, 674, 693, 710, 737, 765, 771 |
| PCA loading | 5 | 557, 633, 705, 716, 747 | |
| SPA | 16 | 813, 833, 896, 767, 867, 507, 908, 513, 930, 535, 501, 743, 557, 696, 649, 707 | |
| CARS | 9 | 558, 564, 571, 604, 657, 662, 766, 809, 833 |
* No. refers to the number.