Table 1.
Successive projections algorithm based on multiple linear regression (SPA-MLR) algorithm variable number and wavelength.
| Soil Type | Temperature | Variable Number | Wavelength (nm) |
|---|---|---|---|
| Loess | 50 °C | 15 | 915, 1428, 1695, 1694, 1693, 1692, 1487, 1550, 1683, 1676, 1673, 1675, 1686, 1582, 1650 |
| 80 °C | 7 | 1160, 1660, 1582, 1682, 1675, 1489,1428 | |
| 95 °C | 4 | 1160, 1428, 1675, 1486 | |
| 25 °C | 4 | 1424, 1488, 1694, 1428 | |
| Calcium soil | 50 °C | 10 | 1651, 1154, 1438, 910,1301, 979, 1450, 1675, 1246, 1677 |
| 80 °C | 7 | 1651, 1675, 1678, 979, 1677, 1058, 1244 | |
| 95 °C | 7 | 1552, 1675, 1487, 1491, 1673, 921, 1650 | |
| 25 °C | 5 | 1651, 1675, 1146, 979, 1167 | |
| Black soil | 50 °C | 5 | 1423, 928, 1654, 1496, 1694 |
| 80 °C | 10 | 928, 1654, 1681, 1682, 1694, 1496, 1423, 915, 1684, 1662 | |
| 95 °C | 18 | 1650, 1680, 1682, 1694, 915, 1684, 1050, 1429, 1491, 1662, 928, 925, 910, 916, 918, 1662, 1675, 1690 | |
| 25 °C | 5 | 1423, 925, 1681, 1496, 1694 |