Multispectral Sensors:
Beyond Visible Light
Capturing the invisible spectrum to decode plant stress parameters and chlorophyll density.
The Mechanics of Spectral Reflectance
Healthy plants contain high levels of chlorophyll, which absorbs visible red light and heavily reflects near-infrared (NIR) light. As a plant becomes stressed by disease, drought, or nutrient deficiency, this reflective signature alters predictably—long before the plant visibly yellows or wilts.
Multispectral sensors isolate distinct light bands (Blue, Green, Red, Red Edge, and NIR) to measure these reflectance variations precisely.
Normalized Difference Vegetation Index (NDVI)
The standard mathematical metric for crop health is NDVI. Calculated using the formula `(NIR - Red) / (NIR + Red)`, it yields a value between -1 and +1.
- 0.6 to 1.0: Dense, vigorously healthy vegetation.
- 0.2 to 0.5: Sparse or stressed vegetation.
- 0 or below: Water, bare soil, or dead infrastructure.
By mapping NDVI across thousands of hectares, farm managers can pinpoint exactly where to deploy nitrogen inputs or investigate irrigation failures.
Thermal Mapping (LWIR)
Beyond reflectance, advanced payloads integrate Long-Wave Infrared (LWIR) thermal sensors. By mapping temperature differentials across a field, thermal imaging identifies moisture stress and faulty irrigation lines.
A plant experiencing drought stress closes its stomata to conserve water, halting transpiration. This causes the plant's surface temperature to rise measurably compared to fully hydrated, actively transpiring crops.
| Spectral Band | Wavelength (nm) | Primary Agronomic Indicator |
|---|---|---|
| Blue | 475 | Atmospheric scattering correction |
| Green | 560 | Reflectance peak (visual plant vitality) |
| Red | 668 | Chlorophyll absorption (photosynthesis) |
| Red Edge | 717 | Early stress detection, nitrogen content |
| Near-Infrared (NIR) | 842 | Biomass, canopy density, cellular structure |