Two of the most commonly requested agricultural deliverables on Vantagr are NDVI maps and NDRE maps. Clients often ask for both without fully understanding the difference — and pilots sometimes deliver the wrong one. This guide covers what each index measures, which sensor you need to acquire it, and which crops and conditions each is suited for.
What multispectral indices actually measure
Vegetation indices are mathematical combinations of reflected light at different wavelengths. Plants absorb strongly in the red band (670nm) and reflect strongly in the near-infrared (NIR, ~800nm) when photosynthetically active. Stressed or sparse vegetation shows lower NIR reflectance and higher red reflectance — and indices exploit this contrast to quantify plant health.
The key difference between NDVI and NDRE lies in which red band is used in the formula. NDRE substitutes the red-edge band (~720nm) for the standard red (~670nm), and that substitution changes everything about what the index can and can’t see in dense crop canopies.
NDVI: Normalised Difference Vegetation Index
Formula: (NIR − Red) / (NIR + Red)
NDVI ranges from −1 to +1, where values above 0.4 typically indicate healthy green vegetation. It is the most widely used vegetation index and the default deliverable for most agricultural drone surveys. NDVI correlates well with biomass and photosynthetic activity in sparse to moderate canopy conditions.
Where NDVI works best: Early-season crop monitoring when canopy cover is low (<60%), detecting bare soil or patchy emergence, grassland and rangeland biomass assessment, and any application where a broad green/not-green signal is sufficient.
Where NDVI breaks down: In dense, closed canopies — mature corn, wheat at heading, or thick alfalfa — the standard red band saturates. The canopy absorbs nearly all incident red light regardless of stress level, so the NDVI signal becomes insensitive to variation in the upper crop layer. You end up with a uniformly high NDVI image that masks the stress variation the client actually needs to see.
NDRE: Normalised Difference Red-Edge
Formula: (NIR − Red-Edge) / (NIR + Red-Edge)
The red-edge band (~717–740nm) sits between the chlorophyll absorption peak in the red and the NIR plateau. It is more sensitive to chlorophyll content than the standard red band and, critically, it is not saturated by dense canopies. The red-edge signal continues to vary with stress even when the canopy is fully closed.
Where NDRE works best: Mid-to-late season monitoring of dense crops (corn at V6+, wheat at heading, dense soybeans), nitrogen stress detection in high-biomass crops, chlorophyll content mapping, and any application where NDVI has already saturated.
Sensor requirements
This is where the practical constraint hits. Not all multispectral sensors capture a dedicated red-edge band, and the band placement matters for accurate NDRE computation.
| Sensor | Red-edge band | NDRE capable | Notes |
|---|---|---|---|
| DJI P4 Multispectral | 730nm | Yes | 5-band sensor. Most widely available on Vantagr. |
| DJI Mavic 3 Multispectral | 730nm | Yes | Consumer-grade but capable for most farm surveys. |
| Micasense RedEdge-P | 717nm | Yes | High accuracy, 5-band, PPK compatible. Best for research. |
| Micasense Altum-PT | 717nm | Yes | 5-band + thermal. Premium sensor for precision ag. |
| Parrot Sequoia | 735nm | Yes | Older system, still functional for moderate accuracy. |
| RGB camera (any) | None | No | Can compute VARI index but not true NDVI or NDRE. |
When commissioning a flight, specify which sensor the pilot is flying. “Multispectral capable” on a pilot profile doesn’t guarantee red-edge band availability. Filter by specific sensor models when NDRE is required.
Crop-specific recommendations
Wheat and cereal crops
Use NDVI during vegetative stages (tillering to jointing) when canopy cover is incomplete. Switch to NDRE from heading onward as the canopy closes and NDVI begins to saturate. Late-season NDRE maps correlate well with grain nitrogen concentration and can guide post-harvest soil management.
Corn / maize
NDRE strongly preferred from V6 onward. Corn canopy closes rapidly and NDVI saturates early in the season. NDRE maps at V8–V12 are the most actionable for identifying nitrogen-deficient zones before the window for side-dress application closes. Typical GSD: 3–5cm for field-scale prescriptions.
Soybeans
NDVI is adequate early season for stand establishment and emergence mapping. NDRE from R1 (beginning flowering) onward provides better sensitivity to iron deficiency chlorosis (IDC) and nitrogen stress. Soybean fields with visible yellowing that shows low NDVI will show even clearer NDRE contrast.
Viticulture (vineyards)
NDVI works well for vineyards due to row structure creating natural within-field variation visible to both indices. NDRE adds value in high-vigour blocks where NDVI saturates. Many vine nutrition prescriptions and variable-rate canopy management programmes use NDRE as the primary input.
Tree crops (orchards)
NDRE strongly preferred. Orchard canopies are optically thick, and NDVI frequently saturates over mature tree crops regardless of stress level. NDRE maps provide meaningful canopy health gradients for irrigation zoning and fertiliser management.
Other indices worth knowing
- ENDVI (Enhanced NDVI): includes blue band to reduce atmospheric scattering. More stable than NDVI for comparing flights across dates.
- VARI (Visible Atmospherically Resistant Index): computed from RGB only. Lower accuracy than multispectral but useful for rapid, low-cost surveys.
- SAVI (Soil Adjusted Vegetation Index): corrects for soil background, important early-season when bare soil is visible between rows.
- CIre (Red-Edge Chlorophyll Index): directly correlates with canopy chlorophyll content. More agronomically interpretable than NDRE in research contexts.
Calibration: the step pilots often skip
Multispectral sensors require a radiometric calibration panel image at the beginning and end of each flight. Without the panel, reflectance values cannot be computed — only radiance — and your images cannot be accurately compared to flights from different days, times, or atmospheric conditions. Panel calibration is non-negotiable for any agronomic application.
Which to specify when booking
When creating a mission on Vantagr, your deliverable specification drives pilot selection. If you need NDRE, specify it explicitly and filter for pilots with the appropriate sensor. The extra information ensures you’re matched with pilots who can actually deliver what you need — not just any pilot with “multispectral” on their profile.
As a rule of thumb: if the crop will have >70% canopy cover at flight time, request NDRE. If it’s an early-season stand assessment or a crop type with inherently open canopy structure, NDVI is sufficient and will save you money on sensor requirements.