Vegetation Monitoring
Indices Explained
Vegetation Index Monitoring computes 11 indices for every clear-sky date over a field, each capturing a different angle on crop and soil condition. Most people start with NDVI and bring in others as specific questions come up.
Which index for which question
| Question | Best index | Backup |
|---|---|---|
| How is overall crop vigor? | NDVI | EVI |
| Is canopy nitrogen low? | NDRE | GNDVI |
| Is the field water-stressed? | NDMI | MSI |
| Has dense canopy plateaued (NDVI saturating)? | EVI | NIRv |
| Is the crop establishing well early-season? | MSAVI | OSAVI |
| Is bare soil exposed where it shouldn't be? | BSI | NDSI |
| How much active photosynthesis is happening? | NIRv | NDVI |
| Is moisture stress severe? | MSI | NDMI |
| Is part of the field unusually dry or bright? | NDSI | BSI |
NDVI: Normalized Difference Vegetation Index
What it measures. General vegetation density and vigor — the most widely used vegetation index.
Bands used. Near-infrared and red.
When to use it. As the default starting view, to answer "is my field doing what it should be doing right now?" Compare against the same date last year on the trend chart to see if you're ahead of or behind schedule.
What good looks like. Healthy, dense vegetation pushes well above 0.5. Marginal sits 0.3–0.5. Below 0.3 signals stressed crop, sparse cover, or bare soil.
Caveat. Saturates on dense canopies — once fully established, NDVI can sit near its ceiling and stop differentiating "healthy" from "very healthy." Switch to EVI or NIRv when that happens.
NDRE: Normalized Difference Red Edge
What it measures. Nitrogen and chlorophyll content in the canopy.
Bands used. Near-infrared and red-edge — the red-edge band is especially sensitive to chlorophyll, closely linked to nitrogen status.
When to use it. Mid-season, once canopy has closed, to check whether a nitrogen program is keeping up. If NDVI looks fine but NDRE is dropping, a deficiency may be developing before it's visible.
What good looks like. Above 0.35 is healthy, 0.2–0.35 marginal, below 0.2 stressed.
Caveat. Most useful once canopy has formed — early-season values are dominated by soil signal and can mislead.
NDMI: Normalized Difference Moisture Index
What it measures. Water content in the canopy.
Bands used. Near-infrared and short-wave infrared (SWIR) — SWIR is absorbed by leaf water, so dry canopies read lower.
When to use it. During dry stretches, around irrigation events, or when water stress is suspected — it typically reacts before the crop looks visibly stressed.
What good looks like. Above 0.1 is well-watered, -0.1 to 0.1 marginal, below -0.1 signals stress.
Caveat. Also influenced by canopy density, not just moisture — on sparse canopy, low NDMI may just mean little vegetation. Cross-check with NDVI.
EVI: Enhanced Vegetation Index
What it measures. Vigor in dense canopies, with reduced influence from atmosphere and soil background.
Bands used. Near-infrared, red, and blue.
When to use it. When NDVI is plateauing on a fully developed canopy — EVI keeps responding where NDVI flattens.
What good looks like. Above 0.4 is healthy dense canopy, 0.2–0.4 marginal, below 0.2 stressed or sparse.
Caveat. Uses three bands, so it's more sensitive to atmospheric conditions than simpler indices — most useful mid- to late-season.
MSAVI: Modified Soil Adjusted Vegetation Index
What it measures. Vegetation cover where bare soil is still visible between plants.
Bands used. Near-infrared and red.
When to use it. Early season, before canopy closure — it suppresses soil background better than NDVI, giving a more reliable read on establishment.
What good looks like. Above 0.3 is good early cover, 0.1–0.3 marginal, below 0.1 poor establishment or mostly bare soil.
Caveat. Converges with other vegetation indices once canopy closes — switch to NDVI, EVI, or NDRE for mid- and late-season monitoring.
BSI: Bare Soil Index
What it measures. How much bare soil is exposed.
Bands used. SWIR, red, near-infrared, and blue.
When to use it. To check for soil exposed where it should be covered — establishment gaps, post-harvest residue cover, erosion-prone areas, cover-crop monitoring.
What good looks like. Lower is better: below 0 is well-vegetated, 0–0.2 partial exposure, above 0.2 significant bare soil.
Caveat. Reversed compared to NDVI — high values are bad. The dashboard's colour scale is flipped accordingly.
GNDVI: Green Normalized Difference Vegetation Index
What it measures. Chlorophyll concentration and nitrogen uptake, using the green band.
Bands used. Near-infrared and green.
When to use it. As a complement to NDRE for tracking nitrogen, especially in crops with strong green pigmentation — some growers find it more responsive than NDRE for specific crops.
What good looks like. Above 0.45 is healthy, 0.25–0.45 marginal, below 0.25 stressed.
Caveat. Can saturate on very dense canopies, like NDVI.
MSI: Moisture Stress Index
What it measures. Severity of water stress.
Bands used. SWIR and near-infrared.
When to use it. Alongside NDMI when checking water status — MSI emphasizes severity, NDMI emphasizes presence.
What good looks like. Lower is better: below 0.8 healthy, 0.8–1.2 marginal, above 1.2 stressed.
Caveat. Reverse-scaled like BSI — high MSI is bad, and the dashboard flips the colour scale accordingly.
NIRv: Near-Infrared Reflectance of Vegetation
What it measures. Active photosynthetic output.
Bands used. Near-infrared, scaled by NDVI.
When to use it. When you want a read on how much the canopy is actually photosynthesizing, not just how much canopy is present — useful for productivity comparisons across seasons.
What good looks like. Above 0.4 is healthy, 0.2–0.4 marginal, below 0.2 stressed.
Caveat. A research-leaning index — most growers won't need it as a primary view, but it adds depth comparing two visually similar canopies.
NDSI: Normalized Difference Snow / Soil Index
What it measures. Surface dryness and exposure of bright soil. Originally built for snow detection, it also responds to dry, bright bare soil.
Bands used. Green and SWIR.
When to use it. In dry seasons or post-harvest, to spot areas that are unusually dry or exposed — combine with BSI for a fuller soil-condition picture.
What good looks like. Lower is better: below 0 healthy/vegetated, 0–0.2 marginal, above 0.2 dry/bright surface.
Caveat. Reverse-scaled — in agricultural use it's read as a soil-exposure/dryness signal rather than literal snow.
OSAVI: Optimized Soil Adjusted Vegetation Index
What it measures. Vegetation cover with reduced soil-background influence, optimized for partial-cover situations.
Bands used. Near-infrared and red.
When to use it. When canopy is partial and a soil-corrected reading is needed — sits between NDVI and MSAVI in soil correction, often preferred in row crops where row spacing shows soil all season.
What good looks like. Above 0.4 is healthy, 0.2–0.4 marginal, below 0.2 stressed.
Caveat. Behaves similarly to NDVI on closed canopies; its value is highest on partial canopies.
Threshold reference
The exact cut-offs the dashboard uses to classify each pixel as healthy, marginal, or stressed. Indices marked "reversed" treat low values as healthy.
| Index | Healthy | Marginal | Stressed |
|---|---|---|---|
| NDVI | > 0.5 | 0.3 – 0.5 | < 0.3 |
| NDRE | > 0.35 | 0.2 – 0.35 | < 0.2 |
| NDMI | > 0.1 | -0.1 – 0.1 | < -0.1 |
| EVI | > 0.4 | 0.2 – 0.4 | < 0.2 |
| MSAVI | > 0.3 | 0.1 – 0.3 | < 0.1 |
| BSI (reversed) | < 0.0 | 0.0 – 0.2 | > 0.2 |
| GNDVI | > 0.45 | 0.25 – 0.45 | < 0.25 |
| MSI (reversed) | < 0.8 | 0.8 – 1.2 | > 1.2 |
| NIRv | > 0.4 | 0.2 – 0.4 | < 0.2 |
| NDSI (reversed) | < 0.0 | 0.0 – 0.2 | > 0.2 |
| OSAVI | > 0.4 | 0.2 – 0.4 | < 0.2 |
A note on cross-checking indices
No single index gives the full picture. A common pattern in practice:
- Start with NDVI to spot anomalies.
- If NDVI flags an issue, check NDRE or GNDVI to see if it's nitrogen-related.
- Check NDMI or MSI to see if it's water-related.
- Check BSI or NDSI to see if it's bare soil.
- Use the trend chart to see whether the issue is acute or developing.
- Use AI Interpretation for a synthesized read across all indices.
For the workflow of using these indices in the dashboard, see Getting started.