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Indices Explained
Vegetation Index Monitoring computes 11 indices for every clear-sky date over your field. Each one captures a different aspect of crop and soil condition. You do not need to use all of them: most users start with NDVI and bring in others when they have a specific question.
This guide is structured for two ways of reading:
- If you want a quick decision shortcut, jump to Which index for which question.
- If you want per-index detail, read on. Each section explains what the index measures, when to use it, what good and bad look like, and a short note on caveats.
- The threshold reference table at the end gives the exact health classification cut-offs used in the dashboard.
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 should not 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 your default starting view. NDVI gives a quick answer to "is my field doing what it should be doing right now?". Compare a date to a previous year on the trend chart to see whether you are ahead of or behind schedule.
What good looks like. Healthy, dense vegetation pushes NDVI well above 0.5. Marginal vegetation sits between 0.3 and 0.5. Below 0.3 you are looking at stressed crop, very sparse cover, or bare soil.
Caveat. NDVI saturates on dense canopies. Once your crop is fully established, NDVI may sit near its ceiling and stop differentiating between "healthy" and "very healthy". Switch to EVI or NIRv when this 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, which is closely linked to nitrogen status.
When to use it. Mid-season, when the canopy has closed and you want to know whether your nitrogen program is keeping up. If NDVI looks fine but NDRE is dropping, you may be heading into a nitrogen deficiency before it shows up visually.
What good looks like. Above 0.35 is healthy. 0.2 to 0.35 is marginal. Below 0.2 is stressed.
Caveat. NDRE is most useful once the canopy has formed. Early-season values are dominated by soil signal and can be misleading.
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 show lower NDMI.
When to use it. During dry stretches, before and after irrigation events, or when you suspect water stress. NDMI typically reacts before the crop looks visibly stressed.
What good looks like. Above 0.1 indicates well-watered canopy. Between -0.1 and 0.1 is marginal. Below -0.1 indicates water stress.
Caveat. NDMI is influenced by canopy density as well as moisture. On a sparse canopy, low NDMI may reflect lack of vegetation rather than dry 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 to changes in dense vegetation where NDVI flattens out.
What good looks like. Above 0.4 is healthy dense canopy. 0.2 to 0.4 is marginal. Below 0.2 is stressed or sparse.
Caveat. EVI uses three bands and is more sensitive to atmospheric conditions than the simpler indices. It is most useful in mid- to late-season comparisons.
MSAVI: Modified Soil Adjusted Vegetation Index
What it measures. Vegetation cover in conditions where bare soil is still visible between plants.
Bands used. Near-infrared and red.
When to use it. Early in the season, before the canopy closes. MSAVI suppresses the soil background better than NDVI, so it is a more reliable read on early establishment.
What good looks like. Above 0.3 is good early cover. 0.1 to 0.3 is marginal. Below 0.1 is poor establishment or still mostly bare soil.
Caveat. Once the canopy closes, MSAVI converges with other vegetation indices. 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 whether soil is exposed where it should be covered, for example, gaps in establishment, post-harvest residue cover, or erosion-prone areas. Useful for cover crop monitoring.
What good looks like. Lower is better. Below 0 indicates well-vegetated ground. 0 to 0.2 is partial exposure. Above 0.2 indicates significant bare soil.
Caveat. BSI is interpreted in reverse compared to NDVI: high values are bad, not good. The dashboard color 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 status, especially in crops with strong green pigmentation. Some growers find GNDVI more responsive than NDRE in specific crops.
What good looks like. Above 0.45 is healthy. 0.25 to 0.45 is marginal. Below 0.25 is stressed.
Caveat. Like NDVI, GNDVI can saturate on very dense canopies.
MSI: Moisture Stress Index
What it measures. Severity of water stress.
Bands used. SWIR and near-infrared.
When to use it. In parallel with NDMI when checking water status. MSI emphasizes severity (a stressed canopy reads clearly higher) while NDMI emphasizes presence.
What good looks like. Lower is better. Below 0.8 is healthy. 0.8 to 1.2 is marginal. Above 1.2 is stressed.
Caveat. Reverse-scaled like BSI: high MSI is bad. The dashboard color scale is flipped 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 measure that tracks how much the canopy is actually photosynthesizing, not just how much canopy is there. Useful for productivity comparisons across seasons.
What good looks like. Above 0.4 is healthy. 0.2 to 0.4 is marginal. Below 0.2 is stressed.
Caveat. NIRv is a research-leaning index. Most growers will not need it as a primary view, but it adds depth when comparing two visually similar canopies.
NDSI: Normalized Difference Snow / Soil Index
What it measures. Surface dryness and exposure of bright soil. Originally designed for snow detection, the index also responds to dry, bright bare soil.
Bands used. Green and SWIR.
When to use it. In dry seasons or post-harvest, to detect areas where the surface is unusually dry or exposed. Combine with BSI for a fuller picture of soil condition.
What good looks like. Lower is better. Below 0 is healthy or vegetated. 0 to 0.2 is marginal. Above 0.2 indicates dry, bright surface.
Caveat. Reverse-scaled. In agricultural use, NDSI is interpreted 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 the canopy is partial and you want a soil-corrected reading. OSAVI sits between NDVI and MSAVI in terms of soil correction, and is often preferred in row-crop scenarios where row spacing leaves visible soil all season.
What good looks like. Above 0.4 is healthy. 0.2 to 0.4 is marginal. Below 0.2 is stressed.
Caveat. OSAVI behaves similarly to NDVI on closed canopies. Its value is highest on partial canopies.
Threshold reference
These are 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 to 0.5 | < 0.3 |
| NDRE | > 0.35 | 0.2 to 0.35 | < 0.2 |
| NDMI | > 0.1 | -0.1 to 0.1 | < -0.1 |
| EVI | > 0.4 | 0.2 to 0.4 | < 0.2 |
| MSAVI | > 0.3 | 0.1 to 0.3 | < 0.1 |
| BSI (reversed) | < 0.0 | 0.0 to 0.2 | > 0.2 |
| GNDVI | > 0.45 | 0.25 to 0.45 | < 0.25 |
| MSI (reversed) | < 0.8 | 0.8 to 1.2 | > 1.2 |
| NIRv | > 0.4 | 0.2 to 0.4 | < 0.2 |
| NDSI (reversed) | < 0.0 | 0.0 to 0.2 | > 0.2 |
| OSAVI | > 0.4 | 0.2 to 0.4 | < 0.2 |
A note on cross-checking indices
No single index gives you the full picture. The most common pattern in practice:
- Start with NDVI to spot anomalies.
- If NDVI flags an issue, check NDRE or GNDVI to see if it is nitrogen-related.
- Check NDMI or MSI to see if it is water-related.
- Check BSI or NDSI to see if it is bare soil.
- Use the trend chart to see whether the issue is acute or developing.
- Use the AI Interpretation for a synthesized read across all indices.
For the workflow of using these indices in the dashboard, see Getting started.