What NDVI Measures
NDVI (Normalized Difference Vegetation Index) is calculated as (NIR − Red) / (NIR + Red). Healthy leaves absorb red light for photosynthesis and strongly reflect near-infrared, so a high NDVI means vigorous, dense vegetation. It has been the standard since 1970s satellite remote sensing and remains the most widely understood index in precision agriculture.
Typical values: bare soil reads 0.1–0.2, stressed or sparse crop 0.2–0.5, and healthy vigorous crop 0.6–0.9. Because NDVI is normalized, maps from different dates are broadly comparable, which makes it excellent for early-season scouting, spotting emergence gaps, and delineating management zones. For the full family of indices beyond these two, see our vegetation indices guide.
What NDRE Measures
NDRE (Normalized Difference Red Edge) is calculated as (NIR − RedEdge) / (NIR + RedEdge). Instead of the visible red band, it uses the red edge — the narrow region between visible red and near-infrared where reflectance rises steeply. Red edge light penetrates deeper into the canopy and is sensitive to chlorophyll content within the leaves, not just canopy coverage.
This makes NDRE a stronger indicator of nitrogen status and mid-to-late-season crop health. Where NDVI reports "the canopy is dense," NDRE reports "the plants inside that dense canopy are healthy — or they are not." It requires a multispectral sensor with a dedicated red edge band, such as the DJI Mavic 3 Multispectral.
The Key Difference: Saturation
NDVI has one well-known weakness: saturation. Once a canopy closes — full corn at V8, a wheat field at heading, a healthy vineyard mid-season — NDVI flattens near its maximum. Every dense zone reads 0.85–0.9, so real differences in plant health disappear into a uniform block of dark green. The map looks great and tells you almost nothing.
NDRE does not saturate as quickly. Because red edge light responds to chlorophyll deeper in the canopy, NDRE keeps separating healthy from stressed plants long after NDVI has maxed out. This is the single most important reason to switch indices: on mature, dense crops, NDVI stops resolving variation and NDRE keeps going.
NDVI vs NDRE: When to Use Which
Use NDVI early in the season — emergence, establishment, and any time the canopy is open with visible soil between plants. NDVI excels at counting stands, finding replant zones, and mapping bare or sparse patches. It is also the right choice when you only need a broad vigor overview or need to compare against historical satellite NDVI.
Use NDRE from canopy closure onward — mid-to-late vegetative stages, nitrogen top-dressing decisions, and any dense crop where NDVI has saturated. NDRE is the better guide for variable-rate nitrogen because it tracks the chlorophyll status that nitrogen actually drives. A practical rule: if you can still see soil, NDVI; if the canopy has closed, NDRE. Many agronomists compute both from the same flight and switch based on growth stage.
You Do Not Have to Choose Just One
Both indices come from the same multispectral flight — NIR, red, and red edge bands are captured together, so there is no extra field work in producing both maps. The productive workflow is to generate NDVI and NDRE side by side, then read them together: NDVI confirms where the canopy is thin, NDRE reveals health differences where the canopy is thick.
In DroneField, both indices are computed automatically from a single multispectral survey, and either one can feed directly into a variable-rate prescription. Low-NDRE zones in a dense crop become higher nitrogen rates; thin-canopy zones flagged by NDVI become replant or scouting targets. The point is not to pick a winner but to use each index where it is strongest.