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What is the NDRE index?
Like the Green Index (NDVI), the Normalized Difference Red Edge Index (NDRE) is useful for analyzing plant vigor in multispectral sensor images throughout the crop cycle.
The “red edge” light can penetrate the leaves much more deeply than the red light (used in NDVI), yielding values with less tendency to saturation and expressing variability better than NDVI in some stages, as it is sensitive to a broader range of crop chlorophyll concentration, nitrogen concentration, leaf area index and biomass.
When is it used?
Although it is possible to monitor the entire crop cycle with NDRE, it is especially recommended as a complement to NDVI in:
- late stages, high biomass density (lots of greenery or NDVI saturation).
- vegetative stage of grasses, especially corn, to plan nitrogen fertilizations.
In Farm 360 the NDRE index is presented with the same palette as the rest of the vegetation indices, starting with brown colors (lower index) and then going through a varied range of greens and expressing high index values in blue and violet tones.
The following image compares NDVI / NDRE in some fields. Both indexes allow identifying the increase in biomass, only that the NDVI tends to saturate at very high values, while the NDRE still allows identifying differences: