NDRE (Normalized Difference Red Edge Index)
Definition
The Normalized Difference Red Edge Index (NDRE) is a vegetation index that utilizes the red edge band—the region of sharp increase in vegetation reflectance between the red and near-infrared portions of the electromagnetic spectrum (approximately 700-750 nm). It is particularly sensitive to chlorophyll content in moderate to dense canopies.
Application
NDRE is crucial for assessing crop nitrogen status, monitoring plant stress, and estimating chlorophyll content in mid- to late-season crops when canopies are dense. It is extensively used in precision agriculture for guiding in-season nitrogen management in crops like corn, wheat, and rice, where it can penetrate deeper into the canopy than NDVI.
FAQ
What is the formula for NDRE?
NDRE is calculated as: NDRE = (NIR - RedEdge) / (NIR + RedEdge), where RedEdge is the reflectance in the red edge band (typically around 730-740 nm) and NIR is the near-infrared reflectance. Some variations use specific red edge bands depending on the sensor.
Why is NDRE better than NDVI for mid- to late-season crops?
NDRE is superior in dense canopies because:
1) The red edge band penetrates deeper into the canopy than the red band used in NDVI;
2) It is less prone to saturation under high leaf area index conditions;
3) It maintains sensitivity to chlorophyll content even when canopies are fully developed, whereas NDVI often saturates.
What types of sensors can provide NDRE data?
NDRE requires sensors with a dedicated red edge band. These include:
1) Specialized agricultural multispectral sensors (e.g., MicaSense RedEdge, Parrot Sequoia);
2) Some high-resolution satellite sensors (e.g., WorldView-2/3, Sentinel-2 MSI);
3) Certain hyperspectral sensors. Standard RGB or NIR-only sensors cannot calculate NDRE.
What are the main applications of NDRE in agriculture?
Primary applications include:
1) In-season nitrogen management and variable-rate fertilization;
2) Assessment of crop health and early stress detection;
3) Yield prediction and estimation of crop biomass;
4) Monitoring of chlorophyll content for quality assessment in specialty crops.
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