The normalized difference red edge index (NDRE) is a metric that can be used to analyse whether images obtained from multi-spectral image sensors contain healthy vegetation or not.^[1] It does this by measuring the amount of chlorophyll in a plant.^[2]

It is similar to Normalized Difference Vegetation Index (NDVI) but uses the ratio of Near-Infrared and the edge of Red as follows:^[3]

${\displaystyle {\mbox{NDRE}}={\frac {({\mbox{NIR}}-{\mbox{RE}})}{({\mbox{NIR}}+{\mbox{RE}})}}}$

The red edge is the part of the spectrum centered around 715 nm.

The Index will give a value between -1.0 to +1.0, with a higher value showing a healthy plant environment.^[3]

• Normalized difference water index

• IEE Explore website, Normalized Difference Red-Edge Estimation With Modified DiscoGAN Model, article by Hyeon-Beom Choi, Kwon-Hee Han and Jeongwook Seo (2006)
• Spectral Reflectance Changes Associated with Autumn Senescence of Aesculus hippocastanum L. and Acer platanoides L. Leaves. Spectral Features and Relation to Chlorophyll Estimation

• [2]
• Chlorophyll Absorption
• Barnes, T.R., Clarke, S.E. Richards et. al. 2000. Coincident Detection of Crop Water Stress, Nitrogen Status and Canopy Density using Ground-Based Multispectral Data. Proceedings of the Fifth International Conference on Precision Agriculture

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