NDRE - Normalized Difference RedEdge

NDRE Normalized Difference Red Edge

Normalized difference red edge index (NDRE) is a method of measuring the amount of chlorophyll in the plants. The best timing to apply NDRE is mid-to-late growing season when the plants are mature and ready to be harvested. At this point, other indices would be less effective to use.

It is represented by a certain value calculated using a combination of a Near-InfraRed (NIR) band and the RedEdge range between visible Red and NIR

Generic Formula (R is the reflectance at the wavelengths (nm) denoted by the subscripts):

Formula by Sentinel-2 bands: 

Since chlorophyll is crucial to the process of photosynthesis, its quantity is an important indicator of the plant’s health. On EOSDA Crop Monitoring, we’re using a standard scale of -1 to 1 for the NDRE index. It’s important to know how to correctly interpret the values:

• -1 to 0.2 indicate bare soil or a developing crop;

• 0.2 to 0.6 can be interpreted as either an unhealthy plant or a crop that is not mature yet;

• 0.6 to 1 are good values indicating healthy, mature, ripening crops.

References:

• Zhang, K., Ge, X., Shen, P., Li, W., Liu, X., Cao, Q., ... & Tian, Y. (2019). Predicting rice grain yield based on dynamic changes in vegetation indexes during early to mid-growth stages. Remote sensing, 11(4), 387.