The NDRE (Normalized Difference Red Edge Index) is used to measure the light waves (approximately the 715 nm range of the spectrum) that are collected from multispectral image sensors. The images are processed and analyzed to determine how healthy the target crop and field is. It is very similar to the NDVI vegetation index it simply uses light wavelengths from a different part of the spectrum. NDRE is sensitive to the amount of chlorophyll present, changes across the leaf’s surface, and how the soil is affecting the growth process of the crop. It’s formula is the ratio of NIR and RE (Red Edge):

NDRE = ( NIR – RE)/(NIR + RE)

Reference:

Wikipedia

PrecisionHawk’s Vegetation indices

(Last Edit 10 Feb 2023, Kellee)