Normalised Difference Red Edge (NDRE) is a method of determining crop health by using the Red Edge part of the spectrum to detect changes in chlorophyll content within the leaf and through the plant canopy.
NDRE provides a more accurate solution for measuring biomass and variations in mid to late season, high biomass crops (including sugar cane), and permanent tree crops, compared to NDVI (Normalised Difference Vegetation Index) as it is able to identify variability where NDVI would often become saturated.
Read more about NDVI, NDRE and MSAVI: