Normalised Difference Vegetation Index (NDVI)
NDVI (Normalised Difference Vegetation Index) is calculated from measurements of electromagnetic radiation reflected from plant canopy surfaces.
NDVI is a standardised index use to measure the state of plant health. Leaf chlorophyll absorbs red light (approximately 680mm), and the cellular structure of the leaves strongly reflect near-infrared light, approximately 730mm. When the plant is water stressed or diseased the spongy layer deteriorates and the plant absorbs more of the near-infrared light (NIR), rather than reflecting it. By observing how NIR changes compared to red light provides an accurate indication of the presence of chlorophyll, which correlates with plant health.