Red edge refers to the region of rapid change inreflectance ofvegetation in thenear infrared range of theelectromagnetic spectrum.Chlorophyll contained in vegetation absorbs most of the light in the visible part of the spectrum but becomes almost transparent at wavelengths greater than 700nm. The cellular structure of the vegetation then causes this infrared light to be reflected because eachcell acts something like an elementarycorner reflector.[citation needed] The change can be from 5% to 50% reflectance going from 680 nm to 730 nm. This is an advantage to plants in avoiding overheating duringphotosynthesis. For a more detailed explanation and a graph of thephotosynthetically active radiation (PAR) spectral region, seeNormalized difference vegetation index § Rationale.
The phenomenon accounts for the brightness of foliage ininfrared photography and is extensively utilized in the form of so-called vegetation indices (e.g.Normalized difference vegetation index). It is used inremote sensing to monitor plant activity, and it has been suggested that it could be useful to detect light-harvesting organisms on distant planets.[1]
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