# Red edge

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Region of change in vegetation reflectance

A false-color image of South Florida as generated by data from [Landsat 5](/source/Landsat_5). Green represents the reflected near infrared light indicative of healthy vegetation.

**Red edge** refers to the region of rapid change in [reflectance](/source/Reflectance) of [vegetation](/source/Vegetation) in the [near infrared](/source/Near_infrared) range of the [electromagnetic spectrum](/source/Electromagnetic_spectrum). [Chlorophyll](/source/Chlorophyll) contained in vegetation absorbs most of the light in the visible part of the spectrum but becomes almost transparent at wavelengths greater than 700 [nm](/source/Nanometer). The cellular structure of the vegetation then causes this infrared light to be reflected because each [cell](/source/Cell_(biology)) acts something like an elementary [corner reflector](/source/Corner_reflector).[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia: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 during [photosynthesis](/source/Photosynthesis). For a more detailed explanation and a graph of the [photosynthetically active radiation](/source/Photosynthetically_active_radiation) (PAR) spectral region, see [Normalized difference vegetation index § Rationale](/source/Normalized_difference_vegetation_index#Rationale).

The phenomenon accounts for the brightness of foliage in [infrared photography](/source/Infrared_photography) and is extensively utilized in the form of so-called vegetation indices (e.g. [Normalized difference vegetation index](/source/Normalized_difference_vegetation_index)). It is used in [remote sensing](/source/Remote_sensing) to monitor plant activity, and it has been suggested that it could be useful to detect light-harvesting organisms on distant planets.[1]

## See also

- [Enhanced vegetation index](/source/Enhanced_vegetation_index) – Index for improving vegetation monitoring

- [Purple Earth hypothesis](/source/Purple_Earth_hypothesis) – Astrobiological hypothesis regarding early photosynthetic organisms

- [Vegetation Index](/source/Vegetation_Index)

## References

1. **[^](#cite_ref-1)** Seager, S.; Turner, E.L.; Schafer, J.; Ford, E.B. (2005). "Vegetation's Red Edge: A Possible Spectroscopic Biosignature of Extraterrestrial Plants". *Astrobiology*. **5** (3): 372–390. [arXiv](/source/ArXiv_(identifier)):[astro-ph/0503302](https://arxiv.org/abs/astro-ph/0503302). [Bibcode](/source/Bibcode_(identifier)):[2005AsBio...5..372S](https://ui.adsabs.harvard.edu/abs/2005AsBio...5..372S). [doi](/source/Doi_(identifier)):[10.1089/ast.2005.5.372](https://doi.org/10.1089%2Fast.2005.5.372). [PMID](/source/PMID_(identifier)) [15941381](https://pubmed.ncbi.nlm.nih.gov/15941381). [S2CID](/source/S2CID_(identifier)) [11589855](https://api.semanticscholar.org/CorpusID:11589855).

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