The Photochemical Reflectance Index (PRI) is a reflectance measurement developed by John Gamon during his tenure as a postdoctorate fellow supervised by

Christopher Field Christopher B. Field is an American scientist and researcher, who has contributed to the field of climate change. The author of more than 300 scientific publications, Field's research emphasizes impacts of climate change, from the molecular to t ...

at the Carnegie Institution for Science at Stanford University. The PRI is sensitive to changes in

carotenoid Carotenoids () are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, cana ...

pigments (e.g.

xanthophyll Xanthophylls (originally phylloxanthins) are yellow pigments that occur widely in nature and form one of two major divisions of the carotenoid group; the other division is formed by the carotenes. The name is from Greek: (), meaning "yellow", an ...

pigments) in live

foliage A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, f ...

. Carotenoid pigments are indicative of photosynthetic light use efficiency, or the rate of

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

uptake by foliage per unit energy absorbed. As such, it is used in studies of vegetation productivity and stress. Because the PRI measures plant responses to stress, it can be used to assess general

ecosystem health Ecosystem health is a metaphor used to describe the condition of an ecosystem.Rapport, David (1998). "Defining ecosystem health." Pages 18-33 in Rapport, D.J. (ed.) (1998). ''Ecosystem Health.'' Blackwell Scientific. Ecosystem condition can vary a ...

using satellite data or other forms of

remote sensing Remote sensing is the acquisition of information about an physical object, object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring inform ...

. Applications include vegetation health in evergreen

shrubland Shrubland, scrubland, scrub, brush, or bush is a plant community characterized by vegetation dominance (ecology), dominated by shrubs, often also including grasses, herbaceous plant, herbs, and geophytes. Shrubland may either occur naturally o ...

s, forests, and agricultural crops prior to

senescence Senescence () or biological aging is the gradual deterioration of Function (biology), functional characteristics in living organisms. Whole organism senescence involves an increase in mortality rate, death rates or a decrease in fecundity with ...

. PRI is defined by the following equation using reflectance (ρ) at 531 and 570 nm wavelength: :

PRI=\frac

Some authors use :

PRI=\frac

The values range from –1 to 1.

Sources

* ENVI Users Guide * John Gamon, Josep Penuelas, and

(1992). A narrow-waveband spectral index that tracks diurnal changes in photosynthetic efficiency. Remote Sensing of environment, 41, 35-44. * Drolet, G.G. Heummrich, K.F. Hall, F.G., Middleton, E.M., Black, T.A., Barr, A.G. and Margolis, H.A. (2005). A MODIS-derived photochemical reflectance index to detect inter-annual variations in the photosynthetic light-use efficiency of a boreal deciduous forest. Remote Sensing of environment, 98, 212-224. Biophysics Botany Remote sensing 1992 introductions {{remote-sensing-stub