Diffuse sky radiation influences the relationship between canopy PRI and shadow fraction

Matti Mõttus (Corresponding Author), Tuure L.H. Takala, Pauline Stenberg, Yuri Knyazikhin, Bin Yang, Tiit Nilson

Research output: Contribution to journalArticleScientificpeer-review

38 Citations (Scopus)


The Photochemical Reflectance Index (PRI) of green leaves is an indicator of photosynthetic downregulation: when the photosynthetic apparatus is close to the saturation limit, PRI becomes dependent on light conditions. Therefore, by measuring the PRI of leaves under different local irradiance conditions, it should be possible to determine the saturation level of the leaves and obtain information on the light use efficiency (LUE) of a vegetation canopy. The dependence of PRI on the ratio of sunlit to shaded foliage (quantified by the canopy shadow fraction) in the field of view of an instrument has been used to remotely measure canopy LUE on clear days. However, besides photosynthetic downregulation, the dependence of canopy PRI on shadow fraction is affected by the blue sky radiation caused by scattering in the atmosphere. To quantify this effect on remotely sensed PRI, we present the underlying definitions relating leaf and canopy PRI and perform the required calculations for typical midsummer conditions in Central Finland. We demonstrate that the effect of blue sky radiation on the variation of PRI with canopy shadow fraction is similar in shape and magnitude to that of LUE variations reported in literature.
Original languageEnglish
Pages (from-to)54-60
JournalISPRS Journal of Photogrammetry and Remote Sensing
Publication statusPublished - 2015
MoE publication typeA1 Journal article-refereed


  • Vegetation
  • Hyper spectral
  • Atmosphere
  • Modelling
  • Geometric
  • Multiangular
  • Light use efficiency
  • Shadow fraction


Dive into the research topics of 'Diffuse sky radiation influences the relationship between canopy PRI and shadow fraction'. Together they form a unique fingerprint.

Cite this