Radiation use efficiency estimation in Mediterranean forests using MODIS Photochemical Reflectance Index (PRI)

Abstract

Garbulsky,  M.  F.,  Peñuelas, J., Ourcival, J. M., Filella, I. (2008). Radiation use efficiency estimation in Mediterranean forests using MODIS Photochemical Reflectance Index (PRI). Ecosistemas 17(3):89-97.

Many of the current models to estimate gross primary productivity (GPP) of terrestrial ecosystems depend on the radiation use efficiency (RUE),  the  ratio  between  absorbed  CO2 and  absorbed  radiation.  A  methodology  for  estimating  the  RUE  from  satellite  data  would  make estimates of primary productivity independent of climate data so far used to estimate the RUE. This study showed that the Mediterranean forests  present  very  mild  seasonal  changes  in  their  vegetation  indices,  indicators  of  green  biomass  and,  by  contrast,  large  seasonal changes  in  absorbed  CO2.  The  Photochemical  Reflectance  Index  (PRI),  calculated  from  the  surface  reflectance  obtained  by  the  MODIS sensor, presented a high correlation with the seasonal variability of the RUE estimated at ecosystem scale with eddy covariance techniques at two Mediterranean forests, along five years. These results showed that it is possible to estimate the temporal variability of RUE using the PRI and to improve the estimates of carbon absorption. This conceptual and technological improvement avoids the need to make assumptions about changes in the EUR and its relation to climate controls.