Remote estimation of carbon dioxide uptake of terrestrial ecosystems

Abstract The estimation of the carbon balance in ecosystems, regions, and the biosphere is currently one of the main concerns in the study of the ecology of global change. Current remote sensing methodologies for estimating gross primary productivity are not satisfactory because they rely too heavily on (i) the availability of climatic data, (ii) the definition of land-use cover, and (iii) the assumptions of the effects of these two factors on the radiation-use efficiency of vegetation (RUE). A new methodology is urgently needed that will actually assess RUE and overcome the problems associated with the capture of fluctuations in carbon absorption in space and over time. Remote sensing techniques such as the widely used reflectance vegetation indices (e.g., NDVI, EVI) allow green plant biomass and therefore plant photosynthetic capacity to be assessed. Nevertheless, detecting how much of this capacity is actually realized is a much more challenging goal. The Photochemical Reflectance Index (PRI) derived from freely available satellite information (MODIS sensor) presented an exponential relationship with the RUE. Thus, we show that it is possible to estimate RUE in real time and therefore actual carbon uptake at ecosystem, regional, and biosphere levels using the PRI. This conceptual and technological advancement avoids the need to rely on either the sometimes unreliable maximum RUE for each ecosystem, hard-to-obtain climate data, or on imprecise land-use/land-cover data.