Impact of satellite based PAR on estimates of terrestrial net primary productivity

Biospheric productivity regulates the supply of food for mankind and therefore, there is a need to estimate its magnitude. The productivity is controlled by the process of photosynthesis driven by solar radiation, primarily in the visible part of the spectrum (0.4–0.7 μm), known as the photosynthetically active radiation (PAR). Current methods to estimate terrestrial net primary production (NPP) use remotely sensed information on vegetation dynamics. Satellite based estimates of PAR are available at a global scale but have seldom been used for estimating NPP. In this study we show that the use of PAR information from satellites does have an impact on estimates of NPP and that there are detectable differences when compared to similar estimates based on conventional PAR information. Net primary production tends to be higher when compared to estimates based on total shortwave (SW) radiation with PAR assumed to be a constant fraction of SW. We focus on the United States during 2004. Net primary production is generally underestimated in regions with mesic environment while overestimated in areas with xeric environment. The most pronounced underestimated region is the southeast United States. The study demonstrates the usefulness of the satellite-based estimates of PAR for modelling terrestrial primary productivity