Application of Advanced Very High Resolution Radiometer vegetation index to study atmosphere‐biosphere exchange of CO₂

Normalized difference vegetation indices derived from radiances measured by the Advanced Very High Resolution Radiometer aboard the NOAA 7 polar‐orbiting satellite were used to prescribe the phasing of terrestrial photosynthesis. The satellite data were combined with field data on soil respiration and a global map of net primary productivity to obtain the seasonal exchange of CO 2 between the atmosphere and the terrestrial biosphere. The monthly fluxes of CO 2 thus obtained were employed as source/sink functions in a global three‐dimensional atmospheric tracer transport model to simulate the annual oscillations of CO 2 in the atmosphere. Reasonable agreement was found between the simulated and observed annual cycles of atmospheric CO 2 at the locations of the remote monitoring stations. The results demonstrate that satellite data of high spatial and temporal resolution can be used to provide quantitative information about seasonal and longer‐term variations of photosynthetic activity on a global scale. Atmospheric CO 2 observations and a three‐dimensional atmospheric model have been used to validate the translation of the nondimensional satellite data into dimensional carbon fluxes. Direct calibration will require extensive ground truth and field measurements at ecosystem scales.