Four-channel sensors for continuous remote sensing of carbon exchenge

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A mechanistic understanding of the biophysical controls on carbon exchange necessitates a study of how intra- and inter-annual climate trends affect surface-atmosphere exchanges. The proposed research will quantify the dynamics of net ecosystem exchange of carbon dioxide between a boreal ecosystem and the atmosphere. Light use efficiency (LUE) will be derived from tower-based measurements of absorbed photosynthetically active radiation and gross ecosystem productivity. The influence of environmental controls on the variation in LUE at each site will be investigated using the set of micrometeorological and biophysical variables. Remotely sensed vegetation indices have been shown to be correlated with LUE at a variety of spatial scales. Upscaling of fluxes will therefore be accomplished using a combination of remote sensing techniques. Tower-mounted radiometers will be used to provide high resolution continuous measurements of vegetation indices. Relationships between vegetation indices and tower-based fluxes will be developed from these field measurements. Ground based algorithms will be applied to comparable satellite-based indices resulting in ecosystem scale estimates of carbon exchange. The research is designed to provide increased knowledge of the critical processes and environmental forcings which drive the atmosphere ecosystem exchange on time scales ranging from instantaneous, seasonal, annual through inter-annual. The sensors requested here therefore represent a means to continuously measure vegetation indices by mounting portable sensors on the flux tower at a height such that the spatial area is comparable to that of the flux footprint. By incorporating pairs of downwelling and upwelling sensors, continuous measurements of the vegetation indices can be made and averaged to the same time step as the CO2 flux data.