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Part 7. Global optimization: how to combine multiple data streams?
At LSCE we also have implemented a global Carbon Cycle Data Assimilation System (CCDAS), which uses many of the different data streams that we've already looked at, plus atmospheric CO2 concentration data from flask measurements around the globe. For this data stream we need to couple the ORCHIDEE model to an atmospheric transport model (LMDz) which transports the net surface CO2 fluxes in the atmosphere, in order to compare to the atmospheric concentration measurements at each station. Figure 7 shows a schematic of the overall CCDAS.
In the first version of the CCDAS we simultaneously assimilate (i.e. all data streams in the same optimization) FluxNet data (as described in Part 4), satellite-derived MODIS NDVI data and the atmospheric CO2 concentrations. The NDVI data are used to constrain the leaf phenology (leaf onset and senescence) at 15 sites per deciduous PFT across the globe.
Figure 8 shows the results when optimizing just with atmospheric [CO2] data, then with both atmospheric [CO2] and MODIS NDVI data, and then with all three datastreams (including FluxNet).
Take a look and closely compare the figure and then answer the questions below.
Reichstein, M., Falge, E., Baldocchi, D., Papale, D., Aubinet, A., Berbigier, P., Bernhofer, C., Buchmann, N., Gilmanov, T., Granier, A., Grünwald, T., Havránková, K., Ilvesniemi, H., Janous, D., Knohl, A., Laurila, T., Lohila, A., Loustau, D., Matteucci, G., Meyers, T., Miglietta, F., Ourcival, J.-M., Pumpanen, J., Rambal, S., Rotenberg, E., Sanz, M., Tenhunen, J., Seufert, G., Vaccari, F., Vesala, T., Yakir, D., and Valentini, R. (2005). On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm. Global Change Biol., 11, 1424-1439.
|← Part 6. Potential of atmospheric data to optimize model parameters||Part 8. Flux versus parameter optimisation using atmospheric CO2 →|