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The integration of in situ and satellite measurements at ECMWF will be made
by using assimilation techniques in global land surface models. ONC will collect
the remote sensing products provided by the geoland “Biogeophysical Parameters”
core service and the atmospheric forcing provided by ECMWF. In order to integrate
the existing approaches and to deliver an assessment based on independent modelling
results, two land surface models will be used: 1) the operational scheme TESSEL
used in the ECMWF numerical weather forecast model, modified to describe an
interactive vegetation (based on ISBA-A-gs, Météo-France); 2)
a carbon-water-energy land surface scheme, fitted with carbon dynamics in biomass
and soil pools, and with ecosystem dynamics (LSCE). The assimilation system
will then be run at the global scale with both carbon models. The assimilated
output fields will be checked against global observations of different nature,
such as eddy covariance networks, long term ecological time series, forest and
soil carbon inventories, or satellite products that were not used at first in
the assimilation procedure. The spatial resolution considered in this project
is about 1/2 degree. At this rather coarse spatial resolution, few homogeneous
grid-cells are observed. A solution is to account for the sub-cell heterogeneity
by simulating distinct water and energy budgets in the same grid-cell for the
main surface types which are likely to be found (for example bare soil, forests,
crops or grasslands). This tiling strategy will be also applied to the remote
sensing data which will be aggregated for each tile. The end-product of the
system will be a near real-time analysis of biospheric CO2 fluxes, released
by ECMWF every 3 or 6 months. The other products of the service will consist
of water and energy fluxes, biomass and soil moisture estimates which are fully
compatible with CO2 exchange.
ONC products
The vegetation-atmosphere CO2 exchange depends on many biophysical factors.
In particular, the leaf area index, the above-ground biomass, the soil carbon
storage, the soil water content and the surface water flux, condition the CO2
flux. All these quantities will be produced at the same time by the physically-based
model used by ONC. Constraining the vegetation biomass and the soil water content
by using remote sensing products will permit to consolidate the estimation of
the CO2 flux.
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