Assimilation of the SMOS Soil Moisture Product into a Model of the Global Terrestrial Biosphere
Scholze, Marko¹; Grant, Jennifer¹; Kaminski, Thomas²; Knorr, Wolfgang¹; Vossbeck, Michael^2
1Lund University, SWEDEN; ²FastOpt GmbH, GERMANY

Carbon dioxide (CO₂) is the most important anthropogenic greenhouse gas contributing to about half of the total anthropogenic change in the Earth's radiation budget. And about half of the anthropogenic CO₂ emissions stay in the atmosphere, the remainder is taken up by the land and ocean. It is of paramount importance to understand CO₂ sources and sinks and their spatio-temporal distribution. In the context of climate change this information is needed to improve the projections of future trends in carbon sinks and sources. SMOS-NEE (http://smos.CCDAS.org) is a research project funded by ESA. It aims at investigating the benefit of assimilating remotely sensed soil moisture into a process-based model of the terrestrial carbon cycle to constrain CO₂ exchange fluxes. The soil moisture observations are derived from the Soil Moisture Ocean Salinity (SMOS) mission. We will employ the Carbon Cycle Data Assimilation Systems (CCDAS) to constrain the process parameters in the Biosphere Energy Transfer HYdrology Scheme (BETHY) by applying the SMOS soil moisture observations in a mathematically rigorous way together with prior information. The calibrated model will then deliver constrained CO₂ exchange fluxes, which will be validated against independent observations of the carbon cycle. In addition, in the modelling process chain the observations are used to reduce uncertainties in the values of BETHY's process parameters, and then the uncertainty in the process parameters is mapped forward to uncertainties in the net carbon fluxes. We outline the study concept and will show first results at site scale.