The activities of LSCE about the inverse problem are at the crossroads between statistical modelling, physical modelling and measurement processing. The methodological expertise of the laboratory facilitates avariety of applications for the study of biogeochemical cycles, strengthened by numerous national and international collaborations. The sharing of numerictools allows it to reach a critical mass to develop complex systems, particularly for data assimilation, while also covering smaller scientific applications.
Within these activities, SATINV studies the processes that affect the composition of the atmosphere ingreenhouse gases and aerosols. For this, it develops and implements inverse methods to estimate the this composition and the variables of the underlying processes, such as sources and sinks of the species concerned at the Earth’s surface and in the atmosphere. More specifically, SATINV is mainly concerned with the three main gases of anthropogenic origin, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), with someprecursors of CO2 (CO, HCHO ), with molecular hydrogen (H2) and with aerosols. It assimilates direct measurements of the concentration of these species carried out by conventional instruments and indirect measurements made by remote sensing from space or ground. These studies cover the micro-scale (for the forest or the city), the regional scale (e.g., Europe) and the global one. With its expertise and tools SATINV contributes to the design and development of innovative observation systems, in particular for space agencies (space missions Microcarb, MERLIN, CarbonSat, etc.).
Since 2011, SATINV generates twice a year the official product of the European atmosphere monitoring service (www.copernicus-atmosphere.eu) for the inversion of the CO2 sources and sinks. This product covers all years from 1979 until last year homogeneously. For work on tracers at theglobal scale, like thisone, the team uses the general circulation model of the atmosphere LMDZ (http://lmdz.lmd.jussieu.fr/), guided by the winds of weather analyses and in an off-line mode (solving mass conservation only). With LMDZ, LSCE participates in international inter-comparison exercises for transport models (Transcom program). The team also developed a simplified chemistry module for the oxidation of the chain of hydrocarbons, which allows simultaneous optimization of CO, HCHO, H2, CH4, and the hydroxyl radical (OH), by assimilating together measirements of these compounds over extended periods of time.
SATINV also develops regional inversion systems at kilometer or deca-kilometer resolution, based on the transport model CHIMERE (http://www.lmd.polytechnique.fr/chimere/). The high resolution obtained makes it possible to cross the gap between the scale of the inverted fluxes and that of the local flux measurements. SATINV initiated the inversion of CO2 fluxes for the Paris megapole.
