French Roadmap for complex Systems 2008-2009

This second issue of the French Complex Systems Roadmap is the outcome of the Entretiens de Cargese 2008, an interdisciplinary brainstorming session organized over one week in 2008, jointly by RNSC, ISC-PIF and IXXI. It capitalizes on the first roadmap and gathers contributions of more than 70 scientists from major French institutions. The aim of this roadmap is to foster the coordination of the complex systems community on focused topics and questions, as well as to present contributions and challenges in the complex systems sciences and complexity science to the public, political and industrial spheres

Robustness and autonomy in biological systems: how regulatory mechanisms enable functional integration, complexity and minimal cognition through the action of second-order control constraints

Living systems employ several mechanisms and behaviors to achieve robustness and maintain themselves under changing internal and external conditions. Regulation stands out from them as a specific form of higher-order control, exerted over the basic regime responsible for the production and maintenance of the organism, and provides the system with the capacity to act on its own constitutive dynamics. It consists in the capability to selectively shift between different available regimes of self-production and self-maintenance in response to specific signals and perturbations, due to the action of a dedicated subsystem which is operationally distinct from the regulated ones. The role of regulation, however, is not exhausted by its contribution to maintain a living system’s viability. While enhancing robustness, regulatory mechanisms play a fundamental role in the realization of an autonomous biological organization. Specifically, they are at the basis of the remarkable integration of biological systems, insofar as they coordinate and modulate the activity of distinct functional subsystems. Moreover, by implementing complex and hierarchically organized control architectures, they allow for an increase in structural and organizational complexity while minimizing fragility. Finally, they endow living systems, from their most basic unicellular instances, with the capability to control their own internal dynamics to adaptively respond to specific features of their interaction with the environment, thus providing the basis for the emergence of minimal forms of cognition

Assessment of C-band SRTM DEM in a dense equatorial forest zone

International audienceA Digital Elevation Model issued from the SRTM mission was assessed on a study area located in a dense equatorial forest setting in French Guiana. The SRTM DEM defined on a 90-m grid was compared to three check sources: (1) airborne laser altimeter data, (2) an accurate heliborne DEM, and (3) spot heights. The paper also includes a comparison with a radargrammetric RADARSAT DEM. The results show that the accuracy of the SRTM DEM is about 10 m (standard deviation of errors). For a given slope aspect, the absolute value and the standard deviation of elevation errors increase almost linearly with the slope value. The slope aspect has a major influence on the sign of the elevation error: elevations are underestimated for slope facing SRTM signal (foreslopes, northwest), and conversely in the opposite direction (backslopes, southeast). Maximum errors are observed along these two direction

Geostatistical analysis of water quantity and quality spatiotemporal data

Regulatory environmental reporting on groundwater levels and various substance concentrations in ground water involves statistical analysis of a large number of data. However, statistical calculations have to take into account seasonality or temporal correlation; usual statistical calculations are not valid. Many questions arises as regards to automation of this processes: specific definition of variables, calculation simplification and robustness. We consider three main aspects: 1. Outliers or singularities detection for each time series, for instance the intermittent pumping presence on a groundwater level observation. Firstly the temporal nature of the measures is determined. Abnormality detection algorithms are proposed (interquantile deviation, multimodality of values or of their increments,...). 2. Accuracy of environmental indicators (mean, quantile) and characterization of their interannual variations. Approximations in the variance estimation calculations are required for automated processing, so that validity their validity is discussed. Furthermore due to the presence of quantization threshold, "micropolluant" concentration can be censured. What is the consequence in practice? 3. Detection of trends and breaks for time series. After a detailed comparison between different methods, BRGM selected the Mann-Kendall test for trend characterization. However, other procedure can be considered, for example mean comparison (or quantile) calculated on temporal support in order to introduce time scale aspect. Then, we study possible definition of trends and their breaks. These different approaches for trends and breaks are studied, they are compared and then combined. Finally, spatialization of indicators is discussed: definition, simplified calculation and precision estimation

Generation of a ground-level DEM in a dense equatorial forest zone by merging airborne laser data and a top-of-canopy DEM

International audienceThis paper describes the generation of a ground-level digital elevation model (DEM) by merging airborne elevation data and a top-of-canopy DEM. The study area is located in a dense equatorial forest setting in French Guiana, for which it is assumed that no topographic map is available. The data used consist of airborne laser data distributed along flight lines spaced at 500 m (with a data interval every 7 m) and a top-of-canopy DEM obtained by merging a stereoradargrammetric DEM with airborne laser data. Generation of the ground-level DEM involves the following steps: (i) selecting ground points from the airborne data and deducing a pseudo canopy height for these points, (ii) characterizing the canopy height from a statistical and geostatistical standpoint, (iii) kriging the canopy height and subtracting the resulting model from the top-of-canopy DEM to obtain a DEM corresponding to a ground-level DEM, and (iv) validation. Validation consists of comparing the results with topographic maps and a local heliborne DEM and studying the relationship between the configuration of the airborne trials, in terms of flight-line spacing, and accuracy of the resulting kriged DEM. The results show that the accuracy of the kriged ground-level DEM is significantly better than that of the initial radargrammetric DEM. The standard deviation of elevation errors is reduced from 21.2 to 11.9 m or from 25.3 to 11.1 m, depending on the validation source adopted (French National Geographic Institute spot heights and local heliborne DEM, respectively). In addition, the relationship between flight-line spacing and accuracy of the resulting kriged DEM helps estimate what flightline spacing is needed to obtain a given accurac

3D Fault Model of the Bouillante Geothermal Province Interpreted from Onshore and Offshore Structural Knowledge (French West Indies)

International audienceThe Bouillante area is known for its high-temperature geothermal field which produce electricity in a 15 MWe installed power plant (Guadeloupe Island, French West Indies). This zone is a complex geodynamic area. It stands at the convergence of the major tectonic and volcanic structures of the inner arc of the Lesser Antilles. The two main regional fault systems joining at the Bouillante geothermal field are the NW–SE Montserrat–Bouillante (MB) fault system, and the ESE–WNW to E–W Bouillante–Capesterre (BC) fault system. Two other factors make rather difficult the interpretation of the geological structuration. Firstly, Bouillante is located on the West coast of the Guadeloupe Island. It means that data and observations both from the Island and from the sea are needed. Secondly, a wet tropical climate prevails in that region. That is why exposures suitable for direct structural measurements are almost only found on the seaside where coastal erosion has stripped away the soil. The available data show that, on one hand, faults observed on the field mainly elongate along the E-W direction. On the other hand, offshore structures interpreted from marine seismic lines show a larger range of directions. In order to achieve a coherent interpretation of the Bouillante geothermal area, a 3D fault model is completed from onshore and offshore structural knowledge. A 15 km x 16 km zone crossing the island coastline is investigated down to 2 km depth. The fault network constructed reveals a hierarchy in the family of structures and highlights the prevalence of the NNW-SSE direction, associated with secondary NE-SW-trending structures, and the E-W direction. On a geographical point of view, the modelled faults are gathered in 3 clusters along the coast. The 3D model facilitates a coherent interpretation of the faults in the Bouillante province but this model can also be a cradle for hydro dynamic simulation