Publications

2005

• Modélisation de la dispersion atmosphérique du mercure, du plomb et du cadmium à l'échelle européenne.
  
  • Roustan Yelva
  , 2005. Le plomb, le mercure et le cadmium sont les métaux lourds identifiés comme les plus préoccupants dans le cadre de la pollution atmosphérique à longue distance. Comprendre et modéliser leur comportement permet la prise de décision efficace pour réduire leur impact sur l'homme et son environnement. Les deux premières parties de cette thèse portent sur la modélisation de ces polluants trace en vue de l'étude d'impact à l'échelle européenne. Le mercure en étant principalement présent sous forme gazeuse et susceptible d'interagir chimiquement se distingue des autres métaux lourds essentiellement portés par les particules fines et considérés comme inertes. La troisième partie de cette thèse présente un développement méthodologique basé sur l'utilisation d'une approche adjointe permettant de quantifier les sensibilités du modèle développé aux différents forçages utilisés mais également d'affiner ceux-ci par modélisation inverse.
• Estimation de l'incertitude et prévision d'ensemble avec un modèle de chimie transport - Application à la simulation numérique de la qualité de l'air
  
  • Mallet Vivien
  , 2005. La thèse s'attache à évaluer la qualité d'un modèle de chimie-transport, non pas par une comparaison classique aux observations, mais en estimant ses incertitudes a priori dues aux données d'entrées, à la formulation du modèle et aux approximations numériques. L'étude de ces trois sources d'incertitude est menée respectivement grâce à des simulations Monte Carlo, des simulations multi-modèles et des comparaisons entre schémas numériques. Une incertitude élevée est mise en évidence, pour les concentrations d'ozone. Pour dépasser les limitations dues à l'incertitude, une stratégie réside dans la prévision d'ensemble. En combinant plusieurs modèles (jusqu'à quarante-huit modèles) sur la bases des observations passées, les prévisions peuvent être significativement améliorées. Ce travail a aussi été l'occasion de développer un système de modélisation innovant, Polyphemus.
• Inverse modeling of NOx emissions at regional scale over northern France: Preliminary investigation of the second-order sensitivity
  
  • Quélo Denis
  • Mallet Vivien
  • Sportisse Bruno
  Journal of Geophysical Research, American Geophysical Union, 2005, 110 (D24310). The purpose of this article is to perform the inverse modeling of emissions at regional scale for photochemical applications. The case study is the region of Lille in northern France for simulations in May 1998. The chemistry-transport model, Polair3D, has been validated with 1 year of model-to-observation comparisons over Lille. Polair3D has an adjoint mode, which enables inverse modeling with a variational approach. A sensitivity analysis has been performed so as to select the emission parameters to be modified in order to improve ozone forecasts. It has been shown that inverse modeling of the time distribution of nitrogen oxide emissions leads to satisfactory improvements even after the learning period. A key issue is the robustness of the inverted emissions with respect to uncertain parameters. A brute force second-order sensitivity analysis of the optimized emissions has been performed with respect to other parameters and has proven that the optimized time distribution of NOx emissions is robust. (10.1029/2005JD006151)
  DOI : 10.1029/2005JD006151
• A comprehensive study of ozone sensitivity with respect to emissions over Europe with a chemistry-transport model
  
  • Mallet Vivien
  • Sportisse Bruno
  Journal of Geophysical Research, American Geophysical Union, 2005, 110 (D22302). A detailed sensitivity analysis of ozone concentrations with respect to anthropogenic and biogenic emissions is performed at European scale in summer 2001 through the use of the chemistry-transport model Polair3D. We estimate the time evolution of the sensitivities and the extent of the sensitive regions. We discriminate the chemical species to which photochemistry is the most sensitive. This work is intended as a preliminary study for inverse modeling of emissions. Local sensitivities are computed using a tangent linear model and an adjoint model of the underlying chemistry-transport model. Global sensitivities are approximated by means of Monte Carlo simulations. It is shown that NO emissions have a prominent impact and that VOC emissions also play an important role. Major emission sources are associated with the highest sensitivities, although a non-negligible sensitivity of the concentrations at observation stations can cover the whole domain. A typical relative sensitivity of ozone concentrations to NO emissions is about 6 μg * m−3, which is low as to compared to the error and the uncertainty in output concentrations. (10.1029/2005JD006234)
  DOI : 10.1029/2005JD006234
• Coupling Two and One Dimensional Model Through a Thin Interface
  
  • Hérard Jean-Marc
  • Hurisse Olivier
  , 2005. (10.2514/6.2005-4718)
  DOI : 10.2514/6.2005-4718
• Schemes to Couple Flows Between Free and Porous Medium
  
  • Hérard Jean-Marc
  , 2005. (10.2514/6.2005-4861)
  DOI : 10.2514/6.2005-4861
• Emergence of a tracer source from air concentration measurements, a new strategy for linear assimilation
  
  • Issartel J.-P.
  Atmospheric Chemistry and Physics, European Geosciences Union, 2005, 5 (1), pp.273. The measurement of atmospheric concentrations by a monitoring network is a promising tool for the identification of the widespread sources of trace species. The paper addresses the case of the species scattered linearly by a known meteorology. The question is classical: what can be said about the source from a set of measurements? Is it possible to guess from the values observed by the measurements that the source is spread close to the detectors, or that the tracer comes from a remote region? And, if the source was a point source, would it be possible to understand it by just considering these values? A part of the answers is a matter of practical sense: the resolution with which an emission can be retrieved will always be limited and probably lower for a remote region, even if the detectors and dispersion model are error free. The paper proposes a linear strategy of inference: to any set of values taken by the observed concentrations is associated linearly an estimate of the source. Doubled values lead to a doubled estimate. The method, based on adjoint techniques, is intended to optimise the resolution by quantifying, with the concept of illumination, which regions are well, poorly or not seen at all. The illumination tied to ordinary adjoint functions becomes excessive close to the detectors thus leading to inversion artefacts. This may be corrected by attributing each point of the space time domain a geometric and statistical weight. The adjoint functions are transformed. The choice of this renormalising function is constrained by an unambiguous entropic criterion preventing any overestimation of the available information that would lead to artefacts. It amounts to evenly distribute the information between the points organised with their weights as a "known domain". The theory is illustrated by calculations performed with the experimental source ETEX1.
• Toward ensemble-based air-quality forecasts
  
  • Mallet Vivien
  • Sportisse Bruno
  , 2005. No abstract
• Apparent motion estimation for turbulent flows with vector spline interpolation
  
  • Isambert Till
  • Berroir Jean-Paul
  • Herlin Isabelle
  • Huot Etienne
  , 2005, 4, pp.2862-2865. No abstract
• Continuous update of classification on a sequence of satellite images
  
  • Herlin Isabelle
  • Berroir Jean-Paul
  • Auger Michel
  • Guldner Baptiste
  • Ducrot Danielle
  • Gouaux Pierrette
  • Maisongrande Philippe
  • Dedieu Gérard
  , 2005. No abstract
• Reconstruction of an atmospheric tracer source using the principle of maximum entropy. I: Theory
  
  • Bocquet Marc
  Quarterly Journal of the Royal Meteorological Society, Wiley, 2005, 131 (part B 610), pp.2191. Over recent years; tracing back sources of chemical species dispersed through the atmosphere has been of considerable importance, with an emphasis on increasing the precision of the source resolution. This need stems from many problems: being able to estimate the emissions of pollutants; spotting the source of radionuclides; evaluating diffuse gas fluxes; etc. We study the high-resolution retrieval on a continental scale of the source of a passive atmospheric tracer, given a set of concentration measurements. In the first of this two-part paper, we lay out and develop theoretical grounds for the reconstruction. Our approach is based on the principle of maximum entropy on the mean. It offers a general framework in which the information input prior to the inversion is used in a flexible and controlled way. The inversion is shown to be equivalent to the minimization of an optimal cost function, expressed in the dual space of observations. Examples of such cost functions are given for different priors of interest to the retrieval of an atmospheric tracer. In this respect, variational assimilation (4D-Var), as well as projection techniques, are obtained as biproducts of the method. The framework is enlarged to incorporate noisy data in the inversion scheme. (10.1256/qj.04.67)
  DOI : 10.1256/qj.04.67
• Data assimilation and Air Pollution forecast Berlin Cases
  
  • Torres German Ariel
  • Unger Steffen
  • Asselmeyer-Maluga Torsten
  • Mallet Vivien
  • Quélo Denis
  • Sportisse Bruno
  • Herlin Isabelle
  • Berroir Jean-Paul
  ERCIM News, ERCIM, 2005 (61), pp.20-21. No abstract
• Reconstruction of an atmospheric tracer source using the principle of maximum entropy. II: Applications
  
  • Bocquet Marc
  Quarterly Journal of the Royal Meteorological Society, Wiley, 2005, 131 (part B (610)), pp.2209. A new method of performing the source inversion of a passive tracer at continental scale was proposed in Part I of this two-part paper. The method made use of prior information, general or specific (depending on the situation), to perform a better reconstruction using only the prior information and the field measurements of the tracer. In this paper the method is tested on its first applications. It is used on several test examples, using the meteorological conditions of the European Joint Research Centre ETEX-I campaign. The retrieval of a temporal profile of emission from a source whose location is known is studied before testing the method on a full reconstruction of the space-time profile of the source. Synthetic, but also real-measurement, inversions are tested, thanks to the extension of the formalism to noisy data. (10.1256/qj.04.68)
  DOI : 10.1256/qj.04.68
• Data assimilation for short range atmospheric dispersion of radionuclides : a case study of second-order sensitivity
  
  • Quélo Denis
  • Sportisse Bruno
  • Isnard Olivier
  Journal of Environmental Radioactivity, Elsevier, 2005, 84-3, pp.393-408. This article presents the application of variational data assimilation to a simple Gaussian plume model for radionuclides. Adjoint modeling is applied to the model in order to minimize discrepancies between contamination observations and model outputs. The interest of such an approach is to get a better estimation of some parameters such as emissions or dispersion parameters. A second-order analysis is also performed to assess the sensitivity of the optimized parameters to some poorly known parameters. Sensitivity with respect to network design is also done. (10.1016/j.jenvrad.2005.04.011)
  DOI : 10.1016/j.jenvrad.2005.04.011
• Vers une représentation multi-échelles du mouvement fluide turbulent observé sur des images satellitaires
  
  • Isambert Till
  • Herlin Isabelle
  • Berroir Jean-Paul
  • Graffigne Christine
  , 2005. No abstract
• Estimation du mouvement fluide apparent dans un cadre de splines vectorielles
  
  • Isambert Till
  • Herlin Isabelle
  • Berroir Jean-Paul
  • Huot Etienne
  , 2005, Session S04. No abstract