Publications

2006

• Data assimilation for short-range dispersion of radionuclides : An application to Wind Tunnel Data
  
  • Krysta Monika
  • Bocquet Marc
  • Sportisse Bruno
  • Isnard Olivier
  Atmospheric Environment, Elsevier, 2006, 40 (38), pp.7267-7279. This work contributes to improvement in consequences evaluation for a release of radioactivity to the atmosphere at local scale. An investigation of how such an improvement could be achieved with the help of variational data assimilation is presented. The measurements collected in a wind tunnel experiment are coupled to a Gaussian puff model. Capacity of finding the true source emission rate is tackled in the first place. Secondly, data assimilation is employed to accommodate the computed concentration profiles to the measured ones. Benefit from data assimilation is subject to the quantity of information contained in the measurements. Therefore, posterior analysis of the monitoring network is carried out and its quality assessed. (10.1016/j.atmosenv.2006.06.043)
  DOI : 10.1016/j.atmosenv.2006.06.043
• Technical Note: A new SIze REsolved Aerosol Model (SIREAM)
  
  • Debry E.
  • Fahey K.
  • Sartelet K.
  • Sportisse B.
  • Tombette M.
  Atmospheric Chemistry and Physics Discussions, European Geosciences Union, 2006, 6 (6), pp.11845-11875. We briefly present in this short paper a new SIze REsolved Aerosol Model (SIREAM) which simulates the evolution of atmospheric aerosol by solving the General Dynamic Equation (GDE). SIREAM segregates the aerosol size distribution into sections and solves the GDE by splitting coagulation and condensation/evaporation. A moving sectional approach is used to describe the size distribution change due to condensation/evaporation and a hybrid method has been developed to lower the computational burden. SIREAM uses the same physical parameterizations as those used in the Modal Aerosol Model, MAM sartelet05development. It is hosted in the modeling system POLYPHEMUS (Mallet et al., 2006) but can be linked to any other three-dimensional Chemistry-Transport Model.
• Metodologia para monitoramento da degradacao das terras na Bacia do Alto Taquari atravès da deteccao de mudancas no use e cobertura do solo a partir da fusao de dados dos satélites NOAA/AVHRR e Landsat/TM
  
  • Fragoso Marcelo Cerqueira
  • Meirelles Margareth Simões Penello
  • Berroir Jean-Paul
  • Herlin Isabelle
  , 2006, pp.447-456. Este trabalho descreve uma metodologia capaz de detectar automaticamente mudanças no uso e cobertura do solo em uma imagem de satélite Landsat/TM, através do uso de perfis temporais de reflectâncias das classes de uso/cobertura do solo obtidas a partir do sensor NOAA/AVHRR ao longo de um ano e de uma classificação de referência realizada em uma imagem Landsat/TM, ambos obtidos no mesmo ano (t0). A partir das mudanças detectadas pela metodologia descrita, dois produtos são gerados: um mapa temático indicando as áreas onde houve mudanças e uma nova classificação para uma nova data (t1) baseada na atualização automática da classificação de referência.
• Estimation of a motion field on satellite images from a simplified ocean circulation model
  
  • Herlin Isabelle
  • Huot Etienne
  • Berroir Jean-Paul
  • Le Dimet François-Xavier
  • Korotaev Gennady K.
  , 2006, pp.1077-1080. This paper aims at estimating the apparent velocity from sequences of satellite images. This study is an illustration of a more general methodology for generating, from satellite images, pseudo-observations of physical variables, that are assimilated within a geophysical forecast model in view of improving the quality of its results. In the case of the presented study, the used satellite images are sequences of Sea Surface Temperature (SST), from which pseudo-observations of sea surface velocities are generated, and assimilated within an ocean circulation model. The originality of the approach lies in the definition of an Image Model, that predicts the evolution of image information -here, SST- as a function of the pseudo-observations -here, surface velocity-. Satellite data are then assimilated within the Image Model, yielding an estimation of the pseudo-observations. In the case of this paper, this methods allows the estimation of sea surface velocities, even when large parts of the satellite images are corrupted by clouds. The Image Model plays the role of an intermediate model, between satellite data and the forecast model, and allows the assimilation of image information which is not directly linked to the state variables of the forecast model. (10.1109/ICIP.2006.312742)
  DOI : 10.1109/ICIP.2006.312742
• Modélisation numérique et assimilation de données de la dispersion de radionucléides en champ proche et à l'échelle continentale
  
  • Krysta Monika
  , 2006. La prévision des conséquences de rejets radioactifs dans l'atmosphère repose sur des modèles de dispersion qui fournissent des solutions analytiques (pX 0.1 développé par IRSN/ECL) ou numériques (Polair3D développé au CEREA) de l'équation d'advection-diffusion. Les modèles s'appuient d'une part sur des champs météorologiques possédant une résolution limitée et intègrent d'autre part des processus d'appauvrissement d'un nuage radioactif dont la description est imparfaite. Afin de contourner ces difficultés nous exploitons dans cette thèse les opportunités offertes par le couplage des modèles aux mesures, connu sous le nom d'assimilation de données. Dans un premier temps nous confrontons les modèles utilisés à des observations. Ces dernières sont fournies par des expériences effectuées avec des traceurs passifs ou collectées suite a des rejets de radionucléides. La dispersion sur une maquette de la centrale de Bugey dans une soufflerie en champ proche, l'expérience ETEX-I à l'échelle continentale et les rejets accidentels de Tchernobyl et Algésiras font l'objet d'études dans ce travail. Dans un deuxième temps, les modèles de dispersion sont associés aux mesures dans le but d'améliorer l'évaluation de conséquences de rejets radioactifs et d'inverser leur sources si la qualité du modèle le permet. En champ proche, l'approche variationnelle standard est utilisée. L'adjoint de pX 0.1 est construit à l'aide d'un différenciateur automatique. Les mesures collectées dans la soufflerie sont assimilées afin d'inverser le débit de la source. Dans le but d'obtenir un meilleur accord entre le modèle et les mesures, l'optimisation des paramètres gouvernant la distribution spatiale du panache est ensuite abordée. L'avantage de l'emploi de mesures est conditionné par leur contenu informatif. Ainsi, l'analyse a posteriori du réseau de mesures est effectuée et des possibilités de réduire sa taille en vue des applications opérationnelles sont exploitées. A l'échelle continentale, malgré la restriction aux mailles contenant des sites nucléaires, l'espace engendré par des sources est de dimension considérablement plus grande que l'espace d'observations. Par conséquent le problème inverse de reconstruction de la position et du profil temporel des sources est mal posé. Ce problème est régularisé en utilisant le principe du maximum d'entropie sur la moyenne. Des nouvelles fonctions coût prenant en compte le confinement spatio-temporel des sources accidentelles sont construites dans l'espace d'observations. Le lien entre la source recherchée et les mesures est décrit par l'adjoint de Polair3D. Les observations assimilées par la méthode sont constituées de mesures synthétiques, parfaites ou bruitées. Une série d'expériences se focalisant sur des sensibilités de la méthode est menée et leur qualité évaluée à l'aide d'un indicateur objectif. Un algorithme de réduction des sites suspectés pour des applications opérationnelles est testé. Finalement, les résultats de l'inversion du profil temporel de la source de l'accident d'Algésiras sont présentés.
• Ensemble-based air quality forecasts: A multimodel approach applied to ozone
  
  • Mallet Vivien
  • Sportisse Bruno
  Journal of Geophysical Research, American Geophysical Union, 2006, 111 (D18302). The potential of ensemble techniques to improve ozone forecasts is investigated. Ensembles with up to 48 members (models) are generated using the modeling system Polyphemus. Members differ in their physical parameterizations, their numerical approximations, and their input data. Each model is evaluated during 4 months (summer 2001) over Europe with hundreds of stations from three ozone-monitoring networks. We found that several linear combinations of models have the potential to drastically increase the performances of model-to-data comparisons. Optimal weights associated with each model are not robust in time or space. Forecasting these weights therefore requires relevant methods, such as selection of adequate learning data sets, or specific learning algorithms. Significant performance improvements are accomplished by the resulting forecasted combinations. A decrease of about 10% of the root-mean-square error is obtained on ozone daily peaks. Ozone hourly concentrations show stronger improvements. (10.1029/2005JD006675)
  DOI : 10.1029/2005JD006675
• Inverse modelling for mercury over Europe
  
  • Roustan Y.
  • Bocquet Marc
  Atmospheric Chemistry and Physics, European Geosciences Union, 2006, 6 (10), pp.3098. The fate and transport of mercury over Europe is studied using a regional Eulerian transport model. Because gaseous elemental mercury is a long-lived species in the atmosphere, boundary conditions must be properly taken into account. Ground measurements of gaseous mercury are very sensitive to the uncertainties attached to those forcing conditions. Inverse modelling can help to constrain the forcing fields and help to improve the predicted mercury concentrations. More generally, it allows to reduce the weaknesses of a regional model against a global or hemispherical model for such diffuse trace constituent. Adjoint techniques are employed to relate rigorously and explicitly the measurements to the forcing fields. This way, the inverse problem is clearly defined. Using EMEP measurements of gaseous mercury and performing the inversions, it is shown that boundary conditions can be improved significantly as well as the forecast concentrations. Using inverse modelling to improve the emission inventory is however much more difficult. Indeed, there are currently not enough mercury monitoring stations, and they are located far away from the center of Europe.
• Sensitivity analysis for mercury over Europe
  
  • Roustan Yelva
  • Bocquet Marc
  Journal of Geophysical Research: Atmospheres, American Geophysical Union, 2006, 111 (D14304). Adjoint techniques are introduced to perform a sensitivity analysis for mercury over Europe, using a regional model. This approach differs from other techniques such as the direct and indirect approaches developed to compute sensitivities for air quality modeling. With gaseous elemental mercury lifetime being of order one year, global or hemispherical models are usually preferred to analyze its fate and transport. In an area-limited domain, respective influences of incoming mercury and inner emissions fluxes have to be weighted. A local measurement depends on the potential ground emissions, the potential incoming mass from domain borders, and the potential initial content in mercury of the atmosphere. The sensitivities of the measurement to entire maps of emissions, boundary conditions, etc., are computed thanks to the adjoint method since other techniques do not allow to perform these computations directly. As an application to these methodological developments, we use the numerical transport model Polair3D. Quantitative sensitivity maps are provided for European Monitoring and Evaluation Program (EMEP) mercury monitoring stations. With the adjoint approach, sensitivities of a given country to other countries emissions are computed in a straightforward manner. The yearly average sensitivity of a measurement of gaseous elemental mercury to distant sources is shown to decrease like a power law r −2.4, where r is the distance to a source. It is eventually explained how the method developed here can be generalized to account for a more complex mercury chemistry and the modeling of oxidized species. In particular, sensitivities of dry and wet deposition fluxes of oxidized species are computed for one EMEP station. (10.1029/2005JD006616)
  DOI : 10.1029/2005JD006616
• Assimilation of images in geophysical models
  
  • Le Dimet François-Xavier
  • Antoniadis Anestis
  • Ma Jianwei
  • Herlin Isabelle
  • Huot Etienne
  • Berroir Jean-Paul
  , 2006.
• A Method to Couple Two-Phase Flow Models
  
  • Ambroso Annalisa
  • Hérard Jean-Marc
  • Hurisse Olivier
  , 2006. (10.2514/6.2006-3900)
  DOI : 10.2514/6.2006-3900
• Peut-on modéliser la qualité de l'air de manière déterministe ?
  
  • Mallet Vivien
  • Sportisse Bruno
  , 2006.
• Assimilation of EPS tropospheric ozone for air quality forecast
  
  • Sportisse Bruno
  • Bocquet Marc
  • Mallet Vivien
  • Herlin Isabelle
  • Berroir Jean-Paul
  • Boisgontier Hervé
  , 2006. This paper describes the objectives, proposed methodology and preliminary results of the EPS-MetOp RAO project 3029, which objective is to evaluate the feasibility of using EPS tropospheric ozone information to constrain the forecast of air quality at European scale: data assimilation methodologies will be applied in view of improving the analysis of ozone concentrations in the boundary layer. The project builds on two main methodological steps. First, a feasibility study is based on twin numerical experiments, and aims to assess the interest of assimilating tropospheric ozone columns and profiles, to be provided by IASI, for analysing boundary layer ozone. Second, experiments will be performed to evaluate the improvement brought by assimilating IASI tropospheric ozone information: these experiments will be conducted using simulated data, obtained from the IASI instrument model, and with real IASI data when available. The project expects to demonstrate the feasibility of assimilating IASI tropospheric ozone measurements for boundary layer ozone analysis.
• Data Assimilation of Satellite Images within an Oceanographic Circulation Model
  
  • Huot Etienne
  • Isambert Till
  • Herlin Isabelle
  • Berroir Jean-Paul
  • Korotaev Gennady K.
  , 2006, pp.265-268. We tackle the problem of coupling a geophysical simulation model with data coming from image processing. It needs to define the image observation space and to design an operator to transform results from the image space to the model space. In this study, we use a shallow-water oceanographic circulation model developed at MHI. We propose a processing chain first based on an image processing step relying on a dedicated motion estimation operator, and then a data assimilation step of the estimated velocity. We illustrate the method on different results without and with assimilation. (10.1109/ICASSP.2006.1660330)
  DOI : 10.1109/ICASSP.2006.1660330
• Regional scale land use/land cover classification using temporal series of MODIS data
  
  • Jonathan Milton
  • Meirelles Margareth Simões Penello
  • Berroir Jean-Paul
  • Herlin Isabelle
  , 2006, pp.522-527. This paper describes a methodology for systematic land use/land cover classification on a regional scale, with emphasis on a low cost and highly automatized approach. This methodology is based on multitemporal analyses of surface reflectance data from the Moderate Resolution Imaging Spectroradiometer (MODIS), which is located on board NASA's Terra and Aqua satellites and features high temporal frequency, extensive coverage, and extremely low costs for data acquisition. A sequence of automatized procedures were developed for MODIS data pre-processing, as well as for the training and execution of a supervised classification algorithm, where temporal profiles are fitted to smooth polynomial curves and intelligent curve features are then computed in order to reduce data dimensionality and improve profile interpretability, thus providing a more robust classification approach. A case study was performed in the High Taquari Basin, in the states of Mato Grosso do Sul and Mato Grosso, Brazil, which showed that the method was indeed capable of generalizing well over the entire region of study (over 25,000km2), effectively discriminating between areas of agriculture, pasture, and savannah. The methodology was also seen to be quite successful in identifying areas of deforestation, which is of particular interest for the monitoring of land use and land use change in the region.
• Inverse modelling for mercury over Europe
  
  • Roustan Y.
  • Bocquet Marc
  Atmospheric Chemistry and Physics Discussions, European Geosciences Union, 2006, 6 (1), pp.795-838. The fate and transport of mercury over Europe is studied using a regional Eulerian transport model. Because gaseous elemental mercury is a long-lived species in the atmosphere, boundary conditions must be properly taken into account. Ground measurements of gaseous mercury are very sensitive to the uncertainties attached to those forcing conditions. Inverse modelling can help to constrain the forcing fields and help to improve the predicted mercury concentrations. More generally, it allows to reduce the weaknesses of a regional model against a global or hemispherical model for such diffuse trace constituent. Adjoint techniques are employed to relate rigorously and explicitly the measurements to the forcing fields. This way, the inverse problem is clearly defined. Using EMEP measurements of gaseous mercury and performing the inversions, it is shown that boundary conditions can be improved significantly as well as the forecast concentrations. Using inverse modelling to improve the emission inventory is however much more difficult since there are currently not enough mercury monitoring stations, and their location far from Europe centre.
• Assimilation de données images dans un modèle de circulation océanographique
  
  • Huot Etienne
  • Herlin Isabelle
  • Isambert Till
  • Korotaev Gennady K.
  , 2006. L'assimilation de données permet de coupler un modèle de prévision à des observations. Dans cette étude nous nous intéressons à l'intégration de caractéristiques images dans un modèle de simulation de la circulation océanique. Nous proposons une chaîne de traitement permettant d'estimer la vitesse de circulation sur une séquence d'images de température de l'océan et l'assimilation de cette observation image dans un modèle de prévision.
• Uncertainty in a chemistry-transport model due to physical parameterizations and numerical approximations: An ensemble approach applied to ozone modeling
  
  • Mallet Vivien
  • Sportisse Bruno
  Journal of Geophysical Research, American Geophysical Union, 2006, 111 (D01302). This paper estimates the uncertainty in the outputs of a chemistry-transport model due to physical parameterizations and numerical approximations. An ensemble of 20 simulations is generated from a reference simulation in which one key parameterization (chemical mechanism, dry deposition parameterization, turbulent closure, etc.) or one numerical approximation (grid size, splitting method, etc.) is changed at a time. Intercomparisons of the simulations and comparisons with observations allow us to assess the impact of each parameterization and numerical approximation and the robustness of the model. An ensemble of 16 simulations is also generated with multiple changes in the reference simulation in order to estimate the overall uncertainty. The case study is a four-month simulation of ozone concentrations over Europe in 2001 performed using the modeling system Polyphemus. It is shown that there is a high uncertainty due to the physical parameterizations (notably the turbulence closure and the chemical mechanism). The low robustness suggests that ensemble approaches are necessary in most applications. (10.1029/2005JD006149)
  DOI : 10.1029/2005JD006149
• Modélisation du mercure, du plomb et du cadmium à l'échelle européenne
  
  • Roustan Yelva
  • Bocquet Marc
  • Musson-Genon Luc
  • Sportisse Bruno
  Pollution Atmosphérique : climat, santé, société, APPA, 2006, 48 (191), pp.317-327. Le mercure, le plomb et le cadmium sont actuellement un objet de préoccupations pour les instances concernées par la pollution atmosphérique. La dénomination commune de " métaux lourds " cache en fait des comportements variables de ces composés dans l'atmosphère qui influencent fortement leur transfert vers les écosystèmes. La modélisation numérique de ces comportements doit permettre de mieux comprendre leur devenir, une attention particulière devant être portée aux processus de déposition. L'utilisation pertinente d'un modèle numérique ne peut se faire sans étudier sa sensibilité aux données et paramètres qu'il utilise. Des techniques ont été développées en ce sens puis appliquées au modèle de chimie-transport POLAIR 3D. Elles permettent par ailleurs de mener à bien un travail de modélisation inverse.
• Environmental degradation analysis using NOAA/AVHRR data
  
  • Singh Dharmendra
  • Meirelles Margareth Simões Penello
  • Costa G.A.
  • Herlin Isabelle
  • Berroir Jean-Paul
  • Silva E.F.
  Advances in Space Research, Elsevier, 2006, 37 (4), pp.720-727. This paper proposes a particular approach to assess information about soil degradation, based on a methodology to calculate soil color from NOAA/AVHRR data. As erosive processes change physical and chemical properties of the soil, altering, consequently, the superficial color, monitoring the change in color over time can help to identify and analyze those processes. A relationship among the soil color (described in the Munsell Color System, i.e., in terms of Hue, Value and Chroma), vegetation indices, surface temperature and emissivity has been established, which is based on the theoretical model. The methodology has three main phases: determination of the regression models among soil color and vegetation indices, emissivity and surface temperature; generation of digital soil color models; and statistical evaluation of the estimated color. The tests showed that the methodology is efficient in determining soil color using the various vegetation indices (i.e., Normalized vegetation index NDVI, Modified soil adjusted vegetation index MSAVI). One vegetation index, i.e., Purified adjusted vegetation index (PAVI) is proposed to subsidies the effect of vegetation over the soil. Best results were obtained for the Hue color component. To further test the methodology, the estimated digital color models were compared with the characteristic color of soil classes in the test area. The results of this application confirmed the methodology's capacity to determine the soil color from NOAA/AVHRR data. This type of study is quite helpful to know the erosion of soil as well as some abrupt change in soil due to natural hazards by space borne or air-borne sensors. (10.1016/j.asr.2004.12.052)
  DOI : 10.1016/j.asr.2004.12.052