References of "Boreux, Jean-Jacques"
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See detailTemporal evolution and extreme value analysis of precipitations in Burkina Faso
Bel, Liliane; Weiss, Jérôme; Boreux, Jean-Jacques ULg et al

Poster (2011, March 23)

Modeling of damaging extreme events is of great interest for the risk managers who want to implement some protections. It is based on the so-called generalized extreme values model. In the environmental ... [more ▼]

Modeling of damaging extreme events is of great interest for the risk managers who want to implement some protections. It is based on the so-called generalized extreme values model. In the environmental sciences, we need to model the extremes of two or more processes like the daily rainfall recorded in various points of a given region. Each individual process could be modeled using univariate technique, but this strategy could not take into account for dependence of extreme values. For instance, consider two sites A and B fairly close to one another. If we observe an extreme value of the daily rainfall at site A, this information impacts the probability to observe an extreme value at site B even if we never recorded such value at B. The basic modeling tool is formed by so-called max-stable processes which take into account the possible spatial dependence through so-called extremal coefficient. We illustrate with annual maximum daily rainfall values recorded in 41 stations in Burkina Faso. [less ▲]

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See detailPratique du calcul bayésien
Boreux, Jean-Jacques ULg; Parent, Eric; Bernier, Jacques

Book published by Springer-Verlag (2010)

"Pratique du calcul bayésien" est né de l’expérience acquise lors des cours donnés en sciences de l’environnement, tant à l’université de Liège (Arlon), qu’à la grande école AgroParisTech (Paris). Son fil ... [more ▼]

"Pratique du calcul bayésien" est né de l’expérience acquise lors des cours donnés en sciences de l’environnement, tant à l’université de Liège (Arlon), qu’à la grande école AgroParisTech (Paris). Son fil conducteur peut se résumer par la locution « de la plume à la souris », tournure empruntée à un opuscule retraçant la vie d’une école fréquentée jadis par le 1er auteur. La première partie privilégie les modèles statistiques paramétriques calculables « à la plume » et cependant très riches, tant du point de vue de la présentation des concepts fondateurs du paradigme bayésien, que de leurs applications opérationnelles, notamment en matière d’aide à la décision. Dès le premier chapitre, la représentation du modèle par un graphe acyclique orienté permet de distinguer clairement la phase où la créativité du chercheur s’exprime de celle où il calcule. A cette fin, le logiciel libre WINBUGS sera très utile à l’apprenti modélisateur. La seconde partie présente des applications réelles, plus sophistiquées, qui nécessitent souvent d’introduire une couche de variables latentes entre les observables et les paramètres. Conduire une inférence bayésienne sur ces modèles hiérarchiques implique un recours intensif aux méthodes modernes de calcul et mobilise donc « la souris » de l’ordinateur. Cet ouvrage est dédié aux étudiants et chercheurs qui souhaitent apprendre le calcul bayésien avec des visées opérationnelles. Le lecteur est invité à l’utiliser comme un tremplin lui permettant d’aller aussi loin que son intérêt et/ou ses besoins l’exigent. C’est pourquoi, les treize chapitres offrent un compromis entre la rigueur du langage mathématique et la souplesse de la langue de Molière. Le côté opérationnel est mis en avant. De nombreux exemples, le plus souvent réels, justifient les efforts et illustrent les raisonnements sous-jacents. Les développements théoriques sont donc volontairement limités à l’essentiel et le lecteur désireux de les poursuivre trouvera deux ouvrages de référence publiés dans la même collection. [less ▲]

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See detailExtracting a common high frequency signal from Northern Quebec black spruce tree-rings with a Bayesian hierarchical model
Boreux, Jean-Jacques ULg; Naveau, P.; Guin, O. et al

in Climate of the Past (2009), 5

One basic premise of dendroclimatology is that tree rings can be viewed as climate proxies, i.e. rings are assumed to contain some hidden information about past climate. From a statistical perspective ... [more ▼]

One basic premise of dendroclimatology is that tree rings can be viewed as climate proxies, i.e. rings are assumed to contain some hidden information about past climate. From a statistical perspective, this extraction problem can be understood as the search of a hidden variable which represents the common signal within a collection of tree-ring width series. Classical average-based techniques used in dendrochronology have been applied to estimate the mean behavior of this latent variable. Still, depending on tree species, regional factors and statistical methods, a precise quantification of uncertainties associated to the hidden variable distribution is difficult to assess. To model the error propagation throughout the extraction procedure, we propose and study a Bayesian hierarchical model that focuses on extracting an inter-annual high frequency signal. Our method is applied to black spruce (Picea mariana) tree-rings recorded in Northern Quebec and compared to a classical average-based techniques used by dendrochronologists. [less ▲]

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See detailParameterization of a process-based tree growth model : comparison of optimization, MCMC and particle filtering algorithms
Gaucherel, C.; Campillo, F.; Misson, L. et al

in Environmental Modelling & Software (2008), 23(10-11), 1280-1288

Finely tuned process-based tree-growth models are of considerable help in understanding the variations of biomass increments measured in the dendrochronological series. Using site and species parameters ... [more ▼]

Finely tuned process-based tree-growth models are of considerable help in understanding the variations of biomass increments measured in the dendrochronological series. Using site and species parameters, as well as daily climate variables, the MAIDEN model computes the water balance at ecosystem level and the daily increment of carbon storage in the stem through photosynthesis processes to reproduce the structure of the tree-ring series. In this paper, we use three techniques to calibrate this model with Pinus halepensis data sampled in the Mediterranean part of France: a standard optimization (PEST), Monte Carlo Markov Chains (MCMC) and Particle Filtering (PF). Contrary to PEST, which tries to find an optimum fit (giving the lowest error between observations and simulations), the principle of MCMC and PF is to walk, from a priori distributions, in the parameter space according to particular statistical rules to compute each parameter distribution. The PEST and MCMC calibrations of our dendrochronological series lead to rather similar adjustments between simulations and observations. PF and MCMC calibrations give different parameter distributions, showing how complementary are these methods, with a better fit for MCMC. Yet, independent validations over 11 independent meteorological years show a higher efficiency of the recent PF method over the others. [less ▲]

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See detailLe climat du Québec : un passé pour quel avenir ?
Boreux, Jean-Jacques ULg; Bernier, J.; Perreault, L.

Conference (2006)

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See detailLe rôle pivot des variables latentes pourle raisonnement statistique conditionnel. Exemples d'applications environnementales des processus ponctuels marqués.
Parent, E.; Bernier, J.; Boreux, Jean-Jacques ULg

in Revue de Statistique Appliquée (2006), 54(4), 85-111

En statistique bayésienne, le raisonnement conditionnel probabiliste fonde la solidarité étroite entre modélisation et inférence. Dans le cadre de ce raisonnement, un rôle pivot est joué par les variables ... [more ▼]

En statistique bayésienne, le raisonnement conditionnel probabiliste fonde la solidarité étroite entre modélisation et inférence. Dans le cadre de ce raisonnement, un rôle pivot est joué par les variables latentes. Ce mode de raisonnement peut s’avérer utile aussi en statistique fréquentiste. On présente trois séries hydrométéorologiques décrites par des modèles de processus ponctuels marqués de complexité croissante. Sur ces exemples, on montre comment récolter les fruits de la souplesse de modélisation et des facilités de calcul apportées par les variables latentes. Ces variables améliorent la conceptualisation de variables de structure dans les modèles statistiques et permettent aux calculs d’inférence de bénéficier des algorithmes MCMC en relation avec les techniques «d’augmentation de données». [less ▲]

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See detailThe main results of a european research project : improvement of transport safety by control of fog production in a chamber ("FOG")
Andre, Philippe ULg; Aparecida Silva, Cl.; Balocco, E. et al

Conference (2004, October)

The issue of transport safety is identified as a major goal in the European Union. The mid term objective declared in the European White Paper for Transport aims at halving the number of deaths on the ... [more ▼]

The issue of transport safety is identified as a major goal in the European Union. The mid term objective declared in the European White Paper for Transport aims at halving the number of deaths on the roads by 2010. Low visibility conditions, especially due to fog, increase the risk of major accidents (chain collision) and a number of innovative products are developed by the automotive industry, including equipment manufacturers, in order to increase the level of safety of the cars passengers and drivers. Testing of these products require the simulation or artificial reproduction of adequate low visibility (fog) conditions with good stability and reproductibility characteristics. The main objective of the “FOG” project was to develop a prototype of innovative fog chamber in which the mechanistic production of fog (by high pressure spraying of water) in a chamber was assisted by an efficient control of the indoor climate. This prototype was installed in a new building constructed on the campus of the University of Liège in Arlon (Belgium). The developments of the project also include a number of additional products enhancing the capabilities of the prototype: - an improved fog production spraying device, including an optimized management - a laser-based visibility measurement device - a reduced scale transmissiometer - a combined indoor climate - fog production simulation software All these products were successfully tested in the conclusive part of the project making the prototype fully operational and ready for use by researchers in the field of transport safety as well as industrial products manufacturers. The capability of the testing facility to test the interaction with the driver was also investigated. The paper will present the major developments of the project and the potential future perspectives of the work. [less ▲]

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See detailInnovative artificial fog production device - A technical facility for research activities.
Colomb, M.; Dufour, J.; Hirech, M. et al

Conference (2004)

A new innovative fog production device has been developed in close cooperation with partners of a European project called “FOG” funded by the EU. It is set up in the fog chamber of the road and bridges ... [more ▼]

A new innovative fog production device has been developed in close cooperation with partners of a European project called “FOG” funded by the EU. It is set up in the fog chamber of the road and bridges laboratory at Clermont-Ferrand. Most of the activities of this laboratory are dedicated to road safety but the facility is open to any other activity, such as environmental research. The recent developments consist in setting up a controllable device able to produce stable visibility levels and homogeneous fog, representative of various types of natural water droplet distribution. The fog characteristics were determined and compared to natural fog. Results are presented for a selection of conditions including stabilized visibility levels for dense fog, less than 50 metres meteorological visibility and two kinds of droplet distribution. [less ▲]

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See detailDifferent approaches for the simulation of an experimental building hosting a climate chamber devote to artificial fog production
Andre, Philippe ULg; Kelly, N.; Boreux, Jean-Jacques ULg et al

(2003, August)

In the context of a european project dealing with the issue of transport safety improvement in fog conditions, an experimental building has been constructed on the FUL campus, in the southern part of ... [more ▼]

In the context of a european project dealing with the issue of transport safety improvement in fog conditions, an experimental building has been constructed on the FUL campus, in the southern part of Belgium. This building hosts a climatic chamber in which a given indoor climate is to be maintained (temperature and relative humidity) whatever the external climate, in order to promote the artifical production of fog by water droplets spraying. During the design of the building and of the HVAC plant, different simulation approaches were carried out in order to evaluate and possibly optimize the technical choices concerning: - the building envelope - the material for the climatic chamber - the control strategy of the HVAC system Two categories of simulation tools were used to solve the different tasks: - building simulation tools - CFD programs For the first category, simulations were performed using both ESP-r and TRNSYS with the objective of solving the following questions: optimization of the building envelope (orientation and shading of the building, insulation, fenestration); sizing of the HVAC system; comparison of control strategies (direct control, indirect control, radiative and/or convective conditioning); estimation of energy consumption and comfort Within the second category, the FLUENT and ESP-r software were used and compared in order to predict the homogeneity of the thermal state within the test room and to calculate the effect of injecting a high amount of small water droplets on fog production, maintenance and visibility. Therefore, the ESP-r CFD module program was augmented with a specific model of water droplet diffusion. The paper will tackle the main modelling assumptions at the basis of each simulation experiment, the data preparation and the results of the calculations. For each phase, advantages and limitations of the simulation approach will be highlighted. These developments are considered as a first step towards the implementation of a virtual testing environment in the field of automotive transport which could be complemented by additional issues dealing with passengers comfort, acoustics, air quality, level of illuminance generated by the virtual production of fog. [less ▲]

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See detailApplications de l'approche bayésienne à la représentation des pluies mensuelles africaines par la loi des fuites.
Bernier, Jacques; Parent, Eric; Boreux, Jean-Jacques ULg

Conference (2003, May)

Ce texte présente une analyse bayésienne d'un processus ponctuel marqué particulier (la loi des fuites) avec application à des problèmes de modélisation environnementale hydrométéorologique sur les ... [more ▼]

Ce texte présente une analyse bayésienne d'un processus ponctuel marqué particulier (la loi des fuites) avec application à des problèmes de modélisation environnementale hydrométéorologique sur les données africaines de Ghezala (Tunisie) et Ataktamé (Togo). [less ▲]

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See detailStatistique bayésienne des processus ponctuels marqués. Le rôle des variables latentes dans la démarche de modélisation.
Bernier, Jacques; Parent, Eric; Boreux, Jean-Jacques ULg

Conference (2003)

En statistique bayésienne le raisonnement conditionnel est à la base de la solidarité étroite entre modélisation et calcul par algorithmes MCMC. Un des aspects les plus fructueux de son utilisation est l ... [more ▼]

En statistique bayésienne le raisonnement conditionnel est à la base de la solidarité étroite entre modélisation et calcul par algorithmes MCMC. Un des aspects les plus fructueux de son utilisation est l'utilisation explicite des variables latentes ou cachées. On présente trois exemples de séries météorologiques représentées par des modèles de processus ponctuels marqués de complexité croissante. Sur ces exemples on montre la souplesse de modélisation et les facilités de calcul apportées par les variables latentes en relation avec les techniques "d'augmentation de données de Tanner". [less ▲]

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See detailStudy of a method of scale reduction to test sign legibility in fog.
Dore, J.; Colomb, M.; Cavallo, V. et al

Conference (2003)

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See detailSimulation of a non conventional HVAC plant in an experimental building devoted to artificial fog production.
Andre, Philippe ULg; Boreux, Jean-Jacques ULg; Lacôte, P. et al

in Proceedings of SSB'2002 Congress (2002, December)

In the frame of a european project dealing with the issue of transport safety improvement in fog conditions, a new experimental building is being constructed on the FUL campus, in the southern part of ... [more ▼]

In the frame of a european project dealing with the issue of transport safety improvement in fog conditions, a new experimental building is being constructed on the FUL campus, in the southern part of Belgium. This building hosts a climatic chamber in which a given indoor climate is to be maintained (temperature and relative humidity) whatever the external climate. Control of the internal climate will be performed by means of a specific HVAC plant. The general environmental context of the project led to the selection of non conventional solutions for the plant: solar collectors (both thermal and photovoltaic) are associated with a reversible heat pump in order to either heat or cool the building. In some circumstances, simultaneous heating and cooling of different rooms of the building will be necessary and possible. Energy distribution within the building will be made possible by different systems: - floor heating and/or cooling - cooling or heating ceiling - ventilation and Air handling Unit The paper reports on the use of building and HVAC system simulation in order to support the design of the plant. Simulation is carried out in the TRNSYS environment and gathers the following components: building, reversible heat pump, thermal solar collectors, photovoltaic solar collectors, floor heating, cooling ceiling, Air Handling Unit, storage tanks. Parameters identification for the different components will be developed. The paper will focus on specific problems connected to the simultaneous control of both temperature and relative humidity in situation close to the saturation state. The whole design methodology will be situated in the general context of the building life cycle and will make use of some ideas presented in the IEA Annex 30 research project. [less ▲]

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See detailDetection of a single synchronous growth change in several tree-ring series of south-east France
Nicault, A.; Boreux, Jean-Jacques ULg; Rathegeber, C.

in Proceedings of the 6th international conference on dendrochronology (2002)

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See detailThe metropolis-hastings algorithm, a handy tool for the practice of environmental model estimation : illustration with the biochemical oxygen demand data
Torre, F.; Boreux, Jean-Jacques ULg; Parent, E.

in Cybergeo : Revue Européenne de Géographie = Cybergeo - European Journal of Geography (2001), 187

Environmental scientists often face situations where: (i) stimulus-response relationships are non-linear; (ii) data are rare or imprecise; (iii) facts are uncertain and stimulus-responses relationships ... [more ▼]

Environmental scientists often face situations where: (i) stimulus-response relationships are non-linear; (ii) data are rare or imprecise; (iii) facts are uncertain and stimulus-responses relationships are questionable.In this paper, we focus on the first two points. A powerful and easy-to-use statistical method, the Metropolis-Hastings algorithm, allows the quantification of the uncertainty attached to any model response. This stochastic simulation technique is able to reproduce the statistical joint distribution of the whole parameter set of any model. The Metropolis-Hastings algorithm is described and illustrated on a typical environmental model: the biochemical oxygen demand (BOD). The aim is to provide a helpful guideline for further, and ultimately more complex, models. As a first illustration, the MH-method is also applied to a simple regression example to demonstrate to the practitioner the ability of the algorithm to produce valid results. [less ▲]

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See detailL'opération sources en Belgique : premières analyses statistiques des résultats et légitimité des cartes "nitrates".
Wattecamps, J. M.; Bernier, Jacques; De Backer, Louis et al

in Hydrological Sciences Journal = Journal des Sciences Hydrologiques (2000), 45(1), 43-60

L'opération sources du WWF (Worldwide Fund for Wildlife) est une action éducative de sensibilisation à la qualité des eaux souterraines. Elle implique principalement les élèves de cinquième et sixième ... [more ▼]

L'opération sources du WWF (Worldwide Fund for Wildlife) est une action éducative de sensibilisation à la qualité des eaux souterraines. Elle implique principalement les élèves de cinquième et sixième primaires de Belgique. Depuis 1994, des centaines de dosages des ions nitrates ont été effectués dans un grand nombre de sources et de puits à l'aide de bandelettes colorimétriques. A l'issue de chaque campagne, les points d'eau surveillés ont été reportés sur une carte de Belgique où leur couleur indique leur qualité eu égard à la concentration en nitrates. L'objectif pédagogique étant atteint, la validation de ces cartes en tant qu'image de la réalité pose le problème de la vérification du lien entre la concentration réelle (mg l-1) du point d'eau visité et sa couleur sur la carte. A cette fin, des vérifications ont été réalisées sur 308 points d'eau choisis au hasard dans l'ensemble des sources et puits visités. L'analyse statistique révèle que la relation entre le test colorimétrique et le contrôle réalisé en laboratoire est hautement significative. Ce résultat justifie des investigations ultérieures, notamment la mobilisation de l'information régionale pour la qualification d'un point d'eau peu surveillé et la comparaison des cartes dans le temps. [less ▲]

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See detailInverse vegetation modelling : a tool to reconstruct palaeoclimates under changed CO2 conditions
Guiot, J.; Torre, F.; Jolly, D. et al

in Ecological Modelling (2000), 127

Atmospheric CO2 concentration has greatly fluctuated during the Quaternary. These variations have influenced the vegetation changes. The assumption that the relationship vegetation–climate sensu stricto ... [more ▼]

Atmospheric CO2 concentration has greatly fluctuated during the Quaternary. These variations have influenced the vegetation changes. The assumption that the relationship vegetation–climate sensu stricto was constant through time should be reconsidered taking into account the impact of the atmospheric CO2 content on the plants. Here we propose to use a process-based vegetation model (BIOME3) in an inverse mode to reconstruct from pollen data the most probable climate under precipitation seasonality change and under lowered CO2 concentration in the biosphere. Appropriate tools to match the model outputs with the pollen data are developed to generate a probability distribution associated with the reconstruction (Monte Carlo sampling and neural network techniques). The method is validated with modern pollen samples from Greece and Italy: it proves to be able to reconstruct modern climate with a more or less large error bar from pollen data. The error bar depends in fact on the tolerance of the vegetation to the corresponding climatic variable. The application to six pollen assemblages from Greece and Italy, representing the last glacial maximum (LGM: 18 000 14C-year B.P.), is done into three experiments: (1) modern CO2 concentration; (2) LGM CO2 concentration; (3) LGM CO2 concentration and high winter precipitation. The latter experiment is motivated by evidence of high lake-levels in Greece during the LGM which has been attributed to winter rainfall. These experiments show that winter was ca. 15–20°C colder than the present, in agreement with previous climate reconstruction. The apparent discrepancy between the high lake-levels and the steppe vegetation during the LGM, can be explained by an increase of the winter precipitation (which leads to high lake level) while the summer season is mild and dry (which affects the vegetation). The summer temperature has three stable states (−16°C, −10°C, −2°C), but the warmest one is the most probable if we take into account the lowered CO2 and the high lake-levels. [less ▲]

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See detailStatistique pour l'environnement. Traitement bayésien de l'incertitude
Bernier, Jacques; Parent, Eric; Boreux, Jean-Jacques ULg

Book published by Editions Tec & Doc (2000)

Ce manuel de statistique appliquée traite de l'analyse quantitative des incertitudes. Toutes les applications présentées portent sur les risques concernant les décisions en matière de gestion de l ... [more ▼]

Ce manuel de statistique appliquée traite de l'analyse quantitative des incertitudes. Toutes les applications présentées portent sur les risques concernant les décisions en matière de gestion de l'environnement. Contrairement à beaucoup d'ouvrages de statistiques appliquées, ili exploite l'approche statistique bayésienne. En effet, les principes rationnels qui forment l'ossature de la théorie bayésienne apportent un point de vue neuf et pertinent pour traiter de la gestion des risques environnementaux. Selon cette conception, les données d'observation "objectives" sont combinées aux données "subjectives" (représentation formalisée du phénomène, expertise et savoir préalables) pour une mise à jour des connaissances. Ce livre s'adresse en priorité aux professionnels de l'environnement, ingénieurs, gestionnaires des risques, chercheurs et étudiants, soucieux d'une meilleure exploitation de leurs données et de leur savoir au travers d'une démarche quantitative cohérente. [less ▲]

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See detailStatistique pour l'environnement. Traitement bayésien de l'incertitude.
Bernier, Jacques; Parent, Eric; Boreux, Jean-Jacques ULg

Book published by Tec & Doc (2000)

Ce manuel de statistique appliquée traite de l'analyse quantitative des incertitudes. Toutes les applications présentées portent sur les risques concernant les décisions en matière de gestion de l ... [more ▼]

Ce manuel de statistique appliquée traite de l'analyse quantitative des incertitudes. Toutes les applications présentées portent sur les risques concernant les décisions en matière de gestion de l'environnement. Contrairement à beaucoup d'ouvrages de statistiques appliquées, il exploite l'approche statistique bayésienne. En effet, les principes rationnels qui forment l'ossature de la théorie bayésienne apportent un point de vue neuf et pertinent pour traiter de la gestion des risques environnementaux. Selon cette conception, les données d'observation "objectives" sont combinées aux données "subjectives" (représentation formalisée du phénomène, expertise et savoir préalables) pour une mise à jour des connaissances. Ce livre s'adresse en priorité aux professionnels de l'environnement - ingénieurs, gestionnaires des risques, chercheurs et étudiants - soucieux d'une meilleure exploitation de leurs données et de leur savoir au travers d'une démarche quantitative cohérente. [less ▲]

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See detailQualification of an experimentation centre to test visibility conditions in fog.
Colomb, M.; Serezat, L.; Legoueix, G. et al

Conference (1999, August)

Detailed reference viewed: 4 (2 ULg)