Éditeur(s) : HAL CCSD
Résumé : To appear in TOPOLOGICAL METHODS IN NONLINEAR ANALYSIS (16 pages).
In the last two decades, many algebras of generalized functions have been constructed, particularly the so-called generalized Sobolev algebras. Our goal is to study the latter and some of their main properties. In this framework, we pose and solve a nonlinear degenerated Dirichlet problem with irregular data such as Dirac generalized functions.
https://hal.archives-ouvertes.fr/hal-00004903

Droits : info:eu-repo/semantics/OpenAccess
hal-00004903
https://hal.archives-ouvertes.fr/hal-00004903
https://hal.archives-ouvertes.fr/hal-00004903/document
https://hal.archives-ouvertes.fr/hal-00004903/file/sb_psn_pjm.pdf
ARXIV : math.GM/0505228

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Starting from a locally convex metrisable topological space and from any asymptotic scale, we construct a generalized extension of this space. To those extensions, we associate Hausdorff topologies. We introduce the notion of a temperate map, with respect to a given asymptotic scale, between two locally convex metrisable semi-normed spaces. We show that such mappings extend in a canonical way to mappings between the respective generalized extensions. We give an application to nonlinear Dirichlet boundary value problems with singular data in the framework of generalized extensions
ISSN: 0026-9255

hal-01529549
https://hal.univ-antilles.fr/hal-01529549

Éditeur(s) : HAL CCSD
Résumé : 25 pages, Equipe AANL
We extend the theory of distributional kernel operators to a framework of generalized functions, in which they are replaced by integral kernel operators. Moreover, in contrast to the distributional case, we show that these generalized integral operators can be composed unrestrictedly. This leads to the definition of the exponential, and more generally entire functions, of a subclass of such operators.
https://hal.archives-ouvertes.fr/hal-00004888

hal-00004888
https://hal.archives-ouvertes.fr/hal-00004888
https://hal.archives-ouvertes.fr/hal-00004888/document
https://hal.archives-ouvertes.fr/hal-00004888/file/Article5.pdf
ARXIV : math/0505126

Éditeur(s) : HAL CCSD
Résumé : We extend classical results from the Colombeau algebra, concerning point-value characterizations of generalized functions, to the more general case of multi-parameter (C,E,P)-algebras. Our investigations include considerations about different definitions of subspaces related to tempered generalized functions.
https://hal.univ-antilles.fr/hal-00761114

hal-00761114
https://hal.univ-antilles.fr/hal-00761114
https://hal.univ-antilles.fr/hal-00761114/document
https://hal.univ-antilles.fr/hal-00761114/file/DT2010-05_Hasler_Marti.pdf

Éditeur(s) : HAL CCSD
Résumé : 15 pages
International audience
In analogy to the classical isomorphism between $mathcal{L}left( mathcal{S}left( mathbb{R}^{n}right) ,mathcal{S}^{prime}left( mathbb{R}^{m}right) right) $ and $mathcal{S}^{prime}left( mathbb{R}^{n+m}right) $, we show that a large class of moderate linear mappings acting between the space $mathcal{G}_{mathcal{S}}left( mathbb{R}^{n}right) $ of Colombeau rapidly decreasing generalized functions and the space $mathcal{G}_{ au}left( mathbb{R}^{n}right) $ of temperate ones admits generalized integral representations, with kernels belonging to $mathcal{G}_{ au}left( mathbb{R}^{n+m}right) $. Furthermore, this result contains the classical one in the sense of the generalized distribution equality.
Math. Proc. Camb. Philos. Soc.

Droits : info:eu-repo/semantics/OpenAccess
hal-00019916
https://hal.archives-ouvertes.fr/hal-00019916
https://hal.archives-ouvertes.fr/hal-00019916/document
https://hal.archives-ouvertes.fr/hal-00019916/file/KernelSADelcroixfeb7th.pdf
ARXIV : math.FA/0603035

Éditeur(s) : HAL CCSD International Publishing Service/IPS
Résumé : International audience
We give a description of various algebras of generalized functions based on the introduction of pseudo-ultranorms on spaces of sequences in given locally convex function algebras. We study sheaf properties of these algebras, needed for microlocal analysis, and also consider regularity theory, functoriality and different concepts of association and weak equality in a unified setting. Using this approach, we also give new results on embeddings of ultradistribution and hyperfunction spaces into corresponding algebras of generalized functions.
ISSN: 0012-3862

hal-00758044
https://hal.univ-antilles.fr/hal-00758044
https://hal.univ-antilles.fr/hal-00758044/document
https://hal.univ-antilles.fr/hal-00758044/file/DHPV-26oct-8nov06.pdf
DOI : 10.4064/dm447-0-1

Éditeur(s) : HAL CCSD Oxford University Press (OUP): Policy P - Oxford Open Option A Oxford University Press (OUP)
Résumé : International audience
It is well known that sedimentary rocks having same porosity can have very different pore size distribution. The pore distribution determines many characteristics of the rock, among which its transport properties are often the most useful. Multifractal analysis is a powerful tool that is increasingly used to characterize the pore space. In this study, we performed multifractal analysis of pore distribution on simulated sedimentary rocks using the relaxed bidisperse ballistic deposition model (RBBDM). The RBBDM can generate a 3-D structure of sedimentary rocks of variable porosity by tuning the fraction p of particles of two different sizes. We also performed multifractal analysis on two samples of real sedimentary rock to compare with the simulation studies. One sample, an oolitic limestone is of high porosity (40 per cent) while the other is a reefal carbonate of low porosity, around 7 per cent. 2-D sections of X-ray microtomographs of the real rocks were stacked sequentially to reconstruct the real rock specimens. Both samples show multifractal character. The results from analysis of real rock agree quite well with the simulated structure of low porosity. The simulated rock of high porosity showed a weak multifractal nature though the real rock sample of similar porosity was found to be strongly multifractal. We propose a ‘structure parameter’ ξ which is a function of porosity and the generalized dimensions, and controls the transport properties of the rock.
ISSN: 0956-540X

hal-01174142
https://hal.archives-ouvertes.fr/hal-01174142
DOI : 10.1093/gji/ggu417

Éditeur(s) : HAL CCSD
Résumé : To appear in the Proceeding of GF2004 in ITSF (8 pages).
We extend the theory of distributional kernel operators to a framework of generalized functions, in which they are replaced by integral kernel operators. Moreover, in contrast to the distributional case, we show that these generalized integral operators can be composed unrestrictedly. This leads to the definition of the exponential of a subclass of such operators.
https://hal.archives-ouvertes.fr/hal-00004897

hal-00004897
https://hal.archives-ouvertes.fr/hal-00004897
https://hal.archives-ouvertes.fr/hal-00004897/document
https://hal.archives-ouvertes.fr/hal-00004897/file/GF04BernardDelcroixColombeauNov01.pdf
ARXIV : math.GM/0505179

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Voting rules relying on k-nearest neighbors (k-NN) are an effective tool in countless many machine learning techniques. Thanks to its simplicity, k-NN classification is very attractive to practitioners, as it enables very good performances in several practical applications. However, it suffers from various drawbacks, like sensitivity to "noisy" instances and poor generalization properties when dealing with sparse high-dimensional data. In this paper, we tackle the k-NN classification problem at its core by providing a novel k-NN boosting approach. Namely, we propose a supervised learning algorithm, called Universal Nearest Neighbors (UNN), that induces a leveraged k-NN rule by globally minimizing a surrogate risk upper bounding the empirical misclassification rate over training data. Interestingly, this surrogate risk can be arbitrary chosen from a class of Bregman loss functions, including the familiar exponential, logistic and squared losses. Furthermore, we show that UNN allows to efficiently filter a dataset of instances by keeping only a small fraction of data. Experimental results on the synthetic Ripley's dataset show that such a filtering strategy is able to reject "noisy" examples, and yields a classification error close to the optimal Bayes error. Experiments on standard UCI datasets show significant improvements over the current state of the art.
ISSN: 0925-2312

hal-00664462
https://hal.inria.fr/hal-00664462

Éditeur(s) : HAL CCSD
Résumé : International audience
ABSTRACT :A satellite retrieval of surface solar irradiance (SSI) based on GOES satellite data is presented and validated for the French Guiana with three years of in situ measurements from six ground stations. We propose a particle filter approach combining GOES satellite observations and in situ data. We propose an original observation function based on a joint probability distribution and taking advantages of the characteristics of both the involved type of data. The statistical results are compared with those of existing estimation methods and they are found to be in accordance with them. The daily bias ranges from -12 W/m² (-6% of the mean of measurements) to 12 W/m² (6%), depending on the stations. The daily root mean square difference ranges between 23 W/m² (10%) and 27 W/m² (15%). The correlation coefficient is close to 0.92. There is no seasonal climatic effect on the method, the bias and RMSD remain similar for both the rainy and the dry season, but better correlation is observed in the rainy season than in the dry season. Uncertainties are mainly due to the presence of specific tropical atmospheric conditions during the dry season. The method has been tested through various tests: cross-validation scheme has highlighted the potential generalization of the model in a temporal dimension; the ability of the method to effectively duplicate anomalies in surface solar irradiance time series has also been tested. The robustness of the results shows the interest of the method compared to other existing estimation methods. Because of its simplicity of implementation this method opens new prospects in estimating surface solar irradiance. It is concluded that using a particle filter and original observation function method allow a high-quality surface solar irradiance estimation in French Guiana.RESUMEUne méthode d'estimation de l'irradiance solaire de surface (SSI) à partir de données satellites GOES est présentée et validée par comparaison avec trois années de mesures in situ provenant de six stations météorologiques de Guyane Française. Dans cet article, nous proposons une approche par filtre particulaire combinant observations du satellite GOES et données in situ. Nous proposons une fonction d'observation originale basée sur une distribution de probabilité conjointe des deux types de données. Les résultats statistiques sont conformes à ceux des méthodes existantes. Le biais journalier varie de -16 W / m² (-7% de la moyenne des mesures) à 12 W / m² (6%). L'erreur quadratique moyenne (RMSD) est comprise entre 23 W / m² (10%) et 27 W / m² (15%). Le coefficient de corrélation est de 0,92. La méthode est peu sensible aux variations climatiques saisonnières, le biais et RMSD restent similaires en saison des pluies comme en saison sèche, mais une meilleure corrélation est observée pendant la saison des pluies. Les incertitudes sont principalement dues à la présence de conditions atmosphériques tropicales spécifiques en saison sèche. La méthode a été soumise à différents tests : un processus de validation croisée a mis en évidence la possible généralisation du modèle dans une dimension temporelle, la capacité du modèle à reproduire efficacement des anomalies dans les séries temporelles d'irradiance solaire de surface a aussi été testée. La robustesse des résultats obtenus montrent l'intérêt du modèle par rapport aux autres méthodes d'estimation existantes. A cause de sa simplicité de mise en oeuvre cette méthode ouvre de nouvelles perspectives en matière d'estimation de l'irradiance solaire au sol. Nous concluons que l'utilisation d'un filtre particulaire combinée à une fonction d'observation originale permet une estimation de haute qualité de l'irradiance solaire au sol en Guyane Française.
Canadian Journal of Remote Sensing

meteo-01304574
https://hal-meteofrance.archives-ouvertes.fr/meteo-01304574
DOI : 10.1080/07038992.2015.1040150

Éditeur(s) : HAL CCSD Taylor & Francis
Résumé : International audience
We extend the theory of distributional kernel operators to a framework of generalized functions, in which they are replaced by integral kernel operators. Moreover, in contrast to the distributional case, we show that these generalized integral operators can be composed unrestrictedly. This leads to the definition of the exponential, and more generally entire functions, of a subclass of such operators.
ISSN: 1065-2469

hal-01530753
https://hal.univ-antilles.fr/hal-01530753

Éditeur(s) : HAL CCSD Department of Mathematics and Informatics, Faculty of Sciences, University of Novi Sad
Résumé : International audience
We present some remarks about the embedding of spaces of Schwartz distributions into spaces of Colombeau generalized functions. Following ideas of M. Nedeljkov et alii, we recall how a good choice of compactly supported mollifiers allows to perform globally the embedding of D' () into G (). We show that this embedding is equal to the one obtained with local and sheaf arguments by M. Grosser et alii, this giving various equivalent technics to embed D'() into G ().
ISSN: 1450-5444

hal-01530751
https://hal.univ-antilles.fr/hal-01530751
https://hal.univ-antilles.fr/hal-01530751/document
https://hal.univ-antilles.fr/hal-01530751/file/NS04_25.PDF

Éditeur(s) : HAL CCSD
Résumé : International audience
Given a topological R-module or algebra E and an asymptotic scale MR Λ, we define a natural M-extended topology on the sequence space E Λ, and the M-extension of E as the Hausdorff space associated with the subspace of sequences for which multiplication is continuous with respect to this topology. Colombeau's generalized functions and similar constructions are obtained as special cases, but this new approach also allows the iteration of the construction, which was not possible with previously existing theories. We use only the topology, i.e. neigbourhoods of zero, but not its explicit definition in terms of seminorms, inductive or projective limits etc., which is particularly useful in non-metrizable spaces. Many ideas commonly used in generalized function spaces (functoriality, association, sheaf structure, algebraic analysis, ...) can be applied to a large extent; but reasoning on a category-theoretic level allows the establishment of several results so far only known for particular cases, to the whole class of such spaces.
Integral Transforms and Special Functions
Bedlewo, Poland

hal-00761666
https://hal.univ-antilles.fr/hal-00761666
DOI : 10.1080/10652460802565040

Éditeur(s) : NRC
Résumé : In self-feeding conditions, a few individual sea bass (Dicentrarchus labrax (L., 1758)) display strong activity in striking the food dispenser, whereas the remaining individuals of the group actuate the feeder weakly or never. Here, we investigated the effects of removal of the individuals showing dominant activity on the social and feeding behaviours in groups of juvenile sea bass. Following removal, new fish showing a dominant self-feeding activity quickly appear. They always come from the group of fish that have a low number of triggering actuations. This observation shows that it takes less time, about 5 days after the removal of dominant triggerers vs. 14 days at the beginning, for the re-establishment of the behavioural structure, suggesting the possibility of social transmission between individuals. The fish that show weak triggering activity seem to reach the high-food triggering level without obvious signs of competition. This experiment reveals the importance of the food-demand behavioural structure: the fish displaying the highest activity lead to a general food distribution and play a dominant role in feeding the entire group. Functional plasticity in this role within individuals is also demonstrated, indicating that the high-triggering function is essential for the group and not for the individual themselves.
Au sein d'un groupe de bars (Dicentrarchus labrax (L., 1758)) placés en auto-nourrissage, quelques individus disposent d'une activité forte de déclenchement volontaire du distributeur d'aliments. Les autres poissons du groupe disposent d'une activité de demande faible voire nulle. Ici, nous avons étudié l'impact du retrait des poissons à forte activité sur le comportement alimentaire et social de groupes de bars juvéniles. De nouveaux individus à forte activité réapparaissent rapidement, provenant exclusivement de la classe de poissons de faible demande. Cinq jours en moyenne suffisent après le retrait, contre 14 jours au début de l'expérience, pour que la structure comportementale se rétablisse suggérant l'existence d'une transmission sociale entre les individus. Ces poissons de faible activité semblent de plus atteindre leur nouvelle fonction sans aucun signe de compétition. Cette expérience révèle d'abord l'importance de la structure de la demande alimentaire puisqu'elle réapparaît après le retrait. Elle montre également que l'activité des forts manipulateurs conduit à une distribution générale de l'aliment et contribue à nourrir le groupe en entier. L'étude montre enfin une plasticité fonctionnelle indiquant que seule la fonction de manipulateur fort est essentiel pour la stabilité du groupe, non l'identité des individus par elle-même.
Canadian journal of zoology (0008-4301) (NRC), 2008-09 , Vol. 86 , N. 9 , P. 1015-1023

Droits : 2008 NRC Canada
http://archimer.ifremer.fr/doc/2008/publication-4766.pdf
DOI:10.1139/Z08-077
http://archimer.ifremer.fr/doc/00000/4766/

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Little is known of how linkage patterns between species change along environmental gradients. The small, spatially discrete food webs inhabiting tank-bromeliads provide an excellent opportunity to analyse patterns of community diversity and food-web topology (connectance, linkage density, nestedness) in relation to key environmental variables (habitat size, detrital resource, incident radiation) and predators: prey ratios. We sampled 365 bromeliads in a wide range of understorey environments in French Guiana and used gut contents of invertebrates to draw the corresponding 365 connectance webs. At the bromeliad scale, habitat size (water volume) determined the number of species that constitute food-web nodes, the proportion of predators, and food-web topology. The number of species as well as the proportion of predators within bromeliads declined from open to forested habitats, where the volume of water collected by bromeliads was generally lower because of rainfall interception by the canopy. A core group of microorganisms and generalist detritivores remained relatively constant across environments. This suggests that (i) a highly-connected core ensures food-web stability and key ecosystem functions across environments, and (ii) larger deviations in food-web structures can be expected following disturbance if detritivores share traits that determine responses to environmental changes. While linkage density and nestedness were lower in bromeliads in the forest than in open areas, experiments are needed to confirm a trend for lower food-web stability in the understorey of primary forests.
PLoS ONE

hal-00913931
https://hal.archives-ouvertes.fr/hal-00913931
https://hal.archives-ouvertes.fr/hal-00913931/document
DOI : 10.1371/journal.pone.0071735
OATAO : 10204

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We show that a new definition of the asymptotic structure of the (C,E,P)-algebras (which are a refinement of the Colombeau Generalized Algebras) allows to define a natural topology on them. Furthermore, this topology can be mixed with functorial aspects of the construction in order to give extension principles, which give powerful tools to solve singular differential problems in this framework.
ISSN: 0022-247X

hal-01529551
https://hal.univ-antilles.fr/hal-01529551
DOI : 10.1016/j.jmaa.2009.05.046

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : Tree mortality in tropical forests is a complex ecological process for which modelling approaches need to be improved to better understand, and then predict, the evolution of tree mortality in response to global change. The mortality model introduced here computes an individual probability of dying for each tree in a community. The mortality model uses the ontogenetic stage of the tree because youngest and oldest trees are more likely to die. Functional traits are integrated as proxies of the ecological strategies of the trees to permit generalization among all species in the community. Data used to parametrize the model were collected at Paracou study site, a tropical rain forest in French Guiana, where 20,408 trees have been censused for 18 years. A Bayesian framework was used to select useful covariates and to estimate the model parameters. This framework was developed to deal with sources of uncertainty, including the complexity of the mortality process itself and the field data, especially historical data for which taxonomic determinations were uncertain. Uncertainty about the functional traits was also considered, to maximize the information they contain. Four functional traits were strong predictors of tree mortality: wood density, maximum height, laminar toughness and stem and branch orientation, which together distinguished the light-demanding, fast-growing trees from slow-growing trees with lower mortality rates. Our modelling approach formalizes a complex ecological problem and offers a relevant mathematical framework for tropical ecologists to process similar uncertain data at the community level.
ISSN: 1932-6203

hal-01190561
https://hal.archives-ouvertes.fr/hal-01190561
PRODINRA : 208582
PUBMED : 23675500
DOI : 10.1371/journal.pone.0063678

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : International audience
The elucidation of relationships between biodiversity and ecosystem processes has been limited by the definition of metrics of biodiversity and their integration into experimental design. Functional trait screening can strengthen the performance of these designs.* We suggest the use of Rao's quadratic entropy to measure both functional diversity and phylogenetic diversity of species mixtures proposed for an experimental design, and demonstrate how they can provide complementary information.* We also present an index assessing the statistical performance of these independent variables in different experimental designs. Measurement of independent variables as continuous vs. discrete variables reduces statistical performance, but improves the model by quantifying species differences masked by group assignments.* To illustrate these advances, we present an example from a tropical forest tree community in which we screened 38 species for nine functional traits. The proposed TropiDEP design is based on the relative orthogonality of two multivariate trait axes defined using principal component analysis.* We propose that independent variables describing functional diversity might be grouped to calculate independent variables describing suites of different traits with potentially different effects on particular ecosystem processes. In other systems these axes may differ from those reported here, yet the methods of analysis integrating functional and phylogenetic diversity into experimental design could be universal.
La compréhension des relations pouvant exister entre biodiversité et fonctionnement des écosystèmes a été longtemps limitée par la définition de méthodes de quantification de la diversité biologique et la mise en œuvre de dispositifs expérimentaux permettant sa mesure. L'identification de syndromes de traits fonctionnels clefs influençant des fonctions écosystémiques particulières peut renforcer la performance de ces dispositifs.* Nous suggérons l'utilisation de l'entropie quadratique de Rao pour mesurer la diversité fonctionnelle et phylogénétique dans des assemblages synthétiques d'espèces, et montrons comment ces mesures de diversité sont complémentaires.* Nous présentons également un indice permettant de tester la performance statistique de ces variables indépendantes dans différents modèles expérimentaux. L'utilisation de variables indépendantes continues plutôt que discrètes réduit la performance statistique mais améliore le modèle en quantifiant les différences fonctionnelles entre espèces; différences généralement masquées lors de leur assignation en groupes fonctionnels.* Pour illustrer ces avancées, nous présentons un exemple d'assemblages synthétiques à partir de 38 espèces d'arbres de forêt tropicale sélectionnées pour 9 traits fonctionnels (TropiDEP). Le plan d'expérience de TropiDEP est basé sur l'orthogonalité relative de deux axes multivariés de traits fonctionnels définis par analyse en composantes principales.* Nous proposons que les variables décrivant la diversité fonctionnelle soient groupées pour calculer des variables indépendantes, divisées en plusieurs axes décrivant des combinaisons de différents traits pouvant influencer des processus différents de l'écosystème (e.g. processus du N et du C). Dans d'autres systèmes, ces axes peuvent différer de ceux présentés ici, mais les méthodes d'analyse peuvent être universelles.
ISSN: 1286-4560

Droits : info:eu-repo/semantics/OpenAccess
hal-00883621
https://hal.archives-ouvertes.fr/hal-00883621
https://hal.archives-ouvertes.fr/hal-00883621/document
https://hal.archives-ouvertes.fr/hal-00883621/file/hal-00883621.pdf
DOI : 10.1051/forest/2009110

Éditeur(s) : HAL CCSD EDP Sciences
Résumé : International audience
By means of convenient regularization for an ill posed Cauchy problem, we define an associated generalized problem and discuss the conditions for the solvability of it. To illustrate this, starting from the semilinear unidirectional wave equation with data given on a characteristic curve, we show existence and uniqueness of the solution
ISSN: 0973-5348

hal-01529519
https://hal.univ-antilles.fr/hal-01529519
DOI : 10.1051/mmnp/201611207

Éditeur(s) : Université de la Nouvelle-Calédonie
Résumé : Estimating diversity and abundance of fish is fundamental for the understanding of community structure and dynamics of coral reefs. Observations are generally gathered using Underwater Visual Census (UVC). These informations can also be collected by underwater video techniques involving no diver and allowing a high spatial and temporal coverage. The first part of this PhD thesis is a review of publications using underwater video techniques between 1952 and 2012. The second part present two rotating video systems used to study the diversity of ichthyofauna and habitats in the lagoon of New Caledonia: the STAVIRO (for "STAtion VIdeo ROtative") and the MICADO (for "Module d’Imagerie Côtier, Autonome pour le Développement de l’Observation sous-marine"). The third part of this work is a comparison of these techniques with UVCs and an analysis of the “observer effect” for the rotating video techniques. The comparison between rotating video systems and UVC showed that: (i) fish community data collected by UVC and by STAVIRO differed significantly; (ii) species richness and density of large species were not significantly different between techniques; (iii) species richness and density of small species were higher for UVC; (iv) density of fished species was higher for STAVIRO; and (v) only UVC detected significant differences in fish assemblages structure across reef type. The comparison of fish counts obtained from the same videos by different observers showed that for a defined list of species, estimates of species richness and total abundance can be considered as similar between observers with sufficient experiences (> 6 months). The last part of this PhD is an application of rotating video techniques to the study of daily temporal variations of the ichthyofauna. Daily variations were observed depending on the time of day and the tidal state and typical patterns of variations have been described for some species groups. The outcomes of this work bring original insights of new techniques complementary to traditional techniques in order to enhance our understanding of the functioning and dynamic of coral reef.
L’estimation de la diversité et de l’abondance des espèces de poissons est fondamentale pour comprendre la structure des communautés et la dynamique des récifs coralliens. Les observations sont généralement obtenues par des recensements visuels en scaphandre autonome (UVC). Ces informations peuvent également être obtenues de manière originale grâce aux observations issues des techniques vidéo sous-marines modernes sans plongeur qui permettent des couvertures spatiales et temporelles accrues. La première phase de ce travail de thèse synthétise l’ensemble des travaux ayant été effectués avec des techniques vidéo entre 1952 et 2012. La seconde phase, présente deux systèmes vidéo rotatifs complémentaires, utilisés pour étudier la diversité de l’ichtyofaune et des habitats marins dans le lagon de Nouvelle-Calédonie : le STAVIRO (pour « STAtion VIdéo ROtative ») et le MICADO (pour « Module d’Imagerie Côtier, Autonome pour le Développement de l’Observation sous-marine »). La troisième phase de ce travail consiste à comparer ces systèmes vidéo aux UVC puis à examiner l’effet « observateur » inhérent aux techniques vidéo rotatives. Il résulte de cette étude que : (i) les observations des communautés de poissons par UVC et STAVIRO différaient significativement, (ii) la richesse spécifique et la densité des espèces de grande taille n'étaient pas significativement différentes entre les techniques, (iii) la diversité et la densité des espèces de petite taille étaient plus élevés avec les UVC; (iv) la densité des espèces pêchées était plus élevée avec les STAVIRO et (v) seuls les UVC ont détecté des différences de structure des assemblages en fonction du type de récif. L’étude de l’effet « observateur » a montré que sur une liste d’espèces définie, les dénombrements et les identifications des individus peuvent être considérées comme similaires entre observateurs ayant une expérience suffisante (> 6 mois). La dernière phase de ce travail a permis d’appliquer la technique MICADO à l’étude des variations temporelles de l’ichtyofaune d’un site corallien à l’échelle de la journée. Elle a permis de mettre en évidence des variations cycliques journalières en fonction de l’heure et de la marée et des « profils type » de variations ont pu être identifiés pour certains groupes d’espèces. Ce travail de thèse permet ainsi de participer au développement de nouvelles techniques d’observations complémentaires des techniques traditionnelles afin d’enrichir les connaissances du fonctionnement et de la dynamique des écosystèmes coralliens.

Droits : Université de la Nouvelle-Calédonie
http://archimer.ifremer.fr/doc/00189/30050/28536.pdf
http://archimer.ifremer.fr/doc/00189/30050/