1,721,118 research outputs found
Analyse of the agrarian dynamics of agro ecosystems by spatial modelling and satellite images' processing, the case study of Burkina Faso.
No full textL’organisation des territoires ruraux d’Afrique de l’Ouest a été bouleversée ces vingt dernières années par des changements rapides, dus à un accroissement démographique sans précédent, à des politiques favorisant les cultures d’exportation et à l’introduction de nouvelles techniques culturales. On assiste aujourd’hui à une mutation des structures d’exploitation, une pression sur les ressources forestières, un épuisement des sols et une saturation de l’espace cultivé. Les tensions pour l’accès aux ressources se multiplient, faisant souvent ressurgir d’anciens conflits ethniques, et la question de la sécurité alimentaire se pose. Dans ce contexte, des systèmes d’alerte précoce ont été mis en place dans le but d’anticiper et d’endiguer l’insécurité alimentaire par l’analyse des risques de catastrophe.La thèse s’inscrit dans le cadre de ces systèmes d’alerte précoce et traite de l’étude des changements agraires et de leurs mécanismes. Elle se propose d’explorer de nouvelles pistes méthodologiques, basées à la fois sur la modélisation et la télédétection, pour réaliser une analyse rétrospective et prospective des dynamiques agraires de la province du Tuy, située à l’ouest du Burkina Faso.Nous abordons tout d’abord la question du croisement d’échelles dans les modèles de dynamiques des agroécosystèmes en développant un modèle multiscalaire des évolutions passées. Le modèle utilise les graphes d’interaction pour simuler des processus allant de l’échelle de la parcelle à l’échelle régionale (évolution des rendements, évolution des assolements, déforestation). Nous montrons ainsi qu’il est possible d’effectuer un croisement d’échelles dans un modèle sans avoir recours aux méthodes d’agrégation ou de désagrégation habituellement employées pour ce type d’étude.Le modèle est ensuite utilisé pour analyser deux aspects des dynamiques agraires de la province du Tuy. Le premier aborde les dynamiques de défriche, d’abord analysées à la lumière du débat Malthus-Boserup qui porte sur l’impact de la croissance démographique sur les ressources naturelles. Des scénarios prospectifs sont simulés et leurs conséquences sur les surfaces en végétation naturelle sont évaluées : ces scénarios simulent l’émigration d’une partie de la population vers d’autres régions, la création de zones protégées, la mise en place de politiques démographiques et la conversion progressive des systèmes de production à l’agro-écologie.Le second aspect concerne les processus décisionnels des agriculteurs pour constituer leurs assolements. L’étude consiste plus précisément à comprendre les importantes variations des surfaces allouées aux différentes cultures, observées au cours de la période étudiée, via l’analyse de l’évolution simulée du poids des différents facteurs intervenant dans la prise de décision.Dans une dernière partie, nous montrons qu’il est possible de détecter explicitement des empreintes de processus anthropiques dans les images de télédétection en utilisant les simulations multiscalaires du modèle développé. Nous réalisons ensuite une assimilation de l’information satellitaire dans le modèle, pour le ré-étalonner et ainsi renforcer ses capacités à reproduire les dynamiques ayant eu lieu. Cette dernière partie ouvre d’importantes perspectives concernant l’utilisation conjointe de l’information satellitaire et des modèles de dynamiques des agroécosystèmes.Rural areas of West Africa have seen notable transformations these last two decades, mainly due to high population growth, development policies in favor of export crops and introduction of new cropping practices. The results of these developments are a pressure on forestry resources, an evolution of farming systems, a depletion of soils and a saturation of cultivated areas. The number of conflicts for resources access increases, reviving buried ethnical tensions, and the question of food security is raised. In that context, early warning systems have been developed in order to foresee and curb food insecurity by the mean of hazard analyses.The present work deals with agrarian changes and their mechanisms, in the context of early warning systems development. New methodological approaches are explored, based on modeling and remote sensing in order to create a retrospective and prospective analysis of agrarian dynamics of the Tuy province, located in West Burkina Faso.We first focus on the issue of cross-scaling in agro-ecosystems dynamics models, by building a multi-scalar model of past developments. The model uses interaction graphs to simulate processes occurring from the plot scale to the regional scale (crop production, crop rotation and crop area expansion). We show that modelling across scales is achievable without resorting to methods of aggregation or disaggregation, usually applied for this type of study.The model is then used to analyze two aspects of agrarian dynamics of Tuy province. The first one deals with clearances dynamics in the context of Malthus vs Boserup debate, concerning the impacts of demographic growth on natural resources. Prospective scenarios are simulated and their consequences on natural vegetation surfaces are assessed: these scenarios simulate emigrations of a part of the population towards other areas, the implementation of protected areas, a demographic regulation and an ecological intensification of farming systems.The second aspect concerns decisional processes of farmers in order to constitute their crops rotations. The study consists in understanding the important variations of cultivated species, observed during the studied period, by analyzing the simulated weight evolution of different determining factors involved in the decisional processes.Finally, we show that anthropic processes footprints are explicitly detectable in remote sensing images, by using multi-scalar simulations of the model developed. Then, we create an assimilation of satellite data in the model in order to re-calibrate it and reinforce its abilities to reproduce past dynamics. This last part opens important perspectives concerning the joint use of remote sensing data and agro-ecosystems dynamics
Projet ANR-07-BLAN-0121 STAMP Spatial temporal and multiscale primitives for modelling dynamic landscapes. Programme blanc 2007 : compte-rendu de fin de projet
Full text linkProjet Energie domestique. Rapport de mission au Mali du 15 au 27 juin 1998 : appui au service cartographie informatique pour l'analyse d'images satellitales. Aide mémoire
No full textOcelet: a modelling language and a simulation environment for studying landscape dynamics
Full text linkModelling spatial dynamics in landscapes can be a means for better understanding the multiple and complex ongoing processes that underlie important issues facing societies today. Hypotheses and independent knowledge inferred from ground observations can be confronted for consistency, and the mechanisms requiring finer descriptions can also be identified. Different scenarios of landscape management can then be simulated and the possible consequences of the measures taken assessed. However, modelling landscape dynamics at different temporal and spatial scales remains a challenging task. Various approaches have been proposed to address this, including cellular automata, agent-based systems, discrete event systems, system dynamics and geographic information systems, each displaying specific benefits in some domains of application, and weaknesses in others. In this area of research, we are exploring an approach based on the manipulation of graphs (mathematical object expressing a set of entities, some of which are linked) that are employed here in an innovative way for modelling landscape dynamics. Concepts essential for modellers had to be identified and formally defined. A modelling computer language (called Ocelet) was then developed, together with the grammar and syntax needed to manipulate these concepts, the compiler, and the environment/interface for building models and running simulations. Ocelet is thus both a modelling language and a simulation tool. To illustrate its usage in diverse situations, four case studies are presented: 1) land cover changes in an agroforestry landscape; 2) coastal dynamics of mangrove ecosystems; 3) the dissemination of a pathogen among neighbouring agricultural plots; and 4) temporary pond and mosquito population dynamics for understanding Rift Valley Fever (RVF) occurrence. (Texte intégral
Contribution of radar imagery to tropical forest monitoring and management
No full textA general state-of-the-art assessment is presented of the possible usefulness of radar images for tropical forest inventory and monitoring, using examples from Indonesia. This decade has seen the launch of new spaceborne sensors using synthetic aperture radar (SAR) technology: ERS- I and ERS-2 (European Space Agency), J-ERS (NASDA, Japan) and Radarsat (Canadian Space Agency). These tools offer new opportunities to monitor land surfaces and particularly tropical forests, although it has not yet been used operationally for applications at local and regional scales. In addition to their all-weather capabilities, ensuring repetitive acquisition day or night, microwaves used by SAR can probe vegetation covers and are sensitive to some extent to cover structure, biomass and water status. In addition, multi-temporal use of SAR images allows monitoring of environmental and man-made changes such as clear-cutting of primary forest or burnt areas such as were the result of the large Indonesian fires that occurred in 1997. However, this technology is relatively new and the information content relative to tropical forest characteristics and their dynamics still need to be understood for the development of robust applications useful for tropical forest management. In addition, significant limitations, specific to SAR images, exist for which recent research results can hopefully provide operational solutions with in-house or commercial image processing software: availability of I channel for a given sensor speckle noise and image distortions in hilly terrain situations. This paper discusses the main areas where SAR images can play a role in the monitoring of tropical forests: land cover and forest type mapping; forest monitoring and mapping of clear-cutting; and the construction of Digital Elevation Models
Ocelet : un langage de modélisation et un outil de simulation de dynamiques paysagères : Projet ANR STAMP (spatial temporal and multiscale primitives for modelling dynamic landscapes) - ANR-07-blan-0121
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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