Regional analysis of crop and natural vegetation in West Africa based on NDVI metrics

In West Africa, rainfall variability dynamics are often considered as the major driver of vegetation production. Land use shifts have also to be taken into account when analyzing changes in vegetation production. To study how land use changes may impact vegetation response along a climatic gradient, we used three MODIS NDVI metrics time series (2000-2012) and a land cover map from MODIS Land Cover product. We performed a trend analysis and analyzed temporal profiles of the three metrics according to three climatic zones (Sahelian, Sudanian and Guinean zones). Our results indicate differences in NDVI values of Croplands and Natural Vegetation and that these differences are in connection with climatic zones. In the Sahelian zone Croplands tend to have higher values than Natural vegetation, whereas the opposite is observed for the Sudanian and Guinean zones. These results could help improve the interpretation of vegetation trends in a context of climate and land management shifts. (Résumé d'auteur

Herbaceous biomass productivity dynamics monitoring and its drivers in Sahelian croplands and rangelands to support food security policies

Since the Sahelian population livelihood relies mainly on agropastoral activities, accurate information on biomass productivity dynamics and the underlying drivers are needed to manage a wide range of issues such as food security. This study aims to contribute to a better understanding of these drivers in rangeland and cropland, both at the Sahel and local levels (an agropastoral site in South-West Niger). At the Sahel level, the MODIS Land Cover product was used to extract cropland and rangeland pixels. By analyzing MODIS NDVI trends together with TRMM3B43 annual rainfall (2000-2015), we developed a classification scheme allowing to identify areas of persistent decline/improvement in biomass productivity and to separate rainfall-driven dynamics from other factors. The results showed an overall increase of productivity in the rangeland, and both an improvement and a degradation in the cropland. We found strong evidence that rain is not the only import driver of biomass increase, while the decrease could be attributed chiefly to other factors exclusively or to a combination of both climate-and human-induced factors. At the Niger site level, biomass trends have been put in relation with a set of potential drivers via a Random Forest model, to define which were the explanatory factors of the observed trends. The factor set covered 5 categories: climate, natural constraints, demography, physical accessibility and land cover changes. We highlighted that tiger bushes areas were particularly prone to pressure due to overgrazing and overexploitation of wood, while positive trends were mainly observed near rivers and in fossil valleys where new agricultural practices might have been promoted. The approach developped here could help to delineate areas with decrease in crop and grassland production and thus to assess the vulnerability of the population, but also to target zones with good potential for planning long-term food security policies. (Texte intégral

How reliable is the MODIS land cover product for crop mapping Sub-Saharan agricultural landscapes?

Accurate cropland maps at the global and local scales are crucial for scientists, government and nongovernment agencies, farmers and other stakeholders, particularly in food-insecure regions, such as Sub-Saharan Africa. In this study, we aim to qualify the crop classes of the MODIS Land Cover Product (LCP) in Sub-Saharan Africa using FAO (Food and Agricultural Organisation) and AGRHYMET (AGRiculture, Hydrology and METeorology) statistical data of agriculture and a sample of 55 very-high-resolution images. In terms of cropland acreage and dynamics, we found that the correlation between the statistical data and MODIS LCP decreases when we localize the spatial scale (from R2 = 0.86 *** at the national scale to R2 = 0.26 *** at two levels below the national scale). In terms of the cropland spatial distribution, our findings indicate a strong relationship between the user accuracy and the fragmentation of the agricultural landscape, as measured by the MODIS LCP; the accuracy decreases as the crop fraction increases. In addition, thanks to the Pareto boundary method, we were able to isolate and quantify the part of the MODIS classification error that could be directly linked to the performance of the adopted classification algorithm. Finally, based on these results, (i) a regional map of the MODIS LCP user accuracy estimates for cropland classes was produced for the entire Sub-Saharan region; this map presents a better accuracy in the western part of the region (43%-70%) compared to the eastern part (17%-43%); (ii) Theoretical user and producer accuracies for a given set of spatial resolutions were provided; the simulated future Sentinel-2 system would provide theoretical 99% user and producer accuracies given the landscape pattern of the region. (Résumé d'auteur

Disentangling factors of landscape changes in Burkina Faso, the nexus between spatial modeling and remote sensing

Rural areas of West Burkina Faso have seen notable transformations these last two decades due to high population growth and farming systems evolution. Satellite images acquired frequently and covering large areas are essential for detecting such landscape changes and long term trends. However, these images generally have coarse spatial resolutions and can only provide information about changes in the main vegetation patterns. The factors causing these changes are more difficult to determine, although there are essential for monitoring landscape evolution. We hereby present a method based on multi-scalar modelling of past landscape dynamics crossed with changes in vegetation trends identified from coarse resolution satellite images. The aim of our presentation is to use the model to simulate and illustrate how land cover and land use changes may impact vegetation response by improving the qualification and understanding of the observed trends. The cropping systems dynamics of the study area, the Tuy province of West Burkina Faso, were modelled with the Ocelet Modelling Platform over the last fifteen years through a multi-scalar model. The model was validated at local scale with information derived from high resolution images. At the same time, vegetation trends were analysed using Ordinary Least Square regressions based on MODIS NDVI time series. Simulated cropland change maps were then used to decompose the remote sensing-based trends. This allowed the spatial identification of factors responsible for the vegetation changes. The original approach we proposed here opens new opportunities for the understanding and monitoring of landscape changes using time series of coarse resolution satellite images

Observation spatiale pour l'agriculture en Afrique: potentiels et défis

Ce rapport a pour objectif de faire un état des lieux des usages des technologies satellitaires dans le développement et l'analyse des agricultures africaines, afin de mieux cerner les difficultés actuelles, identifier les contraintes sur lesquelles la recherche et le partenariat peuvent avoir un effet, et imaginer les actions nécessaires pour lever ces contraintes à court et moyen termes. L'ensemble du continent africain est traité, avec un focus sur l'Afrique de l'Ouest. L'échelle abordée est l'échelle nationale à laquelle se mettent en place les politiques publiques agricoles. Dans une 1èrepartie est dressé le panorama de la télédétection en Afrique pour l'agriculture, avec l'analyse des besoins prioritaires en informations, et les principaux programmes et projets en cours pour le développement de services. La 2ème partie présente l'offre actuelle et future en imagerie satellitaire et en outils logiciels, et les produits globaux descriptifs des états de surface aux échelles globale et régionale. Les principales applications de la télédétection sont illustrées en 3ème partie. (Résumé d'auteur

Odniesienie do nieobecności w angielskich sekwencjach no + N i w sekwencjach pas de + N i / lub aucun + N w języku francuskim

This paper enquires into the field of negative noun determination in English and in French. It focuses on the English sequences ‘No + countable noun in the singular’ (No + N-Ø) and ‘No + count­able noun in the plural’ (No + N-s), and some of their possible translations in French, namely aucun or pas de, followed by a noun either in the singular or in the plural.The existence in English of the two sequences raises the question of the differences in meaning these two sequences convey and induces one to examine their French possible translations with pas de or aucun. The aim thus is to examine examples in which both constructions are grammatically allowed in English, in order to elucidate the process through which reference is construed, and to examine the similarities and differences in meaning in the French sequences resorting to aucun or pas de. An analysis of each of the constructions will lead us to investigate the linguistic features, pertaining to sets of properties and occurrences, subjective and argumentative factors, which may or may not imply patterns of correspondences through translation. We will address these issues via the examination of translated examples taken from a parallel corpus made up of extracts from contemporary novels written in English after 1980 and of their translations into French.In English, no marks an impossible scanning operation either over a set of items defined in a space and time frame, with a noun in the plural, or over an open set defined according to proper­ties, with a noun in the singular.We have determined that in French, differentiating between two markers depends on defining a different linguistic operation for each of them: a scanning operation for aucun and a blocking of validation for pas de. We have further proved that the meanings construed by their respective operations agreed with their contextual environment.Niniejszy artykuł wkracza w dziedzinę uwarunkowań dotyczących połączeń rzeczownika ze znakiem negacji w języku angielskim i francuskim. Koncentruje się na angielskich ciągach “No + policzalny rzeczownik w liczbie pojedynczej” (No + N-Ø) i “No + policzalny rzeczownik w liczbie mnogiej” (No + N-s) i niektórych z ich możliwych tłumaczeniach w języku francuskim: aucun lub pas de, po którym następuje rzeczownik w liczbie pojedynczej lub w liczbie mnogiej.Istnienie w języku angielskim takich dwóch sekwencji rodzi pytanie o różnice w ich znaczeniu i nakłania do zbadania ich francuskich możliwych tłumaczeń za pomocą pas de lub aucun. Celem jest zatem zbadanie przykładów, w których obie konstrukcje są gramatycznie dopuszczalne w języku angielskim, w celu wyjaśnienia procesu, za pomocą którego interpretowane jest ich odniesienie, oraz w celu zbadania podobieństw i różnic w znaczeniu sekwencji francuskich wykorzystujących aucun lub pas de.Analiza każdej z konstrukcji rzeczownikowej doprowadzi nas do zbadania cech językowych, odnoszących się do zestawów właściwości oraz zdarzeń, czynników subiektywnych i argumentacyjnych, które mogą (lub nie) implikować poprzez tłumaczenie schematy zależności. Zajmiemy się tymi zagadnieniami, badając przetłumaczone przykłady zaczerpnięte z korpusu paralelnego złożonego z fragmentów współczesnych powieści napisanych po angielsku po 1980 roku i ich tłumaczeń na język francuski.W języku angielskim no oznacza niemożliwą operację skanowania zarówno na zestawie ele­mentów zdefiniowanych w ramie przestrzeni i czasu – z rzeczownikiem w liczbie mnogiej, jak i w otwartym zestawie zdefiniowanym według właściwości – z rzeczownikiem w liczbie poje­dynczej.Ustaliliśmy, że w języku francuskim rozróżnianie dwóch markerów zależy od zdefiniowania różnych operacji językowych dla każdego z nich: skanowania dla aucun i blokowania walidacji dla pas de.Udowodniliśmy ponadto, że znaczenia interpretowane przez ich działania są zgodne z ich kontekstowym otoczeniem

Présentation

Ce numéro de la revue Linx fait suite à un colloque international organisé par le Groupe de Recherche en Grammaires, laboratoire affilié au Centre de Recherche d’Études Anglophone (CREA, EA370), à l’Université de Paris Nanterre les 8 et 9 février 2019, et dont le titre était : Approche à visée actionnelle et grammaire en cours de langues étrangères en collège et lycée : quel terrain d’entente ? Ce colloque s’était donné pour objectif de réunir des chercheurs en linguistique et en didactique d..

La conceptualisation grammaticale comme objet du projet en cours d'anglais langue étrangère : bilan d'une expérience en classe de seconde

Cet article tente d’apporter une solution au paradoxe de l’enseignement des langues en milieu institutionnel en France généré par les injonctions contradictoires à destination des enseignants. Les Instructions Officielles françaises soulignent non seulement la nécessité de l’exposition fréquente à la langue mais aussi l’importance d’amorcer une réflexion sur son fonctionnement pour développer autonomie et maîtrise, sans oublier la mise en œuvre d’une pédagogie de projet afin de favoriser les échanges en classe. Les horaires dédiés à l’enseignement des langues ne donnent pas le loisir d’appliquer toutes ces consignes à la fois. L’expérience présentée et analysée dans cet article, est fondée sur le principe de l’efficacité d’une séquence qui prend pour tâche collective et finale la construction d’un outil métalinguistique pour décrire un fait de langue. Partant du constat, suite à évaluation diagnostique, que le système aspectuo-temporel de l’anglais constituait une difficulté conceptuelle particulière pour les apprenants francophones, une classe de 2de a été engagée sur le chemin de l’élaboration d’un outil métalinguistique qui permette à la fois sa description et la remédiation des erreurs. En parallèle, un groupe classe témoin permet de jauger les progrès réalisés dans la classe test. Le versant linguistique de l’analyse prend pour cadre la Théorie des Opérations Prédicatives et Enonciatives, et s’appuie, entre autres, sur les travaux de Berthonneau (1992), de Franckel (1989) et de Trévise (1990). Les résultats montrent que le temps dédié à la réflexion est du temps gagné sur l’apprentissage et sur la compétence à communiquer.This article focuses on the difficulties that the French secondary school teachers encounter when it comes to respecting all the injunctions which govern their profession. The national curriculum states that the pupils should be exposed as often as possible to authentic occurrences of language, exercise their grammatical awareness, take part in conversations with their peers, and elaborate a final collective task, which is not necessarily linguistic. But the foreign language schedule in French schools compels the teachers to make a selection among all those objectives. The experiment presented and analysed here shows that a foreign language teaching sequence in which the final task aims at the elaboration of a metalinguistic tool might gain in efficiency, while respecting the national curriculum.