Ocelet: a modelling language and a simulation environment for studying landscape dynamics

Modelling 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

Ocelet modelling language and simulation tool: possible applications in pest management

Modelling spatial dynamics may be used to gather understanding on how insect populations develop in a given environment. 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 pest management can then be simulated and the possible consequences of the measures taken assessed. However, spatial dynamics are expressions of multiple and complex ongoing processes, and their modelling 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, two case studies possibly pertinent for pest management are presented: 1) the dissemination of a pathogen among neighbouring agricultural plots, and 2) temporary pond and mosquito population dynamics for understanding Rift Valley Fever (RVF) occurrence. (Texte intégral

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

Heat as a proxy to image dynamic processes with 4D electrical resistivity tomography

Since salt cannot always be used as a geophysical tracer (because it may pollute the aquifer with the mass that is necessary to induce a geophysical contrast), and since in many contaminated aquifer salts (e.g., chloride) already constitute the main contaminants, another geophysical tracer is needed to force a contrast in the subsurface that can be detected from surface geophysical measurements. In this context, we used heat as a proxy to image and monitor groundwater flow and solute transport in a shallow alluvial aquifer (< 10 m deep) with the help of electrical resistivity tomography (ERT). The goal of our study is to demonstrate the feasibility of such methodology in the context of the validation of the efficiency of a hydraulic barrier that confines a chloride contamination to its source. To do so, we combined a heat tracer push/pull test with time-lapse 3D ERT and classical hydrogeological measurements in wells and piezometers. Our results show that heat can be an excellent salt substitution tracer for geophysical monitoring studies, both qualitatively and semi-quantitatively. Our methodology, based on 3D surface ERT, allows to visually prove that a hydraulic barrier works efficiently and could be used as an assessment of such installations

Developing a service-oriented component framework for a landscape modeling language

With modeling and simulation, it is possible to study how a system works before trying to predict how it would behave in a variety of situations. However, when modeling landscape processes, issues related to space, time and multiple scales need to be addressed. In order to investigate these issues, a modeling platform based on a Domain Specific Language (DSL) has been developed. One of the main technical challenges of this platform is the ability to build applications with the capacity to themselves dynamically adapt to their environment. In this paper, we present the arguments and motivations behind the choice of the Service- Oriented Computing (SOC) approach when implementing the execution framework of the DSL. The modeling platform is composed of a development environment based on Eclipse IDE, a code generator, and an execution framework. The execution framework, which is the focus of this paper, must meet the constraints set by dynamic landscapes modeling, while capitalizing on the possibilities offered by the SOC approach. (Résumé d'auteur