Valérie Demarez

Valérie Demarez
Paul Sabatier University - Toulouse III | UPS Toulouse · Centre d'Etudes Spatiales de la Biosphère - UM 12 (UMR 5126 / UMRD 113 / UMR CNES) - CESBIO

HDR Remote Sensing

About

82
Publications
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Introduction
Valérie Demarez currently works at the Centre d'Etudes Spatiales de la Biosphère - UM 12 (UMR 5126 / UMRD 113 / UMR CNES) - CESBIO, Paul Sabatier University - Toulouse III. Valérie does research in remonte sensing, Ecology, Irrigation and Water Management.

Publications

Publications (82)
Article
Full-text available
The assessment of rice yield at territory level is important for strategic economic decisions. Assessing spatial and temporal yield variability at regional scale is difficult because of the numerous factors involved, including agricultural practices, phenological calendars, and environmental contexts. New remote sensing data acquired at decametric...
Article
Full-text available
In this study, we present an operational methodology for mapping irrigated areas at plot scale, which overcomes the limitation of terrain data availability, using Sentinel-1 (S1) C-band SAR (synthetic-aperture radar) and Sentinel-2 (S2) optical time series. The method was performed over a study site located near Orléans city of north-central France...
Article
Full-text available
Le Pôle thématique national des surfaces continentales Theia a pour objectif d’accroître l’utilisation par la communauté scientifique et les acteurs publics de la donnée spatiale en complémentarité d’autres types de données, notamment les données in situ et aéroportées. Depuis quelques années, Theia, met à disposition des acteurs publics nationaux,...
Article
Full-text available
The detection of irrigated areas by means of remote sensing is essential to improve agricultural water resource management. Currently, data from the Sentinel constellation offer new possibilities for mapping irrigated areas at the plot scale. Until now, few studies have used Sentinel-1 (S1) and Sentinel-2 (S2) data to provide approaches for mapping...
Article
Full-text available
In the context of monitoring and assessment of water consumption in the agricultural sector, the objective of this study is to build an operational approach capable of detecting irrigation events at plot scale in a near real-time scenario using Sentinel-1 (S1) data. The proposed approach is a decision tree-based method relying on the change detecti...
Article
This letter proposes a deep learning model to deal with the spatial transfer challenge for the mapping of irrigated areas through the analysis of Sentinel-1 data. First, a convolutional neural network (CNN) model called "Teacher Model" is trained on a source geographical area characterized by a huge volume of samples. Then, this model is transferre...
Article
Full-text available
Mapping irrigated plots is essential for better water resource management. Today, the free and open access Sentinel-1 (S1) and Sentinel-2 (S2) data with high revisit time offers a powerful tool for irrigation mapping at plot scale. Up to date, few studies have used S1 and S2 data to provide approaches for mapping irrigated plots. This study propose...
Article
Full-text available
The leaf area index, LAI, of Sahelian rangelands and related variables such as the vegetation cover fraction, fCover, the fraction of absorbed photosynthetically active radiation, fAPAR, and the clumping index, λo, were measured in the Gourma region (Mali) during 13 successive rainy seasons, between 2005 and 2017. These variables, known as climate...
Article
Full-text available
The leaf area index of Sahelian rangelands and related variables such as the vegetation cover fraction, the fraction of absorbed photosynthetically active radiation and the clumping index were measured between 2005 and 2017 in the Gourma region of northern Mali. These variables, known as climate essential variables, were derived from the acquisitio...
Article
Full-text available
Numerous studies have reported the use of multi-spectral and multi-temporal remote sensing images to map irrigated crops. Such maps are useful for water management. The recent availability of optical and radar image time series such as the Sentinel data offers new opportunities to map land cover with high spatial and temporal resolutions. Early ide...
Article
Full-text available
La gestion quantitative de l’eau est un enjeu majeur, en particulier dans les territoires ruraux où l’activité agricole est soutenue par l’irrigation alors même que la ressource en eau est peu abondante. Cet article présente, à partir de 3 exemples (modélisation intégrée, données satellitales, compteurs communicants), tout l’intérêt du numérique po...
Article
Climate change is projected to increase water resources limitation and to impact significantly agricultural production. A big challenge for agriculture will be to reduce the amount of water used to fit the environmental constraints, while maintaining a level of production that ensure food security. In this context, we develop a methodology based on...
Chapter
Full-text available
Agriculture brings with it a number of issues: agricultural production and food security, water and soil resource conservation, limiting the impact of farming on the quality of our environment (water, air, soil). In the context of global changes and the challenges they pose for agriculture sustainability, our ability to characterize how croplands f...
Article
Full-text available
In the context of climate change, agricultural managers have the imperative to combine sufficient productivity with durability of the resources. Many studies have shown the interest of recent satellite missions as suitable tools for agricultural surveys. Nevertheless, they are not predictive methods. A system able to detect summer crops as early as...
Poster
Water resources are under increasing pressure as a result of global change and of a raising competition among the different users (agriculture, industry, urban). It is therefore important to develop tools able to estimate accurately crop water requirements in order to optimize irrigation while maintaining acceptable production. In this context, rem...
Presentation
Full-text available
An example of DA techniques using SPOT data over an agricultural region.
Article
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Sentinel-2 (S2) earth observation satellite mission, launched in 2015, is foreseen to promote within-field decisions in Precision Agriculture (PA) for both: (1) optimizing crop production; and (2) regulating environmental impacts. In this second scope, a set of Leaf Area Index (LAI) derived from S2 type time-series (2006-2010, using Formosat-2 sate...
Article
Agriculture brings with it a number of issues: agricultural production and food security, water and soil resource conservation, limiting the impact of farming on the quality of our environment (water, air, soil). In the context of global changes and the challenges they pose for agriculture sustainability, our ability to characterize how croplands f...
Article
Full-text available
The leaf area index (LAI) and the fraction of photosynthetically active radiation absorbed by green vegetation (FAPAR) are essential climatic variables in surface process models. FCOVER is also important to separate vegetation and soil for energy balance processes. Currently, several LAI, FAPAR and FCOVER satellite products are derived moderate to...
Article
Full-text available
With the ever-increasing number of satellites and the availability of data free of charge, the integration of multi-sensor images in coherent time series offers new opportunities for land cover and crop type classification. This article investigates the potential of structural biophysical variables as common parameters to consistently combine multi...
Article
Full-text available
The growing availability of high-resolution satellite image series offers new opportunities in agro-hydrological research and modeling. We investigated the possibilities offered for improving crop-growth dynamic simulation with the distributed agro-hydrological model: topography-based nitrogen transfer and transformation (TNT2). We used a leaf area...
Conference Paper
Full-text available
Provision of reliable ground reference datasets is mandatory for the validation of satellite products. The ground data should be collected considering the spatial variability of the sites in agreement with the recommendations of the CEOS WGCV Land Product Validation subgroup for validation of moderate resolution satellite products. This paper descr...
Technical Report
Full-text available
The recent and forthcoming availability of high resolution satellite image series offers new opportunities in agro-hydrological research and modeling. We investigated the perspective offered by improving the crop growth dynamic simulation using the distributed agro-hydrological model, Topography based Nitrogen transfer and Transformation (TNT2), us...
Article
This study aims at validating Leaf Area Index (LAI) and Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) products derived from MODIS surface reflectance (MOD09CMG) at coarse resolution (0.05°) over crops. These Essential Climate Variables (ECVs) are estimated by using the inversion of the PROSAIL radiative transfer (BV-NNET tool) ap...
Article
Full-text available
The use of crop models allows simulating plant development, growth and yield under different environmental and management conditions. When combined with high spatial and temporal resolution remote sensing data, these models provide new perspectives for crop monitoring at regional scale. We propose here an approach to estimate time courses of dry ab...
Article
The MCM'10 experiment (Multi-sensors Crop Monitoring, 2010) aims to evaluate the potentialities of optical, microwave and thermal satellite images for monitoring agricultural surfaces. The Experiment is conducted during ten month in 2010, from February to November over a super-site located in the South West of France. Remote sensing data (>150 imag...
Article
Full-text available
Ces dernières années, le CESBIO a mis en place un Observatoire Spatial Régional (OSR), dispositif d'observation couplant mesures de terrain et télédétection dans le sud-ouest de la France. L'OSR se base sur des acquisitions mensuelles de données satellitaires à résolution décamétrique depuis 2002 et sur des sites expérimentaux lourdement instrument...
Article
This paper aims at firstly evaluating the correspondence between Normalized Difference Vegetation Index (NDVI) products from Formosat-2 (F2) and SPOT sensors and then to perform a comparative analysis of two methods for retrieving Green Area Index from high spatial and temporal resolution satellite data (F2 and SPOT). For this purpose, an empirical...
Article
For the last 10 years, CESBIO has been building a Regional Spatial Observatory (OSR), dedicated to coupled terrain and space observations in the southwest of France. The OSR relies on monthly acquisitions of optical images with a 10 meter resolution started in 2002 and on heavily instrumented sites layed out since 2004 (permanent measurements of wa...
Article
We review the main results of land-surface studies obtained in the three sites of the long-term observing system AMMA-CATCH. Runoff in the Sahel enhances the variability of energy partitioning between non-infiltrative areas where sensible heat is dominant and infiltrative areas where soil water availability increases the latent flux. In terms of wa...
Article
We review the main results of land-surface studies obtained in the three sites of the long-term observing system AMMA-CATCH. Runoff in the Sahel enhances the variability of energy partitioning between non-infiltrative areas where sensible heat is dominant and infiltrative areas where soil water availability increases the latent flux. In terms of wa...
Article
The purpose of this paper is to present an application combining remote sensing and modeling approaches for water and energy surface exchanges monitoring at high resolution over an agricultural landscape. This study takes advantage of using high spatial resolution data in the visible and thermal infrared (TIR) domains and at-ground eXtra Large Aper...
Article
Carbon and water cycles are closely related to agricultural activities. Agriculture has been indeed identified by IPCC 2007 report as one of the options to sequester carbon in soil. Concerning the water resources, their consumptions by irrigated crops are called into question in view of demographic pressure. In the prospect of an assessment of carb...
Article
The objectives of the study were to characterize photosynthesis of temperate fallow C3herbaceous species and examine the performance of a simple photosynthesis model (based on the Farquhar’s equations) to simulate carbon fluxes at the leaf and canopy levels. The maximum rate of carboxylation at 25°C (V m0) was estimated for sunlit leaves using in s...
Article
The West African monsoon interacts strongly with the land surface, yet knowledge of these interactions is severely limited by the lack of observations of surface energy fluxes. Within the framework of the AMMA project, three eddy covariance flux stations were installed to sample the three main surface types near Hombori (Mali) in the central Sahel...
Article
The Gourma site in Mali is one of the 3 instrumented meso-scale sites deployed in West- Africa as part of the African Monsoon Multidisciplinary Analysis (AMMA) project. Located both in the Sahelian zone sensu stricto, and in the Saharo-Sahelian transition zone, the Gourma meso-scale window is the northernmost site of the AMMA-CATCH observatory reac...
Conference Paper
The recent availability of high spatial resolution sensors offers new perspectives for terrestrial applications (agriculture, risks). The aim of this work is to develop a methodology for deriving biophysical variables (Green Leaf Area Index - GLAI, phytomass) from multi-temporal observations at high spatial resolution in order to run a crop model a...
Article
Inverting radiative transfer (R-T) models against remote sensing observations to retrieve key biogeophysical parameters such as leaf area index (LAI) is a common approach. Even if new inversion techniques allow the use of three-dimensional (3D) models for that purpose, one-dimensional (1D) models are still widely used because of their ease of imple...
Article
Full-text available
Among many indirect approaches to retrieve effective leaf area index (LAI), hemispherical photography is now widely used by the scientific community in forestry applications. A recent software (CAN_EYE) is used to estimate effective and true LAI from unidirectional gap fractions measured in crops. The effective LAI is computed with the Poisson law...
Article
Le modèle DART (Discrete Anisotropic Radiative Transfer) simule le transfert radiatif optique dans le système "Terre - Atmosphère", du visible à l'infrarouge thermique, pour des paysages urbains et naturels (e.g., forêts multi-espèces), avec atmosphère et relief. Ses deux principales sorties sont : - images de télédétection spatiale (i.e., réflecta...