Search

A three-dimensional (3D) wind profiling Lidar, based on the latest high power 1.5 &micro, m fiber laser development at Onera, has been successfully flown on-board a SAFIRE (Service des Avions Fran&ccedil, ais Instrument&eacute, s pour la Recherche en Environnement) ATR42 aircraft. The Lidar called LIVE (LIdar VEnt) is designed to measure wind profiles from the aircraft down to ground level, with a horizontal resolution of 3 km, a vertical resolution of 100 m and a designed accuracy on each three wind vector components better than 0.5 m.s&minus, 1. To achieve the required performance, LIVE Lidar emits 410 &micro, J laser pulses repeating at 14 KHz with a duration of 700 ns and uses a conical scanner of 30&deg, total opening angle and a full scan time of 17 s.

International audience; This study presents the averaged lidar-relevant radiative properties of numerically generated soot fractal aggregate ensembles. The radiative properties of these aggregates have been computed using the Superposition T-Matrix Method, with emphasis put on those that are most relevant to lidar application; the backscattering and extinction cross-sections, the Lidar Ratio and the Linear Depolarization Ratio. These lidar-relevant radiative properties have been computed over a broad spectrum, going from the ultraviolet to the near infrared, in order to address lidar instrument need for a priori knowledge in signal inversion procedures and measurement analysis. By averaging the computed radiative properties according to each set of morphological parameters, we obtain statistically representative results and we study the impacts of morphological changes on these lidar-relevant radiative properties. Our results show a strong impact of the primary particle radius on all considered radiative properties, while the number of primary particles induce significant variations on the cross-sections only. The fractal dimension, although being an essential morphological parameter, has a weak influences on the lidar-relevant radiative properties.

International audience; In this paper we focus on airborne hyperspectral imaging methodology to characterize PM (Particulate Matter) near industrial emission sources. Two short-term intensive campaigns were carried out in the vicinity of a refinery in the South of France, in September 2015 and February 2016. Different protocols of in-situ PM measurements were performed, at stack measurements (flow rate and offline chemical analysis) and on-line measurement at the refinery border (size distribution, concentration and chemistry of aerosols). A multi temporal methodology to retrieve aerosol type, to map the aerosol concentration and to quantify mass flow rate from airborne hyperspectral data is described in this paper. This method applied to the refinery detected plume from the main stack yields a black carbon to sulfate ratio of 10/90 in mass inside the plume, with an average size distribution smaller than 100 nm. These results are in a good agreement with on-line analysis of aerosols at refinery border. The resulting quantitative map with a metric spatial resolution leads to a flow rate estimated of about 1g/s and is in a good agreement with in-situ stack measurements and modelling.; Ce papier propose une méthodologie de caractérisation des PM (Particulate Matter) proches des sources industrielles par imagerie hyperspectrale aéroportée. Il s’appuie sur deux campagnes de mesures réalisées autour d’une raffinerie dans le sud de la France en Septembre 2015 et Février 2016. Différents protocoles de mesures in-situ des PM ont été réalisées dans ce cadre, mesures au niveau de l’émissaire principal (debit et analyse chimique) et mesures on-line au voisinage de la raffinerie (distribution en taille, concentration et analyse chimique). Une méthodologie multi-temporelle dédiée à l’inversion des types d’aérosols présents dans le panache permettant de fournir une carte en concentration d’aérosols et d’estimer le débit est décrite dans ce papier. Appliquée à ce cas d’étude, les resultats hyperspectraux ont permis d’estimer un rapport suie/sulfate de 10/90 en masse dans le panache avec une distribution en taille inférieure à 100nm. Ces résultats sont en bon accord avec les mesures in-situ. Les cartes en concentration obtenue à une resolution métrique permettent d’estimer un debit de l’ordre de 1g/s en bon accord avec les mesures in-situ au niveau de l’émissaire et avec les résultats de modélisation de dispersion des aerosols.

International audience; In this paper, we propose a novel way of unmixing space-borne hyperspectral images using a co-registered hyperspec-tral image and a high-spatial-resolution panchromatic image. The unmixing is achieved by a two-step approach. First, an extraction of pure pixels using a panchromatic homogeneity criterion is performed and a reconstruction error map is generated. Then, a local semi-supervised Non-negative Matrix Factorization (NMF) is performed on badly reconstructed areas in order to estimate material spectra that are not represented by pure pixels in the image. This approach is tested on real data for the first step, and on both synthetic and real data for the second step.

International audience; The estimation of the bathymetry and the detection of targets located on the seabed of shallow waters using remote sensing techniques is of great interest for many environmental applications in coastal areas such as benthic habitat mapping, monitoring of seabed aquatic plants and the subsequent management of littoral zones. For that purpose, knowledge of the optical effects induced by the neighborhood of a given seabed target and by the water column itself is required to better interpret the subsurface upward radiance measured by satellite or shipborne radiometers. In this paper, the various sources of photons that contribute to the subsurface upward radiance are analyzed. In particular, the adjacency effects caused by the neighborhood of a given seabed target are quantified for three water turbidity conditions, namely clear, moderately turbid and turbid waters. Firstly, an analytical expression of the subsurface radiance is proposed in order to make explicit the radiance terms corresponding to these effects. Secondly, a sensitivity study is performed using radiative transfer modeling to determine the influence of the seabed adjacency effects on the upward signal with respect to various parameters such as the bathymetry or the bottom brightness. The results show that the highest contributions of the adjacency effects induced by the neighborhood of a seabed target to the subsurface radiance could reach 26%, 18% and 9% for clear, moderately turbid and turbid water conditions respectively. Therefore, the detection of a seabed target could be significantly biased if the seabed adjacency effects are ignored in the analysis of remote sensing measurements. Our results could be further used to improve the performance of inverse algorithms dedicated to the retrieval of bottom composition, water optical properties and/or bathymetry.

International audience; A sensor's spatial resolution has traditionally been a difficult concept to define, but all would agree that it is inextricably linked to the Ground Sampling Distance (GSD) and Instantaneous Field of View (IFOV) of an imaging sensor system. As a measure of the geospatial quality of imagery, the Modulation Transfer Function (MTF) of the system is often used along with the signal-to-noise ratio (SNR). However, their calculation is not fully standardized. Further, consistent measurements and comparisons are often hard to obtain. Therefore, in the Infrared and Visible Optical Sensors (IVOS) subgroup of the Working Group on Calibration Validation (WGCV) of the Committee for Earth Observation Satellites (CEOS), a team from various countries and professional entities who are involved in MTF measurement was established to address the issue of on-orbit MTF measurements and comparisons. As a first step, a blind comparison of MTF measurements based on the slanted edge approach has been undertaken. A set of both artificial and actual satellite edge images was developed and a first comparison of processing results was generated. In all, seven organizations contributed to the experiment and several significant results were generated in 2016. No single participant produced the best results for all test images as measured by either the closest to the mean result, or closest to the truth for the synthetic test images. In addition, close estimates of the MTF value at Nyquist did not ensure the accuracy of other MTF values at other spatial frequencies. Some algorithm results showed that the accuracy of their estimates depended upon the type of MTF curve that was being analyzed. After the initial analysis, participants were allowed to modify their methodology and reprocess the test images since, in several cases, the results contained errors. Results from the second iteration, in 2017, verified that the anomalies in the experiment's first iteration were due to errors in either coding or methodology, or both. One organization implemented a third trial to fix software errors. This emphasizes the importance of fully understanding both methodology and implementation, in order to ensure accurate and repeatable results. To extend this comparison study, a reference data set, which is composed of edge images and corresponding MTF curves, will be built. A broader audience will be able to access the edge images through the CEOS CalVal Portal (http://calvalportal.ceos.org/. This paper, which is associated with the reference data set, can serve as a new tool to either implement or check, or both, the MTF measurement that relies on the slanted edge method.; La résolution spatiale d’un capteur a toujours été un concept difficile à définir, mais il est acquis qu’elle est intimement liée à au pas d’échantillonnage au sol et au champ de vue instantanné d’un système imageur. En tant que mesure de la mesure de la qualité image géospatiale, la Fonction de Transfert de Modulation (FTM) du système est souvent utilisée avec le Rapport Signal à Bruit (RSB). Cependant, le calcul de ces grandeurs n’est pas totalement standardisé et des mesures et de comparaisons cohérentes sont souvent difficiles à obtenir. De ce fait, dans le cadre du sous groupe Capteurs Optiques Visibles du groupe de travail sur l’étalonnage et la validation du Comité pour les satellites d’observation de la terre, un groupe de personnes issues de différents pays et de différentes entités professionnelles impliquées dans la mesure de FTM a été formé pour travailler sur la problématique de la mesure de FTM et des comparaison de mesures. Pour la première étape du travail, une comparaison en aveugle, concernant la méthode du bord de plage, a été organisée. Un jeu d’images satellitaires, à la fois artificielles et réelles, a été créé et une première comparaison des résultats de calcul de FTM a été faite. En tout, sept organisations différentes ont participé à l’expérience et ont conduit à des résultats intéressants en 2016. Aucun participant n’a obtenu le meilleur résultat, au sens le plus proche de la moyenne ou bien le plus proche de la FTM attendue, dans tous les cas. Il est également apparu qu’une bonne estimation de la valeur de la FTM à la fréquence de Nyquist ne garantissait pas une bonne estimation pour les autres fréquences spatiales. Certains algorithmes ont des résultats dont la précision dépend de la forme de la FTM. Après cette première analyse des résultats, les participants ont pu modifier leur méthodologie et retraiter les données car il y avait clairement des erreurs dans les premiers résultats. Les second résultats, en 2017, ont permis de vérifier cela. Une organisation a fait un troisième retraitement des données pour corriger un bug et valider son résultat. Tout ceci souligne l’importance de bien comprendre non seulement la méthodologie mais également son implémentation, de manière à obtenir des résultats reproductibles et fiables. A la suite de ce travail, un jeu de données de référence composé d’images et des courbes de FTM correspondantes va être construit. Il est prévu de donner accès aux images à travers le CalVal Portal et de les rendre disponibles à un large ensemble d’utilisateurs.

International audience; The monitoring of the water cycle at the Earth surface which tightly interacts with the climate change processes as well as a number of practical applications (agriculture, soil and water quality assessment, irrigation and water resource management, etc...) requires surface temperature measurements at local scale. Such is the goal of the Indian-French high spatio-temporal TRISHNA mission (Thermal infraRed Imaging Satellite for High-resolution Natural resource Assessment). The scientific objectives of the mission and research work conducted to consolidate the mission specifications are presented. Progress in modelling of surface fluxes is then discussed. The main specifications of the mission such as the revisit, the spatial resolution, the overpass time, the spectral bands and the orbit are analyzed and justified. The resulting baseline of the mission is given.

International audience; In California, water is a perennial concern. As competition for water resources increases due to growth in population, California’s tree nut farmers are committed to improving the efficiency of water used for food production. There is an imminent need to have reliable methods that provide information about the temporal and spatial variability of crop water requirements, which allow farmers to make irrigation decisions at field scale. This study focuses on estimating the actual evapotranspiration and crop coefficients of an almond and pistachio orchard located in Central Valley (California) during an entire growing season by combining a simple crop evapotranspiration model with remote sensing data. A dataset of the vegetation index NDVI derived from Landsat-8 was used to facilitate the estimation of the basal crop coefficient (Kcb), or potential crop water use. The soil water evaporation coefficient (Ke) was measured from microlysimeters. The water stress coefficient (Ks) was derived from airborne remotely sensed canopy thermal-based methods, using seasonal regressions between the crop water stress index (CWSI) and stem water potential (Ψstem). These regressions were statistically-significant for both crops, indicating clear seasonal differences in pistachios, but not in almonds. In almonds, the estimated maximum Kcb values ranged between 1.05 to 0.90, while for pistachios, it ranged between 0.89 to 0.80. The model indicated a difference of 97 mm in transpiration over the season between both crops. Soil evaporation accounted for an average of 16% and 13% of the total actual evapotranspiration for almonds and pistachios, respectively. Verification of the model-based daily crop evapotranspiration estimates was done using eddy-covariance and surface renewal data collected in the same orchards, yielding an R2 ≥ 0.7 and average root mean square errors (RMSE) of 0.74 and 0.91 mm·day−1 for almond and pistachio, respectively. It is concluded that the combination of crop evapotranspiration models with remotely-sensed data is helpful for upscaling irrigation information from plant to field scale and thus may be used by farmers for making day-to-day irrigation management decisions.; En Californie, l’eau est une préoccupation constante. À mesure que la concurrence pour les ressources en eau augmente, la croissance de la population augmente. Il existe un besoin imminent de disposer de méthodes fiables pour fournir des informations sur la variabilité temporelle et spatiale des besoins en eau des cultures. Cette étude porte sur l'estimation des coefficients d'évaporation et des cultures d'un verger d'amandiers et de pistaches situé dans la Central Valley, en Californie, pendant toute une saison de croissance, en combinant un modèle simple d'évapotranspiration des cultures avec des données de télédétection. Un ensemble de données de l'indice de végétation NDVI dérivé de Landsat-8 a été utilisé pour faciliter l'estimation du coefficient de culture de base (Kcb) ou de l'utilisation potentielle de l'eau par la culture. Le coefficient d'évaporation de l'humidité du sol (Ke) a été mesuré à partir de microlysimètres. Le coefficient de stress hydrique (Ks) a été calculé à l'aide de méthodes thermiques basées sur le couvert forestier et télédétectées en vol, à l'aide de régressions saisonnières entre l'indice de stress hydrique des cultures (CWSI) et le potentiel hydrique de la tige (stem). Ces régressions étaient statistiquement significatives pour les deux cultures, indiquant de nettes différences saisonnières dans les pistaches, mais pas dans les amandes. Dans les amandes, les valeurs maximales estimées de Kcb se situaient entre 1,05 et 0,90, tandis que pour les pistaches, elles se situaient entre 0,89 et 0,80. Le modèle indiquait une différence de transpiration de 97 mm au cours de la saison entre les deux cultures. L'évaporation du sol représentait en moyenne 16% et 13% de l'évapotranspiration réelle totale d'amandes et de pistaches, respectivement. La vérification de l'évapotranspiration quotidienne des cultures basée sur un modèle a été effectuée à l'aide des données de covariance de Foucault et de renouvellement de la surface recueillies dans les mêmes vergers, conduisant à un R2 ≥ 0,7 et des erreurs moyennes de racine carrée (RMSE) de 0,74 et 0,91 mm · jour-1 pour amande et pistache, respectivement. Il est conclu que la combinaison de modèles d'évapotranspiration de cultures et de données de télédétection est utile pour augmenter l'information d'irrigation de l'échelle de la plante au champ et peut donc être utilisée par les agriculteurs pour prendre des décisions quotidiennes de gestion de l'irrigation.

International audience; With the current expansion of cities, urban trees have an important role for preserving the health of its in- habitants. With their evapotranspiration, they reduce the urban heat island phenomenon, by trapping CO2 emission, improve air quality. In particular, street trees or alignment trees, create shade on the road network, are structuring elements of the cities and decorate the roads. Street trees are also subject to specific conditions as they have little space for growth, are pruned and can be affected by the spread of diseases in single-species plantations. Thus, their detection, identification and monitoring are necessary. In this study, an approach is proposed for mapping these trees that are characteristic of the urban environment. Three areas of the city of Toulouse in the south of France are studied. Airborne hyperspectral data and a Digital Surface Model (DSM) for high vegetation detection are used. Then, contextual information is used to identify the street trees. Indeed, Geographic Information System (GIS) data are considered to detect the vegetation canopies close to the streets. Afterwards, individual street tree crown delineation is carried out by modeling the discriminative contextual features of individual street trees (hypotheses of small angle between the trees and similar heights) based on Marked Point Process (MPP). Compared to a baseline individual tree crown delineation method based on region growing, our method logically provides the best results with F-score values of 91%, 75% and 85% against 70%, 41% and 20% for the three studied areas respectively. Our approach mainly succeeds in identifying the street trees. In addition, the contribution of the angle, the height and the GIS data in the street tree mapping has been studied. The results encourage the use of the angle, the height and the GIS data together. However, with only the angle and the height, the results are similar to those obtained with the inclusion of the GIS data for the first and the second study cases with F-score values of 88%, 79% and 62% against 91%, 75% and 85% for the three study cases respectively. Finally, it is shown that the GIS data only is not sufficient.

International audience; L’imagerie hyperspectrale ou spectro-imagerie combine deux techniques de télédétection : l’imagerie et la spectrométrie. L’imagerie enregistre la distribution spatiale d’un flux énergétique issu de phénomènes de réflexion ou/et d’émission thermique d’un milieu. La spectrométrie mesure les variations, dans le domaine électromagnétique, du flux énergétique dépendant de la composition chimique de l’objet observé à laquelle s’ajoute la température de surface dans le domaine émissif. La spectro-imagerie délivre ainsi une image complexe de dimension 3 dont deux dimensions représentent l’information spatiale et la troisième l’information spectrale. La richesse de l’information spectrale nécessite, pour une bonne interprétation des mesures, une connaissance précise des phénomènes physiques à observer et une maîtrise des moyens à mettre en oeuvre pour extraire la caractéristique recherchée. Cet article a pour objet de décrire les notions de base nécessaires pour comprendre cette technique : – propriétés optiques spectrales des observables ; – transfert radiatif dans le système Terre-atmosphère afin de comprendre les différents contributeurs radiatifs au signal mesuré ; – principales techniques de spectro-imagerie, de prétraitements pour convertir les comptes numériques enregistrés par l’instrument en grandeur physique ; – méthodes d’estimation des propriétés optiques. Le domaine électromagnétique considéré couvre le domaine optique de l’UV (0,4 μm) à l’infrarouge thermique (12,0 μm).

International audience; Blind source separation is a common processing tool to analyse the constitution of pixels of hyperspectral images. Such methods usually suppose that pure pixel spectra (endmembers) are the same in all the image for each class of materials. In the framework of remote sensing, such an assumption is no longer valid in the presence of intra-class variability due to illumination conditions, weathering, slight variations of the pure materials, etc. In this paper, we first describe the results of investigations highlighting intra-class variability measured in real images. Considering these results, a new formulation of the linear mixing model is presented leading to two new methods. Unconstrained pixel-by-pixel NMF (UP-NMF) is a new blind source separation method based on the assumption of a linear mixing model, which can deal with intra-class variability. To overcome the limitations of UP-NMF, an extended method is also proposed, named Inertia-constrained Pixel-by-pixel NMF (IP-NMF). For each sensed spectrum, these extended versions of NMF extract a corresponding set of source spectra. A constraint is set to limit the spreading of each source’s estimates in IP-NMF. The proposed methods are first tested on a semi-synthetic data set built with spectra extracted from a real hyperspectral image and then numerically mixed. We thus demonstrate the interest of our methods for realistic source variabilities. Finally, IP-NMF is tested on a real data set and it is shown to yield better performance than state of the art methods.

With the expansion of urban areas, air pollution and heat island effects are increasing, leading to state of health issues for the inhabitants and global climate changes. In this context, urban trees are a valuable resource for both improving air quality and promoting freshness islands. On the other hand, canopies are subject to specific conditions in the urban environment, causing the spread of diseases and life expectancy decreases among the trees.This thesis explores the potential of remote sensing for the automatic urban tree mapping, from the detection of the individual tree crowns to their species estimation. This is an essential preliminary task for designing the future green cities, and for an effective vegetation monitoring. Based on airborne hyperspectral, panchromatic and Digital Surface Model data, the first objective of this thesis consists in taking advantage of several data sources for improving the existing urban tree maps, by testing different fusion strategies (feature and decision level fusion). The nature of the results led us to optimize the complementarity of the sources.In particular, the second objective is to investigate deeply the richness of the hyperspectral data, by developing an ensemble classifier approach based on species specific classifiers. The features are built owing to vegetation indices selection, specific for each species.Finally, the first part highlighted to interest of discriminating the street trees from the other structures of urban trees. In a Marked Point Process framework, the third objective is to detect trees in urban alignment. Through the first objective, this thesis demonstrates that the hyperspectral data (especially the VNIR) are the main driver of the species prediction accuracy. The decision level fusion strategy is the most appropriate one for improving the performance in comparison the hyperspectral data alone, but slight improvements are obtained (a few percent) due to the low complementarity of textural and structural features in addition to the spectral ones.The ensemble classifier approach developed in the second part allows the tree species to be classified from ground-based spectral references (leaf and canopy levels), with significant improvements in comparison to a standard feature level classification approach. Finally, the street trees can be mapped thanks to the proposed model integrating contextual features (alignment and similar heights). This work could be extended to the phenological monitoring of urban vegetation and the analysis of the state of health.; Avec l'expansion des zones urbaines, la pollution de l'air et les effets des îlots de chaleur augmentent, entraînant des problèmes d'état de santé pour les habitants et des changements climatiques globaux. Dans ce contexte, les arbres urbains sont une ressource précieuse à la fois pour améliorer la qualité de l'air et promouvoir les îlots de fraîcheur. D'autre part, les canopées sont soumises à des conditions spécifiques dans l'environnement urbain, provoquant la propagation de maladies et une diminution de l'espérance de vie parmi les arbres.Cette thèse explore le potentiel de la télédétection pour la cartographie automatique des arbres urbains, depuis la détection des couronnes d'arbres jusqu'à l'estimation de leur espèce. C'est une tâche préliminaire essentielle pour la conception des futures villes vertes et pour un suivi efficace de la végétation. Fondé sur des données hyperspectrales aéroportées, panchromatiques et Digital Surface Model, le premier objectif de cette thèse consiste à exploiter plusieurs sources de données pour améliorer les cartes urbaines existantes, en testant différentes stratégies de fusion (fusion de caractéristiques et de décision). La nature des résultats nous a conduit à optimiser la complémentarité des sources.En particulier, le second objectif est d'étudier en profondeur la richesse des données hyperspectrales, en développant un ensemble de classifieurs fondé sur des classifieurs spécifiques aux espèces. Les caractéristiques sont construites grâce à une sélection d'indices de végétation, spécifique à chaque espèce.Enfin, la première partie a mis en évidence l'intérêt de discriminer les arbres d'alignement des autres structures d'arbres urbains. Dans un cadre de processus de points marqués, le troisième objectif est de détecter les arbres appar¬tenant à un alignement. Grâce au premier objectif, cette thèse démontre que les données hyperspectrales (en particulier le VNIR) sont le principal moteur de la précision de la prédiction de l'espèce. La stratégie de fusion au niveau de la décision est la plus appropriée pour améliorer les performances par rapport aux données hyperspectrales seules, mais de légères améliorations sont obtenues (quelques pourcents) en raison de la faible complémentarité des caractéristiques texturales et structurales en plus des caractéristiques spectrales.L'approche d'ensemble développée dans la seconde partie permet de classer les espèces d'arbres à partir de mesures spectrales terrain (à l'échelle de la feuille ou de la canopée), avec des améliorations significatives par rapport à une approche standard de classification au niveau des caractéristiques. Enfin, les arbres d'alignement peuvent être cartographiés grâce au modèle proposé intégrant des caractéristiques contextuelles (alignement et hauteurs similaires). Ce travail pourrait être étendu au suivi phénologique de la végétation urbaine et à l'analyse de l'état de santé.

As compared to near InfraRed passive instruments, lidars reduce the blases on the measurement of concentrations in the presence of diffusion by aerosols, but until recent days they were limited to one active wavelength at a time.CNES and ONERA conceived a novel type of lidar based on short frequency combs that provides the spectrum of a complete absorption line of the target molecule. The technique of Dual Comb Spectroscopy is adapted to short (up to 13 teeth) combs, as a compromise between spectral richness and Signal to Noise Ratio. The advantages of DCS remain: reduction of the impact of scene evolutions and spectral mis-calibration. The latter will make the high power laser emitters easier. Above all, the acquisition of a complete absorption line opens the path to the retrieval of two or more independent elements in the vertical profile of molecule concentration.We describe the technique of comb generation, the layout of the emitter section and the detection principles. Then we introduce the Short Comb Atmospheric Lidar Experiment (SCALE) project led by CNES in the frame of a new advance "phase 0" study. We expose the preliminary performances of this space lidar that could fit on a microsatellite platform in the case of CO2 sounding at 1.57 or 2 um.Results of CNES-ONERA four-year R&T activities are also presented that validate in the laboratory and in open space the short comb lidar.Finally first results of retrieval simulations are exposed., Les lidars réduisent l'imprécision des instruments passifs sur l'estimation de la distance sondée, donc sur la concentration de la molécule ciblée dans l'atmosphère. Mais jusqu'à récemment, les lidars étaient limités à une seule longueur d'onde active à la fois.Le CNES et l'ONERA ont conçu un nouveau type de lidar basé sur des mini- peignes de fréquence qui fournissent le spectre d'une ligne d'absorption complète de la molécule cible. La technique de la spectroscopie à double peigne (DCS) est adaptée aux mini-peignes (jusqu'à 13 dents), qui fait un compromis entre la richesse spectrale et le rapport signal/bruit. Les avantages du DCS sont : réduction de l'impact des évolutions temporelles de la scène, étalonnage auto spectral, étalement spectral de l'énergie par rapport au seuil de Brillouin. Ce dernier avantage facilitera la réalisation des émetteurs laser à haute puissance. L'acquisition d'une ligne d'absorption complète ouvre la voie à la récupération de deux ou plusieurs éléments indépendants (DOFS) dans le profil vertical de la concentration moléculaire.Nous décrivons la technique de génération de peigne, l'architecture de la section émettrice et les principes de détection. Nous présentons ensuite le projet SCALE (Short Comb Atmospheric Lidar Experiment) que le CNES étudiera prochainement dans le cadre d'une nouvelle étude avancée de "phase 0". Nous exposons les performances préliminaires de ce lidar spatial qui pourrait tenir sur une plate-forme microsatellite dans le cas d'un sondage CO2 à 1,5 µm.Enfin, les résultats des activités de R&T quadriennales du CNES-ONERA sont présentés pour valider en laboratoire et en espace libre le lidar a mini-peigne.

L'imagerie hyperspectrale (IH) est à l’heure actuelle encore trop peu considérée, pourtant ses spécificités en font un auxiliaire de poids pour le suivi des éléments du milieu urbain. Le projet HYEP a pour objectif de proposer un panel de méthodes et de traitements appliqués à l’imagerie hyperspectrale tout en comparant à celles d’autres capteurs existants. Si l’IH est complémentaire aux capteurs actuels car plus riche spectralement, elle permet d'identifier et de caractériserautrement les éléments naturels ou anthropiques. Pour ce faire les méthodes d'extraction d'information doivent être adaptées, voire créées. Le volet méthodologique du projet est ancré à la fois dans la solidification des approches actuelleset le test de méthodes ou adaptées ou nouvelles. Nos résultats ont été présentés tout au long du projet à la communauté scientifique et aux collectivités territoriales. Un des intérêts des travaux a été la comparaison des résultats à différentesrésolutions spatiales pour préciser le gain d’un tel capteur hyperspectral par rapport à ceux existants ou à venir. Données et Méthodes : Utilisation et adaptation de méthodes courantes en télédétection 1200. Les méthodes déployées ont été choisies parmi l’ensemble des méthodes existantes en les adaptant au type de signal, au nombre de bandes spectrales et aux caractéristiques du milieu. Ainsi les données étant issues de survol aérien les premiersdéveloppements ont été réalisés pour s’affranchir des effets de l’atmosphère (correction atmosphérique des images hyperspectrales– 3 méthodes testées) et une base de données de signatures morphospectrales pour divers éléments d'occupation du sol en ville (toits, routes, la végétation etc.) permettant de mieux cerner les valeurs spectrales des matériaux a été établie. Elle comprend des données de littérature, des mesures in situ et en laboratoire. Ses apports dans différents traitements declassification ont été testés. Des méthodes d’extraction, de fusion ou de classification ont été utilisées à différentes résolutions spatiales et spectrales afin de spécifier les gains par rapport à d’autres capteurs. Des méthodes de classifications et de démélange ont été adaptées. Des indices de forme facilitant la classification d’image en milieux urbain ont été testés et/ou développés. Résultats majeurs et faits marquant - 3 méthodes de correction atmosphériques développées et comparées en fonction de la résolution spatiale ; - Adaptation de méthodes de fusion (pan ou multi sharpening) et de démélange. - Transfert : Mise en place à Kaunas (Lituanie) du développement complet de l’approche. - Algorithmes : Dépôt sur la plateforme ouverte : http://openremotesensing.net/ et des outils de fusion PANhyperspectrale - Un résultat particulièrement intéressant porte sur l’extraction et l’identification des panneaux solaires. Une validation a été réalisée par le calcul des surfaces des panneaux. Ce développement est une des réussites du projet HYEP. - Ecole thématique CNRS en 2017. Productions scientifiques Présentation des travaux à ISPRS GeospatialWeek 2015, JURSE 2017, IGARSS 2017-2018, WHISPERS 2016-2018, GeoHyper (2015), aux ateliers TEMU, AFIGEO, dans des sessions de GDRs (Madics et ISIS) ou dans le cadre de la mission Hypxim. Elle a organisé des sessions de conférences nationales SFPT hyperspectral (2016) et 2 à l’international en 2018 IGARSS, WHISPERS. Elle a monté une école thématique CNRS (28 Août - 1 Septembre 2017- 25 participants). 10 publications et 38 communications avec actes, 3 chapitres de livre, 1 numéro spécial dans la revue « Remote Sensing - Hyperspectral Imageryfor Urban Environement » ont été produites.

International audience; Detecting onshore hydrocarbon is a major topic for both environmental monitoring and exploration. In this work, a hyperspectral image acquired nearby an old oil extraction site is analyzed. The area of interest includes a pit filled with bio-degraded heavy oil, surrounded by herbaceous vegetation and many lagoons. First, we focused on methodologies that allow tracking hydrocarbon pollution in non-supervised setting. Based on the assumption that such pits are rare events in the image, statistical approach for anomalies detection, derived from the Reed-Xiaoli detector, is used for their detection. In order to decrease the false alarms rate, some a priori knowledge about the spectral signature of the pits and about the background is introduced. This approach succeeds in detecting the pit with very few false alarms.Hydrocarbon pollution can have an impact on vegetation. It can induce a stress, or conversely it can boost some vegetation species. In order to map the polluted area without any a priori knowledge, several un-supervised classification, including an original frame of automatic classification combining unmixing approach and SVM (support Vector Machine) are applied and compared. The results are compared with a partial “ground truth map” that has been derived from visual observations on the field, and with areas of stressed vegetation that have been mapped using combination of vegetation spectral indices. The classification results are consistent with the ground truth map and the retrieved the stressed vegetation areas.; La détection des hydrocarbures à terre est un sujet majeur tant pour la surveillance de l'environnement que pour l'exploration. Dans ce travail, une image hyperspectrale acquise à proximité d'un ancien site d'extraction pétrolière est analysée. La zone d'intérêt comprend un bourbier remplie de pétrole lourd biodégradé, entourée d'une végétation herbacée et de nombreuses lagunes. Tout d'abord, nous nous sommes concentrés sur les méthodologies qui permettent de détection la pollution par les hydrocarbures manière non supervisée. En partant de l'hypothèse que ces bourbiers sont des événements rares dans l'image, une approche statistique pour la détection des anomalies, dérivée de la méthode proposée par Reed-Xiaoli, est utilisée pour leur détection. Afin de diminuer le taux de fausses alarmes, des connaissances a priori sur la signature spectrale de ces bourbiers et sur la nature de l’environnement sont introduites. Cette approche réussit à détecter le bourbier avec très peu de fausses alarmes.La pollution par les hydrocarbures peut avoir un impact sur la végétation. Elle peut induire un stress, ou inversement, elle peut stimuler certaines espèces végétales. Afin de cartographier la zone polluée sans aucune connaissance a priori, plusieurs classifications non supervisées, y compris une approche originale de classification automatique combinant le dé-mélange spectral et le SVM (Support Vector Machine) sont appliquées et comparées. Les résultats sont comparés à une "carte de vérité terrain" partielle dérivée d'observations visuelles sur le terrain et à des zones de végétation stressée qui ont été cartographiées à l'aide d'indices spectraux de végétation. Les résultats de la classification sont cohérents avec la carte de vérité au sol et les zones de végétation stressée.

International audience; Detecting onshore hydrocarbon is a major topic for both environmental monitoring and exploration. In this work, a hyperspectral image acquired nearby an old oil extraction site is analyzed. The area of interest includes a pit filled with bio-degraded heavy oil, surrounded by herbaceous vegetation and many lagoons. First, we focused on methodologies that allow tracking hydrocarbon pollution in non-supervised setting. Based on the assumption that such pits are rare events in the image, statistical approach for anomalies detection, derived from the Reed-Xiaoli detector, is used for their detection. In order to decrease the false alarms rate, some a priori knowledge about the spectral signature of the pits and about the background is introduced. This approach succeeds in detecting the pit with very few false alarms.Hydrocarbon pollution can have an impact on vegetation. It can induce a stress, or conversely it can boost some vegetation species. In order to map the polluted area without any a priori knowledge, several un-supervised classification, including an original frame of automatic classification combining unmixing approach and SVM (support Vector Machine) are applied and compared. The results are compared with a partial “ground truth map” that has been derived from visual observations on the field, and with areas of stressed vegetation that have been mapped using combination of vegetation spectral indices. The classification results are consistent with the ground truth map and the retrieved the stressed vegetation areas.; La détection des hydrocarbures à terre est un sujet majeur tant pour la surveillance de l'environnement que pour l'exploration. Dans ce travail, une image hyperspectrale acquise à proximité d'un ancien site d'extraction pétrolière est analysée. La zone d'intérêt comprend un bourbier remplie de pétrole lourd biodégradé, entourée d'une végétation herbacée et de nombreuses lagunes. Tout d'abord, nous nous sommes concentrés sur les méthodologies qui permettent de détection la pollution par les hydrocarbures manière non supervisée. En partant de l'hypothèse que ces bourbiers sont des événements rares dans l'image, une approche statistique pour la détection des anomalies, dérivée de la méthode proposée par Reed-Xiaoli, est utilisée pour leur détection. Afin de diminuer le taux de fausses alarmes, des connaissances a priori sur la signature spectrale de ces bourbiers et sur la nature de l’environnement sont introduites. Cette approche réussit à détecter le bourbier avec très peu de fausses alarmes.La pollution par les hydrocarbures peut avoir un impact sur la végétation. Elle peut induire un stress, ou inversement, elle peut stimuler certaines espèces végétales. Afin de cartographier la zone polluée sans aucune connaissance a priori, plusieurs classifications non supervisées, y compris une approche originale de classification automatique combinant le dé-mélange spectral et le SVM (Support Vector Machine) sont appliquées et comparées. Les résultats sont comparés à une "carte de vérité terrain" partielle dérivée d'observations visuelles sur le terrain et à des zones de végétation stressée qui ont été cartographiées à l'aide d'indices spectraux de végétation. Les résultats de la classification sont cohérents avec la carte de vérité au sol et les zones de végétation stressée.

International audience; This paper is focused on the retrieval of industrial aerosol optical thickness (AOT) and microphysical properties by means of airborne imaging spectroscopy. Industrial emissions generally lead to optically thin plumes requiring an adapted detection method taking into account the weak proportion of particles sought in the atmosphere. To this end, a semi-analytical model combined with the Cluster-Tuned Matched Filter (CTMF) algorithm is presented to characterize those plumes, requiring the knowledge of the soil under the plume. The model allows the direct computation of the at-sensor radiance when a plume is included in the radiative transfer. When applied to industrial aerosol classes as defined in this paper, simulated spectral radiances can be compared to ‘real’ MODTRAN (Moderate Resolution Atmospheric Transmission) radiances using the Spectral Angle Mapper (SAM). On the range from 0.4 to 0.7 µm, for three grounds (water, vegetation, and bright one), SAM scores are lower than 0.043 in the worst case (a both absorbing and scattering particle over a bright ground), and usually lower than 0.025. The darker the ground reflectance is, the more accurate the results are (typically for reflectance lower than 0.3). Concerning AOT retrieval capabilities, with a pre-calculated model for a reference optical thickness of 0.25, we are able to retrieve plume AOT at 550 nm in the range 0.0 to 0.4 with an error usually ranging between 9% and 13%. The first test case is a CASI (Compact Airborne Spectrographic Imager) image acquired over the metallurgical industry of Fos-sur-Mer (France). First results of the use of the model coupled with CTMF algorithm reveal a scattering aerosol plume with particle sizes increasing with the distance from the stack (from detection score of 54% near the stack for particles with a diameter of 0.1 µm, to 69% away from it for 1.0 µm particles). A refinement is made then to estimate more precisely aerosol plume properties, using a multimodal distribution based on the previous results. It leads to find a mixture of sulfate and brown carbon particles with a plume AOT ranging between 0.2 and 0.5. The second test case is an AHS (Airborne Hyperspectral Scanner) image acquired over the petrochemical site of Antwerp (Belgium). The first CTMF application results in detecting a brown carbon aerosol of 0.1 µm mode (detection score is 51%). Refined results show the evolution of the AOT decreasing from 0.15 to 0.05 along the plume for a mixture of brown carbon fine mode and 0.3 µm radius of sulfate aerosol.

International audience; Sea bottom unmixing is a challenging task for the analysis of coastal zones. Actually the upward photons are attenuated and diffused by the water column layer, giving low signal to noise hyperspectral data. A classical approach is to perform inversion of the water column using semi-analytical parametric models and estimation process, and obtain the water column constituents (chlorophyll, suspended matter, dissolved organic matter and bathymetry), and the coefficients of pure materials reflectance spectra (endmembers), given in spectral libraries, for each pixel. We consider here the case of unknown endmembers, and we suppose that the water column components have been obtained by a classical inversion method or in-situ measurements. For each observed pixel the upward luminance is analysed and decomposed into three terms, respectively issued after interaction with the target bottom pixel, its neighbours, and the water column. We show that in some conditions the adjacent pixels effect is not negligible, due to the diffusion in the water column, and we develop in accordance a new mixing model for the sea bottom. We propose a non-negative matrix factorisation based unmixing method to solve the problem, and present results for hyperspectral data simulations.

International audience; Hyperspectral remote sensing data offer unique opportunities for the characterization of land surface in urban areas. However, no hyperspectral-unmixing based studies have been conducted to automatically detect photovoltaic panels, which represent one of the important components of energy systems in such areas. In this paper, a hyperspectral-unmixing based method is proposed to detect photovoltaic panels and to estimate their areas. This approach is based on an original multiplicative nonnegative matrix factorization (NMF) algorithm with some known photovoltaic panel spectra. The proposed method can be considered as a partial/informed NMF approach. Experiments are conducted on realistic synthetic and real data to evaluate the performance of the proposed approach. In both cases, obtained results show that the proposed method yields much better overall performance than a method from the literature.

International audience; Hydrocarbon detection is important for both environment monitoring and hydrocarbon exploration. Hyperspectral imaging and derived spectral indices are used to detect hydrocarbons. With appropriate indices, light hydrocarbons on bare ground are detected. Heavier hydrocarbons are more difficult to detect. Plastic items are very well detected. Shadows and vegetation are generating some false alarms. Detection of hydrocarbon in urban environment, or on bare soils will be possible using spectral indices while detection of hydrocarbon in remote vegetated country areas will be difficult.

International audience; As part of the Copernicus programme of the European Commission (EC), the European Space Agency (ESA) operates the Sentinel-2 mission that acquires high spatial resolution optical imagery. The consistency of the image time series is ensured by some specific performance requirements such as multi-temporal spatial registration and radiometric stability, routinely monitored by the Sentinel-2 Mission Performance Centre (S2MPC). The products also provide a rich set of metadata and auxiliary data to support high-level processing activities. This presentation provides a description of the main level-1 products calibration and validation activities, performed by the S2MPC including several Expert Support Laboratories (ESL). Measured performances and analysed results show the good quality of the mission products both in terms of radiometry and geometry. The current performances for Sentinel-2A and Sentinel-2B are compared to mission product quality requirements.

International audience; Towns are characterized by a strong intern dynamic, a very high spatial heterogeneity of their elements, their 3D geometric shapes (horizontal and vertical) inducing shadows, and their large variety of materials. These characteristics make the collection of information of land surface properties and urban descriptors more delicate. Due to the enhancement of spatial resolution capacities,[virgule] multispectral imagery can provide a wide range of information to deepen the observation of urban areas. Nevertheless, such a type of sensors would not contribute to the characterization of the urban land surface properties (chemical composition of materials, species of vegetation, quality of soils, etc.). Hyperspectral imagery capacities might be considered as providing useful products by themselves and show great potentials but it becomes mandatory to define which type of information can be delivered by these different sensors. The ANR HYEP project 1 has the purpose to demonstrate the benefit of a second generation of hyperspectral space borne mission characterized by a high spatial resolution (8m GSD) and a high temporal revisit. After a detailed description of the motivation of such a proposal, applications are given focused on urban vegetation, sealed and impervious areas, solar panel area estimation.

International audience; The paper presents some of the technology maturing activity on lidar for standoff gas sensing at ONERA.

International audience; A fully physical retrieval scheme for land surface emissivity spectra is presented, which applies to high spectral resolution infrared observations from satellite sensors. The surface emissivity spectrum is represented with a suitably truncated Principal Component Analysis (PCA) transform and PCA scores are simultaneously retrieved with surface temperature and atmospheric parameters. The retrieval methodology has been developed within the general framework of Optimal Estimation and, in this context, is the first physical scheme based on a PCA representation of the emissivity spectrum. The scheme has been applied to IASI (Infrared Atmospheric Sounder Interferometer) and the retrieved emissivities have been validated with in situ observations acquired during a field experiment carried out in 2017 at Gobabeb (Namib desert) validation station. It has been found that the retrieved emissivity spectra are independent of background information and in good agreement with in situ observations.

International audience; With the current expansion of cities, 5 billion citizens and 1.2 millions km2 more by 2030, urban trees have an important role for preserving the health of its inhabitants. With their evapotranspiration, they reduce the urban heat island phenomenon, by trapping CO2 emission, improve air quality. Urban tree structures including street trees and park ones do not have necessarily the same functions/roles in the urban context. In particular, street trees or alignment trees, create shade on the road network, are structuring elements of the cities and decorate the roads. Street trees are also subject to specific conditions as they have little space for growth, are pruned and can be affected by the spread of diseases in single-species plantations. As a case in point, a pruned lime tree (Tilia) has a life expectancy of 150 years against 800 years without constraint. Thus, their detection, identification and monitoring are necessary. In this study, an approach is proposed for mapping these trees that are characteristic of the urban environment. Three areas of the city of Toulouse in the south of France are studied. Airborne hyperspectral data and a Digital Surface Model (DSM) for high vegetation detection are used. Then, contextual information (from Geographic Information System (GIS) data) is used to detect the vegetation canopies close to the streets. Afterwards, individual street tree crown delineation is carried out by modeling the contextual features of individual street trees (hypotheses of small angle between the trees and similar heights) based on Marked Point Process (MPP). Compared to a standard individual tree crown delineation method based on region growing, our method logically provides the best results with F-score values of 91%, 79% and 85% against 70%, 41% and 20% for the three studied areas respectively. These results are illustrated in the figure 1. Our approach mainly succeeds in identifying the street trees. In addition, the contribution of the angle, the height and the GIS data in the street tree mapping has been studied. The results encourage the use of the angle (alignment), the height and the GIS data together. However, with only the angle and the height, the results are similar to those obtained with the inclusion of the GIS data for the first and the second study cases with F-scores values of 88%, 79% and 62% against 91%, 75% and 85% for the three study cases respectively. Finally, it is shown that the GIS data only is not sufficient. This study highlights the interest of taking into account the contextual characteristics of the studied objects. As an urban manager, this type of information is useful for a specific urban planning and a specific monitoring. Moreover, it can be integrated in species classification schemes in order to improve the accuracy in single species-plantations.

International audience

International audience; Currently, photovoltaic panels constitute an important part of renewable energy systems in urban areas of developed countries. They are expected to generate greener electrical energy from non-polluting solar resources. Therefore, government agencies, electricity grid operators and decision makers encourage their setting up by funding and tax reduction. To avoid frauds with these substitute energies, several organizations are interested in detailed information, including localization and energy production, about these solar systems. Field surveys constitute one of the methods to obtain the above information on photovoltaic panels. However, this approach consumes a lot of time and can be very expensive, which leads to the use of other less expensive and faster approaches. The integration of remote sensing data is an interesting alternative for automatic detection of photovoltaic installations and their localization. Some remote sensing-based methods use high spatial resolution airborne/spaceborne images with a limited number of spectral bands. Such data do not allow an effective detection of photovoltaic panels principally due to their material properties. Indeed, when the visual properties of these panels are altered by specular reflections, their detection becomes difficult. High spectral resolution hyperspectral data may be considered to overcome the above limitation. These data are acquired by sensors that gather images from hundreds of narrow and contiguous bands of the electromagnetic spectrum, which offer unique opportunities for precise material recognition. In the investigation reported here, a hyperspectral-unmixing based method is proposed to detect photovoltaic panels and to estimate their areas. This approach is based on a new multiplicative nonnegative matrix factorization (NMF) algorithm which exploits known panel spectra. The designed approach, which can be considered as a partial NMF method, is applied to real airborne hyperspectral data acquired over the urban region of Toulouse, France. The obtained results (detection and area estimation) are confirmed by using a very high spatial resolution ortho-image of the same region. Also, these results are compared with those obtained by the standard multiplicative NMF algorithm introduced by Lee and Seung. This comparison shows that the proposed method yields much better overall performance than the considered method from the literature.

International audience

Most of the methods used to retrieve land surface temperature (LST) from thermal infrared (TIR) satellite data in urban areas do not take into account the complexity of the surface. Cities are characterized by high surface roughness and one of the main constraints to estimate LST over those areas is the difficulty to define an effective emissivity for a given pixel at a given scale. When working with mixed pixels, the emissivity used to estimate the LST is an effective emissivity composed of the emissivities of each basic element constituting the pixel. In urban areas, the surface geometry has a strong impact on this effective emissivity. Its estimation from TIR satellite data must be carried out considering multiple surface reflections and diffusions within the urban canopy in order to retrieve accurate LST values. The objective of this study is then to evaluate the impact of the surface geometry within the pixel on effective emissivity estimation and to propose a method to derive an effective emissivity corrected for those effects. Emissivity can be derived at 90 m of spatial resolution from the TIR data acquired by ASTER. To evaluate the impact of the geometry at the scale of an ASTER pixel, several urban canyon configurations are designed to develop and test the correction method. The basic principle behind the method is to accurately estimate the downwelling TIR radiation received by a pixel integrating contributions from both the atmosphere and the scene inside this pixel and then derive the corrected effective emissivity from ASTER data using the TES (temperature emissivity separation) algorithm. First, the total downwelling TIR radiation is estimated from the geometric characteristics of the scene, using morphological indicators and integrating the non-isothermal behavior of the pixel thanks to 3D thermo-radiative model simulations. The validation of those estimations for each canyon configuration provides a maximum RMSE (Root Mean Square Error) value of 2.2 W·m−2. The validation performed over a district extracted from the 3D numerical model of Strasbourg (France) shows a RMSE of 2.5 W·m−2. Once the method to estimate the total downwelling TIR radiation is validated, LSE and LST maps are retrieved from an ASTER image over three districts of Strasbourg, showing that accounting for the surface geometry highlights thermal behavior differences inside districts, and that the impact of the geometry seems more influenced by building height than street width or building density.

Optical wavelengths are an alternative to radio-frequency for future satellite-ground data transmissions. They are envisaged for future satellite telemetry systems (downlink optical links from LEO satellites) or communication (bidirectional optical links with GEO satellites). While going through the atmosphere the optical wave is affected by atmospheric turbulence. This may result in fading and surges when the incident flux is coupled to a single-mode optical fiber. To mitigate this potential source of information losses, several levers can be actuated: opto-mechanical correction methods such as adaptive optics, and numerical methods based on error correction coding and / or interleaving.This thesis has been devoted to the joint optimization of adaptive optics and numerical methods. An analytical model of fades and surge statistics of the adaptive optics-corrected signal has been proposed and validated by numerical modeling. A transmission performance model incorporating the effect of adaptive optics correction, and a distributed coding interleaving scheme on the physical layer (corrector coding and symbol interleaving) and the high layers (erase code and packet interleaving) has been developed. The joint optimization carried out thanks to these developments makes it possible to quantify the contribution of a correction by partial adaptive optics.The results obtained demonstrate that in cases of favorable signal-to-noise ratio, interleaving carried out exclusively on the high layer could be envisaged. These software oriented mechanisms make it possible to limit the use of dedicated memories, opening new perspectives for the realization of future optical communications payloads.; Les longueurs d’onde optiques sont une alternative aux liens radio-fréquences pour les transmissions satellite-sol du futur. Elles sont envisagées pour les futurs systèmes de télémesure satellitaires (liens optiques descendants en provenance de satellites LEO) ou de communication (liens optiques bidirectionnels avec des satellites GEO). A sa traversée de l’atmosphère l’onde optique est affectée par la turbulence atmosphérique. Des pertes peuvent en découler lors du couplage du flux incident à un détecteur optronique ou à une fibre optique monomode. Ces pertes se traduisent par des atténuations du signal reçu et donc par une potentielle perte d’informations. Pour s’en abstraire plusieurs leviers peuvent être exploités : des méthodes de correction opto-mécaniques comme l’optique adaptative, et des méthodes numériques s’appuyant sur du codage correcteur d’erreur et/ou de l’entrelacement.Cette thèse a été consacrée à l’optimisation conjointe de l’optique adaptative et des méthodes numériques. Un modèle analytique des durées d’atténuation et des durées entre atténuation du signal corrigé par optique adaptative a été proposé et validé par modélisation numérique (voir illustration, évaluation des durées moyenne entre atténuation en fonction du seuil appliqué sur le flux incident pour un cas de lien descendant GEO-sol). Un modèle de performance de transmission intégrant l’effet d’une correction par optique adaptative, et un schéma d’entrelacement codage réparti sur la couche physique (codage correcteur et entrelacement symbole) et les couches hautes (code à effacement et entrelacement paquets) a été élaboré. L’optimisation conjointe menée grâce à ces développements permet de quantifier l’apport d’une correction par optique adaptative partielle.Les résultats obtenus démontrent que dans les cas de rapport signal à bruit favorables un entrelacement réalisé exclusivement sur la couche haute pourrait être envisagé. Ces mécanismes logiciels permettent de limiter l’emploi de mémoires dédiées, ouvrant des perspectives nouvelles pour la réalisation de futures charges utiles de communications optiques.

Remote sensing technologies can be applied for a wide range of gas leak flowrates and in three main cases: (1) major leaks in crisis management; (2) medium size leaks in safety monitoring; (3) small leaks in environmental monitoring.A gas test campaign, conducted by Total, the ONERA – the French Aerospace Lab – and ADCIS in September 2015 using three hyperspectral infrared cameras from Telops, confirmed our capacity to visualize in 3D and quantify in real time plumes of methane in the range of 1 g/s to 50g/s. The R&D project on gas remote quantification continued with a second gas test campaign in 2017.The second gas test campaign was organized on Total's Lacq Pilot Platform in France and involved several gas spectral imaging systems: (1) mobile hyperspectral cameras in the Long-Wavelength InfraRed (LWIR) band (7.7-12μm); (2) a multispectral camera in the LWIR band (7-9μm); (3) a multigas lidar (LIght Detection And Ranging) system coupled with a wind lidar system; (4) five other international teams (US, Spain, Norway and France) were also invited to assess the capacity of their remote-sensing systems to quantify methane and carbon dioxide releases.The two-week test demonstrated that methane leak emissions ranging from 0.7 g/s to 140 g/s could be visualized and quantified in real time using a mobile Telops Hyper-Cam. This campaign also served to validate the performance of several remote sensing technologies.Total's Lacq Pilot Platform is a test area for qualifying cost-effective systems designed to complement the gas detection system of a plant and provide valuable information should a gas leak incident occur. New methodologies for the early detection of anomalies using remote observation systems including drones, robots and artificial intelligence data processing systems are currently being investigated there.

Optical wavelengths are an alternative to radio-frequency for future satellite-ground data transmissions. They are envisaged for future satellite telemetry systems (downlink optical links from LEO satellites) or communication (bidirectional optical links with GEO satellites). While going through the atmosphere the optical wave is affected by atmospheric turbulence. This may result in fading and surges when the incident flux is coupled to a single-mode optical fiber. To mitigate this potential source of information losses, several levers can be actuated: opto-mechanical correction methods such as adaptive optics, and numerical methods based on error correction coding and / or interleaving.This thesis has been devoted to the joint optimization of adaptive optics and numerical methods. An analytical model of fades and surge statistics of the adaptive optics-corrected signal has been proposed and validated by numerical modeling. A transmission performance model incorporating the effect of adaptive optics correction, and a distributed coding interleaving scheme on the physical layer (corrector coding and symbol interleaving) and the high layers (erase code and packet interleaving) has been developed. The joint optimization carried out thanks to these developments makes it possible to quantify the contribution of a correction by partial adaptive optics.The results obtained demonstrate that in cases of favorable signal-to-noise ratio, interleaving carried out exclusively on the high layer could be envisaged. These software oriented mechanisms make it possible to limit the use of dedicated memories, opening new perspectives for the realization of future optical communications payloads., Les longueurs d’onde optiques sont une alternative aux liens radio-fréquences pour les transmissions satellite-sol du futur. Elles sont envisagées pour les futurs systèmes de télémesure satellitaires (liens optiques descendants en provenance de satellites LEO) ou de communication (liens optiques bidirectionnels avec des satellites GEO). A sa traversée de l’atmosphère l’onde optique est affectée par la turbulence atmosphérique. Des pertes peuvent en découler lors du couplage du flux incident à un détecteur optronique ou à une fibre optique monomode. Ces pertes se traduisent par des atténuations du signal reçu et donc par une potentielle perte d’informations. Pour s’en abstraire plusieurs leviers peuvent être exploités : des méthodes de correction opto-mécaniques comme l’optique adaptative, et des méthodes numériques s’appuyant sur du codage correcteur d’erreur et/ou de l’entrelacement.Cette thèse a été consacrée à l’optimisation conjointe de l’optique adaptative et des méthodes numériques. Un modèle analytique des durées d’atténuation et des durées entre atténuation du signal corrigé par optique adaptative a été proposé et validé par modélisation numérique (voir illustration, évaluation des durées moyenne entre atténuation en fonction du seuil appliqué sur le flux incident pour un cas de lien descendant GEO-sol). Un modèle de performance de transmission intégrant l’effet d’une correction par optique adaptative, et un schéma d’entrelacement codage réparti sur la couche physique (codage correcteur et entrelacement symbole) et les couches hautes (code à effacement et entrelacement paquets) a été élaboré. L’optimisation conjointe menée grâce à ces développements permet de quantifier l’apport d’une correction par optique adaptative partielle.Les résultats obtenus démontrent que dans les cas de rapport signal à bruit favorables un entrelacement réalisé exclusivement sur la couche haute pourrait être envisagé. Ces mécanismes logiciels permettent de limiter l’emploi de mémoires dédiées, ouvrant des perspectives nouvelles pour la réalisation de futures charges utiles de communications optiques.

International audience

International audience

International audience; Many Earth observing sensors have been designed, built and launched with primary objectives of either terrestrial or ocean remote sensing applications. Often the data from these sensors are also used for freshwater, estuarine and coastal water quality observations, bathymetry and benthic mapping. However, such land and ocean specific sensors are not designed for these complex aquatic environments and consequently are not likely to perform as well as a dedicated sensor would. As a CEOS action, CSIRO and DLR have taken the lead on a feasibility assessment to determine the benefits and technological difficulties of designing an Earth observing satellite mission focused on the biogeochemistry of inland, estuarine, deltaic and near coastal waters as well as mapping macrophytes, macro-algae, sea grasses and coral reefs. These environments need higher spatial resolution than current and planned ocean colour sensors offer and need higher spectral resolution than current and planned land Earth observing sensors offer (with the exception of several R&D type imaging spectrometry satellite missions). The results indicate that a dedicated sensor of (non-oceanic) aquatic ecosystems could be a multispectral sensor with ~26 bands in the 380-780 nm wavelength range for retrieving the aquatic ecosystem variables as well as another 15 spectral bands between 360-380 nm and 780-1400 nm for removing atmospheric and air-water interface effects. These requirements are very close to defining an imaging spectrometer with spectral bands between 360 and 1000 nm (suitable for Si based detectors), possibly augmented by a SWIR imaging spectrometer. In that case the spectral bands would ideally have 5 nm spacing and Full Width Half Maximum (FWHM), although it may be necessary to go to 8 nm wide spectral bands (between 380 to 780nm where the fine spectral features occur -mainly due to photosynthetic or accessory pigments) to obtain enough signal to noise. The spatial resolution of such a global mapping mission would be between ~17 and ~33 m enabling imaging of the vast majority of water bodies (lakes, reservoirs, lagoons, estuaries etc.) larger than 0.2 ha and ~25% of river reaches globally (at ~17 m resolution) whilst maintaining sufficient radiometric resolution.

Laser emission wavelength is limited by the gain bandwidth of available laser media. Optical frequency converters rely on second order nonlinear processes to overcome this limitation, and give access to new wavelengths outside of the emission range of lasers.Besides, coherent beam combining with active phase control is an efficient technique to power scale laser sources. However, it requires fast phase modulators, some commercially available devices, but only at standard laser wavelengths.The objective of this thesis is to perform coherent combining of frequency converters, thanks to the phase-matching condition required for efficient nonlinear processes to take place.This relation allows for indirect phase control, where the converted-wave phase is tuned through direct phase control of the pump wave.A theoretical study has been carried out to confirm that indirect phase control was compatible with frequency-tagging coherent combining.Then, coherent combining through indirect phase control has been demonstrated experimentally in the simplest case of the second harmonic generators, where two of the three waves involved are degenerate.Finally, coherent combining has been experimentally performed in the non-degenerate case of mid-infrared difference frequency generators.In both experimental demonstrations, an excellent beam combination efficiency has been achieved., Les convertisseurs de fréquences optiques utilisant les processus non linéaires d’ordre deux permettent d’étendre la gamme spectrale accessible aux sources lasers. Celle-ci est en effet limitée par les bandes de gain des milieux lasers disponibles. Par ailleurs, la combinaison cohérente par contrôle actif de la phase est une technique efficace permettant la montée en puissance des sources lasers. Elle nécessite toutefois des modulateurs de phase rapides qui ne sont disponibles commercialement qu’aux longueurs d’onde standard.L’objectif de cette thèse est d'appliquer la combinaison cohérente à des convertisseurs de fréquences en utilisant la relation de phase inhérente au processus non linéaire.Cela permet de contrôler la phase de l’onde générée en agissant sur la phase de l’onde de pompe. C’est ce qu’on appelle le contrôle indirect de la phase.Pour cela, une étude théorique a été menée afin de s’assurer de la compatibilité de la technique de combinaison cohérente par marquage en fréquence avec le contrôle indirect de la phase.La démonstration expérimentale a d’abord été effectuée dans le cas le plus simple, la génération de seconde harmonique, qui met en jeu trois ondes dont deux dégénérées.Enfin, on s’est intéressé au cas de la génération de différence de fréquences dans le moyen infrarouge, où trois ondes sont mises en jeu.Dans ces deux cas, la qualité de mise en phase mesurée est excellente.

Laser emission wavelength is limited by the gain bandwidth of available laser media. Optical frequency converters rely on second order nonlinear processes to overcome this limitation, and give access to new wavelengths outside of the emission range of lasers.Besides, coherent beam combining with active phase control is an efficient technique to power scale laser sources. However, it requires fast phase modulators, some commercially available devices, but only at standard laser wavelengths.The objective of this thesis is to perform coherent combining of frequency converters, thanks to the phase-matching condition required for efficient nonlinear processes to take place.This relation allows for indirect phase control, where the converted-wave phase is tuned through direct phase control of the pump wave.A theoretical study has been carried out to confirm that indirect phase control was compatible with frequency-tagging coherent combining.Then, coherent combining through indirect phase control has been demonstrated experimentally in the simplest case of the second harmonic generators, where two of the three waves involved are degenerate.Finally, coherent combining has been experimentally performed in the non-degenerate case of mid-infrared difference frequency generators.In both experimental demonstrations, an excellent beam combination efficiency has been achieved.; Les convertisseurs de fréquences optiques utilisant les processus non linéaires d’ordre deux permettent d’étendre la gamme spectrale accessible aux sources lasers. Celle-ci est en effet limitée par les bandes de gain des milieux lasers disponibles. Par ailleurs, la combinaison cohérente par contrôle actif de la phase est une technique efficace permettant la montée en puissance des sources lasers. Elle nécessite toutefois des modulateurs de phase rapides qui ne sont disponibles commercialement qu’aux longueurs d’onde standard.L’objectif de cette thèse est d'appliquer la combinaison cohérente à des convertisseurs de fréquences en utilisant la relation de phase inhérente au processus non linéaire.Cela permet de contrôler la phase de l’onde générée en agissant sur la phase de l’onde de pompe. C’est ce qu’on appelle le contrôle indirect de la phase.Pour cela, une étude théorique a été menée afin de s’assurer de la compatibilité de la technique de combinaison cohérente par marquage en fréquence avec le contrôle indirect de la phase.La démonstration expérimentale a d’abord été effectuée dans le cas le plus simple, la génération de seconde harmonique, qui met en jeu trois ondes dont deux dégénérées.Enfin, on s’est intéressé au cas de la génération de différence de fréquences dans le moyen infrarouge, où trois ondes sont mises en jeu.Dans ces deux cas, la qualité de mise en phase mesurée est excellente.

International audience; The rapid development of Unmanned Aerial Vehicle (UAV) technology, -also known as drones- has raised concerns on the safety of critical locations such as governmental buildings, nuclear stations, crowded places etc. Computer vision based approach for detecting these threats seems as a viable solution due to various advantages. We envision an autonomous drone detection and tracking system for the protection of strategic locations. It has been reported numerous times that, one of the main challenges for aerial object recognition with computer vision is discriminating birds from the targets. In this work, we have used 2-dimensional scale, rotation and translation invariant Generic Fourier Descriptor (GFD) features and classified targets as a drone or bird by a neural network. For the training of this system, a large dataset composed of birds and drones is gathered from open sources. We have achieved up to 85.3% overall correct classification rate.

With the expansion of urban areas, air pollution and heat island effects are increasing, leading to state of health issues for the inhabitants and global climate changes. In this context, urban trees are a valuable resource for both improving air quality and promoting freshness islands. On the other hand, canopies are subject to specific conditions in the urban environment, causing the spread of diseases and life expectancy decreases among the trees.This thesis explores the potential of remote sensing for the automatic urban tree mapping, from the detection of the individual tree crowns to their species estimation. This is an essential preliminary task for designing the future green cities, and for an effective vegetation monitoring. Based on airborne hyperspectral, panchromatic and Digital Surface Model data, the first objective of this thesis consists in taking advantage of several data sources for improving the existing urban tree maps, by testing different fusion strategies (feature and decision level fusion). The nature of the results led us to optimize the complementarity of the sources.In particular, the second objective is to investigate deeply the richness of the hyperspectral data, by developing an ensemble classifier approach based on species specific classifiers. The features are built owing to vegetation indices selection, specific for each species.Finally, the first part highlighted to interest of discriminating the street trees from the other structures of urban trees. In a Marked Point Process framework, the third objective is to detect trees in urban alignment. Through the first objective, this thesis demonstrates that the hyperspectral data (especially the VNIR) are the main driver of the species prediction accuracy. The decision level fusion strategy is the most appropriate one for improving the performance in comparison the hyperspectral data alone, but slight improvements are obtained (a few percent) due to the low complementarity of textural and structural features in addition to the spectral ones.The ensemble classifier approach developed in the second part allows the tree species to be classified from ground-based spectral references (leaf and canopy levels), with significant improvements in comparison to a standard feature level classification approach. Finally, the street trees can be mapped thanks to the proposed model integrating contextual features (alignment and similar heights). This work could be extended to the phenological monitoring of urban vegetation and the analysis of the state of health., Avec l'expansion des zones urbaines, la pollution de l'air et les effets des îlots de chaleur augmentent, entraînant des problèmes d'état de santé pour les habitants et des changements climatiques globaux. Dans ce contexte, les arbres urbains sont une ressource précieuse à la fois pour améliorer la qualité de l'air et promouvoir les îlots de fraîcheur. D'autre part, les canopées sont soumises à des conditions spécifiques dans l'environnement urbain, provoquant la propagation de maladies et une diminution de l'espérance de vie parmi les arbres.Cette thèse explore le potentiel de la télédétection pour la cartographie automatique des arbres urbains, depuis la détection des couronnes d'arbres jusqu'à l'estimation de leur espèce. C'est une tâche préliminaire essentielle pour la conception des futures villes vertes et pour un suivi efficace de la végétation. Fondé sur des données hyperspectrales aéroportées, panchromatiques et Digital Surface Model, le premier objectif de cette thèse consiste à exploiter plusieurs sources de données pour améliorer les cartes urbaines existantes, en testant différentes stratégies de fusion (fusion de caractéristiques et de décision). La nature des résultats nous a conduit à optimiser la complémentarité des sources.En particulier, le second objectif est d'étudier en profondeur la richesse des données hyperspectrales, en développant un ensemble de classifieurs fondé sur des classifieurs spécifiques aux espèces. Les caractéristiques sont construites grâce à une sélection d'indices de végétation, spécifique à chaque espèce.Enfin, la première partie a mis en évidence l'intérêt de discriminer les arbres d'alignement des autres structures d'arbres urbains. Dans un cadre de processus de points marqués, le troisième objectif est de détecter les arbres appar¬tenant à un alignement. Grâce au premier objectif, cette thèse démontre que les données hyperspectrales (en particulier le VNIR) sont le principal moteur de la précision de la prédiction de l'espèce. La stratégie de fusion au niveau de la décision est la plus appropriée pour améliorer les performances par rapport aux données hyperspectrales seules, mais de légères améliorations sont obtenues (quelques pourcents) en raison de la faible complémentarité des caractéristiques texturales et structurales en plus des caractéristiques spectrales.L'approche d'ensemble développée dans la seconde partie permet de classer les espèces d'arbres à partir de mesures spectrales terrain (à l'échelle de la feuille ou de la canopée), avec des améliorations significatives par rapport à une approche standard de classification au niveau des caractéristiques. Enfin, les arbres d'alignement peuvent être cartographiés grâce au modèle proposé intégrant des caractéristiques contextuelles (alignement et hauteurs similaires). Ce travail pourrait être étendu au suivi phénologique de la végétation urbaine et à l'analyse de l'état de santé.

Impact de la résolution spatiale pour l’identification d’essences forestières en milieu tempéré à partir d’une image hyperspectrale du domaine réflectif. 6. Colloque de la Société Française de Photogrammétrie et Télédétection - Groupe Hyperspectrale (SFPT-GH)

International audience; With increasing number of Unmanned Aerial Vehicles (UAVs) -also known as drones- in our lives, safety and privacy concerns have arose. Especially, strategic locations such as governmental buildings, nuclear power stations etc. are under direct threat of these publicly available and easily accessible gadgets. Various methods are proposed as counter-measure, such as acoustics based detection, RF signal interception, micro-doppler RADAR etc. Computer vision based approach for detecting these threats seems as a viable solution due to various advantages. We envision an autonomous drone detection and tracking system for the protection of strategic locations. In this work, 2-dimensional scale, rotation and translation invariant Generic Fourier Descriptor (GFD) features (which are analyzed with a neural network) are used for classifying aerial targets as a drone or bird. For the training of this system, a large dataset composed of birds and drones is gathered from open sources. We have achieved up to 85.3% overall correct classification rate.

International audience; Maritime accidents around the Korean Peninsula are increasing, and the ship detection research using remote sensing data is consequently becoming increasingly important. This study presented a new ship detection algorithm using hyperspectral images that provide the spectral information of several hundred channels in the ship detection field, which depends on high resolution optical imagery. We applied a spectral matching algorithm between the reflection spectrum of the ship deck obtained from two field observations and the ship and seawater spectrum of the hyperspectral sensor of an airborne visible/infrared imaging spectrometer. A total of five detection algorithms were used, namely spectral distance similarity (SDS), spectral correlation similarity (SCS), spectral similarity value (SSV), spectral angle mapper (SAM), and spectral information divergence (SID). SDS showed an error in the detection of seawater inside the ship, and SAM showed a clear classification result with a difference between ship and seawater of approximately 1.8 times. Additionally, the present study classified the vessels included in hyperspectral images by presenting the adaptive thresholds of each technique. As a result, SAM and SID showed superior ship detection abilities compared to those of other detection algorithms.

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]INSPIRE [ADD1_IRSTEA]Équiper l'agriculture; International audience; The use of digital soil mapping, with the help of spectroscopic data, provides a non-destructive and cost-efficient alternative to soil property laboratory measurements. Visible, near-infrared and short wave infrared (VNIR/ SWIR, 400–2500 nm) hyperspectral imaging is one of the most promising tools for topsoil property mapping. The aim of this study was to test the sensitivity of soil property prediction results to coarsening image spectral resolution. This may offer an analysis of the potential of forthcoming hyperspectral satellite sensors, e.g., HYPerspectral X IMagery (HYPXIM) or Environmental Mapping and Analysis Program (EnMAP), and existing multispectral sensors, e.g., SENTINEL-2 Multispectral Sensor Instrument (MSI) or LANDSAT-8 Operational Land Imager (OLI), for soil properties mapping. This study used VNIR/SWIR hyperspectral airborne data acquired by the AISA-DUAL sensor (initial spectral and spatial resolutions of approximately 5 nm and 5 m, respectively) over a 300 km2 Mediterranean rural region. Ten spectral configurations were built and divided in the following two groups: i) six spectral configurations corresponding to simulated sensors with regular spectral resolution from 5 nm to 200 nm (i.e., the Full Width at Half Maximum (FWHM) remains constant throughout the considered spectral domain; this includes the simulation of the forthcoming HYPXIM and EnMAP hyperspectral satellites) and ii) four spectral configurations corresponding to existing multispectral sensors with irregular spectral resolution (i.e., the FWHM differs from spectral sampling interval; Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), SENTINEL-2 MSI, LANDSAT-7 Enhanced Thematic Mapper (ETM+) and LANDSAT-8 OLI). The soil property studied in this paper is the clay content, defined as the percentage of granulometric fraction finer than 2 μm by weight of the soil, which will be estimated using the partial least squares regression method. Our results showed that i) spectral configurations with regular spectral resolutions from 5 to 100 nm provided similar and good clay content prediction performances (R2val > 0.7 and RPIQ > 3) and allowed clay mapping with correct short-scale variations, ii) the spectral configuration with a regular spectral resolution of 200 nm provided unsatisfactory clay content prediction performance (R2val ≃ 0.01 and RPIQ ≃ 1.65) and iii) the ASTER sensor was the only existing multispectral sensor that provided both correct performance of clay content estimation (R2val ≃ 0.8 and RPIQ ≃ 3.72) and correct clay mapping. Therefore, clay mapping by the ASTER multispectral data should be pursued while awaiting the launch of forthcoming hyperspectral satellite sensors (e.g., HYPXIM and EnMAP), which will be good candidates for future large clay mapping campaigns over bare soils.

International audience; The ability to evaluate wheel-rail adhesion of trains on rail tracks is important in various fields of Intelligent Transportation System ITS: Environment Perception, Safety and Driver Support, Automatic Driving, Transport Management. Adhesion is degraded when rails are polluted. Each pollution material has its proper impact on adhesion. Moreover, each material (due to its composition) reflects the light in its own way, allowing it to differentiate itself from others. In this paper we will characterise recurrent rail pollutant using a custom light and spectrometer system and associate each spectrum with an adhesion or friction coefficient.

International audience; A laboratory experiment is set up to study both surface and in-depth soil moisture content (SMC). For that purpose, an aquarium is filled successively with two soils, a clay loam and a sand. Reflectance spectra are acquired in the solar domain (400–2400 nm) on the soil surface using an ASD FieldSpec 3 HR spectroradiometer and in-depth through the aquarium glass wall using two hyperspectral cameras. Successive amounts of water ranging from low to heavy rainfall in a temperate region are uniformly poured into the aquarium. The MARMITforSMC method based on the MARMIT (MultilAyer Radiative Transfer Model for soIl reflecTance) model is applied to each reflectance spectrum to determine gravimetric SMC. In particular, vertical profiles of SMC are provided with unprecedented spatial accuracy (~0.287 mm). The results are compared with volumetric SMC measured by two time-domain reflectometry (TDR) sensors. The in-depth SMC image produced on the sand shows lower values within the first 2 cm (5%) than below (17%). In contrast, the SMC image produced on the clay loam shows evenly distributed values whatever the position in the aquarium, even 1 h after moistening. The difference in grain size between the soils explains this result.; Une expérience est montée en laboratoire pour étudier l’humidité (SMC) du sol à la fois en surface et en profondeur. Pour cela, un aquarium est successivement rempli avec deux sols, un limon argileux et un sable. Les spectres en réflectance sont acquis dans le domaine solaire (400-2400 nm) en utilisant un spectroradiomètre ASD FieldSpec 3 HR pour la surface et deux caméras hyperspectrales pour le profil derrière la paroi de l’aquarium. Des quantités successives d’eau, allant de la pluie faible à forte pour une région tempérée, sont versées uniformément dans l’aquarium. La méthode MARMITforSMC s’appuyant sur le modèle MARMIT (Modèle de Transfert Radiatif Multicouches pour la réflectance du sol) est appliquée à chaque spectre en réflectance pour déterminer l’humidité gravimétrique correspondante. Ceci permet en particulier d’obtenir des profils verticaux d’humidité avec une résolution spatiale sans précédent (0 ,287 mm). Les résultats sont comparés aux mesures d’humidité volumétrique obtenues à l’aide de sonde de réflectométrie dans le domaine temporel (TDR). Les cartes de profil d’humidité générées pour le sable montrent des valeurs plus faibles pour les 2 premiers centimètres (5 %) qu’au-delà (17 %). Par contre, les cartes de profil d’humidité générées pour le limon argileux montrent des valeurs homogènes quelle que soit la profondeur, même 1 heure après l’humidification. La différence de granulométrie des sols explique ces résultats.

We investigated the use of multispectral thermal imagery to retrieve land surface emissivity and temperature. Conversely to concurrent methods, the temperature emissivity separation (TES) method simply requires single overpass without any ancillary information. This is possible since TES makes use of an empirical relationship that estimates the minimum emissivity epsilon-min from the emissivity spectral contrast captured over several channels, so-called maximum-minimum difference (MMD). In previous studies, the epsilon-min-MMD empirical relationship of TES was calibrated and validated for various sensor spectral configurations, where the proposed calibrations involved single or linearly mixed spectra of emissivity at the leaf or soil level. However, cavity effect should be taken into account at the vegetation canopy level, to avoid an underestimation of emissivity, especially for intermediate vegetation conditions between bare soil and full vegetation cover. The current study aimed to evaluate the performances of the TES method when applied to vegetation canopies with cavity effect. We used the SAIL-Thermique model to simulate a library of emissivity spectra for a wide range of soil and plant conditions, and we addressed the spectral configurations of recent and forthcoming sensors. We obtained good results for calibration and validation over the simulated library, except for full cover canopies because of the TES gray body problem. Consistent with previous studies, the calibration/validation results were better with more channels that capture emissivity spectral contrast more efficiently. Our TES calibrations provided larger epsilon-min values as compared to former studies, especially for intermediate vegetation cover. We explained this trend by the simulated spectral library that involved numerous vegetation canopies with cavity effect, thereby shifting up the epsilon-min-MMD empirical relationship. Consequently, our TES calibration provided larger (respectively lower) estimates of emissivity (respectively radiometric temperature) that were likely to be more realistic as compared to previous calibrations. Finally, SAIL-Thermique simulations permitted to show that increasing Leaf Area Index induced a displacement of the (epsilon-min, MMD) pairs along the empirical relationship. This was consistent with the TES underlying assumption, where any change in epsilon-min induces changes in MMD since epsilon-max is bounded on [0.98-1]. Further investigations should focus on validating the outcomes of the current study against ground-based measurements, and on assessing TES performances when accounting for instrumental and atmospheric perturbations.

International audience; La première partie met en lumière de nombreuses applications en milieu urbain avec un premier chapitre sur l’utilisation de la télédétection dans la planification urbaine (étalement urbain, pollution lumineuse, qualité de l’air…). Un second chapitre analyse des scènes urbaines avec un véhicule de cartographie mobile et la reconnaissance d’objets. Le chapitre suivant aborde l’usage de la télédétection en milieu urbain et périurbain dans les processus de décision territoriale, avec des exemples en France et dans des territoires du Sud. Une deuxième partie de ce volume commence par un chapitre sur l’utilisation de la télédétection pour l’application à la couleur de l’océan. Le deuxième chapitre évoque les paramètres physiques atteignables par lidar dans les eaux côtières et continentales, avec en particulier la bathymétrie et l’altimétrie, ainsi que la caractérisation des propriétés de la colonne d’eau. Le troisième chapitre concerne des applications littorales avec l’utilisation de plus en plus fréquente de la technique lidar pour l’étude de la dynamique côtière, avec en particulier l’identification du trait de côte et l’estimation des bilans sédimentaires. La troisième partie, composée de deux chapitres, analyse la dynamique des mangroves, une des forêts les plus fragiles sur terre.

International audience; The most standard blind source separation (BSS) methods address the situation when a set of signals are available, e.g. from measurements, and all of them are linear memoryless combinations, with unknown coefficient values, of the same limited set of unknown source signals. BSS methods aim at estimating these unknown source signals and/or coefficients. This generic problem is e.g. faced in the field of Earth observation (where it is also called “unsupervised unmixing”), when considering the commonly used (over)simplified model of hyperspectral images. Each pixel of such an image has an associated reflectance spectrum derived from measurements, which is defined by the fraction of sunlight power reflected by the corresponding Earth surface at each wavelength. Each source signal is then the single reflectance spectrum associated with one of the classes of pure materials which are present in the region of Earth corresponding to the overall considered hyperspectral image. Besides, the associated coefficients define the surfaces on Earth covered with each of these pure materials in each sub-region corresponding to one pixel of the considered image. However, real hyperspectral data e.g. obtained in urban areas have a much more complex structure than the above basic model: each class of pure materials (e.g. roof tiles, trees or asphalt) has so-called spectral or intra-class variability, i.e. it yields a somewhat different spectral component in each pixel of the image. In this complex framework, this chapter shows that Principal Component Analysis (PCA) and its proposed extension are of high interest at three stages of our investigation. First, PCA allows us to analyze the above-mentioned spectral variability of real high-dimensional hyperspectral data and to propose an extended data model which is suited to these complex data. We then develop a versatile extension of BSS methods based on Nonnegative Matrix Factorization, which adds the capability to handle arbitrary forms of intra-class variability by transposing PCA concepts to this original version of the BSS tramework. Finally, PCA again proves to be very well suited to analyzing the high-dimensional data obtained as the result of the proposed BSS method.

International audience