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See detailLes outils géomatiques dans le projet ExTraCar
Cornet, Yves ULg

Conference (2016, May 09)

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See detailProjecting alternative urban growth patterns: The development and application of a remote sensing assisted calibration framework for the Greater Dublin Area
Van de Voorde, Tim; van der Kwast, Johannes; Poelmans, Lien et al

in Ecological Indicators (2016), 60

Land use change models are powerful tools that allow planners and policy makers to assess the long-term spatial and environmental impacts of their decisions. In order for these models to produce a ... [more ▼]

Land use change models are powerful tools that allow planners and policy makers to assess the long-term spatial and environmental impacts of their decisions. In order for these models to produce a realistic output, they should be properly calibrated. This is usually achieved by comparing simulated land-use maps of dates in the past to reference land-use maps of a corresponding date. As land-use data are often not readily or frequently available, we propose a two-stage calibration framework that includes existing land-use maps as well as remote sensing derived maps of the urban extent. Urban growth patterns for the Dublin area represented by remote sensing based maps were compared to simulated growth using spatial metrics in order to fine-tune the calibration of the MOLAND urban growth model of Dublin. We then used the calibrated model to forecast future urban growth according to four urban planning scenarios that have been defined for the Strategic Environmental Assessment of the Greater Dublin Area. We examined a selection of spatial metrics in order to determine their sensitivity to differences in spatial patterns between simulated and remote sensing derived data. We also investigated whether these metrics are useful to characterise future changes in the urban spatial structure that ensue from the planning scenarios. We found that with the exception of some metrics that strongly respond to differences in the amount of urban land, most metrics showed similar trends for simulated and remote sensing derived maps. Most metrics were also able to distinguish the growth patterns induced by the different spatial planning scenarios. The “business as usual scenario” in particular showed a clearly distinct trend compared to the other scenarios. We could also conclude that the urban growth pattern of Dublin as observed from both the remote sensing derived maps and the simulated maps of future land use seems to confirm the theory of alternating phases of diffusive growth and coalescence. [less ▲]

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See detailDu satellite au terrain. Observation de la surface terrestre et processus géographiques
Cornet, Yves ULg

Scientific conference (2015, November 14)

la journée de enseignants des 6ème Journées de la Géographie Belge (VUB, 14 novembre 2015). Proposition d’Yves CORNET (CC, Photogrammétrie et télédétection, Geomatique, ULg) Sujet : « Du satellite au ... [more ▼]

la journée de enseignants des 6ème Journées de la Géographie Belge (VUB, 14 novembre 2015). Proposition d’Yves CORNET (CC, Photogrammétrie et télédétection, Geomatique, ULg) Sujet : « Du satellite au terrain » Forme : Atelier Durée totale : 1h30 Résumé : Je proposerai tout d’abord un bref rappel des notions de « couleur » (vrai couleur, fausse couleur, fausse couleur de synthèse) en visualisation d’images polygéniques enregistrées par des capteurs satellitaires récentes disponibles gratuitement dans les archives de l’USGS et couvrant le territoire wallon (ex. capteur OLI à bord de Landsat 8). Ensuite, j’élargirai la discussion en établissant le lien avec le concept de signature et résolution spectrales pour en arriver à deux applications très exploitées par les géographes et qui reposent sur ces concepts. La première application est la classification d’image. La seconde application est l’extraction de paramètres bio-géo-physiques à partir d’images multi-spectrales en exploitant les parties du spectre permettant cette détermination (ex. couleur des océans - rapports de réflectance entre les canaux visibles permettant de mettre en évidence l’absorption du rayonnement lumineux par la chlorophylle). Nous limiterons notre discours à la partie du spectre dans laquelle le soleil éclaire la surface terrestre (visible et proche infra-rouge) qui est celle la plus facile à appréhender pour des écoliers du secondaire. Ensuite pendant l’atelier, j’exploiterai de façon intuitive l’analyse graphique car elle constitue une spécificité de formations scientifiques et, malheureusement, je constate depuis plusieurs années, de la part de la majorité de nos étudiants, une réelle incapacité de s’exprimer de cette façon. Il me semble que cette compétence peut être aisément exercée par des exercices simples tels que ceux que je proposerai en limitant au maximum l’accès à des outils logiciel. Les données nécessaires à ces analyses graphiques seront fournies ou extraites d’images à l’aide d’outils logiciels de visualisation d’images gratuits qui seront mis à la disposition des enseignants pour qu’ils puissent préparer de nouvelles activités dans leur classe. Les réalisations graphiques seront effectuées sur papier quadrillé. Elle permettront par exemple de représenter la position d’un pixel dans l’espace multispectral (diagramme de dispersion bi-variés combinant les canaux 2 par 2 et éventuellement tri-variés en combinant les canaux par 3), de construire des courbes de signature spectrale de différents type de couverture du sol dans différents contextes topographique et donc dans des conditions d’illumination différentes, de construire des courbes de signature spectrales d’une eau non turbide présentant des concentration en chl-a variable (données fournies). Nous accorderons une attention particulière à la signification physique des valeurs reportées sur les différents axes (unités, ordres de grandeur, variations) et un protocole d’interprétation de ces graphiques sera ensuite proposé. D’une part, nous comparerons les signatures spectrales de différents types de couverture du sol généralement reconnus par classification d’image (surface herbeuse, canopée, sol nu, surface bétonnée, surface macadamisée, eau …). Pour certains types de couverture du sol, nous mettront en évidence l’effet topographique qui est d’autant plus marqué que la longueur d’onde exploitée se rapproche du proche infra-rouge en raison de la réduction de la diffusion du rayonnement solaire incident pour les plus grande longueurs d’onde du visible et le proche infra-rouge que pour les courtes longueur d’onde du visible. Pour limiter la complexité des interprétations, nous limiterons les analyses à des données instantanées (pas de variation temporelle !!). D’autre part, dans la partie consacrée à l’analyse de la couleur des océans nous proposeront la construction différente graphique (diagramme de dispersion ou validation et histogrammes) permettant de mettre en relation le résultat de l’extraction de paramètres bio-optiques de l’eau depuis des images satellitaire et son correspondant mesuré sur le terrain. Nous expliquerons ainsi la signification graphique des notions de biais, d’imprécision et d’incertitude. Nous établirons alors quelques liens entre le processus d’acquisition des images satellitaires (angle d’observation, champs instantané d’observation du capteur satellitaire, résolution radiométrique, influence de l’état de surface des mers et ses interaction avec la géométrie de l’éclairement solaire vis-à-vis de l’observation, altération atmosphériques …) et la signification d’un échantillon des valeurs de référence sur le terrain (campagne de mesure de la concentration de chlorophylle en mer ou dans des lac, dynamique spatiale et temporelle, représentativité spatiale et temporelle). [less ▲]

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See detailBilan de douze années (2002-2014) de limnologie satellitaire du Tanganyika.
Cornet, Yves ULg

Scientific conference (2015, October 07)

Conférence de la SGLg du 7 octobre 2015 Bilan de douze années (2002-2014) de limnologie satellitaire du Tanganyika. Yves CORNET avec la collaboration de N. Poncelet et S. Horion (ULg), P.-D. Plisnier ... [more ▼]

Conférence de la SGLg du 7 octobre 2015 Bilan de douze années (2002-2014) de limnologie satellitaire du Tanganyika. Yves CORNET avec la collaboration de N. Poncelet et S. Horion (ULg), P.-D. Plisnier (MRAC), J.P. Descy (UNamur), Chr. Coquyt (Jardin Botanique National de Belgique), E. Deleersnijder (UCL), J. Jacob (IMT), D. Bompangue et P. Giraudoux (Université de Franche-Comté), R. Piarroux (CHU La Timone, Marseille). Abstract : La fin du siècle dernier marque l’avènement d’une nouvelle génération de capteurs satellitaires à basse résolution spatiale tels SeaWiFs, MODIS et MERIS respectivement à bord de GeoEye's OrbView-2 (SeaStar), lancé en 1997, TERRA et AQUA, lancés en 1999 et 2002, et ENVISAT, lancé en 2002. Ils sont spécialement conçus pour l’analyse des processus océanographiques et limnologiques. Dans la gamme des longueurs d’onde du rayonnement visible et proche infra-rouge réfléchi par la colonne d’eau, leur résolution spectrale est adaptée à l’analyse de la couleur des océans. Dans la gamme des longueurs d’onde du rayonnement thermique émis par la surface des plans d’eau, ils permettent le calcul de sa température. L’extraction, à partir des images enregistrées par ces capteurs, des paramètres bio-optiques (concentration en chl-a ou coefficient d’atténuation de la lumière dans l’eau) et de la température de la surface des eaux ne peut cependant être optimisée et validée qu’en exploitant des mesures réalisées in situ ou d’autres produits de télédétection (ArcLake). Nous présenterons, dans un premier temps, les difficultés de cette procédure d’extraction intrinsèques à l’observation des lacs et océans en général et au milieu lacustre des Grands Lac Africain, en particulier. Cela nous permettra de qualifier les produits obtenus (série temporelles d’images couvrant la période 2002-2014) et souligner les risques de leur utilisation dans différentes applications. Parmi ces applications, nous illustrerons notamment l’exploitation de ces séries temporelles pour une meilleure compréhension (quantitative et qualitative) de l’hydrodynamique du lac, de ses relations avec la production primaire et la gestion des pêches et avec l’épidémiologie du choléra réapparu dans les années ‘70 en Afrique de l’Est. [less ▲]

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See detailDu satellite au terrain. Observation de la surface terrestre et processus géographiques
Cornet, Yves ULg

Scientific conference (2015, August 25)

53ème Congrès des Professeurs de Sciences 2015 Proposition d’Yves CORNET (CC, Photogrammétrie et télédétection, Geomatique, ULg) Sujet : « Du satellite au terrain » Forme : Brève Introduction théorique ... [more ▼]

53ème Congrès des Professeurs de Sciences 2015 Proposition d’Yves CORNET (CC, Photogrammétrie et télédétection, Geomatique, ULg) Sujet : « Du satellite au terrain » Forme : Brève Introduction théorique suivie d’un atelier Durée totale : 1h30 Résumé : Je proposerai tout d’abord un bref rappel des notions de « couleur » (vrai couleur, fausse couleur, fausse couleur de synthèse) en visualisation d’images polygéniques enregistrées par des capteurs satellitaires récentes disponibles gratuitement dans les archives de l’USGS et couvrant le territoire wallon (ex. capteur OLI à bord de Landsat 8). Ensuite, j’élargirai la discussion en établissant le lien avec le concept de signature et résolution spectrales pour en arriver à deux applications très exploitées par les géographes et qui reposent sur ces concepts. La première application est la classification d’image. La seconde application est l’extraction de paramètres bio-géo-physiques à partir d’images multi-spectrales en exploitant les parties du spectre permettant cette détermination (ex. couleur des océans - rapports de réflectance entre les canaux visibles permettant de mettre en évidence l’absorption du rayonnement lumineux par la chlorophylle). Nous limiterons notre discours à la partie du spectre dans laquelle le soleil éclaire la surface terrestre (visible et proche infra-rouge) qui est celle la plus facile à appréhender pour des écoliers du secondaire. Ensuite pendant l’atelier, j’exploiterai de façon intuitive l’analyse graphique car elle constitue une spécificité de formations scientifiques et, malheureusement, je constate depuis plusieurs années, de la part de la majorité de nos étudiants, une réelle incapacité de s’exprimer de cette façon. Il me semble que cette compétence peut être aisément exercée par des exercices simples tels que ceux que je proposerai en limitant au maximum l’accès à des outils logiciel. Les données nécessaires à ces analyses graphiques seront fournies ou extraites d’images à l’aide d’outils logiciels de visualisation d’images gratuits qui seront mis à la disposition des enseignants pour qu’ils puissent préparer de nouvelles activités dans leur classe. Les réalisations graphiques seront effectuées sur papier quadrillé. Elle permettront par exemple de représenter la position d’un pixel dans l’espace multispectral (diagramme de dispersion bi-variés combinant les canaux 2 par 2 et éventuellement tri-variés en combinant les canaux par 3), de construire des courbes de signature spectrale de différents type de couverture du sol dans différents contextes topographique et donc dans des conditions d’illumination différentes, de construire des courbes de signature spectrales d’une eau non turbide présentant des concentration en chl-a variable (données fournies). Nous accorderons une attention particulière à la signification physique des valeurs reportées sur les différents axes (unités, ordres de grandeur, variations) et un protocole d’interprétation de ces graphiques sera ensuite proposé. D’une part, nous comparerons les signatures spectrales de différents types de couverture du sol généralement reconnus par classification d’image (surface herbeuse, canopée, sol nu, surface bétonnée, surface macadamisée, eau …). Pour certains types de couverture du sol, nous mettront en évidence l’effet topographique qui est d’autant plus marqué que la longueur d’onde exploitée se rapproche du proche infra-rouge en raison de la réduction de la diffusion du rayonnement solaire incident pour les plus grande longueurs d’onde du visible et le proche infra-rouge que pour les courtes longueur d’onde du visible. Pour limiter la complexité des interprétations, nous limiterons les analyses à des données instantanées (pas de variation temporelle !!). D’autre part, dans la partie consacrée à l’analyse de la couleur des océans nous proposeront la construction différente graphique (diagramme de dispersion ou validation et histogrammes) permettant de mettre en relation le résultat de l’extraction de paramètres bio-optiques de l’eau depuis des images satellitaire et son correspondant mesuré sur le terrain. Nous expliquerons ainsi la signification graphique des notions de biais, d’imprécision et d’incertitude. Nous établirons alors quelques liens entre le processus d’acquisition des images satellitaires (angle d’observation, champs instantané d’observation du capteur satellitaire, résolution radiométrique, influence de l’état de surface des mers et ses interaction avec la géométrie de l’éclairement solaire vis-à-vis de l’observation, altération atmosphériques …) et la signification d’un échantillon des valeurs de référence sur le terrain (campagne de mesure de la concentration de chlorophylle en mer ou dans des lac, dynamique spatiale et temporelle, représentativité spatiale et temporelle). [less ▲]

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See detailEast African Great Lake Ecosystem Sensitivity to changes final report
Descy, J.-P.; André, L.; Delvaux, C. et al

Report (2015)

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See detailSpatial Analysis of GNSS Measurements from an Equatorial Ionospheric Scintillation Monitoring Receiver (ISMR) Network
Lonchay, Matthieu ULg; Wautelet, Gilles ULg; Cornet, Yves ULg et al

Conference (2014, November 19)

The ionosphere has always been a major limitation for GNSS positioning applications. Free electrons in the ionosphere perturb the propagation of GNSS radio signals involving both refraction and ... [more ▼]

The ionosphere has always been a major limitation for GNSS positioning applications. Free electrons in the ionosphere perturb the propagation of GNSS radio signals involving both refraction and diffraction effects. In particular, small-scale ionospheric irregularities generated by different physical processes may cause scattering effects on GNSS signals, producing rapid fluctuations of the signal phase and amplitude as a result. Such scintillations of GNSS signals are responsible for critical consequences regarding applications, such as precise positioning, due to many resulting effects: cycle slips, signal power fading, receiver loss of lock and poor resulting satellite geometry. Ionospheric Scintillation Monitoring Receivers collect high-rate GNSS data. Specific scintillation parameters, such as the well-known S4 and Phi60 indices, are built on high-rate measurements performed on GNSS signals and provide additional information to characterize the intensity of such an event occurring at a specific geographic location at a given time. Spatial Statistics belong to the field of Spatial Analysis, Geography and GIS (Geographic Information System). This discipline allows to perform analyses of data which are localised in space. Ionospheric Scintillation observations achieved by ISMR stations can be characterized by a set of attributes (S4, Phi60, Rate of TEC, etc.) including also the geographic location of their respective Ionospheric Pierce Point (IPP). By combining the simultaneous Multi-GNSS ISMR measurements from a network of ISMR stations, we can obtain a spatially denser data set, able to support spatial statistics tests. The idea of our research is to provide a spatio-temporal analysis of ionospheric scintillation events over Equatorial regions by applying spatial statistics on ISMR Multi-GNSS measurements. In particular, by using spatial statistics, we aim to resolve specific issues regarding ionospheric scintillation data from an ISMR network established in Brazil. The research consists in spatially describing the data set, detecting and measuring potential spatial autocorrelation, determining the scale of the spatial dependency and finally producing an interpolated scintillation sky map at a given time. In terms of applicability of the methodology, our research project consists in exploiting the spatio-temporal analysis performed on ionospheric scintillation data in order to improve the performances and the reliability of Absolute GNSS Positioning algorithms under moderate ionospheric scintillation conditions. By assessing correlations existing between specific ISMR data and classic GNSS observations, the method could be extended to a more general usage which would be independent of ISMR measurements. [less ▲]

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See detailMICROPHYSIQUE DES NUAGES ET RAYONNEMENT SOLAIRE : COMPARAISON DES MESURES IN SITU AU MONT RIGI EN HAUTE BELGIQUE ET DES DONNÉES CLOUD PHYSICAL PROPERTIES (CPP) OBTENUES À PARTIR DES IMAGES METEOSAT-9
Beaumet, Julien ULg; Clerbaux, Nicolas; Cornet, Yves ULg et al

in Camberlin, Pierre; Richard, Yves (Eds.) Actes du XXVIIe Colloque de l'Association Internationale de Climatologie : CLIMAT : SYSTÈME & INTERACTIONS (2014, July 02)

Le rayonnement solaire global mesuré au mont Rigi a été comparé à l'épaisseur optique des nuages (COT) estimée à l'aide des données SEVIRI. Une relation logarithmique avec un coefficient de détermination ... [more ▼]

Le rayonnement solaire global mesuré au mont Rigi a été comparé à l'épaisseur optique des nuages (COT) estimée à l'aide des données SEVIRI. Une relation logarithmique avec un coefficient de détermination d'environ 0,5 a été trouvée. Ce résultat plutôt faible peut en grande partie s'expliquer par un nombre limité de cas où subsistent des erreurs de positionnement ou par des interactions plus complexes entre nébulosité et rayonnement. De plus, l'incertitude sur l'estimation de l'épaisseur optique des nuages à l'aide des données SEVIRI pour les nuages optiquement plus épais n'est pas négligeable. [less ▲]

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See detailSpatio-Temporal Analysis of Equatorial Ionospheric Scintillations in the Frame of Absolute GNSS Positioning Algorithms
Lonchay, Matthieu ULg; Cornet, Yves ULg; Aquino, Marcio et al

Conference (2014, April 30)

The ionosphere has always been a major limitation for GNSS positioning applications. Free electrons in the ionosphere perturb the propagation of GNSS radio signals involving both refraction and ... [more ▼]

The ionosphere has always been a major limitation for GNSS positioning applications. Free electrons in the ionosphere perturb the propagation of GNSS radio signals involving both refraction and diffraction effects. The ionospheric refraction mainly results in a modification of the propagation speed of the GNSS electromagnetic signals, inducing an error (propagation delay or phase advance depending on the observable) in GNSS measurements. In the frame of absolute positioning techniques, single-frequency algorithms usually exploit an ionospheric model to mitigate the ionospheric error while dual-frequency algorithms, such as the well-known Precise Point Positioning (PPP), take the benefit of the availability of two frequencies and the fact that the ionosphere is a dispersive medium to construct an ionosphere-free mathematical model. But these two strategies are not able to counteract the effect of the ionospheric diffraction which is due to small-scale irregularities in the free electron density. By scattering GNSS signals, these irregularities generate rapid fluctuations (scintillations) in the amplitude and phase of GNSS signals with critical consequences for GNSS applications: cycle slips, signal power fading, receiver loss of lock and poor resulting satellite geometry. The goal of our research is to develop a strategy to mitigate the effect of ionospheric scintillations on absolute GNSS positioning techniques, in particular the SPP (Standard Point Positioning) and the PPP (Precise Point Positioning). The strategy is based on the adjustment of the stochastic model. In order to construct the stochastic model (diagonal and non-diagonal elements) and study the correlation between observables, we adopted a “spatial” and an “empirical” approach. The spatial approach consists in a study of the spatial autocorrelation existing in scintillations effects on GNSS signals. The spatial autocorrelation is detected by using specific spatial analysis techniques applied on data from a network of ISMR (Ionospheric Scintillation Monitoring Receiver) stations located at equatorial and polar latitudes, where scintillations effects are most severe. The knowledge of how scintillation effects are spatially correlated is helpful for determining a coherent stochastic model. The empirical approach does not take into account the phenomenon spatiality and the locations of the measurements but only the observation data. Its objective is to determine the statistical correlation which exists between GNSS measurements during a scintillation event by using a moving filter applied on GNSS observation and scintillation data. The spatial approach exploits data and data locations while the empirical approach is based only the data itself. [less ▲]

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See detailSpatio-Temporal Analysis of Equatorial Ionospheric Scintillations in the Frame of Absolute GNSS Positioning Algorithms
Lonchay, Matthieu ULg; Cornet, Yves ULg; Aquino, Marcio et al

Poster (2014, April 23)

The ionosphere has always been a major limitation for GNSS positioning applications. Free electrons in the ionosphere perturb the propagation of GNSS radio signals involving both refraction and ... [more ▼]

The ionosphere has always been a major limitation for GNSS positioning applications. Free electrons in the ionosphere perturb the propagation of GNSS radio signals involving both refraction and diffraction effects. The ionospheric refraction mainly results in a modification of the propagation speed of the GNSS electromagnetic signals, inducing an error (propagation delay or phase advance depending on the observable) in GNSS measurements. In the frame of absolute positioning techniques, single-frequency algorithms usually exploit an ionospheric model to mitigate the ionospheric error while dual-frequency algorithms, such as the well-known Precise Point Positioning (PPP), take the benefit of the availability of two frequencies and the fact that the ionosphere is a dispersive medium to construct an ionosphere-free mathematical model. But these two strategies are not able to counteract the effect of the ionospheric diffraction which is due to small-scale irregularities in the free electron density. By scattering GNSS signals, these irregularities generate rapid fluctuations (scintillations) in the amplitude and phase of GNSS signals with critical consequences for GNSS applications: cycle slips, signal power fading, receiver loss of lock and poor resulting satellite geometry. The goal of our research is to develop a strategy to mitigate the effect of ionospheric scintillations on absolute GNSS positioning techniques, in particular the SPP (Standard Point Positioning) and the PPP (Precise Point Positioning). The strategy is based on the adjustment of the stochastic model. In order to construct the stochastic model (diagonal and non-diagonal elements) and study the correlation between observables, we adopted a “spatial” and an “empirical” approach. The spatial approach consists in a study of the spatial autocorrelation existing in scintillations effects on GNSS signals. The spatial autocorrelation is detected by using specific spatial analysis techniques applied on data from a network of ISMR (Ionospheric Scintillation Monitoring Receiver) stations located at equatorial and polar latitudes, where scintillations effects are most severe. The knowledge of how scintillation effects are spatially correlated is helpful for determining a coherent stochastic model. The empirical approach does not take into account the phenomenon spatiality and the locations of the measurements but only the observation data. Its objective is to determine the statistical correlation which exists between GNSS measurements during a scintillation event by using a moving filter applied on GNSS observation and scintillation data. The spatial approach exploits data and data locations while the empirical approach is based only the data itself. [less ▲]

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See detailAUTOMATISATION DE LA DÉTECTION DES CRATÈRES LUNAIRES SUR DES IMAGES ET MNT PLANÉTAIRES
Renson, Pierre; Poncelet, Nadia; Vandeloise, Yannick et al

in Bulletin de la Société Géographique de Liège (2014), 61

This research is part of the preparation of a lunar mission. Its objective is to implement, test and validate an automated method that detects craters on the lunar surface from planetary products (images ... [more ▼]

This research is part of the preparation of a lunar mission. Its objective is to implement, test and validate an automated method that detects craters on the lunar surface from planetary products (images and DTM). In this context, the automation of the process is essential because the craters represent a landing risk and landmarks for visual navigation. It is also the key challenge because it is difficult to develop high level automatic processing comparable to the thinking carried out in a traditional visual interpretation. Our method automatically establishes a semantic diagnosis based on the combination of crater descriptors computed on the planetary products used. Finally, this application is part of a decision support tool and an assessment system of landing and mission survival risks. It also aims to feed a landmarks database for automatic visual navigation of a lunar landing spacecraft. [less ▲]

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See detailMethodology used for the European badger (Meles meles) monitoring in Wallonie
Schockert, Vincianne ULg; Lambinet, Clotilde ULg; Cornet, Yves ULg et al

in Lecocq, Yves (Ed.) Abstracts of 31st IUGB congress (2013, August)

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See detailMonitoring the evolution of irrigated areas with Landsat images using backward and forward change detection analysis in the Kou watershed
Traore, Farid ULg; Cornet, Yves ULg; Denis, Antoine ULg et al

in Geocarto International (2013)

The Kou watershed is characterized by important water resources used for drinking, agriculture (especially in the important irrigated areas), industry and the preservation of aquatic fauna and flora. For ... [more ▼]

The Kou watershed is characterized by important water resources used for drinking, agriculture (especially in the important irrigated areas), industry and the preservation of aquatic fauna and flora. For several decades there has been increasing pressure on the Kou’s water resources, partly because of the expansion of the irrigated agricultural areas. This study was conducted to examine this issue, focusing on one specific irrigated area. In order to monitor the expansion of irrigated areas in developing countries, a low-cost remote sensing method based on Landsat images and aerial photographs was developed. The method is based on maximum-likelihood classifications, followed by backward and forward change detection analysis requiring agronomic expertise. Using pixel trajectory analysis, the method connects all pixels to their consecutive states in order to correct their current states. The study showed that the irrigated area has expanded by almost 80% over 20 years, with most of this expansion occurring in the past 10 years. The approach, if validated, could be used to obtain information on past occupation in the rural irrigated areas for which there is no archived data. [less ▲]

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See detailSimilar local and landscape processes affect both a common and a rare newt species
Denoël, Mathieu ULg; Perez, Amélie; Cornet, Yves ULg et al

in PLoS ONE (2013), 8(5), 62727

Although rare species are often the focus of conservation measures, more common species may experience similar decline and suffer from the same threatening processes. We tested this hypothesis by ... [more ▼]

Although rare species are often the focus of conservation measures, more common species may experience similar decline and suffer from the same threatening processes. We tested this hypothesis by examining, through an information-theoretic approach, the importance of ecological processes at multiple scales in the great crested newt Triturus cristatus, regionally endangered and protected in Europe, and the more common smooth newt, Lissotriton vulgaris. Both species were similarly affected by the same processes, i.e. suitability of aquatic and terrestrial components of their habitat at different scales, connectivity among breeding sites, and the presence of introduced fish. T. cristatus depended more on water depth and aquatic vegetation than L. vulgaris. The results show that environmental pressures threaten both common and rare species, and therefore the more widespread species should not be neglected in conservation programs. Because environmental trends are leading to a deterioration of aquatic and terrestrial habitat features required by newt populations, populations of the common species may follow the fate of the rarest species. This could have substantial conservation implications because of the numerical importance of common species in ecosystems and because commonness could be a transient state moving towards rarity. On the other hand, in agreement with the umbrella species concept, targeting conservation efforts on the most demanding species would also protect part of the populations of the most common species. [less ▲]

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See detailAssessing urbanisation effects on rainfall-runoff using a remote sensing supported modelling strategy
Verbeiren, Boud; Van de Voorde, Tim; Canters, Frank et al

in International Journal of Applied Earth Observation and Geoinformation (2013), 21

This paper aims at developing a methodology for assessing urban dynamics in urban catchments and the related impact on hydrology. Using a multi-temporal remote sensing supported hydrological modelling ... [more ▼]

This paper aims at developing a methodology for assessing urban dynamics in urban catchments and the related impact on hydrology. Using a multi-temporal remote sensing supported hydrological modelling approach an improved simulation of runoff for urban areas is targeted. A time-series of five medium resolution urban masks and corresponding sub-pixel sealed surface proportions maps was generated from Landsat and SPOT imagery. The consistency of the urban mask and sealed surface proportion timeseries was imposed through an urban change trajectory analysis. The physically based rainfall-runoff model WetSpa was successfully adapted for integration of remote sensing derived information of detailed urban land use and sealed surface characteristics. A first scenario compares the original land-use class based approach for hydrological parameterisation with a remote sensing sub-pixel based approach. A second scenario assesses the impact of urban growth on hydrology. Study area is the Tolka River basin in Dublin, Ireland. The grid-based approach of WetSpa enables an optimal use of the spatially distributed properties of remote sensing derived input. Though change trajectory analysis remains little used in urban studies it is shown to be of utmost importance in case of time series analysis. The analysis enabled to assign a rational trajectory to 99% of all pixels. The study showed that consistent remote sensing derived land-use maps are preferred over alternative sources (such as CORINE) to avoid over-estimation errors, interpretation inconsistencies and assure enough spatial detail for urban studies. Scenario 1 reveals that both the class and remote sensing sub-pixel based approaches are able to simulate discharges at the catchment outlet in an equally satisfactory way, but the sub-pixel approach yields considerably higher peak discharges. The result confirms the importance of detailed information on the sealed surface proportion for hydrological simulations in urbanised catchments. In addition a major advantage with respect to hydrological parameterisation using remote sensing is the fact that it is site- and period-specific. Regarding the assessment of the impact of urbanisation (scenario 2) the hydrological simulations revealed that the steady urban growth in the Tolka basin between 1988 and 2006 had a considerable impact on peak discharges. Additionally, the hydrological response is quicker as a result of urbanisation. Spatially distributed surface runoff maps identify the zones with high runoff production. It is evident that this type of information is important for urban water management and decision makers. The results of the remote sensing supported modelling approach do not only indicate increased volumes due to urbanisation, but also identifies the locations where the most relevant impacts took place. [less ▲]

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See detailMapping error due to image geometric correction.
Hallot, Eric ULg; Cornet, Yves ULg; Hallot, Pierre ULg

Poster (2012, April)

Nowadays, image processing and GIS tools are more accessible and available to all. Most of diachronical or historical studies use the image geometric correction with several documents like old maps, plans ... [more ▼]

Nowadays, image processing and GIS tools are more accessible and available to all. Most of diachronical or historical studies use the image geometric correction with several documents like old maps, plans or aerial photographs. They are usually based on low-order polynomial equation to perfom these kinds of simplistic uses. Most of commercial softwares provide us a total or by ground control points RMSE but they don’t offer a overview of the spatial error distribution. More this does not guarantee that its significance for the other points of the image. Do not consider these errors can lead to erroneous observations and misinterpretations like historical moving streams or bank erosion rate. Using a least square adjustment (LSA), allow to recalculate the transformation equation from the pairs of control points coordinates. Assuming that residuals are spatially auto-correlated, we can build error vectors whose direction and magnitude symbolize the error at each point of the image. By another way, LSA manage the precision during transformation process by using a stochastic model in addition of the mathematical model during the transformation. This gives us variance on parameters of the transformation. Knowing the precision of all elements and variance/covariance matrix on transformation parameters, we apply variance propagation on the model. As an output, we obtain confidence ellipses on each transformed points, thus a spatial distribution of error for the entire image. Moreover, this leads us to determine statistically if observed movement are significant or not. The represent error is a complex problem that cannot be solved with a quick fix. In this work, we present an interesting example of using well-known topographic methods to solve image processing problems. [less ▲]

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See detailPredicting the spatial distribution of population based on impervious surface maps and modeled land use change
Cornet, Yves ULg; Binard, Marc ULg; Ledant, Martin et al

in Perakis, Konstantinos G.; Moysiadis, Athanasios K. (Eds.) European Association of Remote Sensing Laboratories 32nd EARSeL Symposium Proceedings Advances in Geosciences Mykonos Island, Greece, 21 May - 24 May 2012 (2012)

Land use and changes in the spatial distribution of population are spatially and temporally linked and have an obvious impact on the urban environment. For instance, they influence the mobility and ... [more ▼]

Land use and changes in the spatial distribution of population are spatially and temporally linked and have an obvious impact on the urban environment. For instance, they influence the mobility and accessibility and play an important role in waste water management. This forecasting of the spatial distribution of population is thus a critical issue in planning. In order to allow this forecasting we have adjusted a multiple regression model to estimate the population distribution in function of land-use. The originality in our modeling strategy is the use of sealed surface proportion maps as weighting factor assuming that sealed surface proportion is a proxy of population density. The data exploited to adjust the parameters of the model are three time-series of landuse maps from the EU-MOLAND, census data and medium and high resolution remotely sensed images. We made use of these images in a spectral unmixing procedure that provides the sealed surface proportion maps. In the model, the population was normalized in order to get a model that is independent of time and space. This is required for prediction and spatial extrapolation which assumes a temporally and spatially stable relationship between land use, imperviousness and population density. We validated the model by means of a population disaggregation/re-aggregation procedures and tested its robustness regarding the resolution because predicted sealed surface proportion and predicted landuse maps using the calibrated EU-MOLAND model are generated at lower resolution (200 m) than the resolution used in the model adjustment. The results described in this paper regard the urban zone of Dublin. [less ▲]

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See detailLANDSAFE: LANDING SITE RISK ANALYSIS SOFTWARE FRAMEWORK
Schmidt, Ralph; Bostelmann, Jonas; Cornet, Yves ULg et al

in International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences (2012), XXXIX(B4), 505-510

The European Space Agency (ESA) is planning a Lunar Lander mission in the 2018 timeframe that will demonstrate precise soft landing at the polar regions of the Moon. To ensure a safe and successful ... [more ▼]

The European Space Agency (ESA) is planning a Lunar Lander mission in the 2018 timeframe that will demonstrate precise soft landing at the polar regions of the Moon. To ensure a safe and successful landing a careful risk analysis has to be carried out. This is comprised of identifying favorable target areas and evaluating the surface conditions in these areas. Features like craters, boulders, steep slopes, rough surfaces and shadow areas have to be identified in order to assess the risk associated to a landing site in terms of a successful touchdown and subsequent surface operation of the lander. In addition, global illumination conditions at the landing site have to be simulated and analyzed. The Landing Site Risk Analysis software framework (LandSAfe) is a system for the analysis, selection and certification of safe landing sites on the lunar surface. LandSAfe generates several data products including high resolution digital terrain models (DTMs), hazard maps, illumination maps, temperature maps and surface reflectance maps which assist the user in evaluating potential landing site candidates. This paper presents the LandSAfe system and describes the methods and products of the different modules. For one candidate landing site on the rim of Shackleton crater at the south pole of the Moon a high resolution DTM is showcased. * Corresponding [less ▲]

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