Publications of Yves Cornet
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See detailOptimized extraction of daily bio-optical time series derived from MODIS/Aqua imagery for Lake Tanganyika, Africa
Horion, Stéphanie; Bergamino, Nadia; Stenuite, Stéphane et al

in Remote Sensing of Environment (2010)

Lake Tanganyika is one of the world's great freshwater ecosystems. In recent decades its hydrodynamic characteristics have undergone important changes that have had consequences on the lake's primary ... [more ▼]

Lake Tanganyika is one of the world's great freshwater ecosystems. In recent decades its hydrodynamic characteristics have undergone important changes that have had consequences on the lake's primary productivity. The establishment of a long-term Ocean Color dataset for Lake Tanganyika is a fundamental tool for understanding and monitoring these changes. We developed an approach to create a regionally calibrated dataset of chlorophyll-a concentrations (CHL) and attenuation coefficients at 490 nm (K490) for the period from July 2002 to December 2006 using daily calibrated radiances retrieved from the MODIS-Aqua sensor. Standard MODIS Aqua Ocean Color products were found to not provide a suitable calibration for high altitude lakes such as the Lake Tanganyika. An optimization of the extraction process and the validation of the dataset were performed with independent sets of in situ measurements. Our results show that for the geographical, atmospheric and optical conditions of Lake Tanganyika: (i) a coastal aerosol model set with high relative humidity (90%) provides a suitable atmospheric correction; (ii) a significant correlation between in situ data and CHL estimates using the MODIS specific OC3 algorithm is possible; and (iii) K490 estimates provide a good level of significance. The resulting validated time series of bio-optical properties provides a fundamental information base for the study of phytoplankton and primary production dynamics and interannual trends. A comparison between surface chlorophyll-a concentrations estimated from field monitoring and from the MODIS based dataset shows that remote sensing allows improved detection of surface blooms in Lake Tanganyika. [less ▲]

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See detailUsing information on urban morphology derived from a time-series of medium resolution remote sensing data for the calibration of the moland urban growth model
van der Kwast; Van de Voorde, Tim; Binard, Marc ULiege et al

in Joint SIG Workshop Urban - 3D - Radar - Thermal Remote Sensing and Developing Countries, Book of Proceedings EUROPEAN ASSOCIATION OF REMOTE SENSING LABORATORIES (2010)

Land-use change models are more and more used by planners and policy makers as tools to assess the impacts of their decisions on the spatial systems that they are to manage. To be usefully applicable the ... [more ▼]

Land-use change models are more and more used by planners and policy makers as tools to assess the impacts of their decisions on the spatial systems that they are to manage. To be usefully applicable the models need extensive calibration. Typically the required time series of land-use maps based on identical and consistent mapping methodologies, legends and scales are missing. As a result, the land-use changes measured in the time intervals studied are often the result of mismatches in the mapping procedures rather than real changes in the land-use patterns of interest. As an alternative, land-use products inferred from archived medium resolution remote sensing images have a large potential for usage in the historic calibration of land-use change models. However, inferring land-use classes from remote sensing data is not straightforward. Therefore, a calibration framework for land-use change modelling is being developed which is based on the comparison of spatial metrics derived from both remote sensing images and simulation results. Parameters used in the simulation model are tuned in such a way that the simulated patterns of urban growth, as described by the metrics, match the patterns observed in the remote sensing imagery. This study evaluates the applicability of spatial metrics calculated from urban masks derived from remote sensing images and simulated land-use maps for the historic calibration of the EU-MOLAND model of Dublin. Results show that the historic calibration can be improved by using remote sensing derived spatial metrics. [less ▲]

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See detailLimnological variability and pelagic fish abundance (Stolothrissa tanganicae and Lates stappersii) in Lake Tanganyika
Plisnier, Pierre-Denis ULiege; Mgana, H.; Kimirei, I. et al

in Hydrobiologia (2009), 625(1), 117-134

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See detailLes lithalses allongées des Hautes Fagnes et du Pays de Galles
Pissart, Albert ULiege; Cornet, Yves ULiege

in Environnements périglaciaires (2009), 16

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See detailAnalysis of lateral mobility of channels at different spatial and time scales (Ardenne massif, Belgium)
Houbrechts, Geoffrey ULiege; Van Campenhout, Jean ULiege; Hallot, Eric ULiege et al

Poster (2009)

Lateral mobility of Ardenne rivers has been studied at different scales using three complementary methods. We firstly compared the layout of channels on topographic maps (since the 18th century) and ... [more ▼]

Lateral mobility of Ardenne rivers has been studied at different scales using three complementary methods. We firstly compared the layout of channels on topographic maps (since the 18th century) and aerial pictures. Given that these documents have different scales and projection systems, they were transformed into a common referencing system. This method allowed us to study the lateral shifting of channels, however, as the mobility of Ardenne rivers is relatively low, the errors of geometric rectifications are often more important than lateral displacements. Therefore, to visualize these deformations, georeferenced documents were overlaid with a regular grid of points. We represented the imprecision vector based on x and y residual components for each point. These vectors show the direction of the deformation and its amplitude. Large quantities of iron slag are present in the sediments of Ardenne rivers. These waste products come from hundreds of ironworks built close to rivers since the 14th century. Analyses of slag concentrations in alluvial deposits allowed us to delimitate the sectors of floodplains eroded by rivers during the last centuries. In these sectors, slag elements are present at the contact with the gravel sheet. Finally, we analysed the topography of floodplains from a DEM-LIDAR. This digital elevation model has been established by the Walloon Region for the cartography of flood risk in floodplains. It presents a Z mean error of only 15 cm and a X-Y resolution of 1 m. In order to reveal paleochannels and topographic alluvial units, we subtracted a surface, corresponding to the longitudinal water surface slope, extracted from the DEM. By using this method, we are able to obtain the relative height of any point of the floodplain with regard to the water surface, projected perpendicularly to the layout, on this point. This procedure reveals paleochannels even if they are almost infilled and allows us to delimitate, for several kilometres, alluvial units, which have been formed at different periods. [less ▲]

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See detailCharacterising urban morphology with spectral unmixing and spatial metrics: a case study on Dublin
Canters, Frank; Van de Voorde, Tim; Binard, Marc ULiege et al

in Proceedings of the 24th International Cartographic Conference (ICC 2009), (2009)

In today’s urbanising world, effective urban management and planning strategies are needed to temper the impact of urban change processes on the natural and human environment. To develop and monitor such ... [more ▼]

In today’s urbanising world, effective urban management and planning strategies are needed to temper the impact of urban change processes on the natural and human environment. To develop and monitor such strategies, and to assess their spatial impact, analysing changes in urban structure is essential. Data from earth observation satellites provide regular information on urban development and, as such, may contribute to the mapping and monitoring of cities and the modelling of urban dynamics. Especially images of medium resolution (Landsat, SPOT, …), which are cheap, widely available and often part of extensive historic archives, offer a wealth of information that may be useful for urban monitoring purposes. The lower resolution of this type of imagery, however, hampers the study of urban morphology and change processes at a more detailed, intra-urban level. Spectral unmixing approaches, which allow characterising land-cover distribution at sub-pixel level, may partly compensate for this lack of spatial detail, and may render medium-resolution imagery more useful for urban studies. The main research question addressed in this paper is how medium-resolution imagery could be used to describe urban morphology, by combining spectral unmixing approaches with spatial metrics. Spatial metrics derived from satellite imagery may be useful to quantify structural characteristics of expanding cities, and may provide indications of functional land use. In this study, we develop a set of urban metrics for use on continuous sealed surface data produced by sub-pixel classification of Landsat ETM+ imagery. Two sub-pixel classification approaches are examined for that purpose. In a first approach, we use a linear spectral mixture model with a vegetation and a non-vegetation endmember to deconvolve each pixel’s spectrum into fractional abundances of the two end member spectra, which are determined by visualising mixture space with principal component analysis. In a second approach, we use a linear regression model to estimate the proportion of vegetation cover within each Landsat pixel. In both approaches, an urban mask is used to indicate pixels belonging to urban land cover. Only pixels within the urban mask are subjected to sub-pixel classification. We hereby assume that the urban area does not contain bare soil and that the area of a pixel not covered by vegetation fully consists of sealed surface cover. The resulting sealed surface proportion map is then used to characterise urban morphology and land use by means of the shape of the cumulative frequency distribution of the estimated sealed surface fractions within a building block. A transformed logistic function is fitted to this distribution with a least-squares approach to obtain function parameters that are used as variables in a supervised classification approach, together with spatially explicit metrics (spatial variance and Moran’s I). Our study demonstrates that images from medium resolution sensors can be used to characterise intra-urban morphology, and that the structure of a building block as described by the proposed metrics gives an indication of its membership to certain morphological/functional urban classes. In future research we will incorporate socio-economic data in the metric analysis to further improve the distinction of urban land-use categories. The spatial metrics approach developed in this study will be used in experiments to improve the calibration of the MOLAND urban growth model, which is currently calibrated with historical land-use maps available for approximately 10-year intervals. [less ▲]

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See detailQuantifying intra-urban morphology of the Greater Dublin area with spatial metrics derived from medium resolution remote sensing data
Van de Voorde, Tim; van der Kwast, Johannes; Engelen, Guy et al

in IEEE Proceedings of the 7th International Urban Remote Sensing Conference : Shanghai, May 20-22, 2009 (2009)

Spatial metrics derived from satellite imagery are useful measures to quantify structural characteristics of expanding cities, and can provide indications of functional land use types. Images of medium ... [more ▼]

Spatial metrics derived from satellite imagery are useful measures to quantify structural characteristics of expanding cities, and can provide indications of functional land use types. Images of medium resolution are cheap, widely available and are often part of extensive historic archives. Their lower resolution, on the other hand, inhibits studying urban morphology and change processes at a more detailed, intra-urban level. In this study, we develop spatial metrics for use on continuous sealed surface data produced by a sub-pixel classification of Landsat ETM+ imagery. The metrics characterise the shape of the cumulative frequency distribution of the estimated sub-pixel fractions within a building block by fitting an exponential and a sigmoid function with a least-squares approach. A classification tree is then used to relate the metric variables to urban land-use classes selected from the European MOLAND topology. This approach shows promising results, but still needs improvement which may be achieved by including spatially explicit metrics in the analysis. [less ▲]

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See detailPrédiction des zones propices au ravinement par un modèle de régression logistique intégrant des données de télédétection. Cas du sous-bassin versant de l’oued Alayem - Beni Slimane, Algérie
Daoudi, Mohamed; Ozer, André ULiege; Gérard, Paul ULiege et al

in Randriamanga, Simone; Rakotoniaina, Solofoarisoa; Auda, Yves (Eds.) et al Les XIèmes Journées Scientifiques du Réseau Télédétection de l'AUF (2008, November 03)

Le sous-bassin versant de l'oued Alayem - Beni Slimane, d’une superficie de 118 km², constitue une zone d'étude d'intérêt particulier en raison des caractéristiques physicoclimatiques représentatives de ... [more ▼]

Le sous-bassin versant de l'oued Alayem - Beni Slimane, d’une superficie de 118 km², constitue une zone d'étude d'intérêt particulier en raison des caractéristiques physicoclimatiques représentatives de la zone tellienne méditerranéenne. Le processus de ravinement y est très répandu et constitue un problème majeur. Les facteurs physiques et anthropiques contribuent à une accélération du phénomène. Le présent travail propose une méthode multivariée, basée sur des données multisources, afin de déterminer les variables indépendantes significatives qui favorisent l’existence de l’érosion ravinante et calculer la probabilité des zones de susceptibilité au processus de ravinement. Des variables explicatives toutes liés aux caractéristiques physico-climatiques sont retenues pour le modèle : il s’agit de la lithologie, la pente, l’orientation des versants, l’altitude (MNT), la morphopédologie, la couverture du sol (PVI) et l’agressivité des précipitations (Indice R). Elles permettent de généraliser le modèle prédictif pour des régions semblables du nord de l’Algérie ou du Maghreb. [less ▲]

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See detailDistribution and decline of an endangered amphibian species (Triturus cristatus): Effect of pond characteristics and landscape matrix
Perez, Amélie; Ficetola, Gentile Francesco; Cornet, Yves ULiege et al

Poster (2008, October)

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See detailTracking landslide displacements by multi-temporal DTMs: A combined aerial stereophotogrammetric and LIDAR approach in western Belgium
Dewitte, Olivier ULiege; Jasselette, J. C.; Cornet, Yves ULiege et al

in Engineering Geology (2008), 99(1-2), 11-22

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See detailAn automated method to extract fluvial terraces from digital elevation models: The Vesdre valley, a case study in eastern Belgium
Demoulin, Alain ULiege; Bovy, Benoît ULiege; Rixhon, Gilles ULiege et al

in Geomorphology (2007), 91(1-2), 51-64

Fluvial terraces are a powerful tool for unraveling the combined tectonic and climatic conditions that controlled, directly or indirectly, the Quaternary incision of rivers. Terrace long profiles are ... [more ▼]

Fluvial terraces are a powerful tool for unraveling the combined tectonic and climatic conditions that controlled, directly or indirectly, the Quaternary incision of rivers. Terrace long profiles are usually retrieved from sparse traces of ancient floodplains preserved in the present topography. However, when these traces classically collected from topographic maps, aerial photographs, and field analyses are too few, the inferred profiles may be questionable. Yet the now available high quality and high resolution digital elevation models (DEMs) offer an opportunity to increase greatly the quantity of information usable to reconstruct terrace profiles. Therefore, the purpose of this study was to develop a new DEM-based method of terrace recognition in order to create a larger database and better constrain the profile reconstruction. Moreover, particular procedures of image and numerical processing were defined to fully automate the analysis. Basically, our method relies on the production of bivariate scatter plots depicting the relation between slope and relative altitude (i.e., the altitude above the current alluvial plain) for all pixels of successive sections of the valley. For each scatter plot, the curve of the lowest slope values observed at every relative altitude is smoothed and its minima are assumed to locate the altitudes of the "terrace" elements preserved in the section. We successfully tested this method in the Vesdre valley, incised in the NE Ardenne massif (E Belgium), notably identifying fault deformation of the profiles. The main advantages of our approach are its objectivity, exhaustiveness, and rapidity, allowing fast and coherent analysis of many rivers over extended regions. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailSpatial aggregation of low resolution satellite data for the monitoring of vegetation response to climatic stresses : analysis of the spatial heterogeneity of aggregated entities.
Horion, Stéphanie; Eerens, H.; Tychon, Bernard ULiege et al

in Proceedings Envisat Symposium (2007, July)

Our PhD research consists in analysing and modelling the vegetation response or sensitivity to climatic stresses with low satellite imagery. In that framework, the selection of optimal calibration sites ... [more ▼]

Our PhD research consists in analysing and modelling the vegetation response or sensitivity to climatic stresses with low satellite imagery. In that framework, the selection of optimal calibration sites is very important. These sites should be characterised by a stable and homogenous land cover over large area. Here we analyse the spatial heterogeneity of the aggregation entities (EU-NUTS 2) used by the MARSFOOD programme for the extraction of regional NDVI-means. [less ▲]

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See detailChapitre 7. Approche du contexte géomorphologique de Chagar Bazar et restitution de la paléosurface ''naturelle'' sous le Tell.
Cornet, Yves ULiege

in Tunca, Önhan; McMahon, Augusta; Baghdo (Eds.) Chagar Bazar (Syrie) II. Les vestiges post-akkadiens du chantier D et études diverses (2007)

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See detailStrategies to estimate ground susceptibility to landslide reactivation. A probabilistic application in W Belgium (Oudenaarde)
Dewitte, Olivier ULiege; Chung, Chang-Jo; Cornet, Yves ULiege et al

(2007)

In the hilly region of the Flemish Ardennes in western Belgium, no new big deep-seated landslides have occurred for decades, whereas several reactivation episodes were recently observed in ancient ... [more ▼]

In the hilly region of the Flemish Ardennes in western Belgium, no new big deep-seated landslides have occurred for decades, whereas several reactivation episodes were recently observed in ancient landslides. We selected a test area comprised of 13 rotational landslides located close to the town of Oudenaarde in order to predict the susceptibility of their main scarp to retreat. We propose here two probabilistic models based on a fuzzy set approach. The models use empirical distribution functions (EDFs) as favourability values to build membership values and combine them by using the fuzzy Gamma operator. Based on Kolmogorov-Smirnov tests applied to these EDFs to select the most relevant data, a first model was obtained bases on a combination of 5 quantitative variables: slope angle, distance from cultivation located upstream of the main scarp, slope aspect, elevation and profile curvature. Another, more empirical approach based on the a posteriori analysis of the prediction-rate curves was applied to select the 4 variables of a second model: slope aspect, plan curvature, vegetation index and focal flow. According to the prediction-rate curves and the resulting susceptibility maps, the empirical model appears more efficient in locating the main scarp areas most prone to reactivation. [less ▲]

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See detailTracking landslide evolution over decades: application of aerial digital photogrammetry to the Oudenaarde area (W Belgium)
Dewitte, Olivier ULiege; Jasselette, Jean-Claude; Cornet, Yves ULiege et al

(2007)

In order to include some kinematic information within landslide hazard prediction models, we estimated landslide motion in the medium term (i.e. a few decades) by comparing precise landslide topography ... [more ▼]

In order to include some kinematic information within landslide hazard prediction models, we estimated landslide motion in the medium term (i.e. a few decades) by comparing precise landslide topography reconstructions at different dates. Precise multitemporal 3D data of the 13 old deep-seated landslides developed on two hills close to the town of Oudenaarde (W Belgium) were obtained by digital stereophotogrammetry using aerial photographs of three different periods (1996, 1973 and 1952). From these data, six DTMs (3 different dates for each investigated hill) were produced with an overall RMS error of ~50 cm. The obtained DTMs were subtracted from each other in order to determine the vertical displacement of each pixel during the considered time interval. Globally, movements are observed in all the landslides and they generally correspond to a rotational pattern. [less ▲]

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See detailControlling factors of gully erosion in the upper part of the Isser river watershed (Algiers, N. Algeria)
Daoudi, M.; Dewitte, Olivier ULiege; Gérard, Paul et al

in Geophysical Research Abstracts (2007), 9

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See detailMeasuring and Modeling Urban Dynamics: Impact on Quality of Life and Hydrology. Objectives and methodology
Canters, Frank; Van de Voorde, Tim; Goossens, Rudi et al

(2007)

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See detailActivity patterns, home-range size, and habitat utilization of Sarpa salpa (Teleostei : Sparidae) in the Mediterranean Sea
Jadot, Catherine; Donnay, Annick ULiege; Acolas, M.-L. et al

in ICES Journal of Marine Science (2006), 63(1), 128-139

Acoustic telemetry was used to record diel movement and habitat utilization of the salema (Sarpa salpa) (Teleostei: Sparidae) during three consecutive summers from 2000 to 2002 in the Calvi and Achiarina ... [more ▼]

Acoustic telemetry was used to record diel movement and habitat utilization of the salema (Sarpa salpa) (Teleostei: Sparidae) during three consecutive summers from 2000 to 2002 in the Calvi and Achiarina bays of Corsica in the Mediterranean Sea. A total of 18 fish was equipped with acoustic transmitters inserted in the body cavity, 13 were tracked in the Bay of Calvi (275 mm +/- 26.9 L-F), and 5 in Achiarina Bay (260 mm +/- 33.6 LF). Two different systems were used to track the fish. The one used in the Bay of Calvi was a manual receiver and a directional hydrophone. The second system, used in Achiarina Bay, was a radioacoustic-positioning (RAP) system that continuously monitored the movements of the fish. Fish positions were put in a geographic information system (GIS) with information on the substratum and depth. Two patterns of behaviour could be identified in the three years. Either the fish had clearly defined daytime as opposed to night-time areas of residency, characterized by different depths and substrata or the fish persistently occupied the same sites during both day and night. In the Bay of Calvi, six fish were released I km from the capture site. All of them showed homing ability and returned to the site within 48 h. [less ▲]

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