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See detailForces et faiblesses du système éducatif en Fédération Wallonie-Bruxelles
Baye, Ariane ULg

Scientific conference (2013, July 03)

Detailed reference viewed: 33 (11 ULg)
See detailForcing of a global model of plant productivity with climatic and remote sensing data
Warnant, Pierre ULg; François, Louis ULg; Strivay, David ULg et al

in Veroustraete, F.; Ceulemans, R. (Eds.) Vegetation, modelling and climatic change effects (1994)

Detailed reference viewed: 7 (2 ULg)
See detailForecast assessment in the mediterranean sea : A structure oriented approach
Ben Bouallegue, Z.; Alvera Azcarate, Aïda ULg; Vandenbulcke, Luc ULg et al

Conference (2004, April)

The MFSTEP1 project is an international scientific collaboration program which aims to create an operational forecasting system for the Mediterranean sea. The simulations provided at the basin scale are ... [more ▼]

The MFSTEP1 project is an international scientific collaboration program which aims to create an operational forecasting system for the Mediterranean sea. The simulations provided at the basin scale are 10 days forecasting fields in a 3-D ocean. The hydrodynamic model primitive equations are combined with the data assimilation scheme SOFA2. The data collection is done in a near real time process and the set of XBT and SLA observations are used in one week assimilation cycle. The forecast assessment is traditionally realised using classical statistic tools like RMSE or the bias and the assimilation benefit is estimated by skill scores using as reference the free model, persistence or also climatology. The process is essentially based on the comparison of two fields at a fixed time, one corresponding to the simulations and the other one to the observations. The interest of such statistical methods comes in the quick and sensitive appreciation they provide about the quality, accuracy and consistency of the simulation. However this kind of assessment procedure brings in it self a conceptual contradiction: performances of a dynamical process are measured using a snap shot view of the ocean state. A system evolution assessment procedure is carried out within the framework of the MFSTEP hindcast. The hindcast system is intrinsically analysed (without independent informations) comparing the background forecast evolution with the abrupt variation which occurs at the observations assimilation time steps. The system evolution between two consecutive days is analysed using a decomposition method. The temperature and salinity fields evolution in a sub-region of theWestern Mediterranean basin is seen in a structural point of view and decomposed in three elements : a global spatial(2D) displacement which conserves the internal features, a global intensity variation which expresses the system energy changes, and an internal pattern changes ensemble. The index of evolution used is a mean squared difference between the two consecutive simulations. The displacement contribution is estimated after the determination of the shift (field translation) which minimises the local mean squared difference between the translated field and the next simulation. The intensity variation contribution is calculated as the difference of the squared mean fields. The remaining difference after manipulations is considered as the internal pattern changes contribution to the system evolution. [less ▲]

Detailed reference viewed: 39 (6 ULg)
See detailForecast verification in the Ligurian Sea. Multiresolution analysis and study of the thermocline
Alvera Azcarate, Aïda ULg; Barth, Alexander ULg; Rixen, M. et al

Conference (2004, April)

The results of the GHER 3D model are analysed, in order to establish the benefits of a Sea Surface Temperature (SST) assimilation experiment. The influence of the assimilation into the results of the ... [more ▼]

The results of the GHER 3D model are analysed, in order to establish the benefits of a Sea Surface Temperature (SST) assimilation experiment. The influence of the assimilation into the results of the model is examined first in the studied domain, the Ligurian Sea. Then, the benefit of the assimilation outside this domain (in the nearby zones at the surface, and in the Ligurian Sea at depth) is also studied. Finally, the effect of the SST assimilation on the other variables is examined. The procedure for the skill assessment of the model is as follows. First, the classical verification tools are applied: Root Mean Square Error (RMSE), Anomaly Correlation Coefficient (ACC), and Mean Square Error Skill Score (MSESS). Climatology and a free run of the model are used as reference systems. After this, a multiresolution analysis is carried out, to decompose the model results into different spatial scales. At each scale, the error measures mentioned above are applied. This allows to establish which scales are mainly contributing to the error. For this multiresolution analysis, a Discrete Wavelet Transform is used. The study of the assimilation benefits at depth is made by comparison with CTDs. The aim is to study the position and strength of the thermocline, as this zone presents high variability and it has an important impact into the system. A good representation of the thermocline is thus interesting. [less ▲]

Detailed reference viewed: 7 (1 ULg)
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See detailForecast verification of a 3D model of the Mediterranean Sea. Analysis of model results and observations using wavelets and Empirical Orthogonal Functions.
Alvera Azcarate, Aïda ULg

Doctoral thesis (2004)

The quality assessment of the three-dimensional GHER (GeoHydrodynamics and Environmental Research) model of the Mediterranean Sea is presented in this work. The verification of the model results is done ... [more ▼]

The quality assessment of the three-dimensional GHER (GeoHydrodynamics and Environmental Research) model of the Mediterranean Sea is presented in this work. The verification of the model results is done in a spatio-temporal approach. Traditional error measures (i.e. correlation, mean error, etc) are very useful to assess the quality of a model, but they do not take into account the high complexity of three-dimensional models. The verification process is thus done in three main parts: first, the model is compared to observations and climatology in a qualitative approach, in order to make a preliminar study about the model behaviour. Then, the error assessment is done, using traditional statistic measures. In order to take into account the complexity of the model and observations, the last step in the verification process consists in a spatio-temporal analysis using wavelets and empirical orthogonal functions. This last analysis will allow us to have an insight about the model quality in a more detailed way. This verification process has been applied to the GHER model. This model is implemented in a two-way nesting approach in the Mediterranean Sea, Liguro-Provençal basin and Ligurian Sea, where the highest resolution is reached. Assimilation of sea surface temperature and sea level anomaly is made during a nine-week experiment. Another test is carried out, to assess the quality of sea surface temperature from the SOFT predictor of the Ligurian Sea. The predicted sea surface temperature is assimilated in the model and the quality of the forecast is compared to the first assimilation experiment. The assimilation of the SOFT statistical predictors can be very useful to force models in a real forecast experiment, where no observations are available. [less ▲]

Detailed reference viewed: 28 (4 ULg)
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Peer Reviewed
See detailForecast verification of a 3D model of the Mediterranean Sea. The use of discrete wavelet transforms and EOFs in the skill assessment of spatial forecasts
Alvera Azcarate, Aïda ULg; Barth, Alexander ULg; Ben Bouallegue, Zied et al

in Journal of Marine Systems (2007), 65(1-4), 460-483

The quality assessment of a nested model system of the Mediterranean Sea is realised. The model has two zooms in the Provencal Basin and in the Ligurian Sea, realised with a two-way nesting approach. The ... [more ▼]

The quality assessment of a nested model system of the Mediterranean Sea is realised. The model has two zooms in the Provencal Basin and in the Ligurian Sea, realised with a two-way nesting approach. The experiment lasts for nine weeks, and at each week sea surface temperature (SST) and sea level anomaly are assimilated. The quality assessment of the surface temperature is done in a spatio-temporal approach, to take into account the high complexity of the SST distribution. We focus on the multi-scale nature of oceanic processes using two powerful tools for spatio-temporal analysis, wavelets and Empirical Orthogonal Functions (EOFs). We apply two-dimensional wavelets to decompose the high-resolution model and observed SST into different spatial scales. The Ligurian Sea model results are compared to observations at each of those spatial scales, with special attention on how the assimilation affects the model behaviour. We also use EOFs to assess the similarities between the Mediterranean Sea model and the observed SST. The results show that the assimilation mainly affects the model large-scale features, whereas the small scales show little or no improvement and sometimes, even a decrease in their skill. The multiresolution analysis reveals the connection between large- and small-scale errors, and how the choice of the maximum correlation length of the assimilation scheme affects the distribution of the model error among the different spatial scales. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 88 (15 ULg)
See detailForecast verification using skill scores and wavelets. Application to a two-way nested primitive equation model of the Ligurian Sea.
Alvera Azcarate, Aïda ULg; Barth, Alexander ULg; Rixen, M. et al

Conference (2003, April)

The verification of a forecast is an important part of a forecasting process. It allows to establish the quality of a model, and to make the pertinent improvements. The verification methodology may be ... [more ▼]

The verification of a forecast is an important part of a forecasting process. It allows to establish the quality of a model, and to make the pertinent improvements. The verification methodology may be designed to detect the errors contained in the model. The verification process consist in the comparison of the model results with a reference system (as sample climatology, or the output of a reference version of the model), in order to establish the accuracy and skill of the first one. The Anomaly Correlation Coefficient, the Brier Skill Score and the Root Mean Square Error are used in the present work to quantify the predictive skill. The disadvantage of this kind of measures is its over simplification. They are very useful, since the comparison between the model and the reference system is reduced to a limited set of numbers to establish the error, but it also results in a great loss of information. The method presented here combines the skill score analysis with a more detailed study. The use of wavelet transforms is shown to be useful, because of their capacity to localize in time and frequency the analysed signal. The signal is decomposed at different spatial scales, where the skill score methods can be applied separately. The information obtained with this method is more detailed, and scales where the largest errors occur can be easily identified. This combination of methods has been applied to a two-way nested primitive equation model of the Ligurian Sea. The scale decomposition allows to better understand the differences between the model and the observed field, to establish the weaknesses and strengths of the model, and to propose the possible improvements that can be done. [less ▲]

Detailed reference viewed: 33 (1 ULg)
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See detailForecasting Daily Solar Energy Production Using Robust Regression Techniques
Louppe, Gilles ULg; Prettenhofer, Peter

Conference (2014, February 05)

We describe a novel approach to forecast daily solar energy production based on the output of a numerical weather prediction (NWP) model using non-parametric robust regression techniques. Our approach ... [more ▼]

We describe a novel approach to forecast daily solar energy production based on the output of a numerical weather prediction (NWP) model using non-parametric robust regression techniques. Our approach comprises two steps: First, we use a non-linear interpolation technique, Gaussian Process regression (also known as Kriging in Geostatistics), to interpolate the coarse NWP grid to the location of the solar energy production facilities. Second, we use Gradient Boosted Regression Trees, a non-parametric regression technique, to predict the daily solar energy output based on the interpolated NWP model and additional spatio-temporal features. Experimental evidence suggests that two aspects of our approach are crucial for its effectiveness: a) the ability of Gaussian Process regression to incorporate both input and output uncertainty which we leverage by deriving input uncertainty from an ensemble of 11 NWP models and including convidence intervals alongside the interpolated point estimates and b) the ability of Gradient Boosted Regression Trees to handle outliers in the outputs by using robust loss functions - a property that is very important due to the volatile nature of solar energy output. We evaluated the approach on a dataset of daily solar energy measurements from 98 stations in Oklahoma. The results show a relative improvement of 17.17% and 46.19% over the baselines, Spline Interpolation and Gaussian Mixture Models, resp. [less ▲]

Detailed reference viewed: 74 (12 ULg)
Peer Reviewed
See detailForecasting epidemic outbreaks ofwheat leaf blotch based on meteorological parameters
Junk, Jürgen; El Jarroudi, Moussa ULg; Pogoda, Frederik et al

Poster (2010, April 12)

Detailed reference viewed: 10 (0 ULg)
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See detailForecasting Septoria tritici on winter wheat in the Grand-Duchy of Luxembourg from 2000 to 2005.
El Jarroudi, Moussa ULg; Tychon, Bernard ULg; Maraite, H. et al

in Bibliotheca Fragmenta Agronomica - Book of Proceedings (2006), 11(2), 751-752

This papers presents the results of a wheat diseases model called PROCULTURE for the prediction of septoriosis in the Grand Duchy of Luxembourg

Detailed reference viewed: 17 (3 ULg)
See detailForecasting Skill Assessment of a Doubly, Two-Way Nested Model of the Ligurian Sea driven by Assimilation of Sea Surface Temperature
Barth, Alexander ULg; Alvera Azcarate, Aïda ULg; Rixen, M. et al

Conference (2003)

The GHER 3D primitive equation model is implemented with threedifferent resolutions: a low resolution model (1/4Ž°) coveringthe whole Mediterranean Sea, an intermediate resolution model (1/20Ž°)of the ... [more ▼]

The GHER 3D primitive equation model is implemented with threedifferent resolutions: a low resolution model (1/4Ž°) coveringthe whole Mediterranean Sea, an intermediate resolution model (1/20Ž°)of the Liguro-Provençal basin and a high resolution model (1/60Ž°)simulating the fine mesoscale structures in the Ligurian Sea. Boundaryconditions and the averaged fields (feedback) are exchanged betweentwo successive nesting levels. The model of the Ligurian Sea is also coupled with the assimilationpackage SESAM. It allows to assimilate satellite data and in situobservations using the local adaptative SEEK (Singular EvolutiveExtended Kalman) filter. Instead of evolving the error space by thenumerically expensive Lyapunov equation, a simplified algebraicequation depending on the misfit between observation and modelforecast is used. Starting from the 1st January 1998 the low and intermediate resolutionmodels are spun up for 18 months. The initial conditions for theLigurian Sea are interpolated from the intermediate resolutionmodel. The three models are then integrated until August 1999. Duringthis period AVHRR Sea Surface Temperature of the Ligurian Sea isassimilated. The results are validated by using CTD and XBT profilesof the SIRENA cruise from the SACLANT Center. In a second validation exercise,the AVHRR SST and model forecast %(not yet affected by the SST used for validation) are decomposed at different scalesusing a horizontal wavelet transform.The processes characteristic for each scale are isolated in the model and the SST images.The error statistics calculated on the wavelet amplitudes can thus be related to the ability of the model in forecasting the correspondingmarine processes. In a second validation exercise, the AVHRR SST and model forecast areboth decomposed at different scales using a horizontal wavelet transform.The characteristic processes for each scale are isolated in the modeland the SST images. The error statistics calculated on the waveletamplitudes can thus be related to the ability of the model inforecasting the corresponding marine processes. [less ▲]

Detailed reference viewed: 8 (2 ULg)
See detailForecasting the Dourbes K index by using solar wind parameters
Andonov, Borislav; Kutiev, Ivan; Warnant, René ULg et al

in Proceedings of Beacon Satellite Symposium 2004 (2005)

Detailed reference viewed: 44 (0 ULg)
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Peer Reviewed
See detailForecasting the Effects of Lateral Flooding Basins by Transient Surface Flows Computations
Pirotton, Michel ULg

in Vith Conference the Comtemporary Problems of Hydroengineering (1996, May 06)

Detailed reference viewed: 3 (1 ULg)
See detailForecasts of black and red conditions for RTK users
Warnant, René ULg; Lejeune, Sandrine; Nebdi, Hamid

Report (2004)

Detailed reference viewed: 18 (1 ULg)
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See detailForeign Aid Transaction Costs: What are they and when are they minimised?
Paul, Elisabeth ULg; Vandeninden, Frieda ULg

in Development Policy Review (2012), 30(3),

'Transaction costs' are commonly referred to in the recent literature on aid effectiveness. Aid transaction costs, however, have been neither consistently defined nor measured. This article defines aid ... [more ▼]

'Transaction costs' are commonly referred to in the recent literature on aid effectiveness. Aid transaction costs, however, have been neither consistently defined nor measured. This article defines aid transaction costs as all the economic costs associated with aid management that add no value to aid delivery. This enables the 'net' transaction costs that should be minimised to be identified. An analytical framework is then developed for assessing these costs. This allows the effectiveness of different aid modalities to be compared, according to the characteristics of the aid transaction. The article shows that the choice of aid modality should depend on these characteristics and, therefore, that the minimisation of transaction costs should not be an end in itself. [less ▲]

Detailed reference viewed: 12 (3 ULg)
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See detailForeign Exchange Risk Exposure: Survey and Suggestions
Muller, Aline ULg; Verschoor, Willem

in Journal of Multinational Financial Management (2006), 16(4), 385-410

Detailed reference viewed: 26 (5 ULg)
See detailForeign languages in primary and pre-school education : a review of recent research within the European Union
Blondin, Christiane ULg; Candelier, M.; Edelenbos, P. et al

Book published by Centre for Information on Language Teaching (CILT) (1998)

Detailed reference viewed: 260 (0 ULg)
See detailForeign Origin Politicians in Belgium
Martiniello, Marco ULg

Scientific conference (1996, January 29)

Detailed reference viewed: 1 (0 ULg)
See detailForeign Origin Politicians in Belgium
Martiniello, Marco ULg

in Martiniello, Marco (Ed.) Multicultural Policies and the State: a comparison of two European societies (1998)

Detailed reference viewed: 15 (2 ULg)