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See detailLe assetate
Bernard Quiriny; Ricciardi, Stefania ULg

Book published by Transeuropa (2012)

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See detailL'assiette des Belges en chiffres
Duquesne, Brigitte ULg

Poster (2006)

Detailed reference viewed: 16 (3 ULg)
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See detailL'assiette du Belge en chiffres
Duquesne, Brigitte ULg

Poster (2007)

Detailed reference viewed: 40 (5 ULg)
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See detailAssigned value determination on soil materials throughout the whole analytical field introducing bias correction from reference materials
Planchon, Viviane; Renneson, Malorie ULg; Goffaux, Marie-Julie et al

Poster (2013, September)

Detailed reference viewed: 19 (3 ULg)
Peer Reviewed
See detailAssignment of the human ZNF83 (HPF1) zinc finger gene to chromosome 19q13.3-q13.4
Marine, Jean-Christophe; Bellefroid, Eric J.; Bourguignon, Catherine et al

in Genomics (1994), 21(1), 285-6

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Peer Reviewed
See detailDe assimilatie van stem in de tussentaal van Franstalige leerders van het Nederlands
Baelen, Mélanie; Hiligsmann, Philippe; Rasier, Laurent ULg

in N/F (2008), 8

Detailed reference viewed: 6 (1 ULg)
See detailAssimilation of High-Frequency Radar Currents in a Nested Model of the West Florida Shelf
Barth, Alexander ULg; Alvera Azcarate, Aïda ULg; Weisberg, R. H.

Conference (2007)

High-frequency radar currents are assimilated in a West Florida Shelf (WFS) model based on the Regional Ocean Model System (ROMS), which is nested in the Atlantic Hybrid Coordinate Ocean Model (HYCOM) for ... [more ▼]

High-frequency radar currents are assimilated in a West Florida Shelf (WFS) model based on the Regional Ocean Model System (ROMS), which is nested in the Atlantic Hybrid Coordinate Ocean Model (HYCOM) for the purpose of including both local and deep-ocean forcing, particularly the Gulf of Mexico Loop Current. Tides are not included in this model. An ensemble simulation of the WFS model is carried out under different wind-forcings in order to estimate the error covariance of the model state vector and the covariance between ocean currents and winds. Radial currents measured by high-frequency radar antennas near Saint Petersburg and Venice, Florida, USA, are assimilated using this ensemble-based error covariance. Different assimilation techniques using a time-average ensemble, a filter to reduce surface-gravity waves and an extended state vector including wind stress were tested. Results of the WFS model assimilating surface currents show an improvement of the model currents not only at the surface but also at depth. [less ▲]

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See detailAssimilation of high-frequency radar currents in a nested model of the West Florida Shelf
Barth, Alexander ULg; Alvera Azcarate, Aïda ULg; Weisberg, R. H.

in Journal of Geophysical Research. Oceans (2008), 113(C8),

High-frequency radar currents are assimilated in a West Florida Shelf (WFS) model based on the Regional Ocean Model System (ROMS), which is nested in the Atlantic Hybrid Coordinate Ocean Model (HYCOM) for ... [more ▼]

High-frequency radar currents are assimilated in a West Florida Shelf (WFS) model based on the Regional Ocean Model System (ROMS), which is nested in the Atlantic Hybrid Coordinate Ocean Model (HYCOM) for the purpose of including both local and deep-ocean forcing, particularly the Gulf of Mexico Loop Current. Tides are not included in this model. An ensemble simulation of the WFS model is carried out under different wind-forcings in order to estimate the error covariance of the model state vector and the covariance between ocean currents and winds. Radial currents measured by high-frequency radar antennas near Saint Petersburg and Venice, Florida, USA, are assimilated using this ensemble-based error covariance. Different assimilation techniques using a time-average ensemble, a filter to reduce surface-gravity waves and an extended state vector including wind stress were tested. Results of the WFS model assimilating surface currents show an improvement of the model currents not only at the surface but also at depth. [less ▲]

Detailed reference viewed: 45 (13 ULg)
See detailAssimilation of high-frequency radar currents in the Ligurian Sea
Barth, Alexander ULg; Chiggiato, Jacopo; Alvera Azcarate, Aïda ULg et al

Conference (2011, April)

The circulation in the Ligurian Sea is dominated by strong currents, namely the Western Corsican Current and the East Corsican Current, which jointly form the Northern Current. A high mesoscale activity ... [more ▼]

The circulation in the Ligurian Sea is dominated by strong currents, namely the Western Corsican Current and the East Corsican Current, which jointly form the Northern Current. A high mesoscale activity, including meanders and eddy formation, is associated to those energetic currents. The non-linear instability processes and apparently chaotic behavior of this current system make this region a challenging testbed for data assimilation. High-frequency radar surface currents have been measured by the NATO Undersea Research Centre (NURC), La Spezia, Italy from two sites at the Italian Coast (Isola Palmaria and San Rossore). Each of those sites measures the radial currents relative to the position of the radar system. This WERA system captures well the general circulation and mesoscale flow features. The present study shows an application of the assimilation of those measurements in a nested model con- figuration of the Ligurian Sea. It is assumed that the error in the model surface currents comes primarily from uncertainties in the lateral boundary conditions and surface wind fields. The objective of this study is to reduce the uncertainty in these forcing fields by data assimilation. An ensemble of 100 perturbed lateral boundary conditions and surface wind fields is created to take the uncertainty into account. Using an ensemble-smoother technique described in Barth et al, 2010 (Ocean Science) and Barth et al, 2010 (Ocean Dynamics, in press), improved estimates of the wind forcing and boundary conditions are obtained. By rerunning the model with the updated forcing fields, it is verified that the analyzed model solution is closer to the observed HF radar currents. This technique is similar to 4D-Var, but since it is based on the ensemble covariance between forcing fields and observations, it does not require the formulation of an adjoint. [less ▲]

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See detailAssimilation of high-frequency radar surface currents measurements to optimize tidal boundary conditions and wind forcing
Barth, Alexander ULg; Alvera Azcarate, Aïda ULg; Gurgel, Klaus-Werner et al

Conference (2010)

An ensemble smoother scheme is presented to assimilate high-frequency (HF) radar surface currents to improve tidal boundary conditions and wind forcings of a circulation model of the German Bight. To ... [more ▼]

An ensemble smoother scheme is presented to assimilate high-frequency (HF) radar surface currents to improve tidal boundary conditions and wind forcings of a circulation model of the German Bight. To create an ensemble of dynamically realistic tidal boundary conditions, a cost function is formulated which is directly related to the probability of each perturbation. This cost function ensures that the perturbations are spatially smooth and that the structure of the perturbations satisfies approximately the harmonic linearized shallow water equations. Based on those perturbations an ensemble simulation is carried out using the full three-dimensional General Estuarine Ocean Model (GETM). Optimized boundary values are obtained using all observations within the assimilation period using the covariances of the ensemble simulation. The approach acts like a smoother scheme since past and future observations are taken into account. The final analysis is obtained by rerunning the model using the optimal perturbation of the boundary conditions. The analyzed model solution satisfies thus the model equations exactly and does not suffer from spurious adjustments often observed with sequential assimilation schemes. Model results are also compared to independent tide gage data. The assimilation also reduces the model error compared to those sea level observations. The same scheme is also used to correct surface winds. Surface winds are crucial for accurately modeling the marine circulation in coastal waters. The method is validated directly by comparing the analyzed wind speed to in situ measurements and indirectly by assessing the impact of the corrected winds on sea surface temperature (SST) relative to satellite SST. [less ▲]

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See detailAssimilation of sea surface temperature and sea surface height in a two-way nested primitive equation model of the Ligurian Sea
Barth, Alexander ULg

Doctoral thesis (2004)

A coarse grid primitive equation model of 1/4° resolution is implemented covering the whole Mediterranean Sea. Within this grid a 1/20° resolution model of the Liguro-Provençal basin and the northern part ... [more ▼]

A coarse grid primitive equation model of 1/4° resolution is implemented covering the whole Mediterranean Sea. Within this grid a 1/20° resolution model of the Liguro-Provençal basin and the northern part of the Tyrrhenian Sea is embedded. A third fine resolution model of 1/60° is nested in the latter one and simulates the dynamics of the Ligurian Sea. Comparisons between one-way and two-way nesting in representing the Northern Current (NC) are made. This system of nested models is coupled with a simplified Kalman-filter based assimilation method. The state vector for the data assimilation is composed by the temperature, salinity and elevation of the three models. The forecast error is estimated by an ensemble run by perturbing initial conditions and atmospheric forcings. The leading empirical orthogonal functions (EOF) of this ensemble are taken as the error covariance of the model forecast. This error covariance is assumed to be constant in time. Sea surface temperature (SST) and sea surface height (SSH) are assimilated in this system. Data assimilation is also used to couple the hydrodynamic model with a statistical predictor of SST in the Ligurian Sea. The forecast improvement of this hybrid modelling system is shown and applications to operational models are highlighted. [less ▲]

Detailed reference viewed: 31 (6 ULg)
See detailAssimilation of Sea Surface Temperature in a doubly, two-way nested primitive equation model of the Ligurian Sea
Barth, Alexander ULg; Alvera Azcarate, Aïda ULg; Rixen, M. et al

Conference (2003, April)

The GHER 3D primitive equation model is implemented with three different resolutions: a low resolution model (1/4^o) covering the whole Mediterranean Sea, an intermediate resolution model (1/20^o) of the ... [more ▼]

The GHER 3D primitive equation model is implemented with three different resolutions: a low resolution model (1/4^o) covering the whole Mediterranean Sea, an intermediate resolution model (1/20^o) of the Liguro-Provençal basin and a high resolution model (1/60^o) simulating the fine mesoscale structures in the Ligurian Sea. Boundary conditions and the averaged fields (feedback) are exchanged between two successive nesting levels. The model of the Ligurian Sea is also coupled with the assimilation package SESAM. It allows to assimilate satellite data and in situ observations using the local adaptative SEEK (Singular Evolutive Extended Kalman) filter. Instead of evolving the error space by the numerically expensive Lyapunov equation, a simplified algebraic equation depending on the misfit between observation and model forecast is used. Starting from the 1st January 1998 the low and intermediate resolution models are spun up for 18 months. The initial conditions for the Ligurian Sea are interpolated from the intermediate resolution model. The three models are then integrated until August 1999. During this period AVHRR Sea Surface Temperature of the Ligurian Sea is assimilated. The results are validated by using CTD and XBT profiles of the SIRENA cruise from the SACLANT Center. The overall objective of this study is pre-operational. It should help to identify limitations and weaknesses of forecasting methods and to suggest improvements of existing operational models. [less ▲]

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See detailAssimilation of Sea Surface Temperature predicted by a satellite-based forecasting system in a doubly nested primitive equation model of the Ligurian Sea
Barth, Alexander ULg; Alvera Azcarate, Aïda ULg; Alvarez, A. et al

Conference (2004)

Data assimilation is traditionally used to combine model dynamics and observations in a statistical optimal way. Assimilation of observations improves therefore hindcasts and nowcasts of the ocean state ... [more ▼]

Data assimilation is traditionally used to combine model dynamics and observations in a statistical optimal way. Assimilation of observations improves therefore hindcasts and nowcasts of the ocean state than otherwise obtained by the model alone. The observational constraints are necessary to reduce uncertainties and imperfections of the ocean model. Due to the obvious lack of future observations, the model forecast cannot be controlled by observations and the predictive skill degrades as the forecast time lag increases. The error grow is not only caused by the chaotic nature of the system but also by the biases and drifts of the model. The later part can be reduced by considering different models with different imperfections. Data assimilation provides the statistical frame for merging the different model results. A primitive equation model of the Mediterranean Sea (1/4° resolution) has been implemented with two successive grid refinements of the Liguro-Provençal Basin (1/20°) and the Ligurian Sea (1/60°) respectively (Barth et al, 2003). The dependence of the ``parent'' model and the embedded ``child'' model is bi-directional; it involves the exchange of boundary conditions and feedback between the models. Alvarez el al. (2004) developed a statistical predictor for forecasting the SST of the Ligurian Sea with a time lag of 7 days based on the previous remote sensed SST. The degrees of freedom of the SST are reduced by an Empirical Orthogonal Function (EOF) analysis. A genetic algorithm trained by the historical SST evolution in the Ligurian Sea is used to predict the EOF amplitudes. Observed and forecasted SST are assimilated in the hydrodynamic model and the results of this two experiments are compared to the model run without assimilation. The assimilation of the forecasted SST reduces the error of the model by an amount comparable to the assimilation of real SST, showing the potential of skill improvement of combining statistical and hydrodynamic models. [less ▲]

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See detailAssimilation of the 1979-2009 microwave satellite data into the regional climate MAR model for studying the Greenland ice sheet melt extent
Fettweis, Xavier ULg; Tedesco, Marco; van den Broeke, Michiel

Conference (2011, April 05)

The 1979-2009 melt extent derived from the amount of produced meltwater by day simulated by the regional climate model MAR and derived from the spaceborne microwave 19GHz horizontal polarizated (T19H ... [more ▼]

The 1979-2009 melt extent derived from the amount of produced meltwater by day simulated by the regional climate model MAR and derived from the spaceborne microwave 19GHz horizontal polarizated (T19H) brightness temperature compares well over the Greenland ice sheet (GrIS). However, some disagreements still occur in some pixels for any days. Therefore, we run the MAR model in an assimilation mode, constrained by the daily SMMR-SSM/I derived melt extent over 1979-2009. As assimilation, we change the MAR near-surface snowpack temperature for the pixels where MAR and satellite disagree. This correction allows to conserve the water equivalent of the snowpack mass in MAR while having a full agreement between model and satellite derived melt extent. The assimilation helps to improve the meltwater production simulation as well as the matching with other satellite data sets (MODIS, GRACE, ...), with the objective to reduce the uncertainties of the current SMB model-based estimates over the GrIS. [less ▲]

Detailed reference viewed: 49 (3 ULg)