References of "Brasseur, Pierre"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailGeneration of analysis and consistent error fields using the Data Interpolating Variational Analysis (Diva)
Troupin, Charles ULg; Barth, Alexander ULg; Sirjacobs, Damien ULg et al

in Ocean Modelling (2012), 52-53

The Data Interpolating Variational Analysis (Diva) is a method designed to interpolate irregularly-spaced, noisy data onto any desired location, in most cases on regular grids. It is the combination of a ... [more ▼]

The Data Interpolating Variational Analysis (Diva) is a method designed to interpolate irregularly-spaced, noisy data onto any desired location, in most cases on regular grids. It is the combination of a particular methodology, based on the minimisation of a cost function, and a numerically efficient method, based on a finite-element solver. The cost function penalises the misfit between the observations and the reconstructed field, as well as the regularity or smoothness of the field. The intrinsic advantages of the method are its natural way to take into account topographic and dynamic constraints (coasts, advection, . . . ) and its capacity to handle large data sets, frequently encountered in oceanography. The method provides gridded fields in two dimensions, usually in horizontal layers. Three-dimension fields are obtained by stacking horizontal layers. In the present work, we summarize the background of the method and describe the possible methods to compute the error field associated to the analysis. In particular, we present new developments leading to a more consistent error estimation, by determining numerically the real covariance function in Diva, which is never formulated explicitly, contrarily to Optimal Interpolation. The real covariance function is obtained by two concurrent executions of Diva, the first providing the covariance for the second. With this improvement, the error field is now perfectly consistent with the inherent background covariance in all cases. A two-dimension application using salinity measurements in the Mediterranean Sea is presented. Applied on these measurements, Optimal Interpolation and Diva provided very similar gridded fields (correlation: 98.6%, RMS of the difference: 0.02). The method using the real covariance produces an error field similar to the one of OI, except in the coastal areas. [less ▲]

Detailed reference viewed: 290 (47 ULg)
Full Text
See detailAdvanced Data Interpolating Variational Analysis. Application to climatological data
Troupin, Charles ULg; Sirjacobs, Damien ULg; Rixen, Michel et al

Poster (2011, April)

DIVA (Data Interpolating Variational Analysis) is a variational analysis tool designed to interpolate irregularly-spaced, noisy data onto any desired location, in most cases on regular grids. It is the ... [more ▼]

DIVA (Data Interpolating Variational Analysis) is a variational analysis tool designed to interpolate irregularly-spaced, noisy data onto any desired location, in most cases on regular grids. It is the combination of a particular methodology, based on the minimization of a functional, and a numerically efficient resolution method, based on a finite elements solver. The intrinsic advantages of DIVA are its natural way to take into account topographic and dynamic constraints (coasts, advection, ...) and its capacity to handle large data sets, frequently encountered in oceanography. In the present work, we describe various improvements to the variational analysis tool. The most significant advance is the development of a full error calculation, whilst until now, only an approximate error-field estimate was available. The key issue is the numerical determination of the real covariance function in DIVA, which is not formulated explicitly. This is solved by two concurrent executions of two DIVA, one providing the covariance for the other. The new calculation of the error field is now perfectly coherent with the inherent background covariance in all cases. The correlation length, which was previously set uniform over the computational domain, is now allowed to vary spatially. The efficiency of the tools for estimating the signal-to-noise ratio, through generalized cross-validation, has also been improved. Finally, a data quality-control method is implemented and allows one to detect possible outliers, based on statistics of the data-reconstruction misfit. The added value of these features are illustrated in the case of a large data set of salinity measured in the Mediterranean Sea. Several analyses are performed with different parameters in order to demonstrate their influence on the interpolated fields. In particular, we examine the benefits of using the parameter optimization tools and the advection constraint. The results are validated by means of a subset of data set apart for an independent validation. The corresponding errors fields are estimated using different methods and underline the role of the data coverage. [less ▲]

Detailed reference viewed: 87 (17 ULg)
Full Text
See detailAdvanced Data Interpolating Variational Analysis. Application to climatological data.
Troupin, Charles ULg; Sirjacobs, Damien ULg; Rixen, Michel et al

Poster (2011, March 21)

Detailed reference viewed: 17 (4 ULg)
Full Text
Peer Reviewed
See detailThe use of data assimilation in coupled hydrodynamic, ecological and biogeochemical models of the ocean
Grégoire, Marilaure ULg; Brasseur, Pierre; Lermusiaux, Pierre

in Journal of Marine Systems (2003), 40-41(1-3), 405

The International Lie`ge Colloquium on Ocean Dynamics is organized annually. The topic differs from year to year in an attempt to address, as much as possible, recent problems and incentive new subjects ... [more ▼]

The International Lie`ge Colloquium on Ocean Dynamics is organized annually. The topic differs from year to year in an attempt to address, as much as possible, recent problems and incentive new subjects in oceanography. Assembling a group of active and eminent scientists from various countries and often different disciplines, the Colloquia provide a forum for discussion and foster a mutually beneficial exchange of information opening on to a survey of recent discoveries, essential mechanisms, impelling question marks and valuable recommendations for future research. The objective of the 2001 Colloquium was to evaluate the progress of data assimilation methods in marine science and, in particular, in coupled hydrodynamic, ecological and bio-geo-chemical models of the ocean. [less ▲]

Detailed reference viewed: 17 (2 ULg)
Peer Reviewed
See detailThree-dimensional General Circulation Model of the Northern Bering Sea’s Summer Ecohydrodynamics
Nihoul, Jacques ULg; Adam, Paul; Brasseur, Pierre et al

in Continental Shelf Research (1993), 13(5-6), 509-542

The main features of the northern Bering Sea's summer ecohydrodynamics are investigated with the help of two three-dimensional—direct and inverse—models developed at theGeoHydrodynamics ... [more ▼]

The main features of the northern Bering Sea's summer ecohydrodynamics are investigated with the help of two three-dimensional—direct and inverse—models developed at theGeoHydrodynamics andEnvironmentResearch Laboratory of the University of Liège (GHER). Each model consists of two interacting sectorial submodels for (i) the general circulation hydrodynamics and synoptic structures, and (ii) the associated plankton ecosystem dynamics. The direct model is used to simulate, from an initial state compatible with historical, climatological and all available data pertinent to the summer season, a typical overview of the northern Bering Sea's ecohydrodynamics during the summer. The inverse model is applied in a two-fold perspective: (i) the reconstruction of typical summer distributions of temperature and salinity by using more than 1500 CTD profiles measured during the months of July, August and September, in the course of the ISHTAR program; (ii) considering the observations from specific ISHTAR surveys as quasi-synoptic, the reconstruction of individual data fields in order to provide additional information to assess the variability of the system. The model's predictions indicate that the summer dynamics are dominated by a few cogent semi-permanent and reproducible mechanisms which govern the main water mass transports, the upwellings, the fronts and the subsequent seasonal patterns of primary and secondary productions. The general circulation fields calculated by the direct model are considered as a standard of reference to give a coherent interpretation of—local and often instantaneous—observations, process studies and related results, in the context of the natural variability of the system. The simulated flow pattern has been validated, using the set of current measurements provided by 1985 and 1986 ISHTAR moorings. The contribution of the Anadyr Stream to the northward transport is reproduced qualitatively and quantitatively. The vertical motions—undetectable from direct experiments—are computed by the model, and represent one of the most efficient constraints on the ecohydrodynamics. For instance, the strong upwelling located along the Siberian coast—the existence of which was only presumed until recently—is now correctly estimated in position and intensity. The exceptionally high concentrations of nutrients found in the upwelled water turn this hydrodynamic structure into a catalyst element for the development of biological species in the region. The pattern of primary production shows two successive maxima: the first appears as a direct consequence of the frontal conditions associated with the Anadyr Stream, whereas the second develops further north, in the Chukchi Sea. The results display a fairly good agreement with the classical descriptions induced from observations, and suggest that the advection-growth coupling is the main physical conditioning factor for biological processes. [less ▲]

Detailed reference viewed: 8 (2 ULg)
See detailVariability of general circulation fields in the Northern Bering Sea investigated by the GHER 3D direct and inverse models
Brasseur, Pierre; Djenidi, Salim ULg

in Oceanography (1991), Suppl. to Vol. 4

Detailed reference viewed: 5 (1 ULg)
See detailMathematical visualization of the Anadyr Western Boundary Current and the associated frontal structures in the Northern Bering Sea
Nihoul, Jacques ULg; Djenidi, Salim ULg; Deleersnijder, Eric et al

in EOS : Transactions, American Geophysical Union (1990), 71(2), 189

Detailed reference viewed: 3 (0 ULg)
See detailMathematical visualization of general circulation fields in the Northern Bering Sea
Nihoul, Jacques ULg; Djenidi, Salim ULg; Deleersnijder, Eric et al

Conference (1989)

Detailed reference viewed: 1 (1 ULg)