References of "Lacroix, Geneviève"
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See detailCloud filling of ocean colour and sea surface temperature remote sensing products over the Southern North Sea by the Data Interpolating Empirical Orthogonal Functions methodology.
Sirjacobs, Damien ULg; Alvera Azcarate, Aïda ULg; Barth, Alexander ULg et al

in Journal of Sea Research (2011), 65(1), 114-130

Optical remote sensing data is now being used systematically for marine ecosystem applications, such as the forcing of biological models and the operational detection of harmful algae blooms. However ... [more ▼]

Optical remote sensing data is now being used systematically for marine ecosystem applications, such as the forcing of biological models and the operational detection of harmful algae blooms. However, applications are hampered by the incompleteness of imagery and by some quality problems. The Data Interpolating Empirical Orthogonal Functions methodology (DINEOF) allows calculation of missing data in geophysical datasets without requiring a priori knowledge about statistics of the full data set and has previously been applied to SST reconstructions. This study demonstrates the reconstruction of complete space-time information for 4 years of surface chlorophyll a (CHL), total suspended matter (TSM) and sea surface temperature (SST) over the Southern North Sea (SNS) and English Channel (EC). Optimal reconstructions were obtained when synthesising the original signal into 8 modes for MERIS CHL and into 18 modes for MERIS TSM. Despite the very high proportion of missing data (70%), the variability of original signals explained by the EOF synthesis reached 93.5 % for CHL and 97.2 % for TSM. For the MODIS TSM dataset, 97.5 % of the original variability of the signal was synthesised into 14 modes. The MODIS SST dataset could be synthesised into 13 modes explaining 98 % of the input signal variability. Validation of the method is achieved for 3 dates below 2 artificial clouds, by comparing reconstructed data with excluded input information. Complete weekly and monthly averaged climatologies, suitable for use with ecosystem models, were derived from regular daily reconstructions. Error maps associated with every reconstruction were produced according to Beckers et al. (2006) [6]. Embedded in this error calculation scheme, a methodology was implemented to produce maps of outliers, allowing identification of unusual or suspicious data points compared to the global dynamics of the dataset. Various algorithms artefacts were associated with high values in the outlier maps (undetected cloud edges, haze areas, contrails, cloud shadows). With the production of outlier maps, the data reconstruction technique becomes also a very efficient tool for quality control of optical remote sensing data and for change detection within large databases. [less ▲]

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See detailEstimating pCO2 from remote sensing in the Belgian coastal zone
Borges, Alberto; Ruddick, Kevin; Lacroix, Geneviève et al

in ESA Special Publication SP-686 (2010)

In coastal waters, a purely field observation based approach will probably be insufficient to better constrain estimates of air-sea CO2 fluxes, to study their inter-annual variability and their long-term ... [more ▼]

In coastal waters, a purely field observation based approach will probably be insufficient to better constrain estimates of air-sea CO2 fluxes, to study their inter-annual variability and their long-term changes. One approach to achieve these goals is to use remotely sensed fields of relevant biogeochemical variables to extrapolate available data, and produce maps of the partial pressure of CO2 (pCO2) and air-sea CO2 fluxes. In the open ocean this approach has to some extent been successfully used based on fields of chlorophyll-a (Chla) and sea surface temperature (SST). This approach remains challenging in coastal waters that have complex optical properties (Case-II waters) and that exhibit highly dynamic pCO2 temporal and spatial variations. In the frame of the Belgian funded BELCOLOUR-II project (Optical remote sensing of marine, coastal and inland waters; http://www.mumm.ac.be/BELCOLOUR/), three field cruises per year (April, July and September) for optical measurements were carried in 2007, 2008, 2009 in the Southern Bight of the North Sea (SBNS). Based on these data-sets, we derived algorithms to compute pCO2 from Chl-a and sea surface salinity (SSS) using multipolynomial regressions (MPR). Here we report the first application of the MPR algorithms to derive pCO2 fields in the Belgian coastal zone based on data gathered in 2007, using remote sensed Chl-a (MERIS) and SSS computed with a 3-D hydrodynamical model of SBNS (COHERENS). [less ▲]

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See detailReconstruction of Missing Satellite Total Suspended Matter Data over the Southern North Sea and English Channel using Empirical Orthogonal Function Decomposition of Satellite Imagery and Hydrodynamical Modelling
Sirjacobs, Damien ULg; Alvera Azcarate, Aïda ULg; Barth, Alexander ULg et al

Poster (2008, October)

Optical remote sensing data archives generally have many gaps caused by clouds or other retrieval problems. However, for the light forcing of ecosystem models continuous fields are required. For ... [more ▼]

Optical remote sensing data archives generally have many gaps caused by clouds or other retrieval problems. However, for the light forcing of ecosystem models continuous fields are required. For parameters exhibiting strong spatial and temporal correlations for regions of similar dynamics or from day to day, the missing data can be estimated by use of statistical techniques. In this context, the Data Interpolation with Empirical Orthogonal Functions (DINEOF) method is used for reconstruction of complete space-time information for surface total suspended matter (TSM) and chlorophyll a from a 5-year archive of MODIS and MERIS products over the Southern North Sea and English Channel. The DINEOF univariate methodology has been previously demonstrated for Mediterranean sea surface temperature data (Alvera-Azcarate et al., 2005, Beckers et al., 2006). Alvera-Azcarate et al (2007) showed that SST reconstructions could be improved by using a multivariate approach in which SST, chlorophyll and wind fields were taken into account together for the analyses. Here, TSM images will be used in combination with information from the COHERENS hydrodynamical model to provide a complete and continuous estimate of surface TSM for the Southern North Sea throughout the period 2003-2005. In addition to the remotely sensed TSM, the DINEOF multivariate analysis will consider wind fields, depth integrated currents, surface elevations and bottom stresses. Reconstucted images are compared with the original incomplete images. Validation of the method is achieved by estimation of information removed from the training data by exclusion of entire images and by addition of artificial clouds. The data reconstruction technique has further applications in the processing and quality control of optical remote sensing data. Perspectives will be outlined for improving the quality control of retrieved parameters and for the improvement of retrievals by adding statistical information to the conventional spectral processing. References: Alvera-Azcarate, A., Barth, A., Rixen, M., and Beckers, J.-M.: Reconstruction of incomplete oceanographic data sets using Empirical Orthogonal Functions. Application to the Adriatic Sea, Ocean Modelling, 9, 325–346, 2005. Alvera-Azcarate, A., Barth, A., Beckers, J. M., and Weisberg, R. H.: Multivariate Reconstruction of Missing Data in Sea Surface Temperature, Chlorophyll and Wind Satellite Fields, Journal of Geophysical Research, 112, C03008, doi:10.1029/2006JC003660, 2007. Beckers J.-M., A. Barth & A. Alvera-Azcarate, DINEOF reconstruction of clouded images including error maps. Application to the Sea-Surface Temperature around Corsican Island, Ocean Sciences, 2: 183–199, 2006. [less ▲]

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See detailEffects of extreme meteorological conditions on coastal dynamics near a submarine canyon
Skliris, Nikolaos ULg; Lacroix, Geneviève; Djenidi, Salim ULg

in Continental Shelf Research (2004), 24(9), 1033-1045

A 3-D hydrodynamic model is applied to assess shelf/slope exchanges in the Calvi Canyon region (Corsica, NW Mediterranean) during the violent storm that affected the Western Europe in December 1999 ... [more ▼]

A 3-D hydrodynamic model is applied to assess shelf/slope exchanges in the Calvi Canyon region (Corsica, NW Mediterranean) during the violent storm that affected the Western Europe in December 1999. Simulations are carried out using high-frequency sampling meteorological data to take into account the short-term variability of the atmospheric conditions. It is shown that the combined effects of canyon topography and of the wind forcing during the storm are responsible for a large increase of both cross-shore and vertical transports in the area. Strong downwelling motion is simulated all along the continental slope with vertical velocities up to 2cm s(-1) within the canyon. High turbulent diffusion levels are obtained leading to the complete mixing of the water column within the canyon. Results suggest that increased turbulent diffusion and downwelling circulation in the canyon during the storm should result in a large transport of coastal water towards the abyssal plain. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

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See detailThe age as a diagnostic of the dynamics of marine ecosystem models
Delhez, Eric ULg; Lacroix, Geneviève; Deleersnijder, Eric

in Ocean Dynamics (2004), 54(2), 221-231

The constituent-oriented age theory (CAT) worked out by Delhez et al. (1999) is a flexible tool that can be applied to diagnose complex models. It is shown here how this can be used to quantify the pace ... [more ▼]

The constituent-oriented age theory (CAT) worked out by Delhez et al. (1999) is a flexible tool that can be applied to diagnose complex models. It is shown here how this can be used to quantify the pace at which an ecosystem model works. At the cost of the introduction of one additional evolution equation for each compartment of the ecosystem model, the mean age of the biological material forming these compartments can be computed. The information obtained in this way complements the information provided by the concentration data; while the latter measures the standing stocks, the former provides an integrated assessment of the interaction rates and matter fluxes. The benefits of the method are demonstrated with a simple Lotka-Volterra system and a one-dimensional vertical model of the nitrogen cycle in the Ligurian Sea. The theory can be used to study the biological compartments individually or the ecosystem as a whole. In particular, the age is a valuable tool to quantify the overall cycling rate of nitrogen in the food web. [less ▲]

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See detailExchange processes and nitrogen cycling on the shelf and continental slope of the Black Sea basin
Grégoire, Marilaure ULg; Lacroix, Geneviève

in Global Biogeochemical Cycles (2003), 17(2),

A 3D coupled biogeochemical-hydrodynamical model has been applied to the Black Sea to simulate nitrogen cycling and to estimate the exchange of biogeochemical components at the shelf break and between the ... [more ▼]

A 3D coupled biogeochemical-hydrodynamical model has been applied to the Black Sea to simulate nitrogen cycling and to estimate the exchange of biogeochemical components at the shelf break and between the continental slope and the deep sea. It was found that biological processes on the northwestern shelf are in approximate balance. Primary production is fueled by river discharge, nitrate input from the open sea at the shelf break, and in situ remineralization. The input of nitrate from the open sea is roughly equivalent to the river nitrate discharge but is half the nitrate export from the shelf toward the open sea. Also, the Black Sea shelf acts throughout the year as a nitrate source for the open sea. The amount of shelf production not remineralized in the euphotic layer is 22.2% and is exported to lower layers (20%) or offshore (2.2%). We estimate that the export of carbon from the shelf to the interior of the basin represents 2.5% of the new production of the open sea. The upper slope adjoining the northwestern shelf is the site of downwelling events responsible for the downward transport to the intermediate layer of the continental slope of biogeochemical components exported from the shelf in the upper layer. The shelf has been found to be an efficient trap for the refractory material discharged by the Danube. [less ▲]

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See detailAtmospheric CO2 flux from mangrove surrounding waters
Borges, Alberto ULg; Djenidi, Salim ULg; Lacroix, Geneviève et al

in Geophysical Research Letters (2003), 30(11),

[1] The partial pressure of CO2 (pCO(2)) was measured at daily and weekly time scales in the waters surrounding mangrove forests in Papua New Guinea, the Bahamas and India. The pCO(2) values range from ... [more ▼]

[1] The partial pressure of CO2 (pCO(2)) was measured at daily and weekly time scales in the waters surrounding mangrove forests in Papua New Guinea, the Bahamas and India. The pCO(2) values range from 380 to 4800 muatm. These data, together with previously published data, suggest that overall oversaturation of CO2 with respect to atmospheric equilibrium in surface waters is a general feature of mangrove forests, though the entire ecosystems (sediment, water and vegetation) are probably sinks for atmospheric CO2. The computed CO2 fluxes converge to about +50 mmolC m(-2) day(-1). If this conservative value is extrapolated for worldwide mangrove ecosystems, the global emission of CO2 to the atmosphere is about 50 10(6) tC year(-1). Based on this tentative estimate, mangrove waters appear to be regionally a significant source of CO2 to the atmosphere and should be more thoroughly investigated, especially at seasonal time scale. [less ▲]

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See detailModelling the time-dependent 3-D circulation around a submarine canyon during stormy weather conditions
Skliris, Nikolaos; Djenidi, Salim ULg; Lacroix, Geneviève

Conference (2002)

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See detailEcosystem model (MODECOGeL) of the Ligurian Sea revisited. Seasonal and interannual variability due to atmospheric forcing
Lacroix, Geneviève; Grégoire, Marilaure ULg

in Journal of Marine Systems (2002), 37(4), 229-258

A one-dimensional coupled hydrodynamical–biological model, MODe`le d’ECOsyste`me du G.H.E.R. et du L.O.V. (MODECOGeL), of the water column is developed and applied to the Ligurian Sea (North Western ... [more ▼]

A one-dimensional coupled hydrodynamical–biological model, MODe`le d’ECOsyste`me du G.H.E.R. et du L.O.V. (MODECOGeL), of the water column is developed and applied to the Ligurian Sea (North Western Mediterranean). It is an extended and improved version of the model presented by Lacroix and Nival [J. Mar. Syst. 16 (1998) 23]. The hydrodynamic model is a 1D version of the 3D turbulent closure G.H.E.R. model, which takes into account momentum and heat surface fluxes computed from a real meteorological data set. The ecosystem model is defined by a nitrogen cycle described by 12 biological state variables including several plankton size classes and an explicit description of the bacterial loop. One data set coming from the FRONTAL missions is used to initialise and validate the model. To assess the impact of the interannual variability of the meteorological conditions on the ecosystem dynamics, the coupled model is run with 4-year real meteorological conditions (October 1984–September 1988). The model estimated percentages of the interannual variability of the annual mean biomass of phytoplankton, zooplankton and bacteria respectively of 31.0%, 16.2% and 16.3%. The ontribution of the zooplankton related to the total plankton biomass (phytoplankton, zooplankton and bacteria) has been found to be the most sensitive to the meteorological conditions variations (21%), followed by the phytoplankton (12%) and finally, by the bacteria (5%). The model estimated percentages of interannual variability of the annual gross primary production, the annual mean f-ratio and the annual bacterial production respectively of 27.9%, 18.5% and 13.4% although the interannual variability of the real winds conditions is only of 11.3%. Due to the more windy and less sunny conditions prevailing during the years ‘‘1985–1986’’ and ‘‘1986–1987’’, the annual primary production was found higher than during the years ‘‘1984–1985’’ and ‘‘1987–1988’’. The bacterial production is always greater than the primary production, showing the importance of the bacteria in such an oligotrophic environment. On a seasonal scale, the highest interannual variability of the primary production and the f-ratio is found in spring like for the wind intensity. [less ▲]

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See detailStudy of the oxygen budget of the Black Sea waters using a 3D coupled hydrodynamical-biogeochemical model
Grégoire, Marilaure ULg; Lacroix, Geneviève

in Journal of Marine Systems (2001), 31(1-mars Sp. Iss. SI), 175-202

The ventilation of the Black Sea waters by physical and biogeochemical processes is investigated using the Geohydrodynamics and Environment Research (GHER) laboratory 3D coupled hydrodynamical ... [more ▼]

The ventilation of the Black Sea waters by physical and biogeochemical processes is investigated using the Geohydrodynamics and Environment Research (GHER) laboratory 3D coupled hydrodynamical-biogeochemical model. In particular, the penetration at depth of the winter mixing, the generation of unstable motions by frontal instabilities, the exchanges between the north-western shelf and the open sea along the shelf break, the primary production distribution, the generation of detritus and the resulting consumption of oxygen for their recycling are studied. The GHER 3D hydrodynamic model is used to simulate the Black Sea's general circulation and the associated synoptic and mesoscale structures. This model is coupled with a simple ecosystem model defined by a nitrogen cycle which is described by seven state variables: nitrate, ammonium, dissolved oxygen, phytoplankton, zooplankton, pelagic and benthic detritus. The model simulates the space-time variations of the biogeochemical state variables. In particular, the spatial variability of the phytoplankton biomass annual cycle, imparted by the horizontal and vertical variations of the physical and chemical properties of the water column, is clearly illustrated. For instance, on the north-western shelf, the seasonal variability of the circulation and in particular, the reversal of the surface current at the end of spring, has a strong influence on the transport of the rich nutrient Danube waters and, thus, on the repartition of the primary production. Furthermore, the results illustrate the seasonal and vertical variations of the dissolved oxygen concentration resulting (a) from its atmospheric and photosynthetic productions in the surface layer, (b) from its loss to the atmosphere in spring and summer and (c) from its consumption associated with the detritus decomposition, the ammonium oxidation during the nitrification process, as well as the oxidation of hydrogen sulfide. The simulated sea surface, phytoplankton fields are compared with satellite estimates of chlorophyll-a fields. Comparisons are made with seasonal mean pictures and snapshot images, illustrating the mesoscale motions of the main coastal current. In the central Black Sea and the Danube delta area, comparisons with available field data are also made. As a general rule, all these comparisons show a quite good qualitative agreement. In particular, at the surface, the simulated phytoplankton space-time distribution is in a good qualitative agreement with satellite observations. However, on a quantitative point of view, the model underestimates the bloom intensity especially in the Danube discharge area. (C) 2001 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailEcosystem response to the atmospheric forcing in the Ligurian Sea in 1997-1999.
Lacroix, Geneviève; Nezlin, Nicolay; Djenidi, Salim ULg

in Proceedings of the 36th CIESM Congress (2001)

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See detailComparative analysis of SST interannual variability in the Western Mediterranean Sea and North-East Atlantic Ocean
Djenidi, Salim ULg; Kostianoy, Andrey; Lacroix, Geneviève et al

in Annales Geophysicae. Series B, Terrestrial and Planetary Physics (1998), 16(suppl. II),

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See detailInterdisciplinary approach and data assimilation in a Mediterranean ecosystem model
Lacroix, Geneviève; Djenidi, Salim ULg; Nihoul, Jacques ULg et al

in EOS Transactions (1998), 79

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See detailModelling the primary production interannual variability in the Ligurian Sea due to meteorological conditions with a 1D hydrodynamic/biological model
Lacroix, Geneviève; Nival, Paul; Djenidi, Salim ULg

in EOS : Transactions, American Geophysical Union (1998), 79

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See detailModélisation de la Baie de Cannes
Dekeyser, Yvan; Djenidi, Salim ULg; Nival, Paul et al

Report (1992)

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See detailExtending the GHER 3D Model to the modelling of ecosystems in Western Mediterranean coastal zones: results from an exploratory study
Lacroix, Geneviève; Djenidi, Salim ULg

in Martin, Jean-Marie; Barth, Hartmut (Eds.) EROS 2000 (European River Ocean System) (1992)

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