Search publications of the members of the Royal Belgian institute of natural Sciences
-
A dual-nutrient-reduction strategy to control eutrophication in the southern North Sea continental waters.
- For decades the marine ecological models have sustained progressive developments and been subjected to an increasing degree of complexity in their processes, forcings and parameterization. In parallel, the validation techniques have evolved from visual to statistical comparisons, allowing fair estimates of the bias and correlations between model results and reference data. Still, it is difficult to estimate in advance what will be the uncertainty attached to any model prediction because of the complexity of the ecological models and the non linearity of their response to a change. Also, it is not trivial to determine the uncertainty of the model response due to one specific forcing, especially when this forcing is variable in time and space. The uncertainty in an ecological model response is somewhat linked to the model sensitivity to a perturbation. Since the non-linear model response to a perturbation may vary in a wide range of possibilities, we chose to base our assessment on the probability theory by applying a “light” Monte-Carlo experiment. It consists in a reduced number of randomly-perturbed simulations where knowledge of the system allows narrowing the range of perturbations. We applied the light Monte-Carlo experiment on a biogeochemical model in the English Channel and the southern North Sea (3D-MIRO&CO). The uncertainty on modelled chlorophyll a prediction was studied as a response, first, to random wind perturbations and, second, to random phytoplankton autolysis values. Statistical and probabilistic quantification of the results is being presented for the Belgian coastal and offshore zones.
-
Optical teledetection of chlorophyll a in estuarine and coastal waters
-
A chlorophyll-retrieval algorithm for satellite imagery (Medium Resolution Imaging Spectrometer) of inland and coastal waters
-
Effect of a waveband shift on chlorophyll retrieval from MERIS imagery of inland and coastal waters
-
Retrieval of oceanic constituents from ocean color using simulated annealing
-
Presentation of a family of turbulence closure models for stratified shallow water flows and preliminary application to the Rhine outflow region
-
Preface - 27th International Liege Colloquium on Ocean Hydrodynamics - Liege, May 8-12, 1995 - Processes in Regions of Freshwater Influence
-
Model of remote-sensing reflectance including bidirectional effects for case 1 and case 2 waters
-
Haline stratification in the Rhine-Meuse freshwater plume - a 3-dimensional model sensitivity analysis
-
Optical remote sensing of chlorophyll a in case 2 waters by use of an adaptive two-band algorithm with optimal error properties
-
Optical remote sensing in support of eutrophication monitoring in Belgian waters
-
A coastal ocean model intercomparison study for a three-dimensional idealised test case
-
The spectral reflectance and transparency of river plume waters
-
On the signatures of river outflow fronts in radar imagery
-
Development and application of an algorithm for detecting Phaeocystis globosa blooms in the Case 2 Southern North Sea waters
- While mapping algal blooms from space is now well-established, mapping undesirable algal blooms in eutrophicated coastal waters raises further challenge in detecting individual phytoplankton species. In this paper, an algorithm is developed and tested for detecting Phaeocystis globosa blooms in the Southern North Sea. For this purpose, we first measured the light absorption properties of two phytoplankton groups, P. globosa and diatoms, in laboratory-controlled experiments. The main spectral difference between both groups was observed at 467 nm due to the absorption of the pigment chlorophyll c3 only present in P. globosa, suggesting that the absorption at 467 nm can be used to detect this alga in the field. A Phaeocystis-detection algorithm is proposed to retrieve chlorophyll c3 using either total absorption or water-leaving reflectance field data. Application of this algorithm to absorption and reflectance data from Phaeocystis-dominated natural communities shows positive results. Comparison with pigment concentrations and cell counts suggests that the algorithm can flag the presence of P. globosa and provide quantitative information above a chlorophyll c3 threshold of 0.3 mg m(-3) equivalent to a P. globosa cell density of 3 x 10(6) cells L(-1). Finally, the possibility of extrapolating this information to remote sensing reflectance data in these turbid waters is evaluated.
-
The COASTCOLOUR dataset
- The objective of the ESA DUE CoastColour project is to fully exploit the potential of the MERIS instrument for remote sensing of the coastal zone. The product requirements have been derived from a user consultation process. Users have provided in-situ data from many locations, which were used for algorithm development and validation. The MERIS data archive from 2005 onwards has been processed with the finally selected algorithms for 27 globally distributed coastal sites. The CoastColour dataset comprises an improved Level 1b product (L1P), a product that contains directional and normalised water leaving reflectances (L2R) and a product for water properties (L2W). The total data volume is 100TB. All data are online and available from the CoastColour Website. A near real time service was operated from October 2011 until end of the ENVISAT mission. Plans exist to continue the service with Sentinel data.
-
Use of ocean color satellite data to study the dynamics of suspended particles in the Yangtze River plume (East China Sea)
- A multi-sensor algorithm is applied to MODIS and MERIS satellite data in order to quantify suspended particulate matter (SPM) in the Yangtze River plume (East China Sea). Several atmospheric correction methods are tested; a simple but operational method is finally selected as appropriate for MODIS, MERIS and GOCI satellite data. As most of the methods for atmospheric corrections of satellite data fail over such highly turbid waters, an adaptation of the black pixel assumption is used to correct for the aerosol contribution. The retrieved seawater reflectance at red wavebands appears as the most sensitive to SPM concentrations but tends to saturate at concentrations beyond 100 mg.l(-1). By opposition the near-infrared seawater reflectance does not saturate even at extremely high concentrations of 1000 mg.l(-1). Overall, the most robust relationship between the SPM concentration and seawater reflectance is obtained considering a spectral ratio between the near-infrared (e. g., 850 nm) and visible (e. g. 550 nm). This relationship is applied to atmospherically corrected ocean color satellite data to retrieve SPM concentrations in the Yangtze River plume. Results show that ocean color satellite data can be used to study the seasonal dynamics of SPM and better understand the role played by the main physical processes involved (river discharge, tidal cycles, wind and regional circulation).
-
Spectral variations of light scattering by marine particles in coastal waters, from visible to near infrared
- Field measurements and Mie calculations of the particulate light-scattering coefficient (b(p), in m(-1)) in the near-infrared and visible spectral domains are combined to quantify and model the effect of particulate absorption on the b(p) spectral variations. The case of particles of coastal origin and assumed to follow a Junge-type size distribution is considered. A simple power-law function closely reproduces the near-infrared b(p) spectral variations, with a spectral slope varying in the range 0.1-1.4. In the visible (e.g., 440 nm), particulate absorption effects systematically lead to b(p) values 5-30\% lower than values predicted using a power-law function fitted in the near infrared and extrapolated to 440 nm. The respective influences of the particle size distribution and composition are investigated for both mineral and organic particle populations. Finally, an empirical model derived from theoretical calculations closely reproduces the actual b(p) spectral variations from near-infrared to short visible wavelengths, taking into account particulate absorption effects.
-
Ostéologie et relations phylogénétiques des Gebrayelichtyidae (Halecostomi, Pycnodontomorpha), une extraordinaire famille de poissons du Crétacé supérieur marin du Liban, avec la description dun nouveau genre
-
À propos de Paramesturus (Pycnodontomorpha) de l'Aptien inférieur marin d'Allemagne et de ses relations systématiques
