References of "Sirjacobs, Damien"
     in
Bookmark and Share    
See detailUsing monovariate and multivariate EOFs to reconstruct missing data with DINEOF
Alvera Azcarate, Aïda ULg; Barth, Alexander ULg; Sirjacobs, Damien ULg et al

Conference (2008)

DINEOF (Data Interpolating Empirical Orthogonal Functions) is an EOF-based method to reconstruct missing data in geophysical data sets. DINEOF can be used to reconstruct monovariate data sets (as sea ... [more ▼]

DINEOF (Data Interpolating Empirical Orthogonal Functions) is an EOF-based method to reconstruct missing data in geophysical data sets. DINEOF can be used to reconstruct monovariate data sets (as sea surface temperature (SST), chlorophyll, etc), and multivariate data sets with little increase in complexity. For multivariate reconstructions, extended EOFs are used, which take into account the interrelationships between related variables to infer data at missing locations. Spatial maps of the standard deviation of the reconstruction error can be also calculated. In the past, DINEOF has been compared to Optimal Interpolation (OI) techniques for the Adriatic Sea SST. The results showed that DINEOF was faster than OI, making it very suitable for operational applications. DINEOF was also more accurate when compared to in situ data. Another advantage of DINEOF is that there is no need for a priori knowledge of the statistics of the reconstructed data set (such as covariance or correlation length), thus reducing the subjectivity of the analysis. DINEOF has been successfully used to reconstruct a large variety of domains over the world ocean, mostly at the regional scale. In addition to an overview of the technique's capabilities, limitations and future developments, recent work aimed to improve the quality of the reconstructions at the global and local scales will be presented. [less ▲]

Detailed reference viewed: 52 (4 ULg)
Full Text
Peer Reviewed
See detailThree-dimensional analysis of oceanographic data with the software DIVA
Troupin, Charles ULg; Ouberdous, Mohamed ULg; Rixen, Michel et al

in Geophysical Research Abstracts (2008)

In oceanography, the process of gridding data is frequently used for various purposes, e.g. initialization of hydrodynamic models, or graphical representation of sparse data. DIVA (Data-Interpolating ... [more ▼]

In oceanography, the process of gridding data is frequently used for various purposes, e.g. initialization of hydrodynamic models, or graphical representation of sparse data. DIVA (Data-Interpolating Variational Analysis) is designed to perform such gridding tasks. It has the advantage of taking into account the intrinsic nature of oceanographic data, i.e. uncertainty in in situ measurements and anisotropy due to advection and irregular coastlines and topography. Three-dimensional reconstruction of temperature and salinity fields is achieved by stacking horizontal layers where independent analysis with DIVA are performed. Nevertheless, analysis in regions void of data may result in the presence of static instabilities between two or more consecutive layers. The method implemented in DIVA to remove such kinds of instabilities is the object of the present work. It consists of adding pseudo-data from one layer to the upper adjacent layer in order to create stable stratification in the vicinity of instabilities. Two approaches for assigning values to the pseudo data are tested: the first is called the mixing approach and aims at simulating a mixing process between two layers; the second is called the minimal perturbation, as it strives to minimise the perturbations inthe pseudo-data. A realistic application using temperature and salinity profiles in the North Atlantic is carried out and the results are compared with World Ocean Atlas climatologies. [less ▲]

Detailed reference viewed: 73 (5 ULg)
Full Text
Peer Reviewed
See detailOn-the-go georeferenced measurements of soil mechanical strength and differenciation of soil structure.
Destain, Marie-France ULg; Sirjacobs, Damien ULg; Hanquet, Bernard et al

in Geophysical Research Abstracts (2008)

Soil strength is defined as the resistance which as to be overcome to obtain a given soil deformation. Amongst the numerous methods developed to measure soil strength, two are classically used. On one ... [more ▼]

Soil strength is defined as the resistance which as to be overcome to obtain a given soil deformation. Amongst the numerous methods developed to measure soil strength, two are classically used. On one hand, a laboratory method based on triaxial tests of undisturbed soil samples allows the estimation of cohesion and internal friction angle by the Mohr-Coulomb equation. On the other hand, measuring soil penetration resistance by pushing a cone into a soil is a widely used technique. Both techniques deliver discontinuous field information and are not suited to produce digital soil mapping. The objectives of this paper are to present a sensor able to continuously measure soil strength variations. The sensor was constituted of a thin blade pulled in the soil at a constant depth and speed and a beam which transferred the soil-blade forces to a transducer fixed on a vehicle. The transducer measures the draft force Fx, the vertical force Fz and the moment My thanks to an octagonal ring dynamometer. A measurement chain was developed to acquire simultaneously the signals provides by the soil strength sensor and those of a DGPS. Signal processing was notably based on geostatistics and allows soil mapping [1]. Four fields representative of the soils used in silty areas for arable production in Belgium were selected. The measurements were repeated several times during 1999-2003. Targeted test plots were chosen in each field to perform reference measurements, namely granulometry, cohesion, friction angle, pF, water content, dry bulk density, and cone index. The within-field studies revealed high variability caused by texture, history, traffic, etc., and showed a correlation between the sensor signals and physical parameters, such as cone index and soil moisture, as long as no over-consolidation of the soil occurred [2]. To assess the similarity of soil strength between the fields, the data Fx, Fz and My were classified by using canonical variates (CV). The two first CV represented 95.9 % of the variability, which means that two main variables contain the essential part of the information. In a plane (Fz, Fx), three clusters could be distinguished. The first one (trials 1 and 5), characterized by a low draft and a high Fz, corresponded to trials performed in March on soils ploughed during the winter, naked or covered with small vegetation, and characterized by small values of cone index. The second one (trials 2, 3, 4, 7) with high values of Fx and Fz grouped measurements done just after wheat harvest in August. The third cluster (trials 6) corresponded to measurements performed during wheat growth. It may be concluded that the signals from the sensor treated by suited statistical analysis have the potential to differentiate soil structures at a field scale. REFERENCES [1] Sirjacobs D., Hanquet B., Lebeau F., Destain M.-F. (2002). On-line mechanical resistance mapping and correlation with soil physical properties for precision agriculture. Soil and Tillage Research 64, 231-242. [2] Hanquet B., Sirjacobs D., Destain M.-F., Frankinet M., Verbrugge J.-C. (2004). Analysis of soil variability measured with a soil strength sensor. Precision Agriculture, 5, 227-246. [less ▲]

Detailed reference viewed: 69 (13 ULg)
Full Text
See detailDIVA: a Data Analysis Software with Generalized-Cross Validation and Quality Control
Troupin, Charles ULg; Rixen, Michel; Sirjacobs, Damien ULg et al

Poster (2007, May 19)

Detailed reference viewed: 21 (1 ULg)
Full Text
See detailDIVA Graphical User Interface
Troupin, Charles ULg; Sirjacobs, Damien ULg; Beckers, Jean-Marie ULg

Conference (2006, November 13)

Detailed reference viewed: 16 (0 ULg)
Full Text
Peer Reviewed
See detailInfluence of the Aral Sea negative water balance on its seasonal circulation patterns: use of a 3D hydrodynamic model
Sirjacobs, Damien ULg; Grégoire, Marilaure ULg; Delhez, Eric ULg et al

in Journal of Marine Systems (2004), 47(1-4), 51-66

A 3D hydrodynamic model of the Aral Sea was successfully implemented to address the complex hydrodynamic changes induced by the combined effect of hydrologic and climatic change in the Aral region. The ... [more ▼]

A 3D hydrodynamic model of the Aral Sea was successfully implemented to address the complex hydrodynamic changes induced by the combined effect of hydrologic and climatic change in the Aral region. The first barotropic numerical experiments allowed us to produce a comparative description of the mean general seasonal circulation patterns corresponding to the original situation (1956-1960) and of the average situation for the period from 1981 to 1985, a very low river flow period. The dominant anticyclonic circulation suggested by our seasonal simulation is in good agreement with previous investigations. In addition. this main anticyclonic gyre was shown to be stable and clearly established from February to September, while winter winds led to another circulation scenario. In winter, the main anticyclonic gyre was considerably limited, and cyclonic circulations appeared in the deep western basin and in the northeast of the shallow basin. In contrast, stronger anticyclonic circulation was observed in the Small Aral Sea during winter. As a consequence of the 10-m sea level drop observed between the two periods considered, the 1981-1985 simulation suggests an intensification of seasonal variability. Total water transport of the main gyre was reduced with sea level drop by a minimum of 30% in May and up to 54% in September. Before 1960, the study of the net flows through Berg and Kokaral Straits allowed us to evaluate the component of water exchange between the Small and the Large Seas linked with the general anticyclonic circulation around Kokaral Island. This exchange was lowest in summer (with a mean anticyclonic exchange of 222 m(3)/s for July and August), highest in fall and winter (with a mean value of 1356 m(3)/s from September to February) and briefly reversed in the spring (mean cyclonic circulation of 316 m(3)/s for April and May). In summer, the water exchange due to local circulation at the scale of each strait was comparatively more important because net flows through the straits were low. After about 20 years of negative water balance, the western Kokaral Strait was dried up and the depth of Berg Strait was reduced from 15 to 5 m. Simulation indicated a quasi-null net transport, except during the seasonal modification of the circulation pattern, in February and October. A limited, but stable, water exchange of about 100 m(3)/s remained throughout the year, as a result of the permanent superposition of opposite currents. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 698 (41 ULg)
Full Text
Peer Reviewed
See detailAnalysis of soil variability measured with a soil strength sensor
Hanquet, Bernard; Sirjacobs, Damien ULg; Destain, Marie-France ULg et al

in Precision Agriculture (2004), 5(3), 227-246

In the context of precision agriculture, the knowledge of soil strength variability at the field scale may be useful for improving site-specific tillage. Moreover, rapid and accurate sensing methods for ... [more ▼]

In the context of precision agriculture, the knowledge of soil strength variability at the field scale may be useful for improving site-specific tillage. Moreover, rapid and accurate sensing methods for soil physical properties determination would favourably replace labour intensive, time-consuming and expensive soil sampling and analysis. This study aims at validating conclusions of a previous study which was conducted to develop a soil strength in field conditions. The coupled acquisition of the sensor's signals and the corresponding DGPS positions allowed establishment of maps for the three measured outputs, namely the horizontal force (Fx), the vertical force (FZ) and the moment (My). In order to study the relationships between measured forces and soil physical parameters, a series of soil properties were measured on soil cores collected in 10 reference plots. Significant correlations were found between Fx and the average resistance to cone penetration at 25 cm depth and between Fx and the average soil moisture at 30 cm depth. The sensing method proved its capability to characterize within-field soil variability. [less ▲]

Detailed reference viewed: 119 (37 ULg)
Full Text
See detailBiogeochemistry of the Scheldt estuary and plume
Sirjacobs, Damien ULg; Shimoni, Michal; Borges, Alberto ULg et al

Conference (2003, September)

Detailed reference viewed: 34 (14 ULg)
Full Text
See detailSCHELDT - Airborne Hyperspectral Potential for Coastal Biogeochemistry of the Scheldt Estuary and Plume
Shimoni, Michal; Sirjacobs, Damien ULg; Borges, Alberto ULg et al

Report (2003)

European estuaries are subject to intense anthropogenic disturbance reflected in elevated loading of detrital organic matter, which induce high respiration rates and the production of large quantities of ... [more ▼]

European estuaries are subject to intense anthropogenic disturbance reflected in elevated loading of detrital organic matter, which induce high respiration rates and the production of large quantities of dissolved CO2. The Scheldt basin covers one of the most populated and industrialised areas of Europe and its tributaries drain an area of about 21,860 km2. The amounts of nutrients discharged by the Scheldt increased considerably during the past 20 years. Due to the dilution and metabolic processes of the downstream river flow in the estuary, an important variability of several parameters can be observed amongst which phytoplankton species and concentration, particulate organic matter, colour dissolved organic matter and suspended matter. In the present days, researches on the functioning of estuarine and coastal ecosystems are based on highly time consuming, costly sea campaigns and laboratory analyses. Although optical spaceborne remote sensing already proved useful in such coastal ecosystem studies, hyperspectroscopy opened a new dimension by allowing improved distinction of various biogeochemical compounds through characteristic spectral signature identification. Water quality variables were examined in the Scheldt estuary and plume, using CASI-2 (Compact airborne Spectrographic Imager) hyperspectral sensor and in situ bio-optical observations. The numerous parameters and spectrum measured in each station were used for further remote sensing analysis, as well as to complete the interpretation of the observed environmental processes. Multiple regression approach has been used to derive correlation between classical ground truth measurements and the rich information provided by the numerous CASI spectral bands. From these relations, some synoptic maps of biogeochemical parameters could be derived in the Scheldt estuary and plume. [less ▲]

Detailed reference viewed: 40 (4 ULg)
See detailAirborne hyperspectral potential for coastal biogeochemistry of the Scheldt estuary and plume
Shimoni, Michal; Sirjacobs, Damien ULg; Borges, Alberto ULg et al

Conference (2003, June)

Estuaries are obligate pathways for the transfer of dissolved and particulate material from the continent to the marine system. The tidal regime of some estuaries leads to an increased residence time of ... [more ▼]

Estuaries are obligate pathways for the transfer of dissolved and particulate material from the continent to the marine system. The tidal regime of some estuaries leads to an increased residence time of the freshwater in the estuarine mixing zone and pronounced changes in the speciation of elements. European estuaries are subject to intense anthropogenic disturbance reflected in elevated loading of detrital organic matter, which induce high respiration rates and the production of large quantities of dissolved CO2. The Scheldt basin covers one of the most populated and industrialised areas of Europe and its tributaries drain an area of about 21,860 km2. The amounts of nutrients discharged by the Scheldt increased considerably during the past 20 years. Due to the dilution and metabolic processes of the downstream river flow in the estuary, an important variability of several parameters can be observed amongst which phytoplankton species and concentration, particulate organic matter, colour dissolved organic matter and suspended matter. In the present days, researches on the functioning of estuarine and coastal ecosystems are based on highly time consuming, costly sea campaigns and laboratory analyses. Although optical spaceborne remote sensing already proved useful in such coastal ecosystems studies, hyperspectroscopy opened a new dimension by allowing improved distinction of various biogeochemical compounds through characteristic spectral signature identification. The goal of this research is to explore the potential of CASI-SWIR airborne hyperspectroscopy in retrieving some of the biogeochemical parameters of interest in the Schedlt estuary and plume (Belgium-Netherlands coastal zone). A 13 sampling stations field survey was realised in order to cover as quickly as possible the wide range of water quality encountered from the mouth of the estuary to the outer limit of the plume. The numerous parameters and spectrum measured in each station were used for further remote sensing analysis, as well as to complete the interpretation of the observed environmental processes. Correlation was searched between classical ground truth measurements and the rich information provided by numerous CASI-SWIR spectral bands carefully chosen. These relations were used as an attempt to derive synoptic view of the spatial distribution of various biogeochemical parameters in the Scheldt estuary and plume. Synthesis of these hyperspectral-mapping products with other complementary satellite maps and ground data set may allow ocean scientists to derive substantial information about ecosystem processes in the Scheldt estuary and adjacent coast. [less ▲]

Detailed reference viewed: 70 (1 ULg)
Full Text
See detailWhat don’t we know about dying and dead seas ?
Sirjacobs, Damien ULg; Nihoul, Jacques ULg

Conference (2003, May)

As conclusions of this NATO Advanced Research Workshop on Dying and Dead Seas, numerous questions remains concerning the various studied water bodies, all along their hydrological cycle and along their ... [more ▼]

As conclusions of this NATO Advanced Research Workshop on Dying and Dead Seas, numerous questions remains concerning the various studied water bodies, all along their hydrological cycle and along their anthropic perturbations. A synthesis of most important open questions is presented. [less ▲]

Detailed reference viewed: 17 (0 ULg)
Full Text
See detailGlobal water and salt budget of the Aral Sea from 1960 to 1991.
Sirjacobs, Damien ULg; Grégoire, Marilaure ULg; Delhez, Eric ULg et al

Conference (2003, May)

Focusing on the global water and salt budget of the Aral sea from 1960 till 1991, a compilation of data available in the litterature is analysed with simple models and compared to the measured evolution ... [more ▼]

Focusing on the global water and salt budget of the Aral sea from 1960 till 1991, a compilation of data available in the litterature is analysed with simple models and compared to the measured evolution of the sea. [less ▲]

Detailed reference viewed: 22 (4 ULg)
See detailSalt budget and salt composition for the Aral Sea
Konovalov, S.; Belokopitov, V.; Ivanov, L. et al

Poster (2003, May)

Detailed reference viewed: 16 (0 ULg)