References of "Sirjacobs, Damien"
     in
Bookmark and Share    
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: 36 (9 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: 16 (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: 9 (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: 542 (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: 97 (29 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: 28 (13 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: 25 (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: 29 (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: 15 (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: 18 (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: 14 (0 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, May)

Detailed reference viewed: 16 (2 ULg)
Full Text
Peer Reviewed
See detailInfluence of the Aral Sea negative water balance on its seasonal circulation and ventilation patterns : use of a 3D hydrodynamic model
Sirjacobs, Damien ULg; Grégoire, Marilaure ULg; Delhez, Eric ULg et al

in Geophysical Research Abstracts (2003, April), 5(09052), 2003509052

Within the context of the EU INCO-COPERNICUS program "Desertification in the Aral Sea Region: A study of the Natural and Anthropogenic Impacts" (Contract IAC2-CT-2000-10023), a large-scale 3D hydrodynamic ... [more ▼]

Within the context of the EU INCO-COPERNICUS program "Desertification in the Aral Sea Region: A study of the Natural and Anthropogenic Impacts" (Contract IAC2-CT-2000-10023), a large-scale 3D hydrodynamic model was adapted to address specifically the macroscale processes affecting the Aral Sea water circulation and ventilation. The particular goal of this research is to simulate the effect of lasting negative water balance on the 3D seasonal circulation, temperature, salinity and water-mixing fields of the Aral Sea. The original Aral Sea seasonal hydrodynamism is simulated with the average seasonal forcings corresponding to the period from 1956 to 1960. This first investigation concerns a period of relative stability of the water balance, before the beginning of the drying process. The consequences of the drying process on the hydrodynamic of the Sea will be studied by comparing this first results with the simulation representing the average situation for the years 1981 to 1985, a very low river flow period. For both simulation periods, the forcing considered are the seasonal fluctuations of wind fields, precipitation, evaporation, river discharge and salinity, cloud cover, air temperature and humidity. The meteorological forcings were adapted to the common optimum one-month temporal resolution of the available data sets. Monthly mean kinetic energy flux and surface tensions were calculated from daily ECMWF wind data. Monthly in situ precipitation, surface air temperature and humidity fields were interpolated from data obtained from the Russian Hydrological and Meteorological Institute. Monthly water discharge and average salinity of the river water were considered for both Amu Darya and Syr Darya river over each simulation periods. The water mass conservation routines allowed the simulation of a changing coastline by taking into account local drying and flooding events of particular grid points. Preliminary barotropic runs were realised (for the 1951-1960 situation, before drying up began) in order to get a first experience of the behaviour of the hydrodynamic model. These first runs provide results about the evolution of the following state variables: elevation of the sea surface, 3D fields of vertical and horizontal flows, 2D fields of average horizontal flows and finally the 3D fields of turbulent kinetic energy. The mean seasonal salinity and temperature fields (in-situ data gathered by the Russian Hydrological and Meteorological Institute) are available for the two simulated periods and will allow a first validation of the hydrodynamic model. Various satellites products were identified, collected and processed in the frame of this research project and will be used for the validation of the model outputs. Seasonal level changes measurements derived from water table change will serve for water balance validation and sea surface temperature for hydrodynamics validation. [less ▲]

Detailed reference viewed: 39 (8 ULg)
Full Text
Peer Reviewed
See detailOn-line soil mechanical resistance mapping and correlation with soil physical properties for precision agriculture
Sirjacobs, Damien ULg; Hanquet, Bernard; Lebeau, Frédéric ULg et al

in Soil & Tillage Research (2002), 64

Measurement of local soil strength may be used for real time regulation of tillage parameters in precision agriculture. Cartography of soil physical properties will also facilitate the study of their ... [more ▼]

Measurement of local soil strength may be used for real time regulation of tillage parameters in precision agriculture. Cartography of soil physical properties will also facilitate the study of their influence on plant development and yields. The aim of this research was to develop and test in field conditions a sensor measuring on-line soil strength variations. The sensor was constituted of a thin blade pulled in the soil at constant depth and speed and a beam which transferred the soil–blade forces to a transducer fixed on the machine. This transducer measured the draft force (Fx), the vertical force (Fz) and the moment (My). A field experiment was performed in 2 ha field of silt soil (Hesbaye, Belgium). A soil strength map of the field was established by pulling the sensor at 5 m interline separation by a tractor equipped with a DGPS receiver. The relationship between the recorded forces and several soil physical parameters was studied by identifying 10 control plots on the sensor track. In each of them, cone index penetrometry profiles and soil water content were measured. Soil samples were taken in the centre of the plots to determine cohesion and internal friction angle, simple compression resistance, Atterberg limits, granulometry and pF curves. Triaxial tests identified over-consolidated soils in plots situated in the pounds of the field. Based on the parameters measured in the other plots, significant relationships were established between (1) a global penetrometry index and the Fx and My solicitations measured by the sensor; (2) gravimetric water content and the vertical force Fz. Interpolation by inverse distance with a range of 45 m gave the best result for the cartography of the three measured signals (Fx, Fz and My). The confrontation of those maps with pedological and topographic maps together with the statistical relationships and the farmer’s knowledge of the field showed high consistency. The results of this experiment in field conditions are encouraging and show the promising perspective of technological innovations allowing on-line characterisation of soil physical state for precision agriculture. [less ▲]

Detailed reference viewed: 152 (34 ULg)