Gilles Grandjean | BRGM - Academia.edu (original) (raw)
Papers by Gilles Grandjean
Landslide Science and Practice, 2013
Near Surface Geophysics
We tackle the problem of characterizing the subsurface, more specifically detecting shallow burie... more We tackle the problem of characterizing the subsurface, more specifically detecting shallow buried objects, using seismic techniques. This problem is commonly encountered in civil engineering when cavities or pipes have to be identified from the surface in urban areas. Our strategy consists of processing not only first arrivals, but also later ones, and using them both in tomography and migration processes, sequentially. These two steps, which form the basis of seismic imaging, can be carried out separately provided that the incident and diffracted wavefields are separated in the data space. Tomography is implemented here as an iterative technique for reconstructing the background velocity field from the first-arrival traveltimes. The later signals are then migrated by a Kirchhoff method implemented in the space domain. To study the reliability of this methodology, it is first applied to synthetic cases in the acoustic and elastic approximation. Both the background velocity field and the local impedance contrasts are reconstructed as defined in the predicted model. An experimental case, specifically designed for the purpose, is then considered in order to test the algorithms under real conditions. The resulting image coincides well with the predicted model when only P-waves are generated. In the elastic mode, surface waves make P-wave extraction difficult, so that the reconstruction remains incomplete. This is confirmed by the real data example. Finally, we demonstrate the appropriateness of the proposed method under such circumstances, provided that suitable preprocessing of data is carried out, in particular, the removal of surface waves.
ABSTRACT The purposes of the multidisciplinary DIGISOIL project are the integration and improveme... more ABSTRACT The purposes of the multidisciplinary DIGISOIL project are the integration and improvement of in situ and proximal measurement technologies for the assessment of soil properties and soil degradation indicators, going from the sensing technologies to their integration and their application in (digital) soil mapping (DSM). In order to assess and prevent soil degradation and to benefit from the different ecological, economical and historical functions of the soil in a sustainable way, high resolution and quantitative maps of soil properties are needed. The core objective of the project is to explore and exploit new capabilities of advanced geophysical technologies for answering this societal demand. To this aim, DIGISOIL addresses four issues covering technological, soil science and economic aspects: (i) the validation of geophysical (in situ, proximal and airborne) technologies and integrated pedo-geophysical inversion techniques (mechanistic data fusion) (ii) the relation between the geophysical parameters and the soil properties, (iii) the integration of the derived soil properties for mapping soil functions and soil threats, (iv) the pre-evaluation, standardisation and sub-industrialization of the proposed methodologies, including technical and economical studies related to the societal demand. With respect to these issues, the preliminary tasks of the DIGISOIL project were to develop, test and validate the most relevant geophysical technologies for mapping soil properties. The different field tests, realized during the project, allow focusing on technological suitable solutions for each of the identified methods: geoelectric, GPR, EMI, seismics, magnetic and hyperspectral. After data acquisition systems, sensor geometry, and advanced data processing techniques have been developed and validated, we present now the solutions for going from such data to soil properties maps. For two test sites, located respectively in Luxembourg (LU) and Mugello (IT) a set of soil properties maps have been produced. They give information about the C content, water content, clays content and soil thickness, allowing to deal with the main threats to soils related to erosion, SOC decreasing, water management and soil erosion.
ABSTRACT The purposes of the multidisciplinary DIGISOIL project are the integration and improveme... more ABSTRACT The purposes of the multidisciplinary DIGISOIL project are the integration and improvement of in situ and proximal measurement technologies for the assessment of soil properties and soil degradation indicators, going from the sensing technologies to their integration and their application in (digital) soil mapping (DSM). In order to assess and prevent soil degradation and to benefit from the different ecological, economical and historical functions of the soil in a sustainable way, high resolution and quantitative maps of soil properties are needed. The core objective of the project is to explore and exploit new capabilities of advanced geophysical technologies for answering this societal demand. To this aim, DIGISOIL addresses four issues covering technological, soil science and economic aspects: (i) the validation of geophysical (in situ, proximal and airborne) technologies and integrated pedo-geophysical inversion techniques (mechanistic data fusion) (ii) the relation between the geophysical parameters and the soil properties, (iii) the integration of the derived soil properties for mapping soil functions and soil threats, (iv) the pre-evaluation, standardisation and sub-industrialization of the proposed methodologies, including technical and economical studies related to the societal demand. With respect to these issues, the preliminary tasks of the DIGISOIL project were to develop, test and validate the most relevant geophysical technologies for mapping soil properties. The different field tests, realized during the project, allow focusing on technological suitable solutions for each of the identified methods: geoelectric, GPR, EMI, seismics, magnetic and hyperspectral. After data acquisition systems, sensor geometry, and advanced data processing techniques have been developed and validated, we present now the solutions for going from such data to soil properties maps. For two test sites, located respectively in Luxembourg (LU) and Mugello (IT) a set of soil properties maps have been produced. They give information about the C content, water content, clays content and soil thickness, allowing to deal with the main threats to soils related to erosion, SOC decreasing, water management and soil erosion.
ABSTRACT The multidisciplinary DIGISOIL project aimed to integrate and improve in situ and proxim... more ABSTRACT The multidisciplinary DIGISOIL project aimed to integrate and improve in situ and proximal measurement technologies for the assessment of soil properties and soil degradation indicators, going from the sensing technologies to their integration and their application in (digital) soil mapping (DSM). In order to assess and prevent soil degradation and to benefit from the different ecological, economical and historical functions of the soil in a sustainable way, high resolution and quantitative maps of soil properties are needed. The core objective of the project is to explore and exploit new capabilities of advanced geophysical technologies for answering this societal demand. To this aim, DIGISOIL addresses four issues covering technological, soil science and economic aspects: (i) the validation of geophysical (in situ, proximal and airborne) technologies and integrated pedo-geophysical inversion techniques (mechanistic data fusion) (ii) the relation between the geophysical parameters and the soil properties, (iii) the integration of the derived soil properties for mapping soil functions and soil threats, (iv) the pre-evaluation, standardisation and sub-industrialization of the proposed methodologies, including technical and economical studies related to the societal demand. With respect to these issues, the DIGISOIL project allows to develop, test and validate the most relevant geophysical technologies for mapping soil properties. The system was tested on different field tests, and validated the proposed technologies and solutions for each of the identified methods: geoelectric, GPR, EMI, seismics, magnetic and hyperspectral. After data acquisition systems, sensor geometry, and advanced data processing techniques have been developed and validated, we present now the solutions for going from geophysical data to soil properties maps. For two test sites, located respectively in Luxembourg (LU) and Mugello (IT) a set of soil properties maps have been produced. They give information about the C content, water content, clays content and soil thickness, allowing to deal with the main threats to soils related to erosion, SOC decreasing, water management and soil erosion.
Review of Economic Design, 2013
Evidence suggests that in developing countries, agents rely on mutual insurance agreements to dea... more Evidence suggests that in developing countries, agents rely on mutual insurance agreements to deal with income or expenditure shocks. This paper analyzes which risk-sharing networks can be sustained in the long run when individuals are far-sighted, in the sense that they are able to forecast how other agents would react to their choice of insurance partners. In particular, we study whether the farsightedness of the agents leads to a reduction of the tension between stability and efficiency that arises when individuals are myopic. We find that for extreme values of the cost of establishing a mutual insurance agreement, myopic and farsighted agents form the same risk-sharing networks. For intermediate costs, farsighted agents form efficient networks while myopic agents don't.
Near Surface Geophysics, 2012
Geophysical methods, such as seismic surveying or electrical resistivity imaging, appear to be ef... more Geophysical methods, such as seismic surveying or electrical resistivity imaging, appear to be efficient in investigating landslide structures and, consequently, for understanding related mechanisms of deformation. They are non-intrusive probing methods that allow the direct measurement of compressional (P), shear (S) wave velocities and also electrical resistivity, three geophysical parameters that are considered as determinants in defining ground properties and identifying anomalies related to structural (faults, fissures), lithological (sand to clay, or calcareous variations) and hydrological (moisture, water flow) conditions. Both the seismic and resistivity methods are commonly used for landslide investigations, having been tested over the last decade or more on various types of landslides, including mudslides, debris flows, unstable slopes, etc. The common approach in these earlier experiments has been to invert the P-and S-wave velocity fields, plus the electrical resistivity field, using suitable algorithms to produce two-dimensional P-and S-wave velocities and resistivity tomograms. A coherent and integrated interpretation of the resulting information is, however, not straightforward because each geophysical method is sensitive to different soil properties.
Journal of Applied Geophysics, 2006
ABSTRACT
Computers & Geosciences, 2009
Data Revues 16310713 V334i7 S1631071302017765, Jun 21, 2010
First Break, 2011
Frequency analysis of surface waves propagation is an efficient tool to retrieve the vertical she... more Frequency analysis of surface waves propagation is an efficient tool to retrieve the vertical shear-wave velocity profile. Surface waves result from the interaction of elastic body waves with a free surface. They are commonly generated by impulsive active sources but are also present in ambient noise. Here we compare the results of interferometric estimation of surface-wave dispersion from controlled-noise sources by using both cross-correlation and deconvolution methods. The crucial step in both methods lies in the dispersion image computation that conditions the reliability of the dispersion curve, and therefore the inversion results. We have found that the dispersion characteristics of surface waves are better defined when the deconvolution method is used. This better definition is probably due to the relative independence of the deconvolved output from the source function.
2009 IEEE International Geoscience and Remote Sensing Symposium, 2009
Supporting military forces in mobility decisions is the aim of this project involving scientists ... more Supporting military forces in mobility decisions is the aim of this project involving scientists and professionals from geotechnical, remote sensing and decision-making system domains. A prototype has been developed, named ECORS, intending to characterize operations theatres from Earth observation data. Observation devices, involved as input sources, include either remote sensing or soil characterization techniques. For each kind of operation, decisions
The aim of this work is to combine the geophysical parameters P-wave velocity (Vp), S-wave veloci... more The aim of this work is to combine the geophysical parameters P-wave velocity (Vp), S-wave velocity (Vs) and electrical resistivity (ρ) for describing the structure of landslides in term of mechanical behavior. The study is focused on the Super-Sauze site, situated in the Barcelonnette Basin (France). The earthflow covers an area of some 17 ha and extends 820 m from its highest point at an elevation of 2105 m, to its base at an elevation of 1740 m, with an average slope gradient of 25°. It is composed of Callovian-Oxfordian black clay-shales, known as "Terres Noires". We present here new results from the fusion of seismic and electrical data that delivers information about the mechanical behavior of the earthflow. The seismic and electric profiles were performed along two orthogonal directions: a 325-m transverse profile perpendicular to the axis of the earthflow. The algorithm consists in first estimating the functions π i defining different hypotheses A i . Considering the three geophysical parameters inverted, we respectively express from Vp, Vs and ρ the possibilities that the medium is fractured (low Vp values), made of compact clays (low Vs values) or saturated (low ρ values). Transitions in the possibility function were estimated from field observations and petrophysics considerations. Then, for each inverted parameters spatially distributed x i , and using the functions π i , the possibility function of hypothesis A (Π(A)) can be computed. The resulting images of the transverse transect clearly reveals the complex behavior of the earthflow.
Eos Transactions American Geophysical Union
ABSTRACT
Computers & Geosciences
ABSTRACT
Landslide Science and Practice, 2013
Near Surface Geophysics
We tackle the problem of characterizing the subsurface, more specifically detecting shallow burie... more We tackle the problem of characterizing the subsurface, more specifically detecting shallow buried objects, using seismic techniques. This problem is commonly encountered in civil engineering when cavities or pipes have to be identified from the surface in urban areas. Our strategy consists of processing not only first arrivals, but also later ones, and using them both in tomography and migration processes, sequentially. These two steps, which form the basis of seismic imaging, can be carried out separately provided that the incident and diffracted wavefields are separated in the data space. Tomography is implemented here as an iterative technique for reconstructing the background velocity field from the first-arrival traveltimes. The later signals are then migrated by a Kirchhoff method implemented in the space domain. To study the reliability of this methodology, it is first applied to synthetic cases in the acoustic and elastic approximation. Both the background velocity field and the local impedance contrasts are reconstructed as defined in the predicted model. An experimental case, specifically designed for the purpose, is then considered in order to test the algorithms under real conditions. The resulting image coincides well with the predicted model when only P-waves are generated. In the elastic mode, surface waves make P-wave extraction difficult, so that the reconstruction remains incomplete. This is confirmed by the real data example. Finally, we demonstrate the appropriateness of the proposed method under such circumstances, provided that suitable preprocessing of data is carried out, in particular, the removal of surface waves.
ABSTRACT The purposes of the multidisciplinary DIGISOIL project are the integration and improveme... more ABSTRACT The purposes of the multidisciplinary DIGISOIL project are the integration and improvement of in situ and proximal measurement technologies for the assessment of soil properties and soil degradation indicators, going from the sensing technologies to their integration and their application in (digital) soil mapping (DSM). In order to assess and prevent soil degradation and to benefit from the different ecological, economical and historical functions of the soil in a sustainable way, high resolution and quantitative maps of soil properties are needed. The core objective of the project is to explore and exploit new capabilities of advanced geophysical technologies for answering this societal demand. To this aim, DIGISOIL addresses four issues covering technological, soil science and economic aspects: (i) the validation of geophysical (in situ, proximal and airborne) technologies and integrated pedo-geophysical inversion techniques (mechanistic data fusion) (ii) the relation between the geophysical parameters and the soil properties, (iii) the integration of the derived soil properties for mapping soil functions and soil threats, (iv) the pre-evaluation, standardisation and sub-industrialization of the proposed methodologies, including technical and economical studies related to the societal demand. With respect to these issues, the preliminary tasks of the DIGISOIL project were to develop, test and validate the most relevant geophysical technologies for mapping soil properties. The different field tests, realized during the project, allow focusing on technological suitable solutions for each of the identified methods: geoelectric, GPR, EMI, seismics, magnetic and hyperspectral. After data acquisition systems, sensor geometry, and advanced data processing techniques have been developed and validated, we present now the solutions for going from such data to soil properties maps. For two test sites, located respectively in Luxembourg (LU) and Mugello (IT) a set of soil properties maps have been produced. They give information about the C content, water content, clays content and soil thickness, allowing to deal with the main threats to soils related to erosion, SOC decreasing, water management and soil erosion.
ABSTRACT The purposes of the multidisciplinary DIGISOIL project are the integration and improveme... more ABSTRACT The purposes of the multidisciplinary DIGISOIL project are the integration and improvement of in situ and proximal measurement technologies for the assessment of soil properties and soil degradation indicators, going from the sensing technologies to their integration and their application in (digital) soil mapping (DSM). In order to assess and prevent soil degradation and to benefit from the different ecological, economical and historical functions of the soil in a sustainable way, high resolution and quantitative maps of soil properties are needed. The core objective of the project is to explore and exploit new capabilities of advanced geophysical technologies for answering this societal demand. To this aim, DIGISOIL addresses four issues covering technological, soil science and economic aspects: (i) the validation of geophysical (in situ, proximal and airborne) technologies and integrated pedo-geophysical inversion techniques (mechanistic data fusion) (ii) the relation between the geophysical parameters and the soil properties, (iii) the integration of the derived soil properties for mapping soil functions and soil threats, (iv) the pre-evaluation, standardisation and sub-industrialization of the proposed methodologies, including technical and economical studies related to the societal demand. With respect to these issues, the preliminary tasks of the DIGISOIL project were to develop, test and validate the most relevant geophysical technologies for mapping soil properties. The different field tests, realized during the project, allow focusing on technological suitable solutions for each of the identified methods: geoelectric, GPR, EMI, seismics, magnetic and hyperspectral. After data acquisition systems, sensor geometry, and advanced data processing techniques have been developed and validated, we present now the solutions for going from such data to soil properties maps. For two test sites, located respectively in Luxembourg (LU) and Mugello (IT) a set of soil properties maps have been produced. They give information about the C content, water content, clays content and soil thickness, allowing to deal with the main threats to soils related to erosion, SOC decreasing, water management and soil erosion.
ABSTRACT The multidisciplinary DIGISOIL project aimed to integrate and improve in situ and proxim... more ABSTRACT The multidisciplinary DIGISOIL project aimed to integrate and improve in situ and proximal measurement technologies for the assessment of soil properties and soil degradation indicators, going from the sensing technologies to their integration and their application in (digital) soil mapping (DSM). In order to assess and prevent soil degradation and to benefit from the different ecological, economical and historical functions of the soil in a sustainable way, high resolution and quantitative maps of soil properties are needed. The core objective of the project is to explore and exploit new capabilities of advanced geophysical technologies for answering this societal demand. To this aim, DIGISOIL addresses four issues covering technological, soil science and economic aspects: (i) the validation of geophysical (in situ, proximal and airborne) technologies and integrated pedo-geophysical inversion techniques (mechanistic data fusion) (ii) the relation between the geophysical parameters and the soil properties, (iii) the integration of the derived soil properties for mapping soil functions and soil threats, (iv) the pre-evaluation, standardisation and sub-industrialization of the proposed methodologies, including technical and economical studies related to the societal demand. With respect to these issues, the DIGISOIL project allows to develop, test and validate the most relevant geophysical technologies for mapping soil properties. The system was tested on different field tests, and validated the proposed technologies and solutions for each of the identified methods: geoelectric, GPR, EMI, seismics, magnetic and hyperspectral. After data acquisition systems, sensor geometry, and advanced data processing techniques have been developed and validated, we present now the solutions for going from geophysical data to soil properties maps. For two test sites, located respectively in Luxembourg (LU) and Mugello (IT) a set of soil properties maps have been produced. They give information about the C content, water content, clays content and soil thickness, allowing to deal with the main threats to soils related to erosion, SOC decreasing, water management and soil erosion.
Review of Economic Design, 2013
Evidence suggests that in developing countries, agents rely on mutual insurance agreements to dea... more Evidence suggests that in developing countries, agents rely on mutual insurance agreements to deal with income or expenditure shocks. This paper analyzes which risk-sharing networks can be sustained in the long run when individuals are far-sighted, in the sense that they are able to forecast how other agents would react to their choice of insurance partners. In particular, we study whether the farsightedness of the agents leads to a reduction of the tension between stability and efficiency that arises when individuals are myopic. We find that for extreme values of the cost of establishing a mutual insurance agreement, myopic and farsighted agents form the same risk-sharing networks. For intermediate costs, farsighted agents form efficient networks while myopic agents don't.
Near Surface Geophysics, 2012
Geophysical methods, such as seismic surveying or electrical resistivity imaging, appear to be ef... more Geophysical methods, such as seismic surveying or electrical resistivity imaging, appear to be efficient in investigating landslide structures and, consequently, for understanding related mechanisms of deformation. They are non-intrusive probing methods that allow the direct measurement of compressional (P), shear (S) wave velocities and also electrical resistivity, three geophysical parameters that are considered as determinants in defining ground properties and identifying anomalies related to structural (faults, fissures), lithological (sand to clay, or calcareous variations) and hydrological (moisture, water flow) conditions. Both the seismic and resistivity methods are commonly used for landslide investigations, having been tested over the last decade or more on various types of landslides, including mudslides, debris flows, unstable slopes, etc. The common approach in these earlier experiments has been to invert the P-and S-wave velocity fields, plus the electrical resistivity field, using suitable algorithms to produce two-dimensional P-and S-wave velocities and resistivity tomograms. A coherent and integrated interpretation of the resulting information is, however, not straightforward because each geophysical method is sensitive to different soil properties.
Journal of Applied Geophysics, 2006
ABSTRACT
Computers & Geosciences, 2009
Data Revues 16310713 V334i7 S1631071302017765, Jun 21, 2010
First Break, 2011
Frequency analysis of surface waves propagation is an efficient tool to retrieve the vertical she... more Frequency analysis of surface waves propagation is an efficient tool to retrieve the vertical shear-wave velocity profile. Surface waves result from the interaction of elastic body waves with a free surface. They are commonly generated by impulsive active sources but are also present in ambient noise. Here we compare the results of interferometric estimation of surface-wave dispersion from controlled-noise sources by using both cross-correlation and deconvolution methods. The crucial step in both methods lies in the dispersion image computation that conditions the reliability of the dispersion curve, and therefore the inversion results. We have found that the dispersion characteristics of surface waves are better defined when the deconvolution method is used. This better definition is probably due to the relative independence of the deconvolved output from the source function.
2009 IEEE International Geoscience and Remote Sensing Symposium, 2009
Supporting military forces in mobility decisions is the aim of this project involving scientists ... more Supporting military forces in mobility decisions is the aim of this project involving scientists and professionals from geotechnical, remote sensing and decision-making system domains. A prototype has been developed, named ECORS, intending to characterize operations theatres from Earth observation data. Observation devices, involved as input sources, include either remote sensing or soil characterization techniques. For each kind of operation, decisions
The aim of this work is to combine the geophysical parameters P-wave velocity (Vp), S-wave veloci... more The aim of this work is to combine the geophysical parameters P-wave velocity (Vp), S-wave velocity (Vs) and electrical resistivity (ρ) for describing the structure of landslides in term of mechanical behavior. The study is focused on the Super-Sauze site, situated in the Barcelonnette Basin (France). The earthflow covers an area of some 17 ha and extends 820 m from its highest point at an elevation of 2105 m, to its base at an elevation of 1740 m, with an average slope gradient of 25°. It is composed of Callovian-Oxfordian black clay-shales, known as "Terres Noires". We present here new results from the fusion of seismic and electrical data that delivers information about the mechanical behavior of the earthflow. The seismic and electric profiles were performed along two orthogonal directions: a 325-m transverse profile perpendicular to the axis of the earthflow. The algorithm consists in first estimating the functions π i defining different hypotheses A i . Considering the three geophysical parameters inverted, we respectively express from Vp, Vs and ρ the possibilities that the medium is fractured (low Vp values), made of compact clays (low Vs values) or saturated (low ρ values). Transitions in the possibility function were estimated from field observations and petrophysics considerations. Then, for each inverted parameters spatially distributed x i , and using the functions π i , the possibility function of hypothesis A (Π(A)) can be computed. The resulting images of the transverse transect clearly reveals the complex behavior of the earthflow.
Eos Transactions American Geophysical Union
ABSTRACT
Computers & Geosciences
ABSTRACT