Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601521
F. Lavoué, R. Brossier, S. Garambois, J. Virieux, L. Métivier
In this study, we present a frequency-domain full waveform inversion (FWI) algorithm of ground-penetrating radar (GPR) data for the simultaneous reconstruction of the dielectric permittivity and electrical conductivity of the investigated material. The inverse problem is formulated as a quasi-Newton optimization scheme, where the influence of the Hessian is approximated by the L-BFGS-B algorithm. Numerical tests on a cross-shaped benchmark from the literature demonstrate the need for an ad hoc scaling between the relative permittivity εr and a relative conductivity σr through a reference conductivity σo We study the behavior of the inversion with respect to this reference conductivity and to the frequency sampling approach (simultaneous vs. sequential inversion), showing that i) the inversion process should be governed by the permittivity update to respect the natural sensitivity of the cost function and provide a reliable kinematic background soon the early iterations, ii) the value of σo should be tuned to find a compromise between resolution and noise in the final image of conductivity. We apply our scaling approach in a realistic synthetic example, illustrating that the quasi-Newton method based on the L-BFGS-B algorithm is able to reconstruct both permittivity and conductivity from multi-offset data acquired with a surface-to-surface acquisition configuration.
{"title":"2D full waveform inversion of GPR surface data: Permittivity and conductivity imaging","authors":"F. Lavoué, R. Brossier, S. Garambois, J. Virieux, L. Métivier","doi":"10.1109/IWAGPR.2013.6601521","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601521","url":null,"abstract":"In this study, we present a frequency-domain full waveform inversion (FWI) algorithm of ground-penetrating radar (GPR) data for the simultaneous reconstruction of the dielectric permittivity and electrical conductivity of the investigated material. The inverse problem is formulated as a quasi-Newton optimization scheme, where the influence of the Hessian is approximated by the L-BFGS-B algorithm. Numerical tests on a cross-shaped benchmark from the literature demonstrate the need for an ad hoc scaling between the relative permittivity εr and a relative conductivity σr through a reference conductivity σo We study the behavior of the inversion with respect to this reference conductivity and to the frequency sampling approach (simultaneous vs. sequential inversion), showing that i) the inversion process should be governed by the permittivity update to respect the natural sensitivity of the cost function and provide a reliable kinematic background soon the early iterations, ii) the value of σo should be tuned to find a compromise between resolution and noise in the final image of conductivity. We apply our scaling approach in a realistic synthetic example, illustrating that the quasi-Newton method based on the L-BFGS-B algorithm is able to reconstruct both permittivity and conductivity from multi-offset data acquired with a surface-to-surface acquisition configuration.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117156587","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601551
Matthias Boger, A. Glasmachers
A directional, monostatic borehole radar system was developed to overcome some disadvantages of the existing bistatic system. The challenges of combining transmitter and receiver in a single module are apparent, since one wants both high transmitting power and high receiver sensitivity. A dead time in the receiver response is unavoidable and thus prevents radar measurements at small distances. With sophisticated electronics consisting of e.g., variable gain control, advanced antenna switching and pulse generation, we are able to keep the dead time below 200 ns for a transmitted pulse with a center frequency of about 50 MHz. Other improvements allow for autonomous measurement mode. With our monostatic system, the probe length is reduced to 2.5 m as compared to a bistatic system of typical 13 m. In this paper, we present the improvements of the receiver electronics as well as the realization of the antenna switching and pulse generation. After a brief discussion of the disadvantages of a bistatic system and the basic theory, the implementations in hardware are discussed. Finally, some results of measurements are presented.
{"title":"A directional monostatic borehole radar system","authors":"Matthias Boger, A. Glasmachers","doi":"10.1109/IWAGPR.2013.6601551","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601551","url":null,"abstract":"A directional, monostatic borehole radar system was developed to overcome some disadvantages of the existing bistatic system. The challenges of combining transmitter and receiver in a single module are apparent, since one wants both high transmitting power and high receiver sensitivity. A dead time in the receiver response is unavoidable and thus prevents radar measurements at small distances. With sophisticated electronics consisting of e.g., variable gain control, advanced antenna switching and pulse generation, we are able to keep the dead time below 200 ns for a transmitted pulse with a center frequency of about 50 MHz. Other improvements allow for autonomous measurement mode. With our monostatic system, the probe length is reduced to 2.5 m as compared to a bistatic system of typical 13 m. In this paper, we present the improvements of the receiver electronics as well as the realization of the antenna switching and pulse generation. After a brief discussion of the disadvantages of a bistatic system and the basic theory, the implementations in hardware are discussed. Finally, some results of measurements are presented.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"124 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123188310","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601526
W. Muller, Xavier Dérobert
The coarse and loose nature of unbound granular road materials presents a number of challenges for conventional permittivity characterisation approaches. An alternative that appears better suited to these materials involves measuring the phase-shift at discrete frequencies through a sample of known thickness. To validate this approach against more established methods, a comparison is required on materials that can be easily measured using either method. To this end phase-shift measurements were undertaken on a range of solid dielectric slabs including various types of stone, plastic and an artificial material. Permittivity predictions from this method were then compared to results from a one-port coaxial cell. As an additional comparison, and to better understand the results, the phase-shift test setup was also modelled using GPRMax software. To improve the predictions, reverberations within the test apparatus were minimized by isolating the direct wave using time-domain Blackman windowing. However, the narrow window necessary for this particular test setup also degraded the ability to detect frequency-dependent permittivity changes. Overall the phase-shift approach produced real relative permittivity predictions similar to that from the one-port coaxial cell. Despite limitations in the current approach, the results validate the phase-shift approach as a simple and rapid method of characterizing the permittivity of larger dielectric material samples of constant thickness.
{"title":"A comparison of phase-shift and one-port coaxial cell permittivity measurements for GPR applications","authors":"W. Muller, Xavier Dérobert","doi":"10.1109/IWAGPR.2013.6601526","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601526","url":null,"abstract":"The coarse and loose nature of unbound granular road materials presents a number of challenges for conventional permittivity characterisation approaches. An alternative that appears better suited to these materials involves measuring the phase-shift at discrete frequencies through a sample of known thickness. To validate this approach against more established methods, a comparison is required on materials that can be easily measured using either method. To this end phase-shift measurements were undertaken on a range of solid dielectric slabs including various types of stone, plastic and an artificial material. Permittivity predictions from this method were then compared to results from a one-port coaxial cell. As an additional comparison, and to better understand the results, the phase-shift test setup was also modelled using GPRMax software. To improve the predictions, reverberations within the test apparatus were minimized by isolating the direct wave using time-domain Blackman windowing. However, the narrow window necessary for this particular test setup also degraded the ability to detect frequency-dependent permittivity changes. Overall the phase-shift approach produced real relative permittivity predictions similar to that from the one-port coaxial cell. Despite limitations in the current approach, the results validate the phase-shift approach as a simple and rapid method of characterizing the permittivity of larger dielectric material samples of constant thickness.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"379 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131995617","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601510
M. Ercoli, C. Pauselli, E. Forte, A. Frigeri, C. Federico
The Mt. Pollino Fault Zone is located in the northern sector of the Calabria region (southern Italy). It represents a segment between the southernmost part of the Apennines and the Calabrian Arc. In the Pollino area, seismic events of magnitude > 5 are not currently reported in literature and within the seismic catalogues, therefore this “gap” zone has been defined “silent”. Due to the geomorphological, geological and paleoseismological evidences of Quaternary faulting, the Pollino-Castrovillari faults are considered active, as demonstrated also by some recent reactivations, that have generated several earthquakes of moderate magnitude (Mmax ≤ 5.0) in a north-western sector, near Mormanno (Mercure Basin) and Morano villages (Morano-Castrovillari Basin). Therefore, the studied area retains many uncertainties in the definition of the seismic hazard. With these premises an integrated project started in 2012 (Agreement INGV-DPC 2012-2013, Project S1) aims to improve the base-knowledge for assessing the seismogenic potential. Among the different geological studies, the project encompasses the GPR fault imaging on several sites, having different goals: 1) define the location and the geologic characteristics of active faults; 2) detect new evidences of “recent” faulting; 3) correctly locate these structural elements on a geologic map; 4) support further paleoseismological surveys. A first 2DGPR survey was done at the Grotta Carbone site, about 4 kilometers from Castrovillari, for which some trench logs were already available, in order to “image” the fault zone and to provide a GPR data calibration using the stratigraphic information. The results of the radargrams interpretation show a characteristic GPR signature of the tectonic structures and faulted units and a different dielectric behavior among the units located across the fault, revealing an excellent matching with the available geological data. Clear tectonic features and their vertical offset between layers have been highlighted within the fault zone. The stratigraphy of the trenches have been extended, along the fault and in depth, providing new useful information essential for a better definition of the seismic hazard of the area and for a future 2D/3D dataset extension across other sites.
{"title":"The Mt. Pollino Fault (southern Apennines, Italy): GPR signature of Holocenic earthquakes in a “silent” area","authors":"M. Ercoli, C. Pauselli, E. Forte, A. Frigeri, C. Federico","doi":"10.1109/IWAGPR.2013.6601510","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601510","url":null,"abstract":"The Mt. Pollino Fault Zone is located in the northern sector of the Calabria region (southern Italy). It represents a segment between the southernmost part of the Apennines and the Calabrian Arc. In the Pollino area, seismic events of magnitude > 5 are not currently reported in literature and within the seismic catalogues, therefore this “gap” zone has been defined “silent”. Due to the geomorphological, geological and paleoseismological evidences of Quaternary faulting, the Pollino-Castrovillari faults are considered active, as demonstrated also by some recent reactivations, that have generated several earthquakes of moderate magnitude (Mmax ≤ 5.0) in a north-western sector, near Mormanno (Mercure Basin) and Morano villages (Morano-Castrovillari Basin). Therefore, the studied area retains many uncertainties in the definition of the seismic hazard. With these premises an integrated project started in 2012 (Agreement INGV-DPC 2012-2013, Project S1) aims to improve the base-knowledge for assessing the seismogenic potential. Among the different geological studies, the project encompasses the GPR fault imaging on several sites, having different goals: 1) define the location and the geologic characteristics of active faults; 2) detect new evidences of “recent” faulting; 3) correctly locate these structural elements on a geologic map; 4) support further paleoseismological surveys. A first 2DGPR survey was done at the Grotta Carbone site, about 4 kilometers from Castrovillari, for which some trench logs were already available, in order to “image” the fault zone and to provide a GPR data calibration using the stratigraphic information. The results of the radargrams interpretation show a characteristic GPR signature of the tectonic structures and faulted units and a different dielectric behavior among the units located across the fault, revealing an excellent matching with the available geological data. Clear tectonic features and their vertical offset between layers have been highlighted within the fault zone. The stratigraphy of the trenches have been extended, along the fault and in depth, providing new useful information essential for a better definition of the seismic hazard of the area and for a future 2D/3D dataset extension across other sites.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116716520","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601513
F. Frezza, L. Pajewski, C. Ponti, G. Schettini
An analytical-numerical model for the electromagnetic characterization of GPR scenarios, with a line-source illumination field, is proposed. Solution is given in the spectral-domain, in the case of a two-dimensional geometry with dielectric scatterers buried in a semi-infinite medium. The source and scattered fields are represented by means of cylindrical-wave expansions; the concept of plane-wave spectrum of a cylindrical wave is used to describe the interaction of the fields with the air-soil interface, following the fundamentals of the Cylindrical Wave Approach. The proposed model has been implemented in a Fortran code and numerical results are presented. The electromagnetic field can be calculated both in the near and far region, for arbitrary size and position of the scatterers, and the method can deal with both the fundamental transverse-electric and transverse-magnetic polarization states.
{"title":"Cylindrical-wave approach for line-source electromagnetic scattering by buried dielectric cylinders","authors":"F. Frezza, L. Pajewski, C. Ponti, G. Schettini","doi":"10.1109/IWAGPR.2013.6601513","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601513","url":null,"abstract":"An analytical-numerical model for the electromagnetic characterization of GPR scenarios, with a line-source illumination field, is proposed. Solution is given in the spectral-domain, in the case of a two-dimensional geometry with dielectric scatterers buried in a semi-infinite medium. The source and scattered fields are represented by means of cylindrical-wave expansions; the concept of plane-wave spectrum of a cylindrical wave is used to describe the interaction of the fields with the air-soil interface, following the fundamentals of the Cylindrical Wave Approach. The proposed model has been implemented in a Fortran code and numerical results are presented. The electromagnetic field can be calculated both in the near and far region, for arbitrary size and position of the scatterers, and the method can deal with both the fundamental transverse-electric and transverse-magnetic polarization states.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"296 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116726499","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601518
K. Jadoon, S. Lambot, M. Dimitrov, L. Weihermuller
We performed off-ground ground-penetrating radar (GPR) measurements over a bare agricultural field to monitor the freeze-thaw cycles over snow-cover. The GPR system consisted of a vector network analyzer combined with an off-ground monostatic horn antenna, thereby setting up an ultra-wideband stepped-frequency continuous-wave radar. Measurements were performed during nine days and the surface of the bare soil was exposed to snow fall, evaporation and precipitation as the GPR antenna was mounted 110 cm above the ground. Soil surface dielectric permittivity was retrieved using an inversion of time-domain GPR data focused on the surface reflection. The GPR forward model used combines a full-waveform solution of Maxwell's equations for three-dimensional wave propagation in planar layered media together with global reflection and transmission functions to account for the antenna and its interactions with the medium. Temperature and permittivity sensors were installed at six depths to monitor the soil dynamics in the top 8 cm depth. Significant effects of soil dynamics were observed in the time-lapse GPR, temperature and permittivity data and in particular freeze and thaw events were clearly visible. A good agreement of the trend was observed between the temperature, permittivity and GPR time-lapse data with respect to five freeze-thaw cycles. The GPR-derived permittivity was in good agreement with sensor observations. The proposed method appears to be promising for the real-time mapping and monitoring of the frozen layer at the field scale.
{"title":"Temporal monitoring of the soil freeze-thaw cycles over snow-cover land by using off-ground GPR","authors":"K. Jadoon, S. Lambot, M. Dimitrov, L. Weihermuller","doi":"10.1109/IWAGPR.2013.6601518","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601518","url":null,"abstract":"We performed off-ground ground-penetrating radar (GPR) measurements over a bare agricultural field to monitor the freeze-thaw cycles over snow-cover. The GPR system consisted of a vector network analyzer combined with an off-ground monostatic horn antenna, thereby setting up an ultra-wideband stepped-frequency continuous-wave radar. Measurements were performed during nine days and the surface of the bare soil was exposed to snow fall, evaporation and precipitation as the GPR antenna was mounted 110 cm above the ground. Soil surface dielectric permittivity was retrieved using an inversion of time-domain GPR data focused on the surface reflection. The GPR forward model used combines a full-waveform solution of Maxwell's equations for three-dimensional wave propagation in planar layered media together with global reflection and transmission functions to account for the antenna and its interactions with the medium. Temperature and permittivity sensors were installed at six depths to monitor the soil dynamics in the top 8 cm depth. Significant effects of soil dynamics were observed in the time-lapse GPR, temperature and permittivity data and in particular freeze and thaw events were clearly visible. A good agreement of the trend was observed between the temperature, permittivity and GPR time-lapse data with respect to five freeze-thaw cycles. The GPR-derived permittivity was in good agreement with sensor observations. The proposed method appears to be promising for the real-time mapping and monitoring of the frozen layer at the field scale.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126579185","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601535
E. Slob, K. Wapenaar
In this paper a scheme is presented to process 3D ground-penetrating radar reflection data acquired on a surface above a vertical transverse isotropic layered medium. The processing steps first decompose the data into Transverse Electric and Transverse Magnetic modes and up and down going waves, where the two modes are fully separated and can be treated separately in the two following steps. The first step that follows is wave field synthesis, where a virtual receiver is constructed in the layered subsurface at any depth level, from which is virtual vertical radar profile can be constructed. This can be done down to the depth level where the waves generated from the upper half space can reach as propagating waves. Once the up and down going vertical radar profiles are obtained at this virtual receiver position, well-known interferometry by deconvolution is used as a second step to obtain an image containing local primary reflection coefficients as a function of incidence angle of the initial plane wave. A numerical example demonstrates the effectiveness of removing multiples from the data and constructing an image free of effects of such internal multiple reflections.
{"title":"GPR wave field decomposition, synthesis and imaging for lossless layered vertically transverse isotropic media","authors":"E. Slob, K. Wapenaar","doi":"10.1109/IWAGPR.2013.6601535","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601535","url":null,"abstract":"In this paper a scheme is presented to process 3D ground-penetrating radar reflection data acquired on a surface above a vertical transverse isotropic layered medium. The processing steps first decompose the data into Transverse Electric and Transverse Magnetic modes and up and down going waves, where the two modes are fully separated and can be treated separately in the two following steps. The first step that follows is wave field synthesis, where a virtual receiver is constructed in the layered subsurface at any depth level, from which is virtual vertical radar profile can be constructed. This can be done down to the depth level where the waves generated from the upper half space can reach as propagating waves. Once the up and down going vertical radar profiles are obtained at this virtual receiver position, well-known interferometry by deconvolution is used as a second step to obtain an image containing local primary reflection coefficients as a function of incidence angle of the initial plane wave. A numerical example demonstrates the effectiveness of removing multiples from the data and constructing an image free of effects of such internal multiple reflections.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125840669","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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