X

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Society of Exploration Geophysicists  (12)
  • 1
    Online Resource
    Online Resource
    Review of crosshole ground-penetrating radar full-waveform inversion of experimental data: Recent developments, challenges, and pitfalls
    Society of Exploration Geophysicists ; 2019
    In:  GEOPHYSICS Vol. 84, No. 6 ( 2019-11-01), p. H13-H28
    Details
    In: GEOPHYSICS, Society of Exploration Geophysicists, Vol. 84, No. 6 ( 2019-11-01), p. H13-H28
    Abstract: Heterogeneous small-scale high-contrast layers and spatial variabilities of soil properties can have a large impact on flow and transport processes in the critical zone. Because their characterization is difficult and critical, high-resolution methods are required. Standard ray-based approaches for imaging the subsurface consider only a small amount of the measured data and suffer from limited resolution. In contrast, full-waveform inversion (FWI) considers the full information content of the measured data and could yield higher resolution images in the subwavelength scale. In the past few decades, ground-penetrating radar (GPR) FWI and its application to experimental data have matured, which makes GPR FWI an established approach to significantly improve resolution. Several theoretical developments were achieved to improve the application to experimental data from crosshole GPR FWI. We have determined the necessary steps to perform FWI for experimental data to obtain reliable and reproducible high-resolution images. We concentrate on experimental crosshole GPR data from a test site in Switzerland to illustrate the challenges of applying FWI to experimental data and discuss the obtained results for different development steps including possible pitfalls. Thereby, we acknowledge out the importance of a correct time-zero correction of the data, the estimation of the effective source wavelet, and the effect of the choice of starting models. The reliability of the FWI results is investigated by analyzing the fit of the measured and modeled traces, the remaining gradients of the final models, and validating with independently measured logging data. Thereby, we found that special care needs to be taken to define the optimal inversion parameters to avoid overshooting of the inversion or truncation errors.
    Type of Medium: Online Resource
    ISSN: 0016-8033 , 1942-2156
    URL: Article
    DOI: 10.1190/geo2018-0597.1
    RVK:
    UA 4068.4
    Language: English
    Publisher: Society of Exploration Geophysicists
    Publication Date: 2019
    detail.hit.zdb_id: 2033021-2
    detail.hit.zdb_id: 2184-2
    SSG: 16,13
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Online Resource
    Open Access Request
    Availability (electronic / print)
  • 2
    Online Resource
    Online Resource
    Crosshole GPR full-waveform inversion of waveguides acting as preferential flow paths within aquifer systems
    Society of Exploration Geophysicists ; 2012
    In:  GEOPHYSICS Vol. 77, No. 4 ( 2012-07-01), p. H57-H62
    Details
    In: GEOPHYSICS, Society of Exploration Geophysicists, Vol. 77, No. 4 ( 2012-07-01), p. H57-H62
    Abstract: High-contrast layers caused by porosity or clay content changes can have a dominant effect on hydraulic processes within an aquifer. These layers can act as low-velocity waveguides for GPR waves. We used a field example from a hydrological test site in Switzerland to show that full-waveform inversion of crosshole GPR signals could image a subwavelength thickness low-velocity waveguiding layer. We exploited the full information content of the data, whereas ray-based inversion techniques are not able to image such thin waveguide layers because they only exploit the first-arrival times and first-cycle amplitudes. This low-velocity waveguide layer is caused by an increase in porosity and indicates a preferential flow path within the aquifer. The waveguide trapping causes anomalously high amplitudes and elongated wavetrains to be observed for a transmitter within the waveguide and receivers straddling the waveguide depth range. The excellent fit of amplitudes and phase between the measured and modeled data confirms its presence. This new method enables detailed aquifer characterization to accurately predict transport and flow and can be applied to a wide range of geologic, hydrological, and engineering investigations.
    Type of Medium: Online Resource
    ISSN: 0016-8033 , 1942-2156
    URL: Article
    DOI: 10.1190/geo2011-0458.1
    RVK:
    UA 4068.4
    Language: English
    Publisher: Society of Exploration Geophysicists
    Publication Date: 2012
    detail.hit.zdb_id: 2033021-2
    detail.hit.zdb_id: 2184-2
    SSG: 16,13
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Online Resource
    Open Access Request
    Availability (electronic / print)
  • 3
    Online Resource
    Online Resource
    Evaluation of starting model approaches and effective source wavelet variations for high-frequency ground-penetrating radar full-waveform inversion
    Society of Exploration Geophysicists ; 2023
    In:  GEOPHYSICS Vol. 88, No. 2 ( 2023-03-01), p. KS27-KS45
    Details
    In: GEOPHYSICS, Society of Exploration Geophysicists, Vol. 88, No. 2 ( 2023-03-01), p. KS27-KS45
    Abstract: High-frequency ground-penetrating radar (GPR) full-waveform inversion (FWI) can enhance the characterization of small-scale structures in the subsurface below the decimeter scale. We have investigated the potential and requirements to use FWI for higher-frequency data. Thereby, we focus on the two most important criteria to achieve reliable FWI results: adequate starting models that fulfill the half-wavelength criterion and the accuracy of the effective source wavelet. Therefore, we have defined a realistic reference model, generated synthetic GPR data sets (200, 450, and 700 MHz), and tested different standard ray-based starting model methods and frequency-hopping approaches to derive results close to our reference model. Although standard starting models provide good parameter reconstruction for lower-frequency data, a frequency-hopping approach is required for the 700 MHz data. In addition, we have seen that the reconstruction of the conductivity results is more sensitive to the presence of noise (25 dB) than the permittivity tomograms. The definition of the effective source wavelets is directly linked to the accuracy of the starting models; therefore, we investigate the effect on the FWI results for high-frequency data by varying the source wavelets in terms of starting time and/or amplitude. Considering the multiparameter nature of FWI, we observe that time shifts have a greater influence on the performance of the FWI than amplitude variations. Large time shifts of approximately 0.1 ns for the 700 MHz data may lead to the failure of the inversion, whereas amplitude variations (±5% of the maximum amplitude) affect the quantitative conductivity results only (no effect on permittivity) with an increased root-mean-square error of the data of up to 20%. Using a stochastically perturbed synthetic model, we determine an improved parameter reconstruction for higher frequencies. On the basis of our findings, we develop a workflow to obtain reliable results for high-frequency GPR FWI for future users.
    Type of Medium: Online Resource
    ISSN: 0016-8033 , 1942-2156
    URL: Article
    DOI: 10.1190/geo2021-0683.1
    RVK:
    UA 4068.4
    Language: English
    Publisher: Society of Exploration Geophysicists
    Publication Date: 2023
    detail.hit.zdb_id: 2033021-2
    detail.hit.zdb_id: 2184-2
    SSG: 16,13
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Online Resource
    Open Access Request
    Availability (electronic / print)
  • 4
    Online Resource
    Online Resource
    Efficient loop antenna modeling for zero-offset, off-ground electromagnetic induction in multilayered media
    Society of Exploration Geophysicists ; 2010
    In:  GEOPHYSICS Vol. 75, No. 4 ( 2010-07), p. WA125-WA134
    Details
    In: GEOPHYSICS, Society of Exploration Geophysicists, Vol. 75, No. 4 ( 2010-07), p. WA125-WA134
    Abstract: Retrieval of the subsurface electrical properties from electromagnetic induction (EMI) data using inverse modeling relies in particular on the accuracy of the considered EMI model. We have developed a new EMI approach whereby a zero-offset, off-ground loop antenna is efficiently modeled using frequency-dependent, complex linear transfer functions and the air subsurface is described by a Green’s function for wave propagation in 3D multilayered media. To ensure proper calibration of the system, vector network analyzer (VNA) technology is used as the transmitter and receiver. An optimal integration path is proposed for fast evaluation of the spatial Green’s function from its spectral counterpart. We validated the antenna model in laboratory conditions with measurements performed with a loop antenna in free space and at different heights above a perfect electrical conductor. Provided that the loop antenna is high enough above the reflector (off-ground condition), the measured and modeled Green’s functions agreed remarkably well. In addition, inversion of the EMI data resulted in accurate estimates of the antenna heights. Yet, as expected, signal-to-noise-ratio issues occurred for the higher antenna heights and frequencies away from the loop resonant frequency. The method appears to be promising for accurate and robust soil characterization, but needs high VNA dynamic range and antenna gain.
    Type of Medium: Online Resource
    ISSN: 0016-8033 , 1942-2156
    URL: Article
    DOI: 10.1190/1.3467936
    RVK:
    UA 4068.4
    Language: English
    Publisher: Society of Exploration Geophysicists
    Publication Date: 2010
    detail.hit.zdb_id: 2033021-2
    detail.hit.zdb_id: 2184-2
    SSG: 16,13
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Online Resource
    Open Access Request
    Availability (electronic / print)
  • 5
    Online Resource
    Online Resource
    Characterization of bimodal facies distributions using effective anisotropic complex resistivity: A 2D numerical study based on Cole-Cole models
    Society of Exploration Geophysicists ; 2009
    In:  GEOPHYSICS Vol. 74, No. 3 ( 2009-05), p. A19-A22
    Details
    In: GEOPHYSICS, Society of Exploration Geophysicists, Vol. 74, No. 3 ( 2009-05), p. A19-A22
    Abstract: Subsurface heterogeneity characteristics are of major importance in hydrologic modeling, and likely result in anisotropic electrical properties. We computed the anisotropic effective complex resistivity of 2D bimodal facies distributions numerically. Complex resistivities of individual facies are described in terms of the Cole-Cole relaxation model. First, we determined that effective DC resistivities of the distributions can be reasonably well described by power averaging the properties of individual facies. We found a clear relationship between the mixing parameter and correlation lengths of the facies distributions with respect to horizontal and vertical directions. Then, we used the power-law mixing model to invert for individual Cole-Cole model parameters by fitting predicted electrical responses to simulated spectral effective complex-resistivity data for the two perpendicular directions. Thus, it is possible to derive the electrical properties of individual facies as well as structural parameters describing bimodal facies distribution by means of a noninvasive measurement approach. In particular, anisotropy of the spectral complex-resistivity response provides information on correlation lengths of the distribution. This finding is relevant for all applications of electrical-impedance spectroscopy where anisotropy might be encountered.
    Type of Medium: Online Resource
    ISSN: 0016-8033 , 1942-2156
    URL: Article
    DOI: 10.1190/1.3113986
    RVK:
    UA 4068.4
    Language: English
    Publisher: Society of Exploration Geophysicists
    Publication Date: 2009
    detail.hit.zdb_id: 2033021-2
    detail.hit.zdb_id: 2184-2
    SSG: 16,13
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Online Resource
    Open Access Request
    Availability (electronic / print)
  • 6
    Online Resource
    Online Resource
    Accounting for soil surface roughness in the inversion of ultrawideband off-ground GPR signal for soil moisture retrieval
    Society of Exploration Geophysicists ; 2012
    In:  GEOPHYSICS Vol. 77, No. 1 ( 2012-01), p. H1-H7
    Details
    In: GEOPHYSICS, Society of Exploration Geophysicists, Vol. 77, No. 1 ( 2012-01), p. H1-H7
    Abstract: We combined a full-waveform ground-penetrating radar (GPR) model with a roughness model to retrieve surface soil moisture through signal inversion. The proposed approach was validated under laboratory conditions with measurements performed above a sand layer subjected to seven different water contents and four different surface roughness conditions. The radar measurements were performed in the frequency domain in the range of 1–3 GHz and the roughness amplitude standard deviation was varied from 0 to 1 cm. Two inversion strategies were investigated: (1) Full-waveform inversion using the correct model configuration, and (2) inversion focused on the surface reflection only. The roughness model provided a good description of the frequency-dependent roughness effect. For the full-waveform analysis, accounting for roughness permitted us to simultaneously retrieve water content and roughness amplitude. However, in this approach, information on soil layering was assumed to be known. For the surface reflection analysis, which is applicable under field conditions, accounting for roughness only enabled water content to be reconstructed, but with a root mean square error (RMS) in terms of water content of [Formula: see text] compared to an RMS of [Formula: see text] for an analysis where roughness is neglected. However, this inversion strategy required a priori information on soil surface roughness, estimated, e.g., from laser profiler measurements.
    Type of Medium: Online Resource
    ISSN: 0016-8033 , 1942-2156
    URL: Article
    DOI: 10.1190/geo2011-0054.1
    RVK:
    UA 4068.4
    Language: English
    Publisher: Society of Exploration Geophysicists
    Publication Date: 2012
    detail.hit.zdb_id: 2033021-2
    detail.hit.zdb_id: 2184-2
    SSG: 16,13
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Online Resource
    Open Access Request
    Availability (electronic / print)
  • 7
    Online Resource
    Online Resource
    2.5D crosshole GPR full-waveform inversion with synthetic and measured data
    Society of Exploration Geophysicists ; 2020
    In:  GEOPHYSICS Vol. 85, No. 4 ( 2020-07-01), p. H71-H82
    Details
    In: GEOPHYSICS, Society of Exploration Geophysicists, Vol. 85, No. 4 ( 2020-07-01), p. H71-H82
    Abstract: Full-waveform inversion (FWI) of cross-borehole ground-penetrating radar (GPR) data is a technique with the potential to investigate subsurface structures. Typical FWI applications transform 3D measurements into a 2D domain via an asymptotic 3D to 2D data transformation, widely known as a Bleistein filter. Despite the broad use of such a transformation, it requires some assumptions that make it prone to errors. Although the existence of the errors is known, previous studies have failed to quantify the inaccuracies introduced on permittivity and electrical conductivity estimation. Based on a comparison of 3D and 2D modeling, errors could reach up to 30% of the original amplitudes in layered structures with high-contrast zones. These inaccuracies can significantly affect the performance of crosshole GPR FWI in estimating permittivity and especially electrical conductivity. We have addressed these potential inaccuracies by introducing a novel 2.5D crosshole GPR FWI that uses a 3D finite-difference time-domain forward solver (gprMax3D). This allows us to model GPR data in 3D, whereas carrying out FWI in the 2D plane. Synthetic results showed that 2.5D crosshole GPR FWI outperformed 2D FWI by achieving higher resolution and lower average errors for permittivity and conductivity models. The average model errors in the whole domain were reduced by approximately 2% for permittivity and conductivity, whereas zone-specific errors in high-contrast layers were reduced by approximately 20%. We verified our approach using crosshole 2.5D FWI measured data, and the results showed good agreement with previous 2D FWI results and geologic studies. Moreover, we analyzed various approaches and found an adequate trade-off between computational complexity and accuracy of the results, i.e., reducing the computational effort while maintaining the superior performance of our 2.5D FWI scheme.
    Type of Medium: Online Resource
    ISSN: 0016-8033 , 1942-2156
    URL: Article
    DOI: 10.1190/geo2019-0600.1
    RVK:
    UA 4068.4
    Language: English
    Publisher: Society of Exploration Geophysicists
    Publication Date: 2020
    detail.hit.zdb_id: 2033021-2
    detail.hit.zdb_id: 2184-2
    SSG: 16,13
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Online Resource
    Open Access Request
    Availability (electronic / print)
  • 8
    Online Resource
    Online Resource
    Radius estimation of subsurface cylindrical objects from ground-penetrating-radar data using full-waveform inversion
    Society of Exploration Geophysicists ; 2018
    In:  GEOPHYSICS Vol. 83, No. 6 ( 2018-11-01), p. H43-H54
    Details
    In: GEOPHYSICS, Society of Exploration Geophysicists, Vol. 83, No. 6 ( 2018-11-01), p. H43-H54
    Abstract: Ray-based radius estimations of subsurface cylindrical objects such as rebars and pipes from ground-penetrating-radar (GPR) measurements are not accurate because of their approximations. We have developed a novel full-waveform inversion (FWI) approach that uses a full-waveform 3D finite-difference time-domain (FDTD) forward-modeling program to estimate the radius including other object parameters. By using the full waveform of the common-offset GPR data, the shuffled complex evolution (SCE) approach is able to reliably extract the radius of the subsurface cylindrical objects. A combined optimization of radius, medium properties, and the effective source wavelet is necessary. Synthetic and experimental data inversion returns an accurate reconstruction of the cylinder properties, medium properties, and the effective source wavelet. Combining FWI of GPR data using SCE and a 3D FDTD forward model makes the approach easily adaptable for a wide range of other GPR FWI approaches.
    Type of Medium: Online Resource
    ISSN: 0016-8033 , 1942-2156
    URL: Article
    DOI: 10.1190/geo2017-0815.1
    RVK:
    UA 4068.4
    Language: English
    Publisher: Society of Exploration Geophysicists
    Publication Date: 2018
    detail.hit.zdb_id: 2033021-2
    detail.hit.zdb_id: 2184-2
    SSG: 16,13
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Online Resource
    Open Access Request
    Availability (electronic / print)
  • 9
    Online Resource
    Online Resource
    Simultaneous calibration and inversion algorithm for multiconfiguration electromagnetic induction data acquired at multiple elevations
    Society of Exploration Geophysicists ; 2019
    In:  GEOPHYSICS Vol. 84, No. 1 ( 2019-01-01), p. EN1-EN14
    Details
    In: GEOPHYSICS, Society of Exploration Geophysicists, Vol. 84, No. 1 ( 2019-01-01), p. EN1-EN14
    Abstract: Electromagnetic induction (EMI) is a contactless and fast geophysical measurement technique. Frequency-domain EMI systems are available as portable rigid booms with fixed separations up to approximately 4 m between the transmitter and the receivers. These EMI systems are often used for high-resolution characterization of the upper subsurface meters (up to depths of approximately 1.5 times the maximum coil separation). The availability of multiconfiguration EMI systems, which measure multiple apparent electrical conductivity ([Formula: see text]) values of different but overlapping soil volumes, enables EMI data inversions to estimate electrical conductivity ([Formula: see text] ) changes with depth. However, most EMI systems currently do not provide absolute [Formula: see text] values, but erroneous shifts occur due to calibration problems, which hinder a reliable inversion of the data. Instead of using physical soil data or additional methods to calibrate the EMI data, we have used an efficient and accurate simultaneous calibration and inversion approach to avoid a possible bias of other methods while reducing the acquisition time for the calibration. By measuring at multiple elevations above the ground surface using a multiconfiguration EMI system, we simultaneously obtain multiplicative and additive calibration factors for each coil configuration plus an inverted layered subsurface electrical conductivity model at the measuring location. Using synthetic data, we verify our approach. Experimental data from five different calibration positions along a transect line showed similar calibration results as the data obtained by more elaborate vertical electrical sounding reference measurements. The synthetic and experimental results demonstrate that the multielevation calibration and inversion approach is a promising tool for quantitative electrical conductivity analyses.
    Type of Medium: Online Resource
    ISSN: 0016-8033 , 1942-2156
    URL: Article
    DOI: 10.1190/geo2018-0264.1
    RVK:
    UA 4068.4
    Language: English
    Publisher: Society of Exploration Geophysicists
    Publication Date: 2019
    detail.hit.zdb_id: 2033021-2
    detail.hit.zdb_id: 2184-2
    SSG: 16,13
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Online Resource
    Open Access Request
    Availability (electronic / print)
  • 10
    Online Resource
    Online Resource
    Quantitative conductivity and permittivity estimation using full-waveform inversion of on-ground GPR data
    Society of Exploration Geophysicists ; 2012
    In:  GEOPHYSICS Vol. 77, No. 6 ( 2012-11-01), p. H79-H91
    Details
    In: GEOPHYSICS, Society of Exploration Geophysicists, Vol. 77, No. 6 ( 2012-11-01), p. H79-H91
    Abstract: Conventional ray-based techniques for analyzing common-midpoint (CMP) ground-penetrating radar (GPR) data use part of the measured data and simplified approximations of the reality to return qualitative results with limited spatial resolution. Whereas these methods can give reliable values for the permittivity of the subsurface by employing only the phase information, the far-field approximations used to estimate the conductivity of the ground are not valid for near-surface on-ground GPR, such that the estimated conductivity values are not representative for the area of investigation. Full-waveform inversion overcomes these limitations by using an accurate forward modeling and inverts significant parts of the measured data to return reliable quantitative estimates of permittivity and conductivity. Here, we developed a full-waveform inversion scheme that uses a 3D frequency-domain solution of Maxwell’s equations for a horizontally layered subsurface. Although a straightforward full-waveform inversion is relatively independent of the permittivity starting model, inaccuracies in the conductivity starting model result in erroneous effective wavelet amplitudes and therefore in erroneous inversion results, because the conductivity and wavelet amplitudes are coupled. Therefore, the permittivity and conductivity are updated together with the phase and the amplitude of the source wavelet with a gradient-free optimization approach. This novel full-waveform inversion is applied to synthetic and measured CMP data. In the case of synthetic single layered and waveguide data, where the starting model differs significantly from the true model parameter, we were able to reconstruct the obtained model properties and the effective source wavelet. For measured waveguide data, different starting values returned the same wavelet and quantitative permittivities and conductivities. This novel approach enables the quantitative estimation of permittivity and conductivity for the same sensing volume and enables an improved characterization for a wide range of applications.
    Type of Medium: Online Resource
    ISSN: 0016-8033 , 1942-2156
    URL: Article
    DOI: 10.1190/geo2012-0045.1
    RVK:
    UA 4068.4
    Language: English
    Publisher: Society of Exploration Geophysicists
    Publication Date: 2012
    detail.hit.zdb_id: 2033021-2
    detail.hit.zdb_id: 2184-2
    SSG: 16,13
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Online Resource
    Open Access Request
    Availability (electronic / print)
Nothing or not found what you are looking for? Please check your search query or use the Interlibrary Loan Search.
Close ⊗
This website uses cookies and the analysis tool Matomo. Further information can be found on the KOBV privacy pages