| 1. |
- Cassiani, Giorgio, et al.
(författare)
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Ground-based remote sensing of the shallow subsurface : Geophysical methods for environmental applications
- 2020
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Ingår i: Remote Sensing of Geomorphology. - 0928-2025. - 9780444641779 - 9780444641786 ; 23, s. 55-89
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Bokkapitel (refereegranskat)abstract
- Noninvasive methods for the characterization of shallow subsurface have been used routinely for some 20–30 years. The growth in these methods has been driven by a variety of breakthroughs in the use of electrical, electromagnetic, and seismic methods, to mention only the most common techniques. Increasing field capabilities and computational power have yet to yield all their potential fruits. In this chapter, we introduce readers to the basic concepts of shallow subsurface methods. We guide them through some of the physical details and present a number of application examples all derived from our own experience, concerning both structural characterization and (fluid)-dynamic understanding of the shallow subsurface. Finally, we propose ideas concerning the future development of this wide and exciting discipline.
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| 2. |
- Rossi, Matteo, et al.
(författare)
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Assessment of Distributed Acoustic Sensing (DAS) performance for geotechnical applications
- 2022
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Ingår i: Engineering Geology. - : Elsevier BV. - 0013-7952. ; 306
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Tidskriftsartikel (refereegranskat)abstract
- Distributed Acoustic Sensing (DAS) is a recent technology that acquires acoustic vibrations via fiber optics sensors. The utilization of such technique for near-surface geotechnical applications has great potential, especially for the characterization and verification of artificially stabilized ground. A popular procedure to stabilize the superficial ground (for example, for the preparation of infrastructure subgrade) is the blend of the natural shallower layer with a binder (lime and/or cement). Quality control is required when the binder hardens, and acoustic surveys are an option for non-invasive and non-destructive testing. Relevant parameters to validate the effectiveness of the stabilization procedure are the mechanical properties of the materials. The distribution of shear-wave velocities in the ground is a critical parameter for the geotechnical characterization, since it depends directly on the shear-modulus of the media. The present experiment verifies the applicability of DAS technology in such geotechnical contexts, which can be representative of a wide range of utilizations, spanning, for example, from road and pavement design to building constructions. The discussed test focuses on the spectral content of the acquired signal and on the estimation of the shear-wave distribution, and compares the DAS responses against signals measured during more traditional seismic surveys using standard geophones. Despite the inevitable differences between the datasets collected with the different techniques, all the reconstructed shear-wave velocity profiles effectively identify the stabilized soil layer. Also for this reason, one of the main conclusions is that, for geotechnical characterizations, DAS can be a convenient non-invasive alternative to more standard approaches.
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| 3. |
- Vignoli, Giulio, et al.
(författare)
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Reconstruction, with tunable sparsity levels, of shear wave velocity profiles from surface wave data
- 2021
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Ingår i: Geophysical Journal International. - : Oxford University Press (OUP). - 0956-540X .- 1365-246X. ; 225:3, s. 1935-1951
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Tidskriftsartikel (refereegranskat)abstract
- The analysis of surface wave dispersion curves is a way to infer the vertical distribution of shear wave velocity. The range of applicability is extremely wide: going, for example, from seismological studies to geotechnical characterizations and exploration geophysics. However, the inversion of the dispersion curves is severely ill-posed and only limited efforts have been put in the development of effective regularization strategies. In particular, relatively simple smoothing regularization terms are commonly used, even when this is in contrast with the expected features of the investigated targets. To tackle this problem, stochastic approaches can be utilized, but they are too computationally expensive to be practical, at least, in case of large surveys. Instead, within a deterministic framework, we evaluate the applicability of a regularizer capable of providing reconstructions characterized by tunable levels of sparsity. This adjustable stabilizer is based on the minimum support regularization, applied before on other kinds of geophysical measurements, but never on surface wave data. We demonstrate the effectiveness of this stabilizer on (i) two benchmark—publicly available—data sets at crustal and near-surface scales and (ii) an experimental data set collected on a well-characterized site. In addition, we discuss a possible strategy for the estimation of the depth of investigation. This strategy relies on the integrated sensitivity kernel used for the inversion and calculated for each individual propagation mode. Moreover, we discuss the reliability, and possible caveats, of the direct interpretation of this particular estimation of the depth of investigation, especially in the presence of sharp boundary reconstructions.
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| 4. |
- Zaru, Nicola, et al.
(författare)
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(Pseudo-)3D Inversion of Geophysical Electromagnetic Induction Data by Using an Arbitrary Prior and Constrained to Ancillary Information
- 2023
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Ingår i: Computational Science and Its Applications – ICCSA 2023 Workshops, Proceedings. - 1611-3349 .- 0302-9743. - 9783031371257 ; 14111 LNCS, s. 624-638
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Konferensbidrag (refereegranskat)abstract
- Electromagnetic induction (EMI) methods are often used to map rapidly large areas with minimal logistical efforts. However, they are limited by a small number of frequencies and by their severe ill-posedness. On the other hand, electrical resistivity tomography (ERT) results are generally considered more reliable, with no need for specific calibration procedures and easy 2D/3D inversion. Still, ERT surveys are definitely more time-consuming, and, ideally, an approach with the advantages of both EMI and ERT would be optimal. The present research addresses this issue by incorporating realistic constraints into EMI inversion, going beyond simplistic spatial constraints like smooth or sharp regularization terms, while taking into consideration the ancillary information already available about the investigated site. We demonstrate how additional pre-existing information, such as a reference model (i.e., an existing ERT section) can enhance the EMI inversion. The study verifies the results against observations from boreholes.
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| 5. |
- Zaru, Nicola, et al.
(författare)
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Spreading of Localized Information across an Entire 3D Electrical Resistivity Volume via Constrained EMI Inversion Based on a Realistic Prior Distribution
- 2023
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Ingår i: Remote Sensing. - 2072-4292. ; 15:16
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Tidskriftsartikel (refereegranskat)abstract
- Frequency-domain electromagnetic induction (EMI) methods are commonly used to map vast areas quickly and with minimum logistical efforts. Unfortunately, they are often characterized by a very limited number of frequencies and severe ill-posedness. On the other hand, electrical resistivity tomography (ERT) approaches are usually considered more reliable; for example, they do not require specific calibration procedures and can be easily inverted in 2D/3D. However, ERT surveys are, by far, more demanding and time consuming, allowing for the deployment of a few acquisition lines per day. Ideally, the optimal would be to have the advantages of both approaches: ease of acquisition while keeping robustness and reliability. The present work raises from the necessity to cope with this issue and from the importance of enforcing realistic constraints to the data inversion without being limited to (over)simplistic spatial constraints (for example, characterizing the smooth and/or sharp regularization). Accordingly, the present research demonstrates, by means of synthetic and field data, how the EMI inversion—based on realistic prior models—can be further enhanced by incorporating additional pre-existing pieces of information. While the proposed scheme is quite general, in the specific examples discussed here, these additional pieces of information are, respectively, a reference model along a line across the survey area, and an ERT section. The field EMI results were verified against extensive ground penetrating radar (GPR) measurements and boreholes.
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