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124 results on '"Vignoli, G."'

2. Focusing inversion technique applied to radar tomographic data

Author

Vignoli, G. and Zanzi, L.

Subjects
Physics - Geophysics, Physics - Computational Physics
Abstract

Traveltime tomography is a very effective tool to reconstruct acoustic, seismic or electromagnetic wave speed distribution. To infer the velocity image of the medium from the measurements of first arrivals is a typical example of ill-posed problem. In the framework of Tikhonov regularization theory, in order to replace an ill-posed problem by a well-posed one and to get a unique and stable solution, a stabilizing functional (stabilizer) has to be introduced. The stabilizer selects the desired solution from a class of solutions with a specific physical and/or geometrical property; e.g., the existence of sharp boundaries separating media with different petrophysical parameters. Usually stabilizers based on maximum smoothness criteria are used during the inversion process; in these cases the solutions provide smooth images which, in many situations, do not describe the examined objects properly. Recently a new algorithm of direct minimization of the Tikhonov parametric functional with minimum support stabilizer has been introduced; it produces clear and focused images of targets with sharp boundaries. In this research we apply this new technique to real radar tomographic data and we compare the obtained result with the solution generated by the more traditional minimum norm stabilizer., Comment: 4 pages, 1 figure

Published
2006

3. Focusing inversion techniques applied to electrical resistance tomography in an experimental tank

Author

Pagliara, G. and Vignoli, G.

Subjects
Physics - Geophysics
Abstract

We present an algorithm for focusing inversion of electrical resistivity tomography (ERT) data. ERT is a typical example of ill-posed problem. Regularization is the most common way to face this kind of problems; it basically consists in using a priori information about targets to reduce the ambiguity and the instability of the solution. By using the minimum gradient support (MGS) stabilizing functional, we introduce the following geometrical prior information in the reconstruction process: anomalies have sharp boundaries. The presented work is embedded in a project (L.A.R.A.) which aims at the estimation of hydrogeological properties from geophysical investigations. L.A.R.A. facilities include a simulation tank (4 m x 8 m x 1.35 m); 160 electrodes are located all around the tank and used for 3-D ERT. Because of the large number of electrodes and their dimensions, it is important to model their effect in order to correctly evaluate the electrical system response. The forward modelling in the presented algorithm is based on the so-called complete electrode model that takes into account the presence of the electrodes and their contact impedances. In this paper, we compare the results obtained with different regularizing functionals applied on a synthetic model., Comment: 4 pages, 7 figures, to appear in the Proceedings of Int. Assoc. for Mathematical Geology XI International Congress

Published
2006

9. (Quasi-)real-time inversion of airborne time-domain electromagnetic data via artificial neural network

Author

Bai, P. (Peng), Vignoli, G. (Giulio), Viezzoli, A. (Andrea), Nevalainen, J. (Jouni), Vacca, G. (Giuseppina), Bai, P. (Peng), Vignoli, G. (Giulio), Viezzoli, A. (Andrea), Nevalainen, J. (Jouni), and Vacca, G. (Giuseppina)

Abstract

The possibility to have results very quickly after, or even during, the collection of electromagnetic data would be important, not only for quality check purposes, but also for adjusting the location of the proposed flight lines during an airborne time-domain acquisition. This kind of readiness could have a large impact in terms of optimization of the Value of Information of the measurements to be acquired. In addition, the importance of having fast tools for retrieving resistivity models from airborne time-domain data is demonstrated by the fact that Conductivity-Depth Imaging methodologies are still the standard in mineral exploration. In fact, they are extremely computationally efficient, and, at the same time, they preserve a very high lateral resolution. For these reasons, they are often preferred to inversion strategies even if the latter approaches are generally more accurate in terms of proper reconstruction of the depth of the targets and of reliable retrieval of true resistivity values of the subsurface. In this research, we discuss a novel approach, based on neural network techniques, capable of retrieving resistivity models with a quality comparable with the inversion strategy, but in a fraction of the time. We demonstrate the advantages of the proposed novel approach on synthetic and field datasets.

Published
2020

16. Caratterizzazione del sito test di Turriaco mediante metodologie geofisiche integrate

Author

Gervasio, Isabella, Brancatelli, Giuseppe, DELLA VEDOVA, Bruno, Boaga, J., Vignoli, G., Cassiani, Giorgio, Forte, Emanuele, Dazzan, Enrico, Slejko D. e Rebez A., Gervasio, Isabella, Brancatelli, Giuseppe, DELLA VEDOVA, Bruno, Boaga, J., Vignoli, G., Cassiani, Giorgio, Forte, Emanuele, and Dazzan, Enrico

Subjects
Caratterizzazione terrazzi fluviali, Piezometri e campo di moto, Georadar GPR, Area golenale Isonzo, Tomografia elettrica in resistività, sismica onde superficiali MOPA
Published
2011

18. Toward participatory decision-making in river corridor management: two case studies from the European Alps.

Author

Mazzorana, B., Nardini, A., Comiti, F., Vignoli, G., Cook, E., Ulloa, H., and Iroumé, A.

Subjects
RIVERS, STREAM restoration, COMMUNITY involvement, SUSTAINABILITY, ENVIRONMENTAL protection planning, FLOODPLAINS, MANAGEMENT
Abstract

River managers are aware that river restoration entails addressing and effectively solving wicked social-ecological problems. Contemporary river corridor management is characterized by a variety of actors with different perspectives and interests, and by complex institutional settings and legal landscapes. Additionally, at the intersection between litho-, hydro-, and biological fields, new research suggests that river restoration should reactivate matter and energy fluxes, re-establish spatial connections with the floodplains, and enhance aquatic and terrestrial habitats without exacerbating flood risk. First, we outline a general structure of participatory river corridor management that addresses the following key requirements: (1) unambiguous, participatory spatial delineation of the river corridor; (2) comprehensive assessment of the river corridor's hydro-geomorphological, ecological, socio-economic and cultural processes; (3) transparency and consistency of the decision-making process; as well as (4) a coherent envisioning process. Subsequently, we present an overview of two river corridor management processes, conducted in South Tyrol, Italy. Specifically, we analysed the Etsch/Adige River corridor between Laas/Lasa and Glurns/Glorenza in the Upper Vinschgau/Venosta valley characterized by intense agricultural land use and the densely populated Eisack/Isarco River corridor in Brixen/Bressanone. Based on structured interviews with project managers, we highlight strengths and shortcomings of the proposed participatory management and envisage procedural improvements. [ABSTRACT FROM AUTHOR]

Published
2018
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21. A COMPARISON BETWEEN ZERO-OFFSET AND VERTICAL RADAR PROFILING GPR TECHNIQUES WITH EMPHASIS ON PROBLEMATIC BOREHOLE EFFECTS

Author

Rossi, Matteo, Vignoli, G., Cassiani, Giorgio, and Deiana, Rita

Abstract

Non-invasive geophysical techniques are increasingly used to study the unsaturated zone. In particular, cross-hole methods can are able to infer more detailed information about the subsoil than surface measurements. Two borehole Ground Penetrating Radar (GPR) techniques are discussed in our contribution: Zero-Offset Profiling (ZOP) and Vertical Radar Profiling (VRP). We make a direct comparison of these methods in a field case (Trecate site, Northern Italy), to explore each method’s capabilities and limitations. Our analysis is focused on the results in the vadose zone and shows that the dielectric relative permittivity profiles recovered from ZOP and VRP first-break inversions are in strong disagreement, providing very different permittivity profiles. The analysis of synthetic radargrams shows the presence of an electromagnetic (EM) wave established by the joint presence of the air-filled borehole within a higher permittivity surrounding soil. This event has a velocity intermediate between the soil and air speed values, and interferes with the picking of first arrivals in the VRP mode. The numerical simulations are performed with different borehole diameters, confirming that the velocity of the first recorded event depends on the ratio between the wave length in air and the finite dimension of the borehole. Once these arrivals in the simulated VRP radargrams are recognized, their contribution can be removed by picking the “direct”ù arrivals, that correspond to the waves that directly propagates from source to receiver, through the unsaturated zone. Once the borehole effects are accounted for, the comparison between the ZOP and VRP permittivity profiles is reasonable and reveals the different resolution of these techniques, focusing on the information that can be inferred for hydrological characterizations. Thus, VRP surveys in vadose zone must be accurately interpreted, as the electromagnetic waves may propagate via guided modes along the borehole. Neglecting this phenomenon might generate misleading estimations of geophysical properties and the subsequently translation in hydrological quantities could leads to erroneous physical states; a very relevant issue in hydrological model calibration.

Published
2012

28. Geophysical monitoring of soil static and dynamic characteristics

Author

Deiana, Rita, Cassiani, Giorgio, Vignoli, G., Boaga, Jacopo, Ursino, Nadia, Blaschek, M., Duttmann, R., Meyer, S., Ludwig, R., Soddu, A., Dietrich, P., and Werban, U.

Subjects
soil properties, hydrological modeling, GEOPHYSICAL DATA
Published
2011

34. Hydro-geophysics for hillslope hydrology

Author

Cassiani, Giorgio, Deiana, Rita, Boaga, Jacopo, Vignoli, G., Rossi, M., Marani, Marco, Putti, Mario, Altissimo, M., Bellin, A., and Cainelli, O.

Published
2010

36. Indagini geofisiche integrate per la caratterizzazione di un sito costiero inquinato (Muggia - TS)

Author

Dazzan, Enrico, DELLA VEDOVA, Bruno, Gervasio, I., Deiana, R., Cassiani, G., Vignoli, G., Slejko D., A. Riggio, Dazzan, Enrico, DELLA VEDOVA, Bruno, I., Gervasio, R., Deiana, G., Cassiani, and G., Vignoli

Subjects
sondaggi ambientali, tomografia elettrica di resistività, indagini geofisiche integrate, CAratterizzazione ambientale, piezometri, sito inquinato costiero, ERT terra-mare
Published
2010

41. Noninvasive monitoring of soil static characteristics and dynamic states: a case study highlighting vegetation effects on agricultural land

Author

Cassiani, G., Ursino, N., Deiana, R., Vignoli, G., Boaga, J., Rossi, M., Perri, M.T., Blaschek, M., Duttmann, R., Meyer, S., Ludwig, R., Soddu, A., Dietrich, Peter, Werban, Ulrike, Cassiani, G., Ursino, N., Deiana, R., Vignoli, G., Boaga, J., Rossi, M., Perri, M.T., Blaschek, M., Duttmann, R., Meyer, S., Ludwig, R., Soddu, A., Dietrich, Peter, and Werban, Ulrike

Published
2012

44. ADER scheme for the shallow water equations in channel with irregular bottom elevation

Author

Vignoli, G. (author), Toro, E.F. (author), Titarev, V. (author), Vignoli, G. (author), Toro, E.F. (author), and Titarev, V. (author)

Abstract

In this paper we develop one dimensional non-linear ADER schemes for the shallow water system with source terms. In contrast to conventional schemes we adopt a formulation given in terms of the free surface elevation and water discharge. Data reconstruction is performed using ENO polynomials both for the conservative variables and for the bottom elevation. The scheme is accurate up to forth order both in time and in space; essentially non-oscillatory results are obtained for discontinuous solutions both for the steady and unsteady case. The resulting numerical schemes can be applied to several realistic cases characterized by non-uniform geometries.

Published
2006

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