Commonly exploited migration algorithms or also well-established linear inverse scattering algorithms [1] for the focusing of GPR data are often based on the hypothesis of a homogeneous soil. However, this assumption is not valid always, and it provides deformed results when it is applied to image scenarios where it is not valid. More complex models of the scattering can afford the situation of a stratified medium, but only if the layers are flat and parallel to each other these model assumes analytic forms. In any case, commonly available commercial codes do not allow to implement the reflections and refraction of the waves associated to these cases [2]. More recently, time reverse migration algorithms have been introduced. They can account efficiently of non-homogeneous soils, but their performances in case of large and strong scattering targets are not yet completely established and they make use of forward numerical solvers, not all the times available and user friendly. At the conference, we will describe a strategy based on suitable combination of migration results achieved from different homogeneous media, accompanied by a time-depth conversion accounting for the occurrence of different values of the wave propagation velocity in the investigated domain. We will show how an improvement of the imaging result is achieved even in the lack of a correct mathematical model of the scattering phenomenon. Last but not least, the proposed strategy exploits software routines easy to be implemented.

How to cite: Persico, R., Morelli, G., Esposito, G., and Catapano, I.: Combined migrations and time-depth conversions: first results, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2106, https://doi.org/10.5194/egusphere-egu23-2106, 2023.

The use of time domain reflectometry (TDR) techniques for in-situ, non-destructive measurement of water content has revolutionized soil water management and it is a rapidly growing area of interest. Additionally, monitoring other soil parameters such as levels of contaminants in soil is becoming an active field of research due to increasing environmental pollution and thus enforcement of contamination levels from policy makers. As a result, in recent years there have been advancements of TDR probe capability in terms of operating range, proven design, multiplexing and automated data collection. However, there is still a strong need for systems that are user-friendly and low cost which provide for quasi-real time and in situ monitoring with high sensitivity of soil parameters with adequate accuracy.

In this paper, we present a system consisting of a bifilar TDR probe interfaced with a miniaturized Vector network analyser which enabled measurements of the reflection coefficient in the frequency-domain.   The reflection coefficient is then related to soil parameters, such as soil water content and percentage of diesel oil (as an example of soil contaminant) through an innovative numerical procedure that retrieves the Debye parameters of different soil samples under different conditions.

This numerical procedure consisted of two main steps:

Firstly, the accurate modelling of the bifilar TDR probe in CST Microwave Studio such that the model is an accurate representation of the experimental setup used in the laboratory. This model was also validated using well-characterised materials such as Methanol and Prop-2-ol, utilising Debye parameters as published in [1].

Finally, the bifilar probes were immersed in soil samples having different moisture levels (dry up to 30%, in steps of 5%) and contaminated soil with different percentages of diesel oil (0%, 5%, 7.5% and 10%) and the Debye parameters were retrieved using the validated model in the first step.

Results illustrate that there exists a correlation between the retrieved Debye parameters and the moisture levels and percentage of diesel oil in soil. This proves that the Debye parameters provide the necessary information to differentiate between water or contaminant content and thus can be used for monitoring purposes rather than conducting measurements of the dielectric permittivity.

References

[1] Gregory, A.P.; Clarke, R.N. Tables of the Complex Permittivity of Dielectric Reference Liquids at Frequencies up to 5 GHz; National Physical Laboratory Report; 2012. Available online: https://eprintspublications.npl.co.uk/2076/ (accessed on 13 September 2022).

How to cite: Farrugia, L., Persico, R., Cataldo, A., Farhat, I., and Schiavoni, R.: Using the Debye parameters of soil for water content and contamination level determination., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15344, https://doi.org/10.5194/egusphere-egu23-15344, 2023.

Effective usage of water resources is a relevant topic to move towards smart and resilient cities, and it demands technologies aimed at monitoring water distribution networks at avoiding wastefulness and assuring environmental safety.

In this frame, research activities designing technological solutions assuring time-constant monitoring and, simultaneously, providing high spatial resolution images from which infer accurate information about the position and extension of the leakage are carried out.

Being this request difficult to be satisfied by means of a single sensor, the pursued idea is the joint and cooperative use of the distributed optical fiber sensor based on the Brillouin scattering phenomenon [1] and the microwave tomography (MWT) enhanced ground penetrating radar (GPR) [2]. The first technology, if integral to the pipe, is able to detect temperature and/or thermal conductivity variations occurring in the soil hosting the pipe and due to water leakages. Therefore, it appears suitable to assure continuous monitoring and to provide low spatial resolution information about leakage detection. Conversely, GPR allows on-demand non-invasive surveys providing high spatial resolution images of the investigated scenario, if the collected raw data are processed properly. An effective way to do it is the use of MWT approaches, which face GPR imaging as an inverse scattering problem [3].

In order to provide a proof of concept assessing the benefits and limits of the cooperative use of the above technologies, a joint experimentation was carried out. Specifically, an ad-hoc experimental scenario allowing to reproduce a water leakage was built. The scenario is a scaled reproduction of a realistic test case and a plastic pipe filled with fresh water and buried in a river-sand terrain makes it up. The optical fiber sensor was buried in the sand few cm underneath the pipe, while GPR data were collected along and across directions with respect to the pipe.

The achieved results confirmed the expected potentialities and encourage going on this activity.

A detailed presentation of the experimental setup and the achieved results will be provided at the conference.

Acknowledgment: The authors would like to thank the SMART WATERTECH project “Smart Community per lo Sviluppo e l’Applicazione di Tecnologie di Monitoraggio e Sistemi di Controllo Innovativi per il Servizio Idrico Integrato” by which the present work has been financed.

[1] Bernini R., Minardo A., Zeni L. (2004) Accuracy enhancement in Brillouin distributed fiber-optic temperature sensors using signal processing techniques, IEEE Photonics Technology Letters 16 (4), pp. 1143-1145.

[2] Catapano, I., Gennarelli, G., Ludeno, G., Persico, R., Soldovieri, F. (2019). Ground Penetrating Radar: Operation Principles and Data, Wiley Encyclopedia of Electrical and Electronics Engineering.

[3] Catapano, I., Palmeri, R., Soldovieri, F., Crocco, L. (2022). GPR Water Pipe Monitoring and Leaks Characterization: A Differential Microwave Tomography Approach. In: Di Mauro, A., Scozzari, A., Soldovieri, F. (eds) Instrumentation and Measurement Technologies for Water Cycle Management. Springer Water. Springer, Cham.

How to cite: Catapano, I., Ludeno, G., Persichetti, G., Bernini, R., and Crocco, L.: Water pipe monitoring via fiber optical sensor and ground penetrating radar: a joint laboratory experiment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12812, https://doi.org/10.5194/egusphere-egu23-12812, 2023.

Nowadays, Ground Penetrating Radar (GPR) systems working in contactless way deserve huge attention because, if mounted onboard of moving platforms like terrestrial and aerial vehicles, they allow the collection of a large amount of data, while keeping low complexity and time of the measurement step [1,2]. At the same time, multiple input multiple output (MIMO) GPR systems are worth being exploited because, being capable of gathering multiview and multistatic data, they allow an improvement of the reconstruction capabilities [3, 4]. However, the effective use of a contactless MIMO GPR requires the availability of properly designed data processing strategies able to manage the information acquired by this kind of systems and to provide an accurate reconstruction of the scenario under test.

This contribute proposes a microwave tomographic approach, which faces the GPR imaging as a linear inverse scattering problem and it is suitable to process contactless multi-view and multi-static data. The approach is referred to the 2D scalar case, exploits a ray-based model of the scattering phenomenon, and accounts for the presence of the air-soil interface. Specifically, the approach extends to the case of MIMO systems the concept of the Interface Reflection Point (IPR) previously exploited to process contactless data gathered by means of a multi-monostatic GPR [2,5].

At the conference, the approach formulation will be described in detail and results referred to virtual experiments will be provided in order to state the achievable imaging capabilities.

[1] Miccinesi, L., Beni, A., & Pieraccini, M. (2022). UAS-Borne Radar for Remote Sensing: A Review. Electronics, 11(20), 3324.

[2] Catapano, G. Gennarelli, G. Ludeno, C. Noviello, G. Esposito, and F. Soldovieri, "Contactless ground penetrating radar imaging: state of the art, challenges, and microwave tomography-based data processing," IEEE Geosci. Rem. Sens. Mag., vol. 10, no. 1, pp. 251-273, 2022.

[3] García-Fernández, M., López, Y. Á., & Andrés, F. L. H. (2020). Airborne multi-channel ground penetrating radar for improvised explosive devices and landmine detection. IEEE Access, 8, 165927-165943.

[4] Leone, G., & Soldovieri, F. (2003). Analysis of the distorted Born approximation for subsurface reconstruction: Truncation and uncertainties effects. IEEE Transactions on geoscience and remote sensing, 41(1), 66-74.

[5] Catapano, L. Crocco, Y. Krellmann, G. Triltzsch, and F. Soldovieri, “Tomographic airborne ground penetrating radar imaging: achievable spatial resolution and on-field assessment,”, ISPRS J. Photogram. Remote Sens., vol. 92, pp. 69–78, June 2014.

How to cite: Soldovieri, F., Gennarelli, G., Ludeno, G., Esposito, G., and Catapano, I.: A microwave tomographic approach for contactless Multiple Input Multiple Output GPR systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12688, https://doi.org/10.5194/egusphere-egu23-12688, 2023.

Over time, urbanized areas have undergone continuous development and growth as they adapt to the changing needs of their residents. This has often involved the construction of new buildings, roads, and infrastructures, as well as the renovation and expansion of existing structures. Subsurface characterization is thus a crucial aspect of urban development, as it is essential for the planning, construction and monitoring of new or existing infrastructures. Urbanized environments may be challenging for conventional subsurface characterization methods such as drilling or excavation due to difficulty of access or the presence of buried networks that are not always properly mapped. Geophysical methods can be seen as an interesting alternative to these traditional characterization approaches but require to be adapted to work properly in such environment. This led to the development of the urban geophysics discipline.

Among the different geophysical methods available, Electrical resistivity tomography (ERT) appears as a useful and robust tool for studying subsurface materials and structures in urban environments. It has already been used to investigate underground utilities such as tunnels, cellars, pipes, tank storages and building foundations as well as natural structures. While ERT minimizes site disturbance, the use of fully non-invasive electrodes is sometimes required for the preservation of investigated sites. The best example remains the investigation of archeological structures. For that purpose, a diversity of non-invasive electrodes such as flat electrodes, bentonite mud or conductive gel has already been used overtime for different purposes but showed different outcomes in terms of contact resistance, measurement uncertainty, durability or signal to noise ratio. To our knowledge, few systematic comparison has been done between the different types of non-invasive electrodes and their impact in terms of imaging/monitoring in specific conditions for urban applications.

The present study proposes an assessment of the use of different non-conventional electrodes on various surfaces often encountered in urban environments at controlled lab-scale. The tested electrodes can be divided into two main categories, the electrolytic and the weight electrodes. The analysis focuses on contact resistance, electrical current transmission, noise measurements, strength and stability of the signal over time. The ease and time of deployment are also taken into account for future uses in larger scale fieldworks. Based on preliminary results, the electrodes based on electrolytic contact demonstrate better performances in highly resistive environments, where a better grounding resistance can globally be achieved compared to weight-based electrodes. However, their implementation are more fastidious slowing the acquisition.

How to cite: Debouny, T., Caterina, D., and Nguyen, F.: Benchmark of multiple non-invasive electrodes for a relevant use in urban environments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12013, https://doi.org/10.5194/egusphere-egu23-12013, 2023.

After the collapse of the Genoa Bridge in August 2018, a renewed interest in permanent monitoring of the structural behavior of civil infrastructures [2] was observed. Such monitoring has to encompass the need to survey a very large number of structures that reach critical age but also new structures. In addition, recent technological advances have helped to make the installation and operation of continuous monitoring systems more practical and economical. In parallel, monitoring approaches based on the use of data acquired by satellite Synthetic Aperture Radar (SAR) may complete and enlarge the observation scale of such ground based monitoring systems, to enhance Structural Health Monitoring (SHM) performances.

Monitoring of civil structures is frequently based on vibration analysis. Anyway, one limitation to the use of SHM algorithms based on modal parameter analysis is its sensitivity to environmental effects and not to damage. Among them, the subsidence around and at structure’s foundation level is a factor that has a great influence on natural frequencies.

In this study, we address quasi-periodic monitoring and subsidence characterization using surface deformation measurements achieved through the Differential Interferometric SAR (DInSAR) technology [1]. Peculiarities of DInSAR have to be taken into account with reference to the application to structures monitoring:

• Robustness of estimated ground deformation obtained throught the combination of the Line-of-sight (LOS) deformation measurements carried out by the processing of complementary ascending and descending orbits data, for which the measurements points and date of acquisition could be different;
• Sparse, or absence of, measurements points on some areas induced by strong decorrelation phenomena;
• Limited range of the actual structure deformation that could reach the accuracy of the DInSAR technology.

Bibliographic study showed that it could be difficult to exploit the DInSAR data directly for the SHM because of the problems mentioned above. The proposed procedure aims at reconstructing the deformations over an area of interest using a regularly spaced grid whose deformations would be interpolated on the available sparse measurements dataset. The interpolation is carried out on each orbit trajectory and for each acquisition date. This allows both to:

• Estimate measurements point on the same, possibly regular, grid for different orbits;
• Estimate deformation in areas lacking of measurement points;

Inspired from research works of Chen et al. [3] we implemented and studied a neural network (NN) kriging based interpolation (introducing the spatial dimension inside the NN). It allows the modelisation of the points correlation (variograms) directly from the data instead of predefined functions.

An overview of the studied method and developed software applied on 2 use-cases will be presented and analysed. Perspectives towards improvements of such approach will be also discussed.

References

[1] Antonio Pepe and Fabiana Calò. “A Review of Interferometric Synthetic Aperture RADAR (InSAR) Multi-Track Approaches for the Retrieval of Earth’s Surface Displacements”. In: Applied Sciences 7.12 (2017). doi: 10.3390/app7121264. 

[2] Riccardo Lanari et al. “Comment on “Pre-Collapse Space Geodetic Observations of Critical Infrastructure: The Morandi Bridge, Genoa, Italy” by Milillo et al. (2019)”. In: Remote Sensing 12.24 (2020). doi:10.3390/rs12244011.

[3] Wanfang Chen et al. “DeepKriging: Spatially Dependent Deep Neural Networks for Spatial Prediction”. In: arXiv:2007.11972 (May 23, 2022).

How to cite: Dumoulin, J., Renier-Robin, A., Reale, D., Toullier, T., Verde, S., and Soldovieri, F.: Feasibility study of Neural Networks interpolation applied to Synthetic Aperture Radar Deformations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14562, https://doi.org/10.5194/egusphere-egu23-14562, 2023.

The inspection of underground scenarios is a challenging task required in several applications, from geophysical to archeological and civil areas. The ground penetrating radar (GPR) is a common tool that has been widely adopted to provide qualitative imaging of the underground scenario [1]. Recently, several approaches to process GPR data and retrieve quantitative images to characterize the inspected region have been developed [2-3]. Moreover, to compensate for the loss of information that usually happens in this scenario, GPR systems have been implemented not only in monostatic and bistatic configurations but also in multistatic settings [4].

In this contribution, a quantitative inverse scattering approach is proposed to retrieve the distribution of the complex dielectric permittivity of a buried region, starting from scattering parameters collected through a multistatic GPR configuration. The approach is based on a finite-element (FE) formulation of the electromagnetic inverse scattering problem and, as solving procedure, a reconstruction method in variable exponent Lebesgue spaces is adopted [5]. On the one hand, the FE model embedded in the method is exploited to describe the structure of the measurement configuration without simplifying assumptions (except for the two-dimensional hypotheses and the numerical discretization of the problem). On the other hand, the inversion procedure in variable exponent Lebesgue spaces has been found quite effective to face the ill-posedness and nonlinearity of the problem. A numerical validation of this approach is reported.

References

[1] R. Persico, “Introduction to ground penetrating radar: Inverse scattering and data processing.” Hoboken, New Jersey: Wiley, 2014.

[2] M. Pastorino and A. Randazzo, “Microwave imaging methods and applications.” Boston, MA: Artech House, 2018.

[3] V. Schenone, A. Fedeli, C. Estatico, M. Pastorino, and A. Randazzo, “Experimental assessment of a novel hybrid scheme for quantitative GPR imaging”, IEEE Geoscience and Remote Sensing Letters, vol. 19, pp. 1–5, 2022.

[4] M. Ambrosanio, M. T. Bevacqua, T. Isernia, and V. Pascazio, “Performance analysis of tomographic methods against experimental contactless multistatic ground penetrating radar”, IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, vol. 14, pp. 1171–1183, 2021.

[5] V. Schenone, C. Estatico, G. L. Gragnani, M. Pastorino, A. Randazzo, and A. Fedeli, “Microwave-based subsurface characterization through a combined finite element and variable exponent spaces technique”, Sensors, vol. 23, no. 1, p. 167, 2023.

How to cite: Fedeli, A., Schenone, V., Pastorino, M., and Randazzo, A.: Quantitative inverse scattering analysis for ground penetrating radar imaging, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5339, https://doi.org/10.5194/egusphere-egu23-5339, 2023.