Surveys in Geophysics

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Seismic Frequency Component Inversion for Elastic Parameters and Maximum Inverse Quality Factor Driven by Attenuating Rock Physics Models

Wed, 07/01/2020 - 00:00
Abstract

Attenuation exists in seismic wave propagation in subsurface layers, and relatively high attenuation occurs in oil-bearing reservoirs. Inversion of frequency components of observed seismic data generates values of attenuation factor 1/Q, which produces potential results for determining oil-bearing reservoirs. Beginning with expressions of seismic wave velocity in attenuating media, we involve P-wave maximum attenuation factor to rewrite P-wave velocity driven by an attenuating rock physics model, and we also employ an empirical relationship between P-wave attenuation factor and S-wave attenuation factor to express S-wave velocity in terms of P-wave maximum attenuation factor. Using the derived P- and S-wave velocities, we extend Zoeppritz equations to compute reflection coefficient for an interface separating two attenuating media. Under the assumption that contrasts in elastic properties of two media across the interface are small and the background attenuation is weak, we propose a linearized reflection coefficient of PP-wave as a function of contrasts in elastic parameters (i.e., P-wave velocity, S-wave velocity and density) and attenuation factor, and expression of elastic impedance (EI) is also presented. Based on the EI, we demonstrate an approach of estimating elastic parameters and attenuation factor from frequency components of partially incidence-stacked seismic data, which is implemented as a two-step inversion involving the prediction of EI datasets using a model-based damping least-squares algorithm and nonlinear inversion for elastic parameters and attenuation factor. Noisy synthetic seismic data generated using the extended Zoeppritz equations are employed to verify the robustness and stability of the proposed inversion approach. Applying the proposed approach to a real dataset acquired over an oil-bearing reservoir, we obtain convincing results of P-wave velocity, S-wave velocity, density and attenuation factor, which can reasonably match corresponding well log data.

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The Santa Fe Intrusion and Other Magmatic Bodies Under the Chichón Volcano Area (Mexico): Inferences from Aeromagnetic and New Petrologic-Geochronologic Data

Wed, 07/01/2020 - 00:00
Abstract

We review the current knowledge of the Pleistocene Modern Chiapanecan Volcanic Arc (MCVA). This arc is related to the subduction of the Cocos plate beneath the North American plate in the State of Chiapas, southeastern Mexico. The MCVA consists of large intrusive bodies, domes, eroded volcanic landforms, and the active El Chichón, which produced the disastrous 1982 eruption, the deadliest in Mexico’s recorded history. The available geological knowledge, and new geological and aeromagnetic data on the arc, reveals a system composed of a sizeable intrusive body called the Santa Fe diorite, and small-size volcanoes such as El Chichón and Catedral, and extinct volcanoes associated with volcaniclastic deposits. A 3D-inversion of the aeromagnetic anomalies indicates that the Santa Fe diorite is a large intrusive body (27 km long, 4 km wide with a minimum volume of 1662 km3) while small volcanoes such as El Chichón have small-size magma chambers (~ 7 km3). Interestingly, our models of the causative bodies for the aeromagnetic anomalies suggest that the El Chichón volcano, as well as of other volcanic areas in the region, are not linked directly to the Santa Fe intrusive. However, new 40Ar/39Ar dates for samples from the Santa Fe intrusive (2.2 Ma), the Catedral volcano (1.6 Ma), and a mafic enclave (1.09 Ma) hosted in 1982 Chichón deposits, along with the aeromagnetic anomalies and geochemical data confirm that these extrusive and intrusive structures belong to the MCVA. The chemistry of these structures suggests that magmas generated in the upper mantle by the subduction system evolved through different processes, such as crustal contamination for the Santa Fe diorite and Catedral volcano, and crystal fractionation for El Chichón volcano.

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Forward Gravity Modelling to Augment High-Resolution Combined Gravity Field Models

Wed, 07/01/2020 - 00:00
Abstract

During the last few years, the determination of high-resolution global gravity field has gained momentum due to high-accuracy satellite-derived observations and development of forward gravity modelling. Forward modelling computes the global gravitational field from mass distribution sources instead of actual gravity measurements and helps improving and complementing the medium to high-frequency components of the global gravity field models. In this study, we approximate the global gravity potential of the Earth’s upper crust based on ellipsoidal approximation and a mass layer concept. Such an approach has an advantage of spectral methods and also avoids possible instabilities due to the use of a sequence of thin ellipsoidal shells. Lateral density within these volumetric shells bounded by confocal lower and upper shell ellipsoids is used in the computation of the ellipsoidal harmonic coefficients which are then transformed into spherical harmonic coefficients on the Earth’s surface in the final step. The main outcome of this research is a spectral representation of the gravitatioal potential of the Earth’s upper crust, computed up to degree and order 3660 in terms of spherical harmonic coefficients (ROLI_EllApprox_SphN_3660). We evaluate our methodology by comparing this model with other similar forward models in the literature which show sub-cm agreement in terms of geoid undulations. Finally, EIGEN-6C4 is augmented by ROLI_EllApprox_SphN_3660 and the gravity field functionals computed from the expanded model which has about 5 km half-wavelength spatial resolution are compared w.r.t. ground-truth data in different regions worldwide. Our investigations show that the contribution of the topographic model increases the agreement up to ~ 20% in the gravity value comparisons.

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Analysis of Plasma Bubble Signatures in Total Electron Content Maps of the Low-Latitude Ionosphere: A Simplified Methodology

Wed, 07/01/2020 - 00:00
Abstract

The ionosphere over the Brazilian region has particular characteristics due to the large geomagnetic declination angle over most of the territory. Furthermore, the equatorial ionization anomaly southern crest is located over the Brazilian territory. In this region, plasma irregularities may arise in the post-sunset hours. These ionospheric irregularities develop in the form of magnetic field-aligned plasma depletions, known as equatorial plasma bubbles, which may seriously affect radio signals that propagate through them. These irregularity structures can cause amplitude and phase scintillation of the propagating signals, thereby compromising the availability, performance, and integrity of satellite-based communication and navigation systems. Additionally, the total electron content (TEC) introduces propagation delays that can contribute to range measurement errors for global positioning system (GPS) users. The ionospheric characteristics change significantly according to the time of day, season, as well as the solar and geomagnetic activities, among other factors. Indeed, the ionosphere is one of the most significant sources of errors in the positioning and navigation systems based on the GPS satellites. Due to these features, there is a strong interest by the scientific community in better understanding and characterizing the ionospheric behavior. In this context, the TEC analysis has wide applicability for space plasma studies and is a well-established tool for investigating the ionospheric behavior and its potential impact on space-based navigation systems. One of the goals of these studies is the generation of TEC maps for a geographic region based on GPS observations. In the present work, some electrodynamic processes of the low-latitude ionosphere are reviewed and the TEC estimation based on GPS measurements is revisited in detail. A methodology aimed at creating the TEC maps is presented and validated by comparison with results from other geophysical instruments, such as all-sky imagers and ionosondes. Finally, examples of the ionospheric behavior displayed by TEC maps during equatorial plasma bubble events and a geomagnetic storm are fully described and discussed.

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Gravity Field Modeling Using Tesseroids with Variable Density in the Vertical Direction

Wed, 07/01/2020 - 00:00
Abstract

We present an accurate method for the calculation of gravitational potential (GP), vector (GV), and gradient tensor (GGT) of a tesseroid, considering a density model in the form of a polynomial up to cubic order along the vertical direction. The method solves volume integral equations for the gravitational effects due to a tesseroid by the Gauss–Legendre quadrature rule. A two-dimensional adaptive subdivision technique, which automatically divides the tesseroids near the computation point into smaller elements, is applied to improve the computational accuracy. For those tesseroids having small vertical dimensions, an extension technique is additionally utilized to ensure acceptable accuracy, in particular for the evaluation of GV and GGT. Numerical experiments based on spherical shell models, for which analytical solutions exist, are implemented to test the accuracy of the method. The results demonstrate that the new method is capable of computing the gravitational effects of the tesseroids with various horizontal and vertical dimensions as well as density models, while the evaluation point can be on the surface of, near the surface of, outside the tesseroid, or even inside it (only suited for GP and GV). Thus, the method is attractive for many geodetic and geophysical applications on regional and global scales, including the computation of atmospheric effects for terrestrial and satellite usage. Finally, we apply this method for computing the topographic effects in the Himalaya region based on a given digital terrain model and the global atmospheric effects on the Earth’s surface by using three polynomial density models which are derived from the US Standard Atmosphere 1976.

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Recursive Analytical Formulae of Gravitational Fields and Gradient Tensors for Polyhedral Bodies with Polynomial Density Contrasts of Arbitrary Non-negative Integer Orders

Wed, 07/01/2020 - 00:00
Abstract

Exact computation of the gravitational field and gravitational gradient tensor for a general mass body is a core routine to model the density structure of the Earth. In this study, we report on the existence of closed-form solutions of the gravitational potential, gravitational field and gravitational gradient tensor for a general polyhedral mass body with a polynomial density function of arbitrary non-negative integer orders that can simultaneously vary in both horizontal and vertical directions. Our closed-form solutions of the gravitational potential and the gravitational field are singularity-free, which implies that the observation sites can have arbitrary geometric relationships with polyhedral mass source bodies. However, weak logarithmic singularities exist on the edges of polyhedra for the gravitational gradient tensor. A simple prismatic mass body with polynomial density contrast varying in the vertical direction and a complicated dodecahedral mass body with quartic-order density contrasts were tested to verify the accuracy of the newly derived closed-form solutions. For the gravitational potential, gravitational fields and gradient tensors, our closed-form solutions are in excellent agreement with previously published analytical solutions and Gaussian numerical quadrature solutions.

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Correction to: Diffusion and Thermodiffusion of Atmospheric Neutral Gases: a Review

Wed, 07/01/2020 - 00:00

The original version of this article unfortunately contained misprints. The corrections of these misprints are given below.

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Elastic Least-Squares Imaging in Tilted Transversely Isotropic Media for Multicomponent Land and Pressure Marine Data

Wed, 07/01/2020 - 00:00
Abstract

Traditional elastic reverse-time migration (RTM) involves P-/S-wave separation for the source and receiver wavefields, followed by applying the zero-lag cross-correlation imaging condition to produce PP and PS images. In anisotropic media, P-/S-wave decomposition requires a higher memory and computational cost than that in isotropic media. In addition, finite acquisition apertures and band-limited source functions result in unsatisfactory resolutions and amplitudes. To mitigate these problems, we present an elastic least-squares imaging method for tilted transversely isotropic media and apply it to land multicomponent and marine pressure data. Unlike traditional RTM, we use the relative perturbations to the product of density and squared axial (compressional/shear) velocities as reflectivity models (\(\Delta \ln{C}_{33}\) and \(\Delta \ln{C}_{55}\)), and estimate them by solving a linear inverse problem. Numerical experiments illustrate that subsurface reflectors can be well resolved in adjoint images for land multicomponent data, because of the presence of both P- and S-waves in seismograms. Least-squares migration helps to further improve spatial resolution and image amplitudes. Since there are no direct S-waves in marine streamer data, adjoint RTM images of \(\Delta \ln{C}_{55}\) are mainly resolved with the converted S-waves and are not as good as those in \(\Delta \ln{C}_{33}\) images. By approximating the Hessian inverse, least-squares migration allows us to take advantage of the weak converted P–S–P-waves and improve the \(\Delta \ln{C}_{55}\) image quality. Numerical experiments for synthetic and field data demonstrate the feasibility and advantage of the proposed least-squares TTI RTM compared with wave-mode separation-based elastic RTM. In field data experiments, we observe that since there are no strong P–S–P converted waves in streamer pressure records from the marine survey, the reflectors in \(\Delta \ln{C}_{55}\) image might be mainly imaged from P-waves due to the amplitude versus offset (AVO) effects.

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Earth Observations for Monitoring Marine Coastal Hazards and Their Drivers

Fri, 06/05/2020 - 00:00
Abstract

Coastal zones have large social, economic and environmental values. They are more densely populated than the hinterland and concentrate large economic assets, critical infrastructures and human activities such as tourism, fisheries, navigation. Furthermore, coastal oceans are home to a wealth of living marine resources and very productive ecosystems. Yet, coastal zones are exposed to various natural and anthropogenic hazards. To reduce the risks associated with marine hazards, sustained coastal zone monitoring programs, forecasting and early warning systems are increasingly needed. Earth observations (EO), and in particular satellite remote sensing, provide invaluable information: satellite-borne sensors allow an effective monitoring of the quasi-global ocean, with synoptic views of large areas, good spatial and temporal resolution, and sustained time-series covering several years to decades. However, satellite observations do not always meet the precision required by users, in particular in dynamic coastal zones, characterized by shorter-scale variability. A variety of sensors are used to directly monitor the coastal zone and their observations can also be integrated into numerical models to provide a full 4D monitoring of the ocean and forecasts. Here, we review how EO, and more particularly satellite observations, can monitor coastal hazards and their drivers. These include coastal flooding, shoreline changes, maritime security, marine pollution, water quality, and marine ecology shifts on the one hand, and several physical characteristics (bathymetry, topography, vertical land motion) of coastal zones, meteorological and oceanic (metocean) variables that can act as forcing factors for coastal hazards on the other hand.

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Progress in the Study of Transient Luminous and Atmospheric Events: A Review

Sun, 05/31/2020 - 00:00
Abstract

Transient luminous events (TLEs) such as sprites, blue jets (BJs) and elves have been studied intensively during the last three decades, and much is now known of their properties. This progress is caused by several factors including satellite optical observations, ground-based measurements of sprite-produced electromagnetic fields, the use of high-speed video observations and telescopic cameras with high resolution that enables one to trace the dynamics of sprite and BJ development. In this paper, we review various types of TLEs, including recently discovered dancing sprites, gnomes, ultraviolet (UV) atmospheric flashes and other effects. The sprite initiation, visible evolution, streamer structure, and their relationship with intra-cloud (IC) process are discussed. Considerable study has been given to ULF/ELF measurements which can provide us with important information on the delayed sprite generation and the role played by IC processes in the perturbation of the lower ionosphere above the sprite. A set of electrodynamic and transport kinetic equations describing the TLEs are complicated because the number densities, mobilities of electrons and ions, reaction constants and other parameters are strongly dependent on altitude. Because of this, the majority of theoretical study of TLEs and other large-scale optical phenomena at high altitude are based on numerical modeling of the basic kinetic, transport and electrodynamic equations describing TLEs evolution, whereas the analytical theory remains a formidable task to be accomplished. In this paper, we review a few analytical results, which have been recently derived from simple physical models of the TLEs phenomena. In the remainder of this paper, we focus our attention on the properties of UV flashes in the mesosphere, which have been observed onboard Russian microsatellites “Universitetsky-Tanyana” and “Vernov.” Such a kind of optical flash is referred to as a transient atmospheric event, which differs from the TLEs in optical energy, duration and other parameters.

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Using Ground Penetrating Radar Methods to Investigate Reinforced Concrete Structures

Fri, 05/01/2020 - 00:00
Abstract

This paper provides an overview of the existing literature on the subject of ground penetrating radar (GPR) methods for the investigation of reinforced concrete structures. An overview of the use of concrete and reinforced concrete in civil engineering infrastructures is given. A review of the main destructive and non-destructive testing methods in the field is presented, and an increase in the use of GPR to reinforced concrete structures is highlighted. It was also observed that research in some application areas has been predominantly or exclusively carried out at a laboratory scale, and that similarly, other more application-oriented research has been developed only on real-life structures. The effectiveness of GPR in these areas is demonstrated. Furthermore, a case study is presented on a new methodological and data processing approach for the assessment of reinforced concrete structures using a high-frequency dual-polarised antenna system. Results have proven the advantages of using the proposed methodology and GPR system in order to improve the detectability of rebars, including secondary bottom lines of reinforcement. The horizontal polarisation was proven to be more stable compared to the vertical. Finally, it has been demonstrated that a more accurate location of the rebars in a high-density grid mesh arrangement can be obtained by means of data migration processing with a scan spacing of 5 cm and wave velocity information through the use of the hyperbola fitting method from at least 30% of the targets.

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Assessment of Modern Roadways Using Non-destructive Geophysical Surveying Techniques

Fri, 05/01/2020 - 00:00
Abstract

The main purpose of modern roadways is to provide roadway users with both a comfortable and safe ride to their destinations. As such, they need pavements in good physical conditions to ensure safe and uninterrupted transportation of the public. During the previous decades, roadway engineers’ interests have shifted towards maintenance and rehabilitation of existing pavement structures, rather than the construction of new structures. Nevertheless, pavement condition assessment (PCA) remains imperative both during construction for quality assurance purposes and during roadways’ service life for efficient maintenance planning. Research and current practices have shifted towards a broadened utilization of advanced non-destructive testing systems that enable non-invasive PCA. The current investigation aims to provide a comprehensive overview of the geophysical methods available for modern roadways’ assessment. Geophysical surveying techniques including ground penetrating radar (GPR) and those based on stress waves theory can substantially improve PCA. They cover roadway applications including layer thicknesses determination, stiffness estimation of asphalt and concrete pavements, as well as the determination of physical properties, subsurface defects detection and most recently density monitoring. In particular, it is demonstrated that GPR can assist pavement engineers at all stages of PCA from the construction process through density control and compaction monitoring. Furthermore, throughout a roadway’s service life, GPR can be effectively incorporated as a supplementary tool for monitoring and evaluation within a pavement management system, contributing to optimizing roadways design and maintenance, preserving durable and sustainable structures, ensuring cost savings for road authorities and highway operators through enhanced decision-making processes.

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Non-destructive Assessment and Health Monitoring of Railway Infrastructures

Fri, 05/01/2020 - 00:00
Abstract

A continuous increase in the worldwide demand for high-speed traffic, freight tonnage as well as of the train operating frequency is worsening the decay conditions of many railway infrastructures. This occurrence affects economy-related business as well as contributing to rising maintenance costs. It is known that a failure of a railway track may result in tremendous economic losses, legal liabilities, service interruptions and, eventually, fatalities. Parallel to this, requirements to maintain acceptable operational standards are very demanding. In addition to the above, a main issue nowadays in railway engineering is a general lack of funds to allow safety and comfort of the operations as well as a proper maintenance regime of the infrastructures. This is mostly the result of a traditional approach that, on average, tends to invest in high-priority costs, such as safety-related costs, compromising lower-priority interventions (e.g., quality and comfort of the operations). A solution to correct this trend can be moving from a reactive to a proactive action planning approach in order to limit more effectively the likelihood of progressive rail track decay. Within this context, this paper reports a review on the use of traditional and non-destructive testing (NDT) methods for the assessment and health monitoring of railway infrastructures. State-of-the-art research on a stand-alone use of NDT methods or a combination of them for quality control, inspection and maintenance tasks in this subject area is discussed.

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Real-Time Density and Thickness Estimation of Thin Asphalt Pavement Overlay During Compaction Using Ground Penetrating Radar Data

Fri, 05/01/2020 - 00:00
Abstract

Achieving desired density is crucial for thin asphalt concrete (AC) overlay construction quality control and quality assurance purposes. Ground penetrating radar (GPR) can be implemented for AC pavement layer thickness and density prediction during compaction. However, the overlapping of GPR reflections from surface and bottom of the thin AC overlay, as well as the presence of surface moisture, jeopardizes the prediction accuracy. In this study, a pavement model with thin AC overlay was simulated using gprMax, a finite-difference time-domain-based tool. Surface moisture was simulated as a 2-mm film with mixed electrical properties of water and AC. A nonlinear optimization method was used to address the overlapping and surface moisture issues simultaneously. The error of the thin AC overlay dielectric constant and thickness prediction results was less than 7% and 10%, respectively. Field test during thin overlay compaction was also performed to validate the proposed method. The AC overlay thickness and density estimation accuracies were 91% and 99%, respectively.

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Transport Infrastructure Monitoring by InSAR and GPR Data Fusion

Fri, 05/01/2020 - 00:00
Abstract

This study reviews research developments in non-destructive assessment of linear transport infrastructures. The main focus will be on the integration between satellite remote sensing and ground-based techniques. Specifically, the potential of using interferometric synthetic aperture radar (InSAR) and high-frequency ground penetrating radar (GPR) techniques as self-standing and integrated survey methodologies will be discussed. To this effect, an overview on data fusion techniques will be given. The last section of the paper reports recent results achieved by using both GPR systems and the permanent scatterers InSAR technique on a real-life railway.

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Geophysical Techniques for Monitoring Settlement Phenomena Occurring in Reinforced Concrete Buildings

Fri, 05/01/2020 - 00:00
Abstract

Geophysical investigations could provide a valid tool for the identification of possible causes of settlement phenomena that affect civil buildings. They provide a non-invasive method of obtaining high-resolution information about the subsoil, saving time and money. However, uncertainties related to the accurate interpretation of the acquired data could potentially reduce the value of these methods. For this reason, the integration of non-invasive tests with direct measurements to support geophysical data interpretation is strongly recommended. This is a fundamental step in the process of defining a sufficiently reliable geological model to explain the cause of failure. Among the various geophysical techniques, electrical resistivity tomography and ground penetrating radar offer significant advantages for monitoring the status of the conservation of civil engineering structures and infrastructures. This paper presents the most recent and beneficial advances of the use of electric and electromagnetic geophysical methods in the field of civil engineering, with particular attention to their applications for monitoring subsidence and settlement phenomena. Finally, the possibilities of the joint use of resistivity and electromagnetic methods for studying the causes of the structural decay that affects two precast buildings are monitored and discussed. The results demonstrate the capability of combining non-destructive geophysical techniques with direct data, for evaluating the safety of building constructions and solving geotechnical problems.

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On the Combined Use of Ground Penetrating Radar and Crack Meter Sensors for Structural Monitoring: Application to the Historical Consoli Palace in Gubbio, Italy

Fri, 05/01/2020 - 00:00
Abstract

The paper deals with joint use of non-invasive monitoring technologies and civil engineering analysis methods aimed at providing multi-sensing information about the structural health of historical and cultural assets. Specifically, linear variable displacement transducers (LVDT) and ground penetrating radar (GPR) are considered for monitoring a significant crack affecting the Consoli Palace in Gubbio, Italy, precisely one of the walls of the cross-hall leading to the Loggia. In this frame, LVDT is adopted to control horizontal amplitude variations of the crack, while GPR is applied to investigate the wall interior and to detect the occurrence of inner issues related to the visible appearance of the crack on the wall surface. The effectiveness of GPR surveys is improved by means of a microwave tomography-based data processing strategy. The main result is that there is a consistency between the monitoring outputs of LVDT, which allowed us to display the crack widening/contraction due to the seasonal temperature variations, and the fact that no significant changes of the geometry of the inner areas of the walls were observed by the GPR.

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Noninvasive Analytical and Diagnostic Technologies for Studying Early Renaissance Wall Paintings

Fri, 05/01/2020 - 00:00
Abstract

Electromagnetic imaging technologies, working at different frequencies, are widely exploited for noninvasive diagnostics since they allow an improvement of knowledge about the surveyed object without affecting its state of conservation. In this paper, imaging technologies, working from microwaves up to ultraviolet frequencies, are considered and their basis is reviewed by focusing the attention on their application in the frame of cultural heritage. Specifically, ultraviolet fluorescence, infrared reflectography, TeraHertz imaging and ground penetrating radar are taken into account and a survey protocol, based on their complementary and cooperative use, is proposed as a best practice for analysis and management of artistic masterpieces. The cooperative use of different technologies makes it, indeed, possible to investigate the same work of art by accounting for different aspects characterizing its drawing, creation and possible restoration, thus providing a global vision from the support up to its outermost layer. The advantages provided by the cooperative use of the above-listed technologies are, herein, discussed with respect to the case study of the wall painting annunciation by Fra Angelico, one of the masterpieces of the early Italian Renaissance located at the Museum of San Marco in Florence, Italy.

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An Interactive Integrated Interpretation of GPR and Rayleigh Wave Data Based on the Genetic Algorithm

Fri, 05/01/2020 - 00:00
Abstract

Ground-penetrating radar (GPR) and the seismic surface wave method are two geophysical techniques commonly used in near-surface surveys up to a depth of tens of meters. GPR can be utilized to clearly distinguish lithologic interfaces, while the seismic surface wave method (hereby referred to as the Rayleigh wave) is employed for its high sensitivity to the shear (S) wave velocity. However, the propagation velocity of the electromagnetic (EM) wave which is both initiated and tracked by GPR is difficult to determine within the stratum. Unfortunately, this can affect the time–depth conversion and interpretation of the radargram. Moreover, both the horizontal resolution and the detectability of the properties of the shallow stratum are limited by the seismic geometry of the Rayleigh wave data. It is important to note that the non-uniqueness of geophysical inversion problem also generates additional biases. To overcome the problems mentioned above, we put forward an interactive integrated geophysical system that utilizes the thickness as a bridge to connect GPR and the Rayleigh wave data in the data processing and inversion. In this study, we employed the velocity of a radagram and the Rayleigh wave dispersion curve inversion based on a genetic algorithm to reconstruct the near-surface distribution. Then, we set the thickness derived from the GPR data as limit of the Rayleigh wave dispersion curve inversion. Hence, we applied the constrained inversion result to determine the most accurate EM wave velocity. As expected, both the constrained inversion of the Rayleigh wave dispersion curve and the velocity correction of the radargram performed better than did the geophysical method alone, both in the numerical models and in the field. Finally, we found the interactive integrated geophysical system to be more conducive for geological interpretation in near-surface surveys.

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Recent Advances in Tree Root Mapping and Assessment Using Non-destructive Testing Methods: A Focus on Ground Penetrating Radar

Fri, 05/01/2020 - 00:00
Abstract

This paper provides an overview of the existing literature on the subject of the assessment and monitoring of tree roots and their interactions with the soil. An overview of tree root system architectures is given, and the main issues in terms of tree health and stability, as well as the impact of trees on the built environment, are discussed. An overview of the main destructive and non-destructive testing methods is presented, and a lack of available research-based outputs in the fields of tree root interconnectivity and soil interaction is highlighted. The effectiveness of non-destructive methods in these areas is demonstrated, in particular that of ground-penetrating radar. The paper references recent developments in estimating tree root mass density and health.

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