No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
An innovative time-depth conversion for the management of buried scenarios with strong discontinuities
ResearchGate has not been able to resolve any citations for this publication.
The traditional Born iterative method (BIM) and distorted Born iterative method (DBIM) are both effective for electromagnetic scattering inversion. But they are inefficient because of the computation of forward scattering problem in each iteration. In this paper, a modified forward-solver scheme based on Born series is proposed for improving the efficiency. By using this scheme, the traditional time-consuming forward scattering procedure, matrix inversion, is replaced by a simple multiplication with low computation complexity in each iteration. Numerical and experimental two-dimensional electromagnetic scattering models are used to validate the proposed method. The imaging results and CPU times indicate that the presented methods have good accuracy and can improve the efficiency greatly.
In this paper, we propose the combination of different migration results achieved on the same data in order to account for different values of the propagation velocities of the electromagnetic waves within the considered Ground Penetrating Radar (GPR) profile. These different values can be the result of a variable lithological composition or (more probably for short Bscans) the results of different moisture levels, or both. Here, we separately consider the two cases of horizontal or vertical variability of the propagation velocity with a transition zone between two zones with constant propagation velocity. Moreover, we also propose a time-depth conversion accounting for these different values of the propagation velocity along the considered GPR Bscan. The method is applied to real data gathered in the field with regard to a concrete coverage containing liner layers.
An innovative computational method to solve inverse scattering problems is proposed for retrieving the electromagnetic properties of unknown targets. The proposed technique is based on the contraction integral equation for inversion ( CIE-I ) method to mitigate multiple scattering contributions when imaging strong scatterers. More specifically, the CIE-I is integrated in an effective multi-resolution ( MR ) scheme to reduce the ratio between unknowns and non-redundant data as well as to exploit iteratively acquired information on the scenario for yielding higher-resolution reconstructions. Some preliminary numerical results are reported to assess the capabilities of the proposed MR-CIE-I method.
The co‐cathedral of St. John in Valetta, Malta represents a unique monument of historical importance. In this article, we present the results of a detailed GPR campaign performed in this co‐cathedral. The campaign was aimed at investigating the distribution of buried tombs under the mosaic floor of the main nave and of the lateral chapels of the co‐cathedral. The floor of the church shows a continuity of grave inscriptions, in the main nave as well as in all lateral chapels. It was suspected, based on available historical documents, that only a part of the present‐day inscriptions corresponds to the original sepultures or tombs. The GPR results presented here further highlight this conjecture and offer additional information regarding this important monument.
This article is protected by copyright. All rights reserved
In this contribution, we show the results of a GPR measurement campaign, combined with temperature and humidity measurements, gathered in a Renaissance monument of the 16th century in Lecce, Southern Italy. The data are processed by means of standard processing and the results interpreted with the aid of an archive research. Moreover, the reconstruction is inserted into a 3D virtual reconstruction of the monument, achieved by means of a laser scanner.
A nonlinear signal processing method based on cepstral filtering has been developed to provide an approximate solution to the inverse scattering problem in two dimensions. It has been used to recover images of strongly scattering objects from measured far-field scattering data and is applied here to synthesize structures with prescribed scattering characteristics. An example is shown to illustrate the synthesis method. The scattering properties of the resulting structures are verified using a finite difference time domain method. The inverse scattering method is straightforward to implement and requires reprocessing of the scattered field data in order to ensure that the function describing the secondary source (contrast source function) has the properties of being a minimum phase function. This is accomplished by a numerical preprocessing step involving an artificial reference wave.
This paper deals with ground‐penetrating radar prospecting and exploits a semi‐heuristic strategy to account for inhomogeneous background media, empty cavities or topography of the surface. We assume here that no more than a commercial processing software is available. Customarily, commercial codes assume a homogeneous soil and a flat interface in order to achieve the focusing of the data. Therefore, this is also the model exploited here, whereas the data are referred to an inhomogeneous soil or to a non‐flat interface. The proposed strategy exploits the principle that ‘the data speak’, even if with some ambiguity and some reticence, and they can reveal or at least suggest important features of the underground scenario. On this basis, heuristically, we exploit features derived from the data themselves as a posteriori information, improving the available focusing and time–depth conversion even having at disposal a basic model of the background scenario.
As part of a multi‐disciplinary programme of archaeological investigation, GPR was used to investigate the Shakespeare family graves below the chancel of Holy Trinity Church in Stratford, Warwickshire, England. Although William Shakespeare's place as perhaps one of the most famous individuals who has ever lived has been cemented in the annals of history, much of his life and death is still shrouded in mystery. As a result, a large number of myths and legends have grown up around his burial place. These included the suggestion of an unusually deep burial or the presence of a large family crypt beneath the chancel floor. A series of multi‐frequency surveys was carried out to establish the depth and structure of the graves and as much burial information as possible. Close survey (using a strategy developed and successfully applied in Westminster Abbey and other churches) was used in order to optimise the quality of patterning in the data. Within Holy Trinity, this strategy was validated by the detection of a known vault.
The use of multiple frequencies was critical in this investigation in order both to detect the graves and also to establish information about the graves. Too low a frequency may result in non‐detection because of the relatively low target resolution whereas too high a frequency risks insufficient depth penetration.
From this process a number of myths can now be discounted, including the presence of a large Shakespeare family vault or crypt. Instead, the GPR survey suggests that a simple, shallow, earth‐cut burial lies beneath William's tombstone. One story however concerning disturbance of William Shakespeare's grave in order to remove his skull does correspond with the evidence.
This paper presents ground penetrating radar (GPR) results joined with and back-upped by endoscopic tests performed in two churches. The aim of this work is to show how the endoscopic tests can help the interpretation of the achieved GPR images, and this will be shown with respect to two case histories in southern Italy. The usefulness of the endoscopic tests depends on the kind of targets, but is expected to be particularly useful in cases of buried cavities, where information about the volume and the possible past use of the cavity can be retrieved. In the examined cases, the endoscopic tests allowed the presence of three cavities to be established, helping also in the interpretation of their possible nature and use, even if the endoscopic probe was not gyroscopic nor equipped with a laser for the precise measure of the distances. Copyright
In this paper, the quantitative imaging of the dielectric characteristics of unknown targets buried in a lossy half-space is performed by suitably processing wide-band ground penetrating radar (GPR) measurements. An innovative multi-frequency (MF) fully non-linear inverse scattering (IS) technique exploiting the integration of a conjugate-gradient (CG) solver within the iterative multi-scaling approach (IMSA) is proposed. Representative results from numerical test cases are presented to provide the interested readers with some indications on the effectiveness, as well as the current limitations, of the proposed approach when directly compared to a state-of-the-art frequency-hopping (FH) based method formulated in the same framework. Such a validation points out that if, on the one hand, the proposed MF strategy is computationally more efficient than the FH one, on the other hand, it turns out to be less reliable and accurate in several situations.
In this paper, we show the results of three case histories where GPR prospecting has been interpreted also with the aid of a specific archive research on documents of the XVI and XVII century. The case histories are related to three churches of the renaissance and baroque period in Lecce, Lecce, Southern Italy. The aim is to deliver the usefulness of GPR prospecting in these kind of monuments and to show how the likelihood of the interpretation can be increased when historical information is available.
The problem of reconstructing dielectric permittivity of a buried object from the knowledge of the scattered field is considered for a two-dimensional rectangular geometry at a fixed frequency. The linearization of the mathematical relationship between the dielectric permittivity function and the scattered field about a constant reference profile function and the approximation of actual internal field with the unperturbed field leads to the so-called Distorted Born Approximation. To analyze the limitations and capabilities of the linear inversion algorithms, we investigate the class of the retrievable profiles. This analysis makes it possible to point out that a very reduced number of independent data is available, so requiring to employ regularization techniques in order to perform in a reliable and stable way the linear inversions. In this paper we present a general algorithm consisting in a regularized Singular Value Decomposition of the matrix resulting from a discretization of the problem. Finally, numerical results of linear inversions are given.
The local-minima question that arises in the framework of a quadratic approach to inverse-scattering problems is investigated. In particular, a sufficient condition for the absence of local minima is given, and some guidelines to ensure the reliability of the algorithm are outlined for the case of data not belonging to the range of the relevant quadratic operator. This is relevant also when an iterated solution procedure based on a quadratic approximation of the electromagnetic scattering at each step is considered.
In this letter, the capabilities of two tomographic approaches for subsurface prospecting have been tested against laboratory-controlled data. The first approach is a noniterative method based on the Born approximation, while the second one is a nonlinear iterative approach. Despite some simplifications adopted in modeling the scenario, both approaches have provided satisfying results.
In this paper, the results of computer simulations used to determine the domains of applicability of the first-order Born and Rytov approximations in diffraction tomography for cross-sectional (or three-dimensional) imaging of biosystems are shown. These computer simulations were conducted on single cylinders, since in this case analytical expressions are available for the exact scattered fields. The simulations establish the first-order Born approximation to be valid for objects where the product of the relative refractive index and the diameter of the cylinder is less than 0.35 lambda. The first-order Rytov approximation is valid with essentially no constraint on the size of the cylinders; however, the relative refractive index must be less than a few percent. We have also reviewed the assumptions made in the first-order Born and Rytov approximations for diffraction tomography. Further, we have reviewed the derivation of the Fourier Diffraction projection Theorem, which forms the basis of the first-order reconstruction algorithms. We then show how this derivation points to new FFT-based implementations for the higher order diffraction tomography algorithms that are currently being developed.
Imaging subsurface cavities using geoelectric tomography and ground penetrating radar
- El-Qadi
Geo-physical detection of underground cavities
- Driad-Lebeau
Notes on perfectly matched layers (PMLs)
- Jhonson