L. Crocco

GPR Response From Buried Pipes: Measurement on Field Site and Tomographic Reconstructions

The identification of the physical nature of an object or target causing a ground-penetrating radar (GPR) anomaly, as well as the estimation of a targets dimensions and geometry, is rather challenging. To improve target identification, basic studies are still required, and they can be addressed primarily using a laboratory- or field-based physical model. The field model (test site) is usually expensive and difficult to build, but it provides data for controlled target properties and geometry from a natural environment that are essential for testing processing techniques. In this paper, we present the results from a field experiment where GPR data were collected on plastic and metallic pipes. The main objective is the comparison of the classical migration technique with a microwave tomography approach for reconstructing the geometrical target properties. The use of the microwave tomography approach will allow us to obtain more focused and stable images of the buried objects compared to the ones obtained using classical migration techniques.

An Effective Procedure for MNP-Enhanced Breast Cancer Microwave Imaging

Magnetic nanoparticles-enhanced microwave imaging has been recently proposed to overcome the limitations of conventional microwave imaging methods for breast cancer monitoring. In this paper, we discuss how to tackle the linear inverse scattering problem underlying this novel technique in an effective way. In particular, our aim is to minimize the required a priori patient-specific information, avoid occurrence of false positives, and keep the computational burden low. By relying on an extensive numerical analysis in realistic conditions, we show that the method can provide accurate and reliable images without information on the inner structure of the inspected breast and with an only rough knowledge of its shape. Notably, this allows moving to an offline stage the computationally intensive part of the image formation procedure. In addition, we show how to appraise the total amount of magnetic contrast agent targeted in the tumor.

Differential Microwave Imaging for Brain Stroke Followup

This paper deals with the possibility of adopting microwave imaging to continuously monitor a patient after the onset of a brain stroke, with the aim to follow the evolution of the disease, promptly counteract its uncontrolled growth, and possibly support decisions in the clinical treatment. In such a framework, the assessed techniques for brain stroke diagnosis are indeed not suitable to pursue this goal. Conversely, microwave imaging can provide a diagnostic tool able to follow up the disease’s evolution, while relying on a relatively low cost and portable apparatus. The proposed imaging procedure is based on a differential approach which requires the processing of scattered field data measured at different time instants. By means of a numerical analysis dealing with synthetic data generated for realistic anthropomorphic phantoms, we address some crucial issues for the method’s effectiveness. In particular, we discuss the role of patient-specific information and the effect of inaccuracies in the measurement procedure, such as an incorrect positioning of the probes between two different examinations. The observed results show that the proposed technique is indeed feasible, even when a simple, nonspecific model of the head is exploited and is robust against the above mentioned inaccuracies.

An Improved Simple Method for Imaging the Shape of Complex Targets

The linear sampling method (LSM) is a simple and effective approach to image the shape of an unknown target through the solution of a linear equation whose known term is the field radiated by an elementary (i.e., monopolar) source located in a set of test points. In this paper, we extend the LSM formulation by generalizing the right-hand side of the equation to higher order multipoles. In particular, we discuss which is the expected methods outcome after such a change and propose a post-processing scheme to combine the results obtained for different multipoles. As shown with simulated and experimental data, the proper combination of higher order multipoles allows to achieve better images of complex shaped targets as compared to the standard LSM and to overcome some of its limitations.

An adaptive wavelet-based approach for non-destructive evaluation applications

In electromagnetic inverse scattering problems the optimal representation of the unknown is a crucial task in the view of an efficient exploitation of the limited available information. With reference to the particular case of detection of defects in homogeneous materials, a non-linear inversion technique taking advantage of multiresolution features of wavelet expansions is presented. Numerical examples confirm the effectiveness of the proposed adaptive approach.

Model-Based Quantitative Cross-Borehole GPR Imaging via Virtual Experiments

In this paper, we present a new model-based linear inversion approach for cross-borehole ground penetrating radar quantitative imaging. The approach is reliable and computationally effective as it consists of the cascade solution of two linear inverse problems. The first problem yields a qualitative image of the targets (i.e., their location and approximate shape) and the information needed to cast a set of virtual experiments wherein a linear scattering model that implicitly depends on unknown targets holds true. By relying on such a model, it is possible to achieve, via linear inversion, a quantitative estimate of the targets electric permittivity and conductivity in a much broader range of cases as compared with traditional approximations, such as the Born approximation. The quantitative imaging capabilities of the proposed method are enhanced by means of an original strategy, in which the features of virtual experiments are exploited to counteract the data reduction caused by the aspect limitation of the measurement configuration. Results against simulated data are reported to show the capability to successfully image nonweak scatters.

A review on ground penetrating radar technology for the detection of buried or trapped victims

The localization of people buried or trapped under snow or debris is an emerging field of application of ground penetrating radar (GPR). In the last years, technological solutions and processing approaches have been developed to improve detection accuracy, speed up localization, and reduce false alarms. As such, GPR can play an active role in cooperative approaches required to tackle such emergencies. In this work, we present and briefly analyze the evolution of research in this field of application of GPR technology. In doing so, we adopt a point of view that takes into account that avalanches and collapsed buildings are two scenarios that call for different GPR approaches, since the former can be tackled through image processing of radar data, while the latter rely on the detection of the Doppler frequency changes induced by physiological movements of survivors, such as breathing.

Focusing Time-Harmonic Scalar Fields in Complex Scenarios: A Comparison

This letter deals with the problem of focusing a time-harmonic wave into a target point embedded into a known complex scenario. In particular, we compare the performances of the Time Reversal approach and the Optimal Constrained Focusing technique, which relies on the formulation of the focusing problem in terms of convex programming. Both techniques guarantee a fast and adaptive design of effective applicators, but the second one allows to control the sidelobes of the field, providing a higher selectivity and a more flexible shaping of the field. Some numerical examples relevant to microwave hyperthermia, including a case where the scenario at hand is not exactly known, are given to appraise the importance of this capability.

Interpreting complex, three-dimensional, near-surface GPR surveys: an integrated modelling and inversion approach

With the increasing computational power of modern personal computers, sophisticated modelling and inversion techniques are becoming popular tools for the interpretation of high-resolution, fully three-dimensional GPR surveys. In this paper, we present the latest results of ongoing practical research into the development of novel, integrated, finite-difference time-domain (FDTD) numerical modelling and linear tomographic inversion methods for the interpretation and analysis of near–surface, 3D GPR data. The proposed approach utilizes the Born approximation solution to the inverse-scattering problem and a truncated singular value decomposition (TSVD) to create the final, inverted reconstructions. A three-dimensional, full-field, O(2,4) accurate FDTD modelling scheme is used to generate the numerical-based Green’s functions and incident fields for the inversion. As such, accurate antenna sources (including the influence of shields) and near-field air/ground interface effects are inherently included in the inversion formulation. The performance of this integrated method is evaluated via a simulated, 3D, forensic-based, test-case example (a 900 MHz survey over a clandestine human burial target) including coherent noise from near-surface clutter. Although the example is simplistic, the results show that the scheme works well, despite some assumptions in the inversion methodology. As such, useful information can be gained on the true form, depth, location and spatial interrelationships of the buried features and, therefore, improved interpretations can be obtained in a three-dimensional context.

Quasi — Invisibility via inverse scattering techniques

The paper investigates the feasibility of an approach to design effective cloaking devices by means of a joint exploitation of available degree of freedom in synthesis strategies and the physical mechanism underlying cloaking. A different point of view in the design of dielectric covers that minimize the scattering cross section of dielectric objects is introduced and new opportunities are outlined to perform an effective synthesis of cloaking profiles via inverse scattering techniques.