Application of coupled-wave Wentzel-Kramers-Brillouin approximation to ground penetrating radar

This paper deals with bistatic subsurface probing of a horizontally layered dielectric half-space by means of ultra-wideband electromagnetic waves. In particular, the main objective of this work is to present a new method for the solution of the two-dimensional back-scattering problem arising when a pulsed electromagnetic signal impinges on a non-uniform dielectric half-space; this scenario is of interest for ground penetrating radar (GPR) applications. For the analytical description of the signal generated by the interaction of the emitted pulse with the environment, we developed and implemented a novel time-domain version of the coupled-wave Wentzel-Kramers-Brillouin approximation. We compared our solution with finite-difference time-domain (FDTD) results, achieving a very good agreement. We then applied the proposed technique to two case studies: in particular, our method was employed for the post-processing of experimental radargrams collected on Lake Chebarkul, in Russia, and for the simulation of GPR probing of the Moon surface, to detect smooth gradients of the dielectric permittivity in lunar regolith. The main conclusions resulting from our study are that our semi-analytical method is accurate, radically accelerates calculations compared to simpler mathematical formulations with a mostly numerical nature (such as the FDTD technique), and can be effectively used to aid the interpretation of GPR data. The method is capable to correctly predict the protracted return signals originated by smooth transition layers of the subsurface dielectric medium. The accuracy and numerical efficiency of our computational approach make promising its further development

TU1208 open database of radargrams. the dataset of the IFSTTAR geophysical test site

This paper aims to present a wide dataset of ground penetrating radar (GPR) profiles recorded on a full-size geophysical test site, in Nantes (France). The geophysical test site was conceived to reproduce objects and obstacles commonly met in the urban subsurface, in a completely controlled environment; since the design phase, the site was especially adapted to the context of radar-based techniques. After a detailed description of the test site and its building process, the GPR profiles included in the dataset are presented and commented on. Overall, 67 profiles were recorded along eleven parallel lines crossing the test site in the transverse direction; three pulsed radar systems were used to perform the measurements, manufactured by different producers and equipped with various antennas having central frequencies from 200 MHz to 900 MHz. An archive containing all profiles (raw data) is enclosed to this paper as supplementary material. This dataset is the core part of the Open Database of Radargrams initiative of COST (European Cooperation in Science and Technology) Action TU1208 “Civil engineering applications of Ground Penetrating Radar”. The idea beyond such initiative is to share with the scientific community a selection of interesting and reliable GPR responses, to enable an effective benchmark for direct and inverse electromagnetic approaches, imaging methods and signal processing algorithms. We hope that the dataset presented in this paper will be enriched by the contributions of further users in the future, who will visit the test site and acquire new data with their GPR systems. Moreover, we hope that the dataset will be made alive by researchers who will perform advanced analyses of the profiles, measure the electromagnetic characteristics of the host materials, contribute with synthetic radargrams obtained by modeling the site with electromagnetic simulators, and more in general share results achieved by applying their techniques on the available profiles

NASA thesaurus. Volume 2: Access vocabulary

The Access Vocabulary, which is essentially a permuted index, provides access to any word or number in authorized postable and nonpostable terms. Additional entries include postable and nonpostable terms, other word entries, and pseudo-multiword terms that are permutations of words that contain words within words. The Access Vocabulary contains 40,738 entries that give increased access to the hierarchies in Volume 1 - Hierarchical Listing

Radar Imaging in Challenging Scenarios from Smart and Flexible Platforms

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NASA thesaurus. Volume 2: Access vocabulary

The access vocabulary, which is essentially a permuted index, provides access to any word or number in authorized postable and nonpostable terms. Additional entries include postable and nonpostable terms, other word entries and pseudo-multiword terms that are permutations of words that contain words within words. The access vocabulary contains almost 42,000 entries that give increased access to the hierarchies in Volume 1 - Hierarchical Listing

Satellite measurement of ocean turbulence

Turbulence and mixing in the surface layer of the ocean is a significant element in the combined ocean-atmosphere system, and plays a considerable role in the transfer of heat, gas and momentum across the air-sea boundary. Furthermore, improving knowledge of the evolution of energy within the ocean system, both globally and locally, holds importance for improving our understanding of the dynamics of the ocean at large- and small-scales. As such, insight into turbulence and turbulent flows at the ocean surface is becoming increasingly important for its role in ocean-atmosphere exchange and, from a wider perspective, climate change.A research project was initiated to understand the role that spacecraft remote-sensing may play in improving observation of “turbulence” (in a broad sense) in the ocean, and for identifying how steps towards such observation may be made. An initial, exploratory study identified the potential benefit of Synthetic Aperture Radar in “bridging the gap” between in-situ and remote observations o

Journal of Telecommunications and Information Technology, 2017, nr 3

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NASA Thesaurus. Volume 1: Hierarchical listing

There are 16,713 postable terms and 3,716 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary

NASA thesaurus. Volume 1: Hierarchical Listing

There are over 17,000 postable terms and nearly 4,000 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary and Volume 3 - Definitions

Propagation of Waves in Inhomogeneous Media

Waves propagating in an inhomogeneous medium differ from waves in uniform surroundings through the dependence of their properties on the variation of the physical parameters of the medium. In this thesis, we will investigate the effects of inhomogeneity on wave propagation in two different cases - introducing the subject via propagation of waves in non-uniform atmospheres and culminating in a full analytic solution of the cold plasma equations describing wave propagation in a plasma with a spatially rotating magnetic field. Plasmas can support a wide variety of waves. In non-uniform plasmas, it is of great interest to consider the possibility of one type of wave undergoing mode conversion to a completely different wave - a phenomenon used to heat plasmas in fusion reactor experiments. In Chapter 1, we present an overview of plasmas in general and consider their widespread natural occurrence and the vast range of their characteristic parameters. This chapter also contains the definition of certain basic plasma quantities, such as plasma frequency, which will be used extensively in later chapters and a discussion of plasma confinement systems, illustrating the magnetic field configurations of interest in the context of fusion reactors. Mode conversion is introduced formally in Chapter 2 where various approaches are discussed. The philosophy behind the powerful WKBJ theory, which applies to slowly-varying media, is presented as a natural extension of the description of waves in uniform media. The "local dispersion relation" method favoured by many authors is examined critically and an alternative description is outlined which is derived from the full differential equation including the gradient terms. The equations of fluid theory are derived from kinetic theory in Chapter 3 using the method of moments. We discuss how a cold (pressureless) plasma may be described satisfactorily using these equations. Thus, we conclude that the same basic set of equations may be applied to propagation of waves in a cold plasma and a neutral atmosphere (with the removal of electromagnetic forces and addition of a gravitational field). As a simple introduction to the study of wave propagation in inhomogeneous media, we consider the propagation of waves in an atmosphere where the temperature (and hence sound speed) varies with height. Oscillations in an isothermal atmosphere are shown to possess two branches corresponding to acoustic and gravity waves. In considering non-uniform atmospheres, the work of authors in the fields of atmospheric and solar physics is combined and reviewed. The isothermal dispersion relation is demonstrated to be inadequate in describing waves in temperature stratified atmospheres. It is found that the ordinary differential equation constructed only has solutions for a limited number of special cases of temperature variation and, in general, requires numerical solution. Chapter 5 contains the analysis of the propagation of cold plasma waves in a constant magnetic field. In particular, we examine propagation perpendicular to the magnetic field direction in order to provide the background for the equivalent inhomogeneous case of Chapter 6. In Chapter 6 we solve the problem of wave propagation in a spatially rotating magnetic field. It is shown that, in order to balance the gradient of the equilibrium magnetic field, a current is required which we partition between the ions and electrons. The number of non-vanishing equilibrium quantities is therefore considerably extended from the uniform situation of Chapter 5, leading to a significant alteration of the form of the Ohm's Law which must now contain the electric field plus its first two derivatives. By transforming reference frame, it becomes possible to eliminate the position-dependent coefficients of the differential equations and thus derive a dispersion relation describing waves in such a field structure. It is shown that the waves consist of a propagating part modulated by a periodic envelope induced by the periodicity of the field. Finally, in Chapter 7, we make suggestions for extensions of the work of Chapter 6