Near-Surface Interface Detection for Coal Mining Applications Using Bispectral Features and GPR

The use of ground penetrating radar (GPR) for detecting the presence of near-surface interfaces is a scenario of special interest to the underground coal mining industry. The problem is difficult to solve in practice because the radar echo from the near-surface interface is often dominated by unwanted components such as antenna crosstalk and ringing, ground-bounce effects, clutter, and severe attenuation. These nuisance components are also highly sensitive to subtle variations in ground conditions, rendering the application of standard signal pre-processing techniques such as background subtraction largely ineffective in the unsupervised case. As a solution to this detection problem, we develop a novel pattern recognition-based algorithm which utilizes a neural network to classify features derived from the bispectrum of 1D early time radar data. The binary classifier is used to decide between two key cases, namely whether an interface is within, for example, 5 cm of the surface or not. This go/no-go detection capability is highly valuable for underground coal mining operations, such as longwall mining, where the need to leave a remnant coal section is essential for geological stability. The classifier was trained and tested using real GPR data with ground truth measurements. The real data was acquired from a testbed with coal-clay, coal-shale and shale-clay interfaces, which represents a test mine site. We show that, unlike traditional second order correlation based methods such as matched filtering which can fail even in known conditions, the new method reliably allows the detection of interfaces using GPR to be applied in the near-surface region. In this work, we are not addressing the problem of depth estimation, rather confining ourselves to detecting an interface within a particular depth range

Site Interiography and Geophysical Scanning: Interpreting the Texture and Form of Archaeological Deposits with Ground-Penetrating Radar

The remarkable potential of geophysical scanning—to assess the internal variability of sites in new ways, to highlight important phenomena in the field, to exercise co-creation of interpretation and commitment to minimal destruction of community partners’ resources, and to aid in the practice of due diligence in avoiding desecration of the sacred—continues to be underutilized in archaeology. While archaeological artifacts, features, and strata remain primary foci of archaeological geophysics, these phenomena are perceived quite differently in scans than in visual or tactile exposures. In turn, new registers of site exploration afforded by geophysical prospection may be constrained by the language of site excavation and visual observation, requiring adjustments in the ways of thinking about and describing what the instruments are measuring. The texture and form of site deposits as rendered in ground-penetrating radar scans can be examined in detail prior to making interpretations of cultural features or stratigraphy. Far more than simple “anomalies” demanding our attention for excavation, patterns in geophysical data can be the focus of extensive archaeological analysis prior to, in conjunction with, or independent from excavation

Ground-penetrating radar evaluation of the ancient Mycenaean monument Tholos Acharnon tomb

The assessment of cultural heritage requires high-resolution and non-destructive methodologies. Ground-penetrating radar is widely applied in the inspection of historical buildings. However, some structures with curved surfaces make the radar data acquisition process difficult and consequently the following data interpretation. This paper describes a case study concerning a circular and buried Greek monument. This monument is a magnificent tomb buried with irregular stones. However, its structure and the internal stones arrangement are unknown. Therefore, a radar survey was carried out to achieve two main objectives: (i) identification of hidden elements and arrangement of the stones and (ii) detection of specific zones where further restoration and maintenance should be recommended. The methodology for the radar data acquisition involves the use of a laser scan in order to define accurately each radar line, covering all the internal surface of the tomb. Radar data processing was developed by converting Cartesian coordinates into polar coordinates. This procedure allows defining better the internal anomalies, improving the radar data interpretation. The main results of the survey were three: (i) the presence of a hidden target buried in the corridor access to the tomb; (ii) the description of the internal structure of the walls of the tomb, defining the stones arrangement and the position and depth to the keystone; and (iii) the existence of delimited zones where the signal is highly attenuated, probably due to a high salt content.Peer ReviewedPostprint (author's final draft

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

How Close are the Edges of a Closed Fracture?

A laboratory experiment is peresented where the theory of amplitude reflection tuning in thin beds is tested. The results show a very good agreement with the theory previsio

6-meter wavelength polarimetric inverse synthetic aperture radar mapping of the Moon

Remote sensing of planetary surfaces is an effective method for gaining knowledge of the processes that shape the planetary bodies in our solar system. This is useful for uncovering the environment of the primordial solar system and to study the current state of the upper crusts of the other planets in our neighborhood. A recent 6-meter wavelength polarimetric radar map of the Moon showed unexpectedly low depolarized radar returns in two regions on the lunar nearside. These two areas were a highland region between Mare Imbrium and Mare Frigoris, and the highland area surrounding the Schiller-Zucchius impact basin. These two regions showed characteristics unlike those of typical highland regions of the lunar surface. So far, there has been no readily available explanation for this observation. In this study, it is shown that the likely cause is an increased loss tangent due to chemical differences in the first few hundred meters of the lunar soil. We also show the absence of any coherent subsurface, which could be the preserved remains of an ancient basaltic plain. We do this by comparing the 6-meter polarimetric radar map to other relevant data sets: 1) surface TiO_2 and FeO abundance, 2) surface rock population, 3) radar maps of the Moon with other wavelengths, and 4) visual spectrum images of the Moon. The area near the Schiller-Zucchius basin was shown to be consistent with other areas with similar surface chemical compositions, but the region between Mare Imbrium and Mare Frigoris showed significantly lower mean power in comparison to otherwise similar regions. While we can not conclusively determine the cause, we hypothesize that the low radar return is explained by an increased concentration of iron and titanium oxides in the volume beneath the surface, potentially due to remnants of primordial lunar volcanism. The results show that long wavelength polarimetric radar measurements of the Moon are very powerful tools for studying the earliest stages of the evolution of the Moon

“Unlocking” the Ground: Increasing the Detectability of Buried Objects by Depositing Passive Superstrates

One of the main problems when trying to detect the position and other characteristics of a small inclusion into lossy earth via external measurements is the inclusion’s poor scattering response due to attenuation. Hence, increasing the scattered power generated by the inclusion by using not an active but a passive material is of great interest. To this direction, we examine, in this work, a procedure of “unlocking” the ground by depositing a thin passive layer of conventional material atop of it. The first step is to significantly enhance the transmission into a lossy half space, in the absence of the inclusion, by covering it with a passive slab. The redistribution of the fields into the slab and the infinite half space, due to the interplay of waves between the interfaces, makes possible to determine the thickness and permittivity of an optimal layer. The full boundary value problem (including the inclusion and the deposited superstrate) is solved semi-analytically via integral equations techniques. Then, the scattered power of the buried inclusion is compared to the corresponding quantity when no additional layer is present. We report substantial improvement in the detectability of the inclusion for several types of ground and burying depths by using conventional realizable passive materials. Implementation aspects in potential applications as well as possible future generalizations are also discussed. The developed technique may constitute an effective “configuration (structural) preprocessing” which may be used as a first step in the analysis of related problems before the application of an inverse scattering algorithm concerning the efficient processing of the scattering dat

“Unlocking” the Ground: Increasing the Detectability of Buried Objects by Depositing Passive Superstrates

One of the main problems when trying to detect the position and other characteristics of a small inclusion into lossy earth via external measurements is the inclusion’s poor scattering response due to attenuation. Hence, increasing the scattered power generated by the inclusion by using not an active but a passive material is of great interest. To this direction, we examine, in this work, a procedure of “unlocking” the ground by depositing a thin passive layer of conventional material atop of it. The first step is to significantly enhance the transmission into a lossy half space, in the absence of the inclusion, by covering it with a passive slab. The redistribution of the fields into the slab and the infinite half space, due to the interplay of waves between the interfaces, makes possible to determine the thickness and permittivity of an optimal layer. The full boundary value problem (including the inclusion and the deposited superstrate) is solved semi-analytically via integral equations techniques. Then, the scattered power of the buried inclusion is compared to the corresponding quantity when no additional layer is present. We report substantial improvement in the detectability of the inclusion for several types of ground and burying depths by using conventional realizable passive materials. Implementation aspects in potential applications as well as possible future generalizations are also discussed. The developed technique may constitute an effective “configuration (structural) preprocessing” which may be used as a first step in the analysis of related problems before the application of an inverse scattering algorithm concerning the efficient processing of the scattering dat

Prehistoric Human Ecodynamics in the Rub Al-Khali Desert: Results of Remote Sensing and Excavations in Dubai, United Arab Emirates

Archaeological investigations in the Emirate of Dubai, UAE conducted by the Dubai Department of Archaeology and the University of Arkansas demonstrate that the desert inland of the Oman Peninsula was occupied not only during the Arabian Neolithic (8000-4400 BC), when the region experienced a moist period referred to as the Holocene Climatic Optimum (HCO), but also during the more arid millennia following the decline of the HCO into the Christian Era. During this period, desert settlement clustered near a band of oases, in contrast to the more widespread spatial distribution of remains of nomadic pastoralists from the Neolithic. Excavations at al- Ashoosh and Saruq al-Hadid, two sites at the southern end of the Emirate of Dubai, coupled with analysis of dune accumulation at Saruq al-Hadid through ground-penetrating radar, and a regional analysis of groundwater availability based on satellite imagery, reveal the varied landscapes that made desert settlement possible and provide a chronology of inland settlement and landscape transformation for a time and place that was not well documented before this study. Evidence presented in this dissertation suggests that these inland oases were dynamic environments that influenced patterns of desert settlement and land use, and in turn were shaped by the varied activities of prehistoric people. Periodic occupation at both sites began with seasonal encampments during a third millennium pluvial and resumed during arid phases in the second and first millennia. Late occupation was likely supported by shallow groundwater that was fed by orographic rainfall in the Oman Mountains, rather than by precipitation on the desert plain. Occupation during the first millennium BC was distinct from earlier periods in that is showed clear integration into a regional political and economic network, first in its incarnation as a cultic site in the Iron Age II period (900-600BC), and following that as a center for metal working at the end of the first millennium. A hiatus in settlement at Saruq al-Hadid following the Iron Age II period and roughly coincident with the Iron Age III (600-300 BC) is marked by significant dune accumulation. The question remains whether this period of active sediment redeposition was a local or regional phenomenon, but the case is made here that it was a regional change triggered by the destabilization of sand dunes as natural vegetative cover was removed by growing herds of grazing animals and an expansion of agriculture in the Iron Age II period. These findings fill gaps in the histories of climate and settlement of southeast Arabia and more broadly, help to move us closer to understanding the complex exchanges between changes in climate, landscapes, and human activities in arid regions through time and worldwide