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Fifth International Conferention on Ground Penetrating Radar
- Conference date: 12 Jun 1994 - 16 Jun 1994
- Location: Kitchener, Canada
- Published: 12 June 1994
21 - 40 of 95 results
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Bridge deck and pavement evaluation using BBL's ground penetrating radar technology
Authors Guy L. Mailhot and Michel ParentThis paper describes ground penetrating radar technology developed by Beauchemin-BeatonLapointe. Inc. as a practical tool in the evaluation of bridge decks and pavements. Described in the paper is the radar equipment used by BBL which includes the 2.5 GHz "Hom Type Antenna" recently developed by GSSI, the sophisticated and state-of-the-art software developed in-house to acquire, process, analyze the data and to present the results in a practical format using AutoCADTM. compatible drawings. Also discussed is the inspection vehicle and set-up used to collect the radar data. Presented in the paper are certain results of an actual survey using the developed technology on the Jacques Cartier Bridge Deck in Montreal, pavement evaluation work performed and currently underway (thickness measurement and void detection) as well as the results of experimental tests performed at McGill University. Also described is the integration of BBL's radar technology with existing and complementary infrared thermography technology for bridge deck evaluation, which enables a complete integration of radar, infrared thermography, and standard video images in order to provide a complete and accurate assessment of bridge decks.
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GPRSIM Forward Modeling Software and Time Slices in Ground Penetrating Radar Surveys
Authors Dean Goodman, Yasushi Nishimura and Kouji TobitaSimulation of ground penetrating radar using an exact ray tracing interactive software, the dispersive nature ofmaterials and their impact they could have on simulating ground penetrating radar, and a useful description and examples on how to create radar time slices that can help to illuminate target features are presented.
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Highway speed radar for pavement thickness evaluation
More LessAccurate knowledge of pavement layer thicknesses is important for accurate backcalculation of pavement layer properties as well as for network-level pavement condition inventories. Often this information is unknown, and records are inaccurate, or difficult to access. This paper describes a self-calibrating Ground penetrating Radar (GPR) system for highway speed pavement layer thickness evaluation. The radar system incorporates air-coupled horn antennas, PC based digital data acquisition, and software for computing pavement properties from raw waveforms. A software system called PAVLAYER~ has been developed and extensively tested for pavement thickness evaluation. This system has demonstrated an accuracy ranging from 5 to 10 percent for asphalt layer thickness, and 10 to 15 percent for base layer thickness. These accuracy figures are based on test data from 100 pavement sections and correlation with data from 594 cores and test pits. The paper describes the details of the hardware and software components and the analytic methods used in the pavement thickness evaluation system. Also presented are descriptions of, and results from, field evaluation programs in which the radar results were correlated with ground truth. These programs have been carried out with federal and local highway agencies in 20 different states in the U.S., in the U.K. and in Germany. Each of these programs have involved radar surveys of pavement sections representing different ages, pavement designs and pavement condition. Extensive coring has been carried out to confirm the radar predictions, and the correlation between core and radar data are presented. The reported results also show how the accuracy of the layer thickness calculations are affected by different variables and how other pavement structure and condition information is revealed in the radar data. Specific results are presented showing repeatability, and the influence of the survey speed, moisture on the pavement surface, surface treatments and thin overlays, and pavement age and structure.
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A comperative study of ground probing radar and impact echo nodestructive techniques for detecting and locating buried objects
Authors M. Momayez, A. Sadri and F.P. HassaniThe comparison of two nondestructive testing methods for detecting flaws and locating buried objects in concrete is the focus of this paper. Applications of Ground Probing Radar (GPR) and Impact Echo (IE) techniques are examined. In addition, this investigation shows thatwhen GPR and IE are used in tandem, extensive information about the integrity of concrete can be obtained in a short period of time. GPR is an electromagnetic reflection technique utilizing nonionized microwaves whereas IE makes use of transient stress wave reflections. Although both techniques are based on wave reflection, the nature of the information carried in the reflection signals from GPR and IE is different and complimentary when combined together. In this study, a large concrete slab was prepared with various types of objects such as rebars, metal and plexiglass plates, rocks and thin plastic sheets simulating cracks placed in it. It is shown that GPR can be used to detect flaws and buried objects rapidly while IE can locate flaws and buried objects accurately and provide reliable data on the mechanical properties of concrete. The combined use of Ground Probing Radar and Impact Echo techniques is an effective tool for concrete monitoring and quality control.
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Pavement evaluations using ground penetrating radar in Texas
Authors T. Scullion, C.L. Lau and Y. ChenThis paper describes the OPR system developed and implemented for the Texas Department of Transportation (TxDOT). The system includes a Penetradar PS-24 OPR system together with a data acquisition and signal processing system developed by the Texas Transportation Institute. The entire system is housed in a data acquisition vehicle which also includes distance measuring equipment and a synchronized video recording system. The OPR has been used on several major pavement projects in Texas. The antenna is air launched and suspended between 250 and 350 mm above the pavement and has been shown to operate adequately at close to highway speeds (50 kph). In this paper the signal processing algorithms will be described together with results from a series of case studies. The signal processing system tracks the reflections and measures their amplitudes and arrival times on a trace by trace basis. Methods of cleaning up the signal with end reflection subtraction and of accommodating antenna bounce have been built into the software. From typical OPR reflections from pavements the layer dielectrics and thicknesses can be calculated for a maximum of 4 distinct layers. The moisture content of typical granular base material has been related to the relative dielectric value of the layer. The detection of pavement defects, such as voids, has been related via decision rules to the measured amplitudes, dielectrics and thicknesses and their variance along a highway. Field measurements and ground truth information will be reported on several in service pavements in Texas. These applications include layer thickness determination, void detection and locating areas of asphalt stripping.
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GPR for snow pack water content
Authors A.P. Annan, S.W. Cosway and T. SigurdssonGPR offers a simple and rapid means of providing information for mapping snow thickness. Snow thickness data are of great importance in hydrological studies where snow melt can lead to floodIng. In many countries with hydroelectric power generation, water storage in the snow pack represents a key input to reservoir level control planning. At first glance, the snow thickness problem would appear trivial, and indeed measurement of snow thickness can be straight forward. Unfortunately, the economic applications of snow thickness data require equivalent water content (not snow thickness)!! To effectively use snow thickness information, it is necessary to develop systematic procedures for transforming GPR snow thickness observations to water content. In this paper we describe the steps required to achieve the water content objective. An illustration of this approach and associated difficulties is provided using multi fold GPR data acquired on an area of multi-year snow in Norway.
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Geotechnical investigations of insulated permafrost slopes along the Norman wells pipeline using ground penetrating radar
Authors Brian Moorman, Alan Judge, Margo Burgess and Tom FridelDuring construction of the Norman Wells pipeline, 56 permafrost slopes were covered with a 0.5 m to 1.8m insulating blanket of wood-chips in an attempt to retard the rate ofpermafrost thaw. Warmer mean annual pipe operating temperatures (OC to 3.5C) than anticipated have led to larger thaw bulbs than predicted beneath many insulated slopes. Initially, manual probing with an active layer probe was used to monitor the development of the thaw bulbs. However, as the depth-of-thaw increased to over 2 m in some areas, manual frost probe measurements became time consuming. A series of experiments were conducted to test the ability of ground penetrating radar to determine the thermal, lithologic, and structural characteristics ofwood-chip slopes. On many ofthe slopes, gridded surveys were conducted enabling three dimensional subsurface analyses and the construction of isopleth maps of the depth-of-thaw. In this paper we show examples of lithologic mapping, including qualitative indications of the ice-content of soils, mapping the boundaries between soil units and imaging internal bedding structures within units. The thermal structure of the subsurface is examinedby interpolating the depth of frost layers on radar profiles, and by mapping the depth ofmultiple frost layers with isopleth maps. An example of mapping the lateral of extent of subsurface cavities is also discussed. In general, the depth of signal penetration ranged from as great as 10min frozen sand to as little as 3 m in unfrozen clayey soil. Surveys at 50 MHz contained the most information and the depth-of-thaw was best mapped when it was deeper than 1.5 m below the surface.
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Airborne snow thickness radar
Authors Louis Lalumiere, James Rossiter and Simon PrinsenbergA ground penetrating radar (GPR) system for measuring snow thickness has been developed as a component of an operational airborne sea ice thickness sensor, Ice Probe. Ice Probe is a helicopter borne sensor utilizing an electromagnetic (EM) induction sensor and a laser profilometer to determine the combined thickness of ice and snow in real-time. With a GPR system to provide snow thickness information, Ice Probe can report ice and snow thicknesses separately.
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The use of ground penetrating radar to search for persons buried by avalanches
Authors Jürgen Niessen, Erich Kliem, Erhard Pöhlking and Klaus-Peter NickAlthough, in areas at risk from avalanches, skiers outside the safe ski-runs should carry an electronic transmitter with them in case they are buried by an avalanche, there is still an urgent need to locate buried persons exactly by means of an independent sensor in the presence of other objects. A demonstration of the ability of ground penetrating radar to help to find people under a snow cover was carried out in the German Alps under fairly realistic conditions. Of course, these measurements were not performed with real victims: the Bavarian Mountain Rescue Service prepared a professional test area for the trials. To prevent the occurrence of avalanches, the Bavarian Avalanche Warning Service regulary checks suspicious snow slopes with the aid of probes. The critical snow layers which are responsible for the production of avalanches were also investigated with the radar.
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Use of ground penetrating radar to study the interaction between permafrost and airport infrastructure on Baffin Island N.W.T.
Authors J.A. Pilon, M. Pilkington, M. Allard and J. FrydeckiIn this paper we present the results of Ground Penetrating Radar (GPR) surveys conducted at three airports on Baffin Island, N.W.T. These airports are Pangnirtung, Broughton Island and Clyde River and are operated by the Arctic Airport Division of the Department of Transportation of the Government of the North West Territories. They were selected because they are scheduled for improvements and resurfacing (Broughton Island and Clyde River) to correct for the occasional "soft spots" on the runways and are experiencing problems related to permafrost (Pangnirtung) where the runway lighting system undergoes annual failures in mid to late winter. The results of the GPR surveys show that in Pangnirtung the problem is related to frost cracking above active ice wedges beneath the runway, whereas the surface instability problems at the other two sites appear to be related to the presence of saline permafrost at some depth beneath the runways.
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The integration of radar, magnetic, and terrain conductivity data in an archaeological investigation of a Hudson Bay's company fur trade post
Authors Paul Bauman, Roderick Heitzmann, John Porter, Janan Sallomy, Mike Brrewster and Chris ThompsonIn 1799, the site of Rocky Mountain House, Alberta, stood at the southwestern comer of the northern fur empires of the North West Company and their competition, the Hudson's Bay Company. Between 1799 and 1875, four forts were constructed by these companies at Rocky Mountain House. The third of these forts, which stood from 1835 until 1861, has been only partially excavated. The goal of this investigation was to evaluate the utility of geophysics as an archaeological aid in studying historic sites in Western Canada. The specific objectives were to identify the position of the rooms and palisades of the 1835 fort, and to locate burial sites associated with this and other forts. A challenging obstacle in describing the 1835 fort using geophysics is the fact that in 1861, the Blackfoot peoples burned the fort to the ground. Information from three geophysical methods are discussed. Ground penetrating radar data provided the greatest detail in describing fort construction and burial locations. The GPR data, however, would have been of limited use if not viewed in conjunction with the information provided by magnetic gradient, and terrain conductivity plots of the particular sites. The integration of the various methods provided an overall plan of the original construction of the 1835 fort. While GPR most clearly identified approximately 50 graves at one large cemetery, terrain conductivity mapping was superior in locating probable coffins at a second, smaller burial site. Beyond being a good example of an archaeogeophysical data set, the significance of this paper is the clarity with which it is shown the need to integrate a number of geophysical techniques at investigations of historic sites in Western Canada.
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Relationships between Dielectric and Hydrogeologic Properties of Sand-Clay Mixtures
Authors Michael D. Knoll and Rosemary KnightA series of laboratory experiments was performed to investigate relationships between dielectric properties and hydrogeologic properties such as lithology, porosity and water saturation of granular materials. Mixtures of sand, clay, air and water were prepared to vary hydrogeologic parameters systematically. Lithologic variation was simulated by varying the relative proportion of sand and clay in the mixtures. Compaction was simulated by packing different volumes of sand and clay (in the same relative proportion) into the sample holder. Water saturation was varied by injecting water into the pore space and by evaporative drying. The experimental data (i.e., measurements of porosity, clay content, water saturation, dielectric constant, electrical conductivity and frequency) may be used to test dielectric mixing formulas and effective medium theories. Results show that much of the scatter in dielectric property-hydrogeologic property crossplots is due to systematic variation in interrelated hydrogeologic and/or dielectric parameters. For instance, the relationship between dielectric constant and porosity for dry or saturated materials may be multi-valued if there are also changes in clay content. However, different mechanisms of porosity reduction may be associated with characteristic dielectric responses. Porosity reduction by compaction results in an increase in dielectric constant for dry materials and a decrease in dielectric constant for saturated materials. Porosity reduction by pore-filling (i.e., changing lithology) results in either an increase or a decrease in dielectric constant depending upon the volume fractions, microgeometries and surface properties of the components. These results provide insight into the types of changes one may expect to see in ground penetrating radar data from different geologic settings, and hence should be of interest to those involved in modeling, inversion and stratigraphic interpretation of ground penetrating radar data.
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White marble dam, North Adams, Massachusetts
Authors Doria Kutrubes, Mark Blackey and Thomas JenkinsGround penetrating radar (GPR) was used to determine the thickness and configuration of a 156 year-old white marble block dam, believed to be the only one of its kind in North America. The dam, currently in disrepair, is within Natural Bridge State Park and is owned and managed by the Commonwealth of Massachusetts, Department of Environmental Management (MADEM). System calibrations on exposed marble blocks determined that average .GPR signal propagation velocity is approximately 0.105 mlns (0.344 ft/ns). The dam's thickness east of the sluice is approximately 1.8 meters (6 feet) at the spillway crest and 2.7 meters (9 feet) at the toe. In contrast, the dam's crest west of the sluice has a measured thickness of only 1.2 meters (5 feet). The marble dam appears to be constructed directly on top of bedrock, and bedrock may be incorporated into the dam's structure in some areas. By identifying the dam's thickness and upstream-face geometry, this GPR survey helped MADEM's consulting engineers to stabilize the dam and design a dredging program for the silted-in upstream impoundment while preserving the structure's historical integrity.
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Geophysical investigations with the georadar in the middle of Athens at Syntagma square and the discovery of the subterranean river Eridanos
Authors Stavros P. Papamarinopoulos and Marina G. PapaioannouDuring extensive geophysical exploration in the middle of Athena for the location of archaeological remains, an unexpected geophysical finding was revealed. The 80 l\AHz monostatic antenna of the georadar was utilized around the Square. At Metropoleos Street, in the extension of Philellenon Street and parallel to it, in five different and parallel vertical sections, the image of a river was depicted. The minimum of the river bed is at 6 m below the asphalt and its width is about 10 m. There is another possible palaeobed 30 m wide at 14 m depth below the level of the pedestrians. This river is the legendary Eridanos mentioned by ancient writers such as Hesiod, Plato, Strabo and Pausanias. It was associated with the earliest traditions of the Hellenes and its location and direction is associated with important buildings of classical Athena. Up to now its very existence, position and direction was doubtful. The river seems to originate from the Lecabettus hill rolling towards lower elevation, intersecting Syntagma Square and meandering towards the West part ofthe city.
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Detection of bedrock fractures and lithologic changes using borehole radar at selected sites
Authors John W. Lane, F.P. Haeni and John H. WilliamsBorehole-radar methods were used to map fractures and lithologic changes in metamorphic and igneous rock at sites in New Hampshire and Massachusetts, and in sedimentary rock at a site in lllinois. Interpretations of single-hole and cross-hole surveys were correlated with other geophysical and hydrologic data. Single-hole borehole-radar surveys using directional antennas were conducted in New Hampshire and Massachusetts. The surveys detected reflectors, which are interpreted as individual fractures or fracture zones that extend laterally up to 40 m (meters) from wells. Average radar velocities at the sites are 0.113 mlns (meters per nanosecond) in gneiss and 0.123 mlns in granite. Single-hole directional surveys were also conducted in lllinois. Reflectors that are interpreted as fracture zones and lithologic changes in dolomite were detected up to 25 m from the wells, and reflectors that are interpreted as solution zones were detected up to 15 m from the wells. The radar velocity in rock at this site is 0.081 mlns. Changes in lithology and permeability appear to correlate with differences in the amplitude and arrival time of the radar pulse that travels through the bedrock directly between transmitter and receiver. Cross-hole radar tomography surveys were conducted at the Massachusetts and lllinois sites to determine velocity and attenuation changes in bedrock between wells. Low-velocitylhighattenuation zones identified can be interpreted as lithologic boundaries and (or) water-saturated fracture zones.
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Analysis of a directional borehole radar signal with a time-frequency distribution
Authors Sato Motoyuki, Ebihara Satoshi and Niitusma HiroakiThe authors developed a directional borehole radar which is equipped with conformal micro array antennas on a conducting cylinder. We estimate the incident angle of incoming reflected wave by measuring the induced surface current at several points on the cylinder. Field measurement was carried out in Kamaish mine, Japan. Measurement was made with a network analyzer based system to obtain broad-band information (O.3MHz - 3GHz). We calculated transient reflection signal from the measured data in the frequency domain by FFT algorithm. However, we found that the measured signal suffers from the direct coupling between transmitting and receiving antennas. Direct coupling is one of the most common problems in ground penetrating radar, it sometimes shades the reflected wave from the surrounding material. Applying time-frequency analysis to the measured signal, we obtained a time-frequency distribution (Choi-Williams distribution). Phase velocity of guided waves along this structure was theoretically analyzed and we could identify them in this time-frequency distribution of the received signal. Consequently, we could extract reflected waves, which contain information inside the surrounding rock.
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Application of ground penetrating radar on Colloseum pillars
Authors M. Bernabini, E. Brizzolari, L. Orlando and G. SantellaniOne very important aspect in restoring monuments is to determine the decay degree of the material forming their structures. To this end three pillars of Colosseum consisting of travertine blocks have been investigated by Ground Penetrating Radar (GPR), in order to test the efficency of various measurement technique and to obtain information on geometry and fracturing monument structural elements. Mesaurements were made each 5 cm, on horizontal and vertical profIles over some faces of investigated pillars. In order to improve resolution and interpret the reflections obtained, seismic-type processing using deconvolutions, filtering in frequency and in wavenumber, migrations etc. has been applied. In parallel, a specific processing programme for SIRlO (Radan III) and a programme of seimic processing have been used. Among various methods applied, the best result have been obtained using FK velocity filter on stack sections. A detailed geometric tridimensional reconstruction of pillars, starting from external geometry, has been allowed us to directly correlate external discontinuity with sigle electromagnetic events. The working procedure has given detailed information on blocks internal geometry and on presence of unknown voids and fractures. This esperimental study has confirmed the efficency of radar in identifying discontinuities in construction elements. Once again, the inadequacy of standard radar processing programmes has been highlighted.
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Polarimetric borehole radar measurements in granite
Authors Sato Motoyuki, Miwa Takashi and Niitsuma HiroakiPolarimetric borehole radar information can be obtained from a combination of co-polarization and cross-polarization reflection measurements in a borehole. Most conventional borehole radars use axially-oriented electric dipole antennas for transmission and reception, resulting in a response only to the co-polarized signal component of the a reflected wave. However, more information can be obtained if the cross-polarized component of the reflected wave is also measured. Cross-polarization borehole radar measurements are presented in which an axiallyoriented slot antenna is used as the receiving antenna and an electric dipole is used as the transmitting antenna. The antenna was excited by a short DC pulse to obtain broadband pulse-echo operation. Measured signals were transmitted through a broad-band optical signal link. Field measurement using the prototype radar sonde was carried out in granite rock. The measured signals showed that detection of the short-range reflections can be improved with crosspolarization measurements since direct coupling between the transmitting and receiving antennas is considerably reduced. We also observed the polarization dependency of a reflectivity of a water containing fracture. For instance, reflection from a layer containing gravels showed significant depolarization. This additional information obtained from the polarimetric borehole radar measurement will give us more knowledge of cracks such as surface roughness and water contaminant.
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Litho-structural characterization in granitic rocks using single-hole and crosshole radar techniques
Authors Kevin Stevens, Richard Everitt, Paul Street and Ganpat LodhaAn experiment was initiated to study the solute transport characteristics of a region of 'Moderately Fractured Rock' between the 130 m and the 240 m levels as part of the continuing geoscience research at ABCL's Underground Research Laboratory (URL). Two coplanar, subhorizontal characterization boreholes, MF-l and MF-2, each approximately 200 m long, were drilled into a region of moderately fractured granite. Detailed single-hole and crosshole geophysical surveys including reflection and transmission borehole radar were performed in these two boreholes. Boreholes MF-l and MF-2 are separated vertically by a domain of xenolithic granite, two domains of pink gneissic granite, and a discontinuous domain of grey gneissic granite. Two regional low-dipping, intrablock fracture zones (FZ-3 and FZ-2) with associated sub-vertical fracturing also straddle the region. Single-hole radar reflection and crosshole radar transmission tomography surveys using the RAMAC borehole radar system, with 22 and 60-MHz antennas, were used to investigate the litho-structural characteristics of the rock mass. Structural projections 'of FZ-3 and FZ-2 in the plane of the boreholes suggest a good correlation between radar reflectors and the fracture-zone interfaces at distances of 10 m to 60 m from the boreholes. The crosshole radar tomographic images show a decrease of the radar wave velocity of approximately 10% within the experiment region. Discrete regions of below and above average radar wave velocity have been interpreted to reveal the approximate positions of intense fracturing, mafic xenoliths and possibly zones of unfractured granite. Information obtained from these borehole radar data sets has been included in the construction of a litho-structural model of the experiment region.
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Evaluation of experimental data from a GPR system for detection and classification of buried mines
Authors Bertil Brusmark, Staffan Abrahamson, Dan Axelsson, Anders Gustafsson and Hans StriforsWe present the software and instrumentation developed to assess the potential of a GPR system to detect and classify buried mines. Preliminary results from the evaluation of detection algorithms on experimental data are displayed. The data have been registered using our recently constructed experimental setup consisting of a sandbox and a computer controlled antenna positioning system.
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