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Fourth International Conference on Ground Penetrating Radar
- Conference date: 08 Jun 1992 - 13 Jun 1992
- Location: Rovaniemi, Finland
- Published: 08 June 1992
21 - 40 of 45 results
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Application of ground penetrating radar techniques to peatland investigations
Authors Pauli Hnninen and Geological Survey of FinlandA need was perceived in the Geological Survey of Finland in 1983 to improve the rapidity and accuracy of fieldwork methods based on traditional drilling methods. The possibilities offered by the Ground penetrating radar technique were then explored. The first measurements to be carried out by the Geological Survey of Finland, in 1983, employed a Swedish Markradar Ab device, and radar equipment from Helsinki University of Technology was tested in 1984. As the preliminary results were highly promising, the Geological Survey of Finland decided to purchase Ground penetrating radar equipment of its own in 1985. The Subsurface Interface Radar (SIR) by the American manufacturer Geophysical Survey Systems ic. was bought.
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GPR application for the definition of unconformities in a Carrara marble quarry (Massa Carrara - Italy)
More LessThe ground penetrating radar (GPR) method finds a variety of applications in the field of nondestructive surveys and can be successfully employed to map unconformities in ornamental stones quarries. A series of GPR tests was carried out in a marble quarry at Massa Carrara, Italy. The tests allowed the mapping of a series of unconformities due both to fractures and to natural stratifications. At the same time it verified the presence of cavities and other altered zones within the carbonate rock. These macro-structures are quickly profiled by means of medium and low frequency transducers. The detailed definition of small fractures and of unconformities 5 and 6 m below the surface is not yet common practice. The objective of the tests at Massa Carrara was therefore to achieve a highresolution mapping of interfaces only centimetres thick. Correct knowledge of their spacial and geometrical distribution allows better planning of excavation work and minimization of waste.
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Geo-radar development at the Norwegian Geotechnical Institute (NGI)
Authors Tore Lasse By, Fan-Nian Kong and Harald WesterdahlGeo-radar offers high resolution subsurface profiling of features at distances of several metres to several tens of metres in low attenuation material such as sand, gravel, rock and fresh water. The distance may decrease to a few metres in high attenuation materials such as clay. With detection distances like these, geo-radar promises to become an important tool not only for geotechnical investigations, but also for environmental and archaeological investigations.
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Assessment of bauxite reserves using ground penetrating radar
Authors Richard Benson and Lynn YuhrThis paper deals with the Southern Plateau of Jamaica, where a large number of localized bauxite deposits occur on top of limestone. The limestone is highly pitted by dissolution, and is typical of tropical karst areas. Dissolution pits of about 10 to 100 m in diameter and about 3 to 15 m or more in depth are not unusual. For years bauxite reserves had been estimated by drilling on 30 m centers and multiplying the depth obtained by 30 x 30 m. Since the bauxite reserves are relatively small and the top of rock is highly irregular with many karst pits, obtaining an assessment of bauxite reserves by drilling on 30 m centers alone yields inaccurate results.
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GPR measurements for locating underground mine workings at an active open-pit mine
Authors Jeffrey J. Daniels, Dwayne Harris, Roger Roberts and Brian SchillingLocating buried voids, tunnels or other openings in the subsurface is one of the more frequently used applications of Ground Penetrating Radar (GPR) (Daniels, 1988). Buried air-filled voids provide an excellent electric permittivity contrast with any rock type. A host rock that is a relatively homogenous and low-loss provides ideal conditions for detecting and delineating subsurface voids. This nearly ideal GPR environment exists in the syenite porphyry rocks at the Zortman Gold Mine in Zortman Montana.
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GPR systems for roads and bridges
Authors N.S. Parry and J.L. DavisGround Penetrating Radar (GPR) surveys over roads pose some unique challenges when compared to conventional site surveys. Data collection rates are several orders of magnitude greater than conventional GPR surveys. It is not unusual to collect up to 50 linear km of data in one day. A current single-receiver radar system, operating at 50 scans/second, can typically collect 1.5 Mbytes per minute of 8 bit data. However, 8 bit data have insufficient amplitude resolution or signal to noise levels for processing subtle amplitude features. Therefore, data are often digitized at 12- or 16-bit, thereby doubling the data rate to 3 Mbytes per minute. As road radar systems move towards multiple receivers, the problem increases accordingly.
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Non-destructive testing of bridge, highway and airport pavements
Authors Gary J. Weil and EnTech EngineeringIn the inspection of metals and metal-based materials nondestructive testing is an accepted practice. For example, radiographic and ultrasonic techniques are routinely used to identify anomalies in steel pipelines and there are recognized national and international standards on their use. However, in the inspection of concrete the use of nondestructive testing is relatively new. The slow development of nondestructive testing techniques for concrete is because, unlike steel, concrete is highly non-homogeneous composite material. Apart from precast concrete units, which like steel products, are fabricated at a plant, most concrete is produced in ready-mixed plants and delivered to the construction site. The placing, consolidation and curing of concrete takes place in the field using labor which is relatively unskilled. The resulting product is, by its very nature and construction method, highly variable and does not lend itself to testing by nondestructive methods as easily as steel products.
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Highway speed radar for pavement and bridge deck evaluation
More LessTraditional GPR applications have been based on the use of ground-coupled antennas and on manual interpretation of graphical data. This approach is very limiting for highway surveys since much larger areas must be covered at lower unit costs. Therefore, recent radar developments for highways have involved the use of high-resolution air-coupled horn antennas, operations at highway speed, and automated data interpretation software for computing pavement properties.
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Using ground penetration radar technology for pavement evaluations in Texas, USA
Authors Chun-Lok Lau, Tom Scullion and Paul ChanIn recent years several investigators have attempted to use Ground Penetrating Radar (GPR) to detect subsurface problems in pavement systems. Much of the initial work focused on manual interpretation of multiple GPR traces collected along a highway. The traces were often color coded and an expert was needed to locate the problem areas. Sometimes the approach worked, other times poor results were obtained. Highway Departments who evaluated the technology recognized potential, but were often disappointed by the manual interpretation system.
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Use of ground-penetrating radar to investigate refilled scour holes at bridge foundations
Authors F.P. Haeni, Gary Placzek and R.E. TrentScour and removal of sediments and bed materials supporting bridge foundations has caused the collapse of many bridges that crossed streams and rivers (Jarrett and Boyle, 1986; Murillo, 1987). The rate and amount of scour depends on sediment type and transport, depth and velocity of the water, and obstructions to flow (Richardson and Richardson, 1989).
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GPR applications in geotechnical investigations of peat for road survey purposes
Authors Timo Saarenkato, Kari Hietala and Tiina SalmiOne third of the land area in Finland is covered with peat and there are parts of Northern Finland where mires can account as much as 50-70 0,10 of the land area. Even though efforts have been made to construct most of the roads on a hard and bearing soil there are hundreds of kilometers of roads and highways in Finland built over peat bogs, most of them resting on the peat itself.
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Limitations of shallow cross-hole radar investigations
Authors A.F. Siggins and CSIRO Division of GeomechanicsSubsurface radar when used as a geophysical tool is noted for its high spatial resolution. This compensates for the relatively modest ranges usually achieved in geological media. When used in its most popular mode of zero offset surface profiling, the presence of moist soils and near surface conductive clays with attenuations often approaching 50 dB/m, limits the useable range still further. Currently available radar equipment, with performance figures of the order of 120 dB, will be restricted to one or two metres range in these materials.
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Ground penetrating and borehole radar surveys in the Borth salt mine (FRG)
Authors Lucien Halleux, Pascal Feller, Albric Monjoie and Raymond PissartThe salt deposit mined in Borth (FRG) lies in the Zechstein basin, which covers a large part of Central Europe. The mine is located north-east of Duisburg. Although the deposit is over 150 metres thick, only the lower part will be considered here.
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Portable short range subsurface radar
Authors P. Vainikainen, M. Tiuri, V Kontra and E. NyforsHigh-resolution radars with large frequency bandwidth are widely used for the detection and location of subsurface objects (Daniels et at. 1988). The most common wideband signal is the very short pulse (impulse) utilized in short pulse radars (impulseradars). In the ideal case the impulse is a one-sided sinusoidal or gaussian signal (Esselle & Stuchly 1991). In practice the signal contains a few oscillation periods at a particular operation frequency. Frequencies of the order of 100 MHz are used in the measurement of large objects (e.g. ground), where high penetration depth is needed and range resolution of 0.1-1 m is adequate. If range resolution of the order of centimetres is desired, the frequency of the radar must be 1000 MHz or more.
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A shielded loop array antenna for a directional borehole radar
Authors Motoyuki Sato and Tatsuya TanimotoA borehole radar measures the distance of a reflecting object from a receiver. However, conventional omnidirectional borehole radars cannot determine the direction of the object. Some earlier attempts have been made to achieve a directional borehole radar. A cross-loop antenna (Mundry et al. 1983) and a dipole array antenna (Olsson et al. 1989, Sato 1990) have been used for the purpose. These antennas have resonance, which increases the maximum detectable range of the radar. However, the antenna resonance also tends to broaden the received signal, with a reduction in the resolution. This paper introduces a new type of array antenna for a directional borehole radar. The new antenna measures the current induced on the conducting sonde surface by an incoming electromagnetic wave. The antenna is broadband and has good potential for direction finding.
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The results of surface and borehole radar profiling from Permit Area B of the Whiteshell Research Area, Manitoba, Canada
Authors A.L. Holloway, K.M. Stevens and G.S. LodhaAECL Research is assessing plutonic rock for its suitability as a host medium for the disposal of nuelear fuel waste (Dormuth and Nuttall, 1987). One aspect of this research involves identifying and characterizing fracture zones within the rock mass using nondestructive geophysical techniques, ineluding surface and borehole radar reflection surveys.
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2-D synthetic radargrams for archaeological investigation
Authors Dean Goodman and Yasushi NishimuraGround radar is being used in archaeological surveys with considerable success. The structures at excavated sites nevertheless often turn out to be different from those determined from raw radar profiles. The primary reason for these differences is the broadness of the microwave beam transmitted into the ground (see Fig. 1). Many radar antennas have significant response over a l20-degree looking angle, which means imaging of objects both directly below the antenna and off to the side. Although there are processing techniques able to eliminate some of the problems of surveying with a broad beam radar (e.g. migration), these techniques also have drawbacks. The raw, unprocessed radar data normally contain maximum information about the surveyed area. To take advantage of the information content of raw radar records in the interpretation of buried structures, we use forward modelling incorporating matching synthetic radargrams that include the entire directional response of the antenna, together with measured radargrams.
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A radar investigation of pyramids
Authors F-N. Kong, J. Kristiansen and T.L. ByThe Norwegian Geotechnical Institute (NGI) has carried out geo-radar investigations at two archaeological sites, one in Peru and the other in the Canary Islands; in both cases anomalies were found in the pyramids. The frequency sweeping radar described in By et al. 1992, was used in the investigations. Generally speaking, there are two kinds of problems involved in the radar investigation of archaeological sites. The first is a technical problem, Le., how to obtain a clear radar image of subsurface reflectors. The second is how to translate the radar results into results useful to archaeologists. Radar sees all reflectors. Preliminary archaeological knowledge is therefore necessary to be able to sort out the useful information. The second problem may vary from case to case, but the first problem is common to all similar investigations. Our emphasis here is thus on the technical problems.The Norwegian Geotechnical Institute (NGI) has carried out geo-radar investigations at two archaeological sites, one in Peru and the other in the Canary Islands; in both cases anomalies were found in the pyramids. The frequency sweeping radar described in By et al. 1992, was used in the investigations. Generally speaking, there are two kinds of problems involved in the radar investigation of archaeological sites. The first is a technical problem, Le., how to obtain a clear radar image of subsurface reflectors. The second is how to translate the radar results into results useful to archaeologists. Radar sees all reflectors. Preliminary archaeological knowledge is therefore necessary to be able to sort out the useful information. The second problem may vary from case to case, but the first problem is common to all similar investigations. Our emphasis here is thus on the technical problems.
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Ground penetrating radar finds disturbed earth over burials
Authors R.R. Unterberger, Texas A and M UniversityWe are doing GPR research with an OYO Georadar unit, using it in a salt mine in Texas and in a potash mine under the North Sea in England. Rocksalt samples from this Texas mine have been measured to show a tan d of 2 x 10-5 by the U.S. National Institute of Standards and Technology in Boulder, Colorado. This is 5 times less lossy at 200 MHz than teflon, the best man-made dielectric used in coaxial cables. Thus we should expect large GPR ranges in rocksalt, and indeed, we found ranges to 62 m, the maximum time scale (1000 ns) for the Georadar unit. Figure 1 shows an example of a GPR record obtained in the Grand Saline salt mine owned by Morton Salt Company. The time scale is 1000 ns (62 m of depth) the profile length is 51 m and the arrows show two saltair interfaces beneath the floor of an upper-level mining operation. The horizontal line across the whole record is an artifact of the system on the 1000 ns mode only. Figure 2 shows a GPR profile in another salt mine location with three different levels of salt-air interfaces caused by previous mining operations. The Georadar artifact is not present. The time scale is 300 ns, equal to a maximum radar range of 18.6 m in salt; the profile length is almost 100 m.
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Location of human remains with ground-penetrating radar
Authors James S. Mellett and New York UniversityThe use of ground-penetrating radar to probe the upper 2 m ofthe earth's surface (Mellett, 1990) is expanding into a variety of fields as more sophisticated hardware and software permit highresolution applications not possible with earlier GPR equipment. A number of recent publications attest to the success of GPR in the location of human remains, in archaeological studies, and in law enforcement applications (Bevan, 1991; Davenport et al, 1989; Killam, 1990; Mellett, 1990, Mellett and Geismar, 1990, Unterberger, this volume). This paper will describe the use of GPR in historical cemeteries, Potter's fields (burial areas for the indigent), at an American Indian archaeological site, and in a police investigation of a missing person. All surveys discussed here involve localities within the United States.
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