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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
61 - 80 of 95 results
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Study of cavity depth estimation behind concrete tunnel lining using GPR
Authors Satoshi Maekawa and Thomas J. FennerIn considering the maintenance and repair of existing tunnels, it is necessary to determine the concrete lining thickness as well as the scope and depth of cavities behind concrete. Since ground penetrating radar (GPR) can rapidly provide high resolution continuous profiles and, is capable of detecting cavities and measuring concrete thickness, results in the frequent use of this method for these applications. Tunnel inspections however, present special problems due to traffic control and difficult access to the tunnel liner, especially in large diameter tunnels. Accurate assessments of cavity volumes is essential in estimating injection quantities during grouting operations. This requires complete coverage of radar profiles with accurate positioning information. As a result a special tunnel inspection vehicle, RAPIDAS, was developed for data acquisition. RAPIDAS is a vehicle mounted with four hydraulic booms. It can position up to four antennas simultaneously to the desired locations for radar measurements. It permits simultaneous and continuous profile measurements while the vehicle is moving. RAPIDAS is equipped with multiple channel radar systems to obtain high quality radar data in a short period of time. Special post processing software was also developed for quantitative analysis of the acquired radar data. For the calculation of cavity depths we have applied the least squares method between the basic wavelet and the observed wavelet in the frequency domain to obtain the reflection coefficient series. The effectiveness of the software was confirmed in model experiments and in field tests. For data processing we used both the newly developed software and RADAN (software ofthe GSSI Corporation). Post processing included background removal, amplitude adjustment and migration to emphasize the reflection wavelet from the reverse side oflining. Next, from features such as the magnitude of the amplitude and inversion of the phase, the scope of the cavity was extracted. Then a reflection coefficient series analysis was carried out with respect to the cavity location. The travel time in the cavity was obtained thereby confirming the cavity depth.
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Application of GPR for a more efficient mine planning
Authors M. Momayez, A. Hara, F.P. Hassani and A. SadriThe Canadian mining industry is faced with international competition, low base metal prices and diminishing mineral reserves. To remain competitive on the international market, the industry must reduce the cost of mining and increase productivity while maintaining a high standard of safety. To do so, there is a great need for improved methods that would allow the detection of geological structures in advance of mining and the monitoring of pillar integrity to reduce dilution and increase safety. This will facilitate planning for optimum exploitation of the mine and to increase production at lower costs. The present paper discusses an example of more efficient mine planning using new technologies such as Ground Probing Radar (GPR). Here, GPR technology is used at the 2500 level of the Kidd Creek mine in Timmins, Ontario to (l) monitor the stability of the sill pillar, (2) locate the presence of disseminated sulfide pockets in the sill pillar for extracting the mineral content and (3) monitor the stope backs and wall structures to evaluate the effect of on-time filling sequences.
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GPR surveys inside an hydroelectric water-supply tunnel to investigate the rock-concrete interface and the fractures affecting the host rocks
Authors Mauro Piccolo and Annalisa ZanelliOn request of the Italian National Electrical Agency, the Company IDROGEO carried out a G.P.R. survey inside an old water-supply tunnel 14 km long belonging to an hydroelectric power plant located in the North East of Italy. The aim of the survey was the geo-structural investigation of the rock formations surrounding the tunnel with particular interest in the mapping of cavities and fractures associated to the water occurrences and circulation. A detailed investigation was also requested to detect the presence of voids at the concrete-rock interface. The tunnel crosses different rock formations belonging to the Alpine sequence with the presence of evaporitic formations affected by strong tectonic deformations. More than 7,000 meters of G.P.R. profiles were recorded by using a GSSI SIR 10 equipped with 100 and 500 MHz antennas with simultaneous data recording on two channels. The survey at 500 MHz .was aimed at the precise determination of the concrete thickness and at the detection of the voids at the concrete-rock interface, whereas the use of 100 MHz transducers permitted the detection of larger unconformities and cavities up to a distance of 15-20 metres. The identified structural elements were divided into 5 groups: - lack of contact and delaminations at the concrete-rock interface - geostructural elements - open fractures - voids and unconformities - honeycomb alterations The survey also permitted the location of some old artifacts whose position and nature were uncertain.
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Ground penetrating radar applications on high grade gold deposits at the Sixteen to One Mine, California
More LessIn general, application of modem technology to ancient mineral deposits is a learning process that can be expensive, time consuming and draining to a company's precious human resources. To stay abreast of new technology and remain competitive in an increasingly environmentally demanding society, hi-tech research has become of primary concern to the management of this company. The principles of Ground Penetrating Radar (GPR) were evaluated at the Sixteen to One mine and found to have good potential for locating high grade pockets underground. This paper presents a description of ore occurrences at the mine, the company's motivation for testing GPR, and its suitability for, locating high grade gold pockets. Also presented are underground test results, and a discussion of findings and suggestions for this application and similar ones in the future. The geologic features at this mine are somewhat unique, and it is doubtful that specific results can be readily adapted to mines elsewhere. Intertwined with technical facts and figures the reader will discover a human factor found to be important in the successful application of this technology and all others. The inquisitive personality in conjunction with a "nuts and bolts" academic personality has proven to be a successful combination for the evaluation of GPR It is however, no substitute for proper planning.
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FDTD2D+ - A finite-difference, time-domain radar modelling program for two dimensional structures
Authors D. Livelybrooks and P.K. FullagarThe two and a half dimensional finite difference program, FDTD2D, of Moghaddam et al. computes the radar responses for an arbitrary 2-D conductivity, permittivity and permeability model with one or more embedded current source(s). After Fourier transformation in the strike direction, the program solves for the six electromagnetic fIeld components as functions of (x, y, k, t), and then inverse transforms them. Fields are calculated via a set of finite-difference, time domain equations on a staggered grid following Yee. Time derivatives are also represented by central differences, and electric and magnetic fields are solved for equal but staggered steps in time. The regular model grid is terminated using the "absorbing" boundary conditions of Liao et al.
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Application of GPR for geological mapping, exploration of industrial mineralization and sulphide deposits
More LessThe ground penetrating radar (GPR) technique is applied to the localization and characterization ofrock types, mineralizations and their associated boundaries, and to the identification of features inside the rock. This is made possible through the determination of variations of electrical properties within the rock units. GPR has been extensively tested at several localities in Sweden and Denmark. The main testing area in Sweden has been several sites in the Skellefte field. The Skellefte field is well known as the biggest sulphide mining district in Scandinavia. The testing area consists mainly of volcanic rocks surrounded by granites of various ages. Test measurements at the Skellefte mining areas are compared directly to geological variations in the rock as they have been exposed through the exploration activities. Electrical property contrasts between orebodies and the host rock gives possibilities of determining the distribution of shallow mineral resources. A combination of the variation in reflection pattern, reflection amplitude and penetration depth is used to determine the boundaries between different rock units. Reflection measurements have been used to identify both fracture zones as well as alteration zones and to determine their location and orientation. Lithological variations of limestone have been studied within the Faxe Kalk exploration area in Sjelland, Denmark. Divisions of the limestone into areas of coral reefs and lagoon deposits are made possible through distinctive reflection patterns and differing penetration depths between the rock units. The effect of tectonics can be studied by means of various reflection patterns from flint horizons within the lagoon deposits. The GPR results are used as a basis for geological modelling and as a foundation for mineral exploration activity.
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Twenty years of Ground-probing radar in salt and potash mines
More LessRadar has been used for twenty years for underground exploration of the boundaries and internal structures of salt deposits in Germany. The method and equipment, developed by the Federal Institute for Geosciences and Natural Resources (BGR) in cooperation with the German mining company Kali und Salz AG in the early 1970s, make it possible to determine the distance to stratigraphic boundaries up to 1000 m from the antenna, especially in anhydrite, claystone, and basalt, and between joints filled with water or brine. The equipment is light weight and battery powered; it can be used almost anywhere in a mine without any preparatory measures. Therefore, the method is very economical. The location of the reflecting discontinuities may be determined using additional directional antennae. For exploration preparatory to mining, various probe systems have been developed for use in drillholes. In cooperation with Prakla-Seismos AG, a special GPR probe was developed for deep boreholes. Salt domes have been explored down to depths of 3000 m with'this probe. A probe has been developed for use in boreholes in mine drifts. This probe is designed so that it is safe to use in mines in which there is the risk of explosions. It is equipped with a directional antenna so that the spatial orientation of the reflecting planes can be determined. The technical aspects of the equipment are discussed and the results of exploration in German and Canadian salt deposits using the radar method are used as examples.
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RAD-SEIS: Direct acces for ground-penetrating radar to reflection seismological techniques
More LessConstant-offset georadar profiles look similar to stacked common mid-point seismic sections. Yet, technologies used for the field aquisition, processing and interpretation of seismic reflection data are significantly advanced with respect to what is common today in ground-penetrating radar. To take advantage of seismic techniques, the recently developed RAD-SEIS system allows: (a) direct digital recording in standard seismic SEGY data format; (b) continous profiling with accurate automatic antennae positioning; (c) programmable aquisition of constant-offset and multi-offset sections and cubes. The upgrade of the relatively inexpensive analog GSSI SIR-3 unit is achieved by adding a 16-bit digitizing board to a portable 486 personal computer and by employing a newly designed method for automatically triggering the system at constant spatial intervals as small as 1 centimeter. Programming of the 486 computer, using software tools provided with the digitizing board, allows the data to be recorded directly in SEGY format. In the multi-offset mode, an end-on "source-receiver" spread geometry, typical of that employed in reflection seismic surveying, is used. At the processing facility, the georadar field data are transferred from the personal computer via a network link directly into a workstation-based seismic processing and interpretation package. 300 Mbytes of field data, typical of a single day's multi-offset profiling, can be transferred in less than 60 minutes. Although turnaround time for processing large georadar datasets is relatively short, analog paper hardcopies, which are recorded directly in the field, remain an essential means for quality control and can help guide the surveying strategy.
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Subsurface sensing for the autonomous retrieval of buried objects
Authors Herman Herman and Anthony StentzUsing surface and subsurface sensing, we have developed a perception system for autonomous retrieval of buried objects. The subsurface sensing system uses Ground Penetrating Radar (GPR) to detect and localize buried objects. An industrial robotic arm is used to position the GPR antenna, and a 2-D laser rangefinder system generates an elevation map which is used to guide the robotic arm. Using this setup we have automated the GPR data collection process. An image processing algorithm is used to locate the object of interest in the GPR data. After the object is located, we use sense and dig cycle to retrieve the object. During this loop the excavator alternately removes a layer of soil and takes a subsurface scan. The electromagnetic (EM) wave propagation velocity in the soil can be computed by comparing the data from the previous subsurface scan with the current one. With each successive iteration, the estimates of the object's size, shape, and location improve. This loop is repeated until the object is within certain distance and able to be retrieved. This "sense and dig cycle" enables the system to handle layered soil to some extent since at every cycle the EM propagation velocity estimate is updated. The computationally intensive parts of the processing are run in parallel on multiple processors to achieve near real-time performance. The system so far has been used to detect, locate and retrieve small buried objects in the testbed.
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Ultra-wideband, high RCS, active calibration targets for foliage/ground penetrating SARs
Authors George Moussaly, Theodore Grosch, F. Jud Heinzmann and Philip FialerThis paper describes the design, development, test, and operation of compact, active electronic targets having high and constant values of radar cross section (RCS of 20 to 40 dBsm). The active targets were specifically designed to be used for reference calibration of airborne synthetic aperture radars (SARs) used in foliage and ground penetrating (FOPEN, GPEN) applications. The use of active (vs. passive) calibration targets in this application was driven by the need to achieve physically compact reference targets with high, constant RCS over the ultra-wide bandwidths and for relatively long radar wavelengths typical of FOPEN/GPEN radars. Two target types were developed. One type operates from 30 MHz to 90 MHz and was designed to respond to a stepped frequency radar waveform. The other target type operates from 100 MHz to 500 MHz and was designed to respond to an impulse radar waveform. For each target type, two different models were built: one for above ground operation and the other for burial below ground. A description of the active targets is provided along with an example of the design methodology which included electromagnetic modeling of the target antennas above and below the ground. Lessons learned during the target development process are discussed. A description of field tests using the active targets is presented along with a comparison of modeled and measured target RCS and an example of the active target imaged by an airborne SAR.
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Recording GPR data by means of a video camera recorder
Authors Gerald B. Rupert and L. John TylerA technique is presented for recording synchronized radar images and a video record of antenna position. This requires a GSSI Model 38/39 video display unit (VDU) or equivalent and a video camera recorder (camcorder) possessing a high fidelity stereo sound track. For this system, a continuous history of antenna position is recorded on the video channel; and simultaneously, radar data is recorded on the audio track. This permits the precise correlation of radar events with antenna position. The resulting data set can be viewed on dual monitors or on a single monitor with "picture in a picture" capabilities. As with other recording systems, the radar data can be down loaded directly into a computer for processing.
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Automatic signal processing of front monitor radar for tunnelling machines
Authors Toru Sato, Ken-ya Takeda, Takashi Nagamatsu, Toshio Wakayama, Iwane Kimura and Tetsuya ShinboIt is planned to install a front monitor radar on the surface of the rotating drill oftunnelling machines in order to detect obstacles such as casing pipes of vertical borings. The conventional aperture synthesis technique can no more be applied to such cases because the radar image of a pipe does not constitute a hyperbola as is the case for linear scanning radars. We have developed a special purpose signal processing algorithm with the aid of the discrete model fitting method, which can be used for any pattern of scanning. The details of the algorithm are presented together with the results of numerical simulations and test site experiments.
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Computerized scanner system SARA
Authors Peter Ulriksen and Christian StolteA meaningful 3-D data presentation requires a high geometric fidelity in the collection of the GPR data. Since Synthetic Aperture Focusing Techniques require several samples per space time wavelength, an enormous amount of data must be collected, which precludes manual movement of the antenna. To permit this new GPR concept, a computer controlled scanner has been built. It consists of a 5 m long linear movement unit with a ball screw connected to a servo motor. A second servo motor is connected to pairs of small wheels used to move the linear unit in the transverse direction. The stroke of the linear unit is 4.5 m and within that length the antenna can be positioned at submillimeter accuracy. At full speed the antenna travels over the linear unit in 12 s. The maximum vertical deflection with a 5 kg load is 1 mm. The weight of the scanner is approx. 75 kg with no load. After a period of evaluation of various concepts, a second scanner will be built to facilitate bistatic measurements. That way the 2-dimensional back scatter field can be determined, generating data suitable for processing in 3-D seismic packages. Using the previously developed 5 channel GPR controller, MRS, and 2 orthogonally polarized antennas on each scanner, it is possible to obtain the polarization matrix. Since MRS allows each connected antenna to work either as a transmitter, a receiver or both it is possible to measure the back scattered field around one point of transmission although the scanners can not cross. Since the computer that acquires all the data and displays it is the same that controls the scanner, it is also possible to draw marks on the ground with a spray can connected to the scanner. To visualize the great quantity of 3-D data, acquired with this scanner, the help of 3-D display and interpretation software was found indispensable. Such software is commonly used in the field of oil exploration to interpret three-dimensional subsurface structures. Before interpretation, the 3-D data cube was prepared for visualisation with several seismic data processing routines including filtering, deconvolution/envelope and migration. Depending on the data quality , "a priory" knowledge, and complexity of the subsurface structure the processed data was found to display a clearer image than the raw data. Several visualization techniques as time slices (windows), cube-, chair-display and flying carpet were compared and evaluated towards their usefulness in enhancing the subsurface image. An animation of the 3-D data was found indispensable for the interpretation of the data and is presented here.
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High speed georadar data acquisition for groundwater exploration in The Netherlands
More LessGeoradar has proved to be a valuable new geophysical technique for non-destructive groundwater exploration in The Netherlands. Under favourable conditions detailed continuous images are obtained to depths of 40 m. To increase the commercial attractiveness of georadar, especially for water supply companies, a high-speed data acquisition system was devised. Sensors & Software Inc. developed a high speed pulseEKKO system and TNO designed and built a polyethylene carrier for the antennas; this carrier is trailed by the "Mule": an All Terrain Vehicle that can move at the required constant low velocities of about 2 km/hour. At this speed a fast portable field computer allows sufficient stacking at common time windows. Continuous georadar data acquisition rates are achieved 10 times higher than conventional manual measurements. The system is distance triggered by pulses produced by an electronic odometer. The carrier is flexible and multi-functional: on loose soil it is dragged, whereas on metalled and rough roads wheels are attached, bringing the antennas at adjustable levels above the ground. The antennas may be rotated 90 degrees, and thus be attuned to the expected strike of geological structures. The carrier can accommodate three antenna-frequencies: 200, 100, and 50 MHz. Prior to the design of the mobile georadar system, tests were run along a profile to examine the influence of antenna elevation and car proximity. This paper shows some of the results of the test surveys, presents the final design of the high speed data acquisition system and illustrates its performance by renewed measurements along the test line. Moreover, some remarkable results recorded by the new system are shown to demonstrate the effectiveness of the high speed georadar system.
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Data acquisition systems for ground penetrating radar with example applications from the air, the surface and boreholes
Authors David Wright, Jerry Bradley and Thomas GroverData acquisition for short-pulse (impulse) ground penetrating radar (GPR) has evolved as new technology has become available but commonly involves equivalent time sampling a radio-frequency signal to produce an audio-frequency replica of the signal. An airborne radar system developed by the U.S. Geological Survey (USGS) in 1978 recorded the sampled signal on analog tape. Low data rates made waveform addition (stacking) for signal-to-noise improvement impractical. Advances in data acquisition and recording that have occurred within the last two decades have made digital recording the norm in modern GPR's. Waveform addition for signal-tonoise enhancement is common. However, all commercial short-pulse GPR's known to the authors still use equivalent time sampling prior to digitizing. Fast single-shot digitizers are a viable alternative to equivalent time sampling in some applications.
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Instantaneous polarization match: Identifies amplitude changes due to anomalous polarization in GPR data
Authors Rob D. Luzitano and Tad J. UlrychInstantaneous polarization match identifies amplitude anomalies due to the altering of wavelet polarization by an interface or the intervening medium. The match factor (p) varies from 0.0 to 1.0 for cross and parallel polarization, respectively, thereby scaling the antenna's effective aperture and thus the received power via the radar equation. Polarization match is defined mathematically from the dot. product of antenna and wavelet polarizations. Calculation of p requires two component data, i.e. transmit and receive antennas parallel (E=) and perpendicular (E.i)' Assumptions regarding the antennas were minimized by using a general equation containing antenna polarization terms which we estimated from a lake bottom reflection. The uncertainty in p values arises primarily from random noise and timing errors. Due to inherent variations in noise level, the standard deviation varies from about 0.06 for low matches (< ~ 0.35), rising at middle match values to about 0.065, then decreasing to about 0.015 at matches greater than 0.95.``
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The development of an advanced GPR system at the Univeristy of Houston
Authors Shiqun Xie, Di Lan, Jin Wang, Yongmin Zhang, Richard Liu and David Shattuck!An advanced ground penetrating radar system is being developed at the University of Houston. The objective of this research is to study the possibility of improving GPR performance by improving hardware structure, data handling, signal processing, and data interpretations of GPR systems. The other goal of this work is to study ways to reduce the complexity of operating the GPR system, namely, parameter set up, field operation, and data processing and interpretation. A prototype GPR system is being designed and implemented in the Department of Electrical Engineering at the University of Houston. Based on the traditional GPR design, the new GPR hardware system features compact size, easier operation, with improved spatial resolution and penetration depth. Circuit modifications are made on the transmitter, sampling head, controller, and data transmission components. A smaller version of resistively loaded printed-circuit-antennas are used for transmitting and receiving probes. Fiber optic links and wireless links are used as data transmission channels. In the data storage and processing station, software has been developed to enhance the radar image. A complex cepstrum computation and the direct wave cancelation can be performed by using the built-in software, along with the standard windowing, filtering and displaying functions. An user friendly control software is developed based on Microsoft Windows and Visual Basic packages. Since the GPR system is still under development, only primary data will be shown. Data inversion is also attempted using a direct-timedomain inversion algorithm recently developed by the authors.
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The application of ground penetrating radar in Israel: selected case histories
Authors Alex Beck and Amit RonenRadar technology has been used in Israel for the past two years by the Institute for Petroleum Research and Geophysics (IPRG) for many applications such as civil engineering, archaeology, infrastructure, environmental problems and geology. For such applications, we use the SIR-10 system equipped with 100, 500 and 1000 MHz antenna. This article discusses four examples of the application of GPR technology in Israel. The first instance concerns karst phenomena under highways, including open cracks and spaces at a depth of 3-4 meters in a fairly homogeneous dolomite rock, which could endanger the stability of the highway. The survey was conducted using a 500 MHz antenna towed by a vehicle. The second example addresses the detection of a tunnel dug in the subsurface by smugglers at the Israel-Egypt border and which was used to transfer merchandise, money and drugs. A radar survey carried out over a stretch of some 600 meters revealed an underground tunnel, 3.5 meters below the surface and about 1 meter in diameter, in a sandy-clayey environment. The third example concerns the inspection of an old 2 km runway using a 1 GHz ground coupled antenna towed by a vehicle. The s~rvey revealed an undulating subsurface strata at a depth of 50-110 em, probably the old runway asphalt surface laid some 50 years ago. The fourth case deals with the detection of oil spills at an oil refinery in a sandy environment using 100 MHz and 500 MHz antenna. The oil spills detected by GPR were in. good correlation with actual oil contaminated samples in drills. Further drills in areas suspected of being oil contaminated were planned on the basis of the GPR results. Most of the oil spills were located in close proximity to oil pipes which were probably to some degree eroded or broken.
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Major natural gas pipeline projects in Germany using GPR
Authors J. Czarnowski, S. Heinzel, P. Brühl, C. Staib, M. Robeck, G. Frank and Dr. R. FruhwirthIn July 1990 DORSCH CONSULT, Munich was engaged by Wintershall AG, Kassel to provide engineering consulting services for one of the longest natural gas pipeline projects in Gennany, the MIDAL pipeline (MITTE DEUTSCHLAND ANBINDUNGSLEITUNG/CENTRAL TIEON LINE) project and the STEGAL pipeline (Saxony-Thuringia Natural Gasline) . .For the first time in a project of this nature the Company employed geophysical methods on a large scale in the preliminatry investigation of the pipeline routes. The application of ground penetrating radar/GPR, in combination with other electromagnetic soundings, yielded rapid and reliable results. Without this ability to quickly and reliably interpret the GPR data on site, the project's success would have been in question.
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The application of ground penetrating radar to detection of shallow faults and caves
Authors Shikun Deng, Zhengrong Zuo and Huilian WangGround penetrating radar (GPR) is the electromagnetic equivalent of the reflection seismic technique for high-resolution shallow geological mapping (Davis and Annan,1989). The records obtained from GPR reflection method are similar to those obtained from single-trace reflection seismic one in appearence. So, some seismic interpretation concepts may be used in the interpretation of GPR data. As a means of engineering geophysical exploration, GPR technique has its unique virtues: it has good performance on less suffering from the enviroment influence in measurements; it has higher resolution than other geophysical technique when penetration is available; and it is a nondestructive detection method with fullautomatization, portability and efficiency. In this paper, the application of GPR to detecting shallow faults and caves were introduced with three case histories, which showed the feasibility of GPR for detailed prospecting of the shallow geological problems and inspection of quality of old engineering structures.
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