An ultra-wide bandwidth (UWB) dielectric rod antenna modified from its previous version developed by Chen (1999) is presented. Such antenna is useful in detecting shallowly buried targets, such as anti-personnel (AP) mines. Broad bandwidth electromagnetic energy is launched, guided and radiated from a dielectric rod that has a constant cross- section area and low-loss permittivity except at the end where the permittivity is gradually reduced to match to that of free air. The electromagnetic waves radiated out from rod end have field behavior similar to that of a Hertzian dipole. The low antenna clutter and weak antenna-ground interaction are two unique features. Its near-field radiation properties are investigated using three-dimensional finite difference time domain (FDTD) simulation technique. Some measurement and numerical simulation results are also included.

With the dramatic growth of interest in nickel laterite resource exploration, fuelled by increased demand and new processing technologies, the need for accurate resource delineation and careful mine planning becomes paramount. The traditional use of borehole grids to calculate ore reserves is neither sufficiently accurate nor cost-effective at many sites due to the complexity of tropical weathering profiles. Although an unconventional approach to laterite mine planning and resource delineation, ground penetrating radar (GPR) has shown tremendous potential for addressing project geology, resource delineation, and mine planning issues. GPR processing techniques have been developed specifically for laterite applications and utilized successfully at a number of sites worldwide. Each site exhibits unique geology, and thus radar characteristics. The GPR data have shown excellent correlation with the weathering profile as confirmed by boreholes and test pits. GPR has significantly increased the database of knowledge regarding project geology, as well as provided invaluable assistance to mine planning by imaging the bedrock weathering texture, including the precise location of subsurface pinnacle structures and fault planes. The information provided by the GPR data, in concert with strategically placed boreholes based on these data, has enabled a laterite project to be upgraded to the measured category of mineral resource.

The paper reports preliminary findings of ground-penetrating radar investigations into the internal structure of Holocene coastal dunes and the association of subsurface sediment properties, determined from borehole samples, to reflected images. The area of investigation is on the north coast of Northern Ireland and the coastal dunes are confined systems of mid-to-late Holocene age (less than 6000 years BP). The major influence on subsurface reflections is moisture and organic content; compaction of sediment is another important factor, albeit difficult to quantify. Dipping reflectors and deflated sections are attributed to former dune ridges. The study highlights the need for other investigative techniques to be used in conjunction with ground-penetrating radar for a more coherent picture of dune internal structure.

Offsite movement of waterborne agrochemicals is increasingly targeted as a nonpoint source of water quality degradation. Our research has indicated that subsurface water movement is variable and site-specific, and that a small soil volume frequently conducts a large volume of flow. This concentrated flow is usually caused by soil morphology, and it often results in water moving rapidly offsite from certain areas of fields; little or no lateral subsurface flow may occur in other areas. Identifying these subsurface regions is difficult using conventional soil survey and vadose zone sampling techniques. In this study, traditional surveying is combined with electromagnetic induction (EMI) and ground penetrating radar (GPR) mapping to identify areas with high potential for subsurface offsite movement of agrochemicals, optimizing these identification techniques, and expanding the mapping procedures to make them useful at the field-scale for agricultural production practices. Conclusions from this research are: (1) EMI mapping provides rapid identification of areas of soil with a high potential for offsite movement of subsurface water, (2) GPR mapping of areas identified by EMI mapping provides a means to identify features that are known to conduct concentrated lateral flow of water, and (3) combining the capabilities of EMI and GPR instrumentation make possible the surveys of large areas that would otherwise be impossible or unfeasible to characterize.

Models of dielectric permittivity of sandy-clayey soils, detailed physical model and a simple model, are proposed. The models are based on mixture formulas, which are applied in several steps, by which different components of the soil are successively combined. For a mixture with very flattened inclusions Maxwell Garnett's mixture formula gives most accurate results. It is shown, that Maxwell-Wagner effect in clay in frequency range below several hundreds of MHz may be accurately described by Maxwell Garnett's formula. Results of modeling are compared with results of measurements. Three models with few parameters, depending only on the soil, are capable to describe the clayey soil having different moisture and temperature. Detailed model takes into account distribution of water between clay and soil solution, change of thickness of bound water layers depending on moisture and when freezing. Conductivity of bound water, its temperature dependence have been found for some soils. Debye relaxation spectrum of bound water was studied.

This paper deals with the application of ultra-wide band time- domain subsurface radars, equipped with special signal processing techniques, to realize non-invasive image testing of the building walls' internal structure that are made with brick, stone, concrete, reinforced concrete and other construction materials. There are two normally associated problems, qualitative and quantitative, considered. Limitations and shortcomings of radar imaging, due to inherent physical features as well as signal processing improving the quality of radar images, are discussed. Actual field data are used to illustrate applications of subsurface radar for non- destructive testing of walls' internal regions.

In this paper we describe a method of minefield reconnaissance with the use of the multi-frequency ground-penetrating radar (GPR) combined with a metal detector. This method allows the mine images in the soil to be obtained in the band of the mine detector sensors. An experimental installation with remote control and scanning sensors has been designed and built. A mine detector of this kind can be used in peacekeeping and humanitarian operations.

By the order of Moscow Region archaeological expedition of the Institute of Archaeology, Russian Academy of Science (RAS), GPR inspection of an ancient settlement excavation (D'yakovsky period, early iron age, 4-3 centuries BC) was carried out. This ancient settlement is located near village Myachikovo in Kolomna district of the Moscow Region. The inspection of the excavation was carried out by the georadar GROT (design of the device has been reported at the 6th GPR Conference in Sendai, Japan). The research problem consisted in the mapping of buried earthen fortification structures of the ancient settlement. According to the data of aerial photography, sectors of two concentric strips, distinguishable due to more saturated color of vegetation, were well visible in the territory surrounding the excavation. According to the archaeologists version, the vegetation indicated the borders of the interred fortification structures. The GPR inspection of the territory around the settlement showed, at the depths of 1.5 to 2 meters, some structures similar to a buried ditch. The 'ditch' width was about 5 - 6 meters; radius from the settlement center was 20 meters for the internal, and 30 meters for the external ditch. Georadar cross sections superimposed on the excavation map allowed us to understand the scheme of ditch arrangement in fortification structures of an early iron century settlement.

This paper suggests an easy way of checking some of main impulsive georadar performances from data acquired by the system itself and preventing their degradation. GPR equipment is thought as a whole system (including control unit, cables, antennas, etc.); on the other hand it is easy to check each sub-systems simply by connecting them to a reference system with known performances, if available. Following parameters are considered to be significant for the purposes of the test: background removal capability, scan-to-scan signal stability, jitter, travel time linearity and noise level.

In order to overcome the limitation of radar resolution, we proposed to use radar polarimetry in borehole radar. Even though the radar resolution is much less than the shape of the scattering object such as subsurface fracture, polarization status contains information about the scatterer. We applied the radar polarimetry to subsurface fracture measurement, and this information was used for classifying fractures. Due to the low resolution of the radar, accurate phase information was not easy to obtain. Therefore, we developed a technique to use power of the gated signal in the actual radar measurement. Using this parameter, we found that the polarimetric ratio of the gated power can be used for evaluation of the fracture. Polarization power ratio indicates that the fractures can be classified into clusters, and we think that this technique can be used for better understanding of each fracture structure.

A radar for use in very wet conditions such as tunnels, sewers and aqueducts is described. Operator safety under such conditions is paramount and communications link is presented which provides data transfer plus 2 way voice communication from the tunnel operator to the surface with good electrical isolation of equipment used. Antenna problems, such as various forms of back radiation, which can lead to misinterpretation of radar data, are discussed.

In this paper we describe three sources of information that radio-echo sounding has provided about the subsurface hydrology of a polythermal glacier: (1) Water input locations: crevasses and moulins provide the main pathway for surface melt to reach the interior of the glacier, and are identifiable as strong reflectors close to the glacier surface. (2) Subglacial flow routing: common mid-point surveys are used to calculate the radio-wave velocity through the glacier. Reflections from the glacier bed are then converted to ice depths, which are subtracted from the surface topography to determine bed topography. These are used to reconstruct the subglacial hydraulic potential surface and likely patterns of basal water flow. (3) Subglacial properties: repeat surveys at the same location over 9 days display diurnal variations and changes in bed reflection power associated with changes in basal water flow.

Ground penetrating radar systems provide an alternative for detection and classification of anti-personnel landmines, in particular, due to the minimal metal content in the structure of modern mines. We propose a new detection scheme based on a discriminator as a functional of time-varying spectra of radar returns. It is experimentally shown that the statistics of the discriminator vary with the terrain properties and must be adaptively estimated from background returns. The proposed scheme is better suited than other techniques due to FFT processing. The results shown are based on radar returns obtained under different environments and outperform previously suggested techniques due to the higher detectability of mines.

Over the past 10 years, ground penetrating radar (GPR) studies in a wide variety of geomorphic and geologic settings have, surprisingly, revealed detailed stratigraphic information. Most of these studies were conducted with lower frequency antennae (50 - 100 MHz) in an effort to better understand subsurface stratigraphy. As GPR systems and data collection methods continue to improve in their ability to collect higher quality digital data, GPR investigations are poised to enter a new era of higher resolution exploration utilizing higher frequency antennae. The paper presents the results of four case studies using a higher frequency (225 - 900 MHz) GPR system to effectively investigate coastal and eolian sedimentary environments. Some drawbacks of higher frequency data are: the lack of penetration depth, in some cases too much detail ('lose the forest for the trees'), and potentially extra equipment in the field.

In this report universal probe of electromagnetic field amplitude is described. The probe is intended for measurements of GPR antenna radiation in upper hemisphere as well as under ground surface. Goedbloed (1991) and de Jongh (1998) used analogous probe for measuring GPR antenna radiation pattern in lower hemisphere. The method described there is not flexible enough and narrows the range of measured parameters (depth of probe is fixed). Here we propose universal EM field probe and method for its use. Such sensor may also be used for in situ measurements of main parameters of sounded ground: (Gamma) ₀ -- linear absorption and (nu) -- EM wave propagation velocity in ground. Example of such probe use is given below.

In this paper, we present a comprehensive two-dimensional technique for preprocessing the data acquired by a continuously moving ultra wideband impulse ground penetrating radar (CM UWB IGPR). The UWB IGPR was developed by the International Research Centre for Telecommunications- transmission and Radar especially for humanitarian land mine detection. The radar was used to collect data in the measurement campaigns which took place at several different types of open-air grounds with permittivities which are weather-dependent. The platform for mounting the system was moved at a velocity of 72 meters/hour. A variety of mines were on the ground surface, flush buried and completely buried in the ground. The designed scheme of 2D data preprocessing has been applied to the measured data. The results show that the non-metallic and metallic anti-personnel and anti-tank land mines that are invisible in the raw data image can be revealed unambiguously. The direct coupling between transmit and receive antennas and surface reflections plus the data acquisition along a slant range (due to continuous moving) give rise to the difficulties of searching for small land mines with diverse ground scenarios which include ore, clay, woodland and sand. The preprocessing is therefore important in that it should give first-hand on-line results for reliably determining of the next step in the operation such as to continue moving and/or searching. It is also important for supplying input data to subsequent processing such as 3D SAR. One can imagine that the signal levels scattered from surface- laid and deeply buried land mines would vary drastically. In this context we developed comprehensive data preprocessing which successfully coped with these problems. The data acquired by CM UWB IGPR have been processed and the results gained by using this technique are promising.

Earthen flood banks/levees in the Odra river valley near Wroclaw (Lower Silesia, Poland) were inspected with the round penetrating radar (RAMAC/GPR). The aim of the investigations was to describe the internal structure of the flood banks and to detect damages failures due to water percolation, fluation, rinsing, outwashing, sinking and erosion. Radar profiling was made along the axes of the earthen constructions using 200 MHz shielded antennas. The geological interpretation of the radar data was verified by drilling. The usefulness of the radar method (GPR) for rapid and non-destructive monitoring of earthen flood banks has been proved.

Assessing internal damage levels in concrete roadways is an excellent opportunity for the application of nondestructive evaluation techniques, such as ground penetrating radar (GPR). Concrete roadways, particularly those on bridges, are high- performance structural elements that are subjected to severe environmental and mechanical stresses. These stresses cause corrosion of reinforcing bars, the promotion of internal cracking, eventually large-scale spalling, and the formation of deep potholes. This damage usually initiates internally and does not appear on the surface until it is at an advanced state. The use of asphalt overlays further exacerbates this problem. One of the most important, yet difficult to identify, defects is a delamination, which can be due to expansion associated with reinforcing bar corrosion. The GPR reflections from a delamination can be relatively weak, whereas the reflection from a reinforcing bar can be fairly strong. This paper presents the results of a laboratory and field study that focused on GPR methods of detecting delaminations in concrete roadways. The measurement technique used 0.5 to 6.0 GHz air-coupled waves to probe the roadways. Delaminations as small as 0.5 mm were stimulated and detected in the laboratory. Field measurements are suggestive that this technique can be effective for field use.

A large (2 km X 1 km) sand bar has been surveyed using ground penetrating radar (GPR), augmented by vibracoring and trenching, to investigate the sedimentary structures and three-dimensional alluvial architecture. Around 8 Km of GPR profiles were collected with nine survey lines running transversely across the bar at 250 m intervals with a profile along the bar. Profiles image structures beneath the water table to depths of up to 15 m. Reflectors from GPR profiles are interpreted as sets of cross-stratification, channel erosion surfaces, bar slipface accretion, mud-drapes, upstream accretion surfaces and the water table. Elements of upstream, downstream, lateral and cross-channel accretion are identified. Apart from the preservation of a range of dunes, the dominant style of deposition within the bar is oblique downstream and cross-channel bar margin accretion with large low angle and angle-of-repose foresets. These GPR facies characteristics are used to construct a three-dimensional model of facies architecture which may be applied in the interpretation of ancient braided alluvium. Bounding surfaces on the GPR can be tied to earlier bathymetric profiles, yielding a unique insight into the chronology of sedimentation and bar evolution. Trenching and coring of the bar top confirms that dunes and bar-margin slipfaces are the predominant facies units.

The design and testing of suitable GPR antennas to be used in the field is both an arduous and challenging task. Presented here is a watertank testing facility incorporating a method of measuring gain and impedance of scaled-down models of prospective GPR antennas. A vertical ground plane is placed in a watertank measuring 1200 mm X 600 mm X 600 mm. A mono- pole version of the test antenna is connected to a 150 mm square plate which fits exactly into the ground plane. Underwater and air probes are placed in a semi-circular fashion on the vertical conducting ground plane around the square plate at radii of 150 mm and 300 mm respectively. Results are presented as gain and impedance plots for a monopole test antenna with two different water levels; 0 mm and 5 mm below the base of the test antenna. Results for a salty solution and Isopropylalcohol dielectrically loaded, cavity backed, slot bowtie antenna are also given. The results show the sudden change in electrical length that occurs near a half-space surface, lateral wave phenomena as an air gap appears between the antennas's base and the water's surface as well as improved fractional bandwidth through dielectric loading.

In previously reported work (Wright and others, 2000) we found that the very early time electromagnetic (VETEM) prototype system produced data from which high resolution images of a buried former foundry site at the Denver Federal Center were made. The soil covering the site is about 30 mS/m conductivity, and is thus relatively unfavorable for ground penetrating radar (GPR) imaging. We have surveyed portions of this site again with new electric field dipole antennas and a new receiver designed for these antennas. Comparisons of the images produced using the loop antennas to those produced using the electric field dipole antennas illustrate that for this application the loop antennas produced more useful images. The larger man-made structures can be seen more clearly because they are not masked by dispersion and/or smaller scale variations as with the electric field dipole antennas. The VETEM system now contains an array of antennas with appropriate transmitters and receivers and can be operated as a low frequency time domain GPR or as a high frequency time domain electromagnetic (EM) system with several possible antenna spacings and polarizations. We plan to examine additional configurations. Numerical modeling of the perpendicular loop antenna configuration has been done and depth estimates produced. We conclude that, as with other GPR and time domain EM systems, the best choice of operating parameters depends on the application and the environment, but the inherent flexibility of the VETEM system allows a wide range of options.

Public funding for road network maintenance has decreased 30% during the last few years in Finland. Reduced resources, together with the current rehabilitation strategies, will in the long term result in increasing deterioration of the Finnish road network. For this reason road rehabilitation funding should be focused more specifically on those roads and road sections requiring measures and these measures should be optimized to ensure that only the specific problem structure will be repaired. Roadscanners Oy, in cooperation with the Finnish National Road Administration (Finnra), has developed a new and effective Road Analysis technique to survey the condition of roads and road networks. Road Analysis is based on the integrated analysis of the measured data collected from the road under survey. The basic survey methods used in Road Analysis include Ground Penetrating Data (GPR), falling weight deflectometer (FWD), roughness and rutting measurements, pavement distress mapping and GPS-positioning, as well as reference drilling based on preliminary GPR data analysis. The collected road survey data is processed, interpreted, analyzed and classified using Road Doctor software, specifically developed for this purpose. GPR measurements in road analysis are carried out using a 400 MHz ground-coupled antenna and a 1.0 GHz horn antenna. Horn antenna data is used to measure the thickness of the pavement and base course layers, as well as to evaluate their quality based on their dielectric properties. The 400 MHz ground-coupled data is used to estimate the thickness of the pavement structure and embankment. Ground-coupled antenna data is used for subgrade quality estimations and in evaluating the causes of subgrade- related frost defects. GPR data also provides important location information about special structures, such as steel reinforcements, cables and pipelines. Road Analysis includes a classification of the critical elements affecting the lifetime of the road: (1) overall pavement condition, (2) condition assessment of the unbound pavement structure, (3) road fatigue related to subgrade frost-action, (4) drainage condition and (5) local damages, such as settlements of the surveyed road. The results of Road Analysis provide a better understanding of the causes of defects occurring on the road and allow more precise rehabilitation measures for problem layers.

A lot of different logging methods are established for many exploration purposes. The borehole radar or Electro Magnetic Reflection (EMR) method is not that popular. There are two main reasons for this situation: Borehole radar measurements are not applicable in situations where drilling mud or other conductive materials are in the borehole and the available borehole radar equipment need special logging cables like optical or coaxial cables. The first aspect limits the application of borehole radar to stable drillholes where no hydrostatic pressure is necessary or where only pure water may replace the drilling mud. Especially a dry salt environment is suitable for borehole radar. The second aspect is related to the equipment. A very ruggedised borehole tool with easy assembling and fitting to standard cableheads and standard logging cables is desirable. This paper describes the development and the outline of a directional borehole radar system which may be integrated in standard logging programs. This system makes it easier for companies to carry out borehole radar measurements at their drilling locations.

GPR borehole surveys provide important spatial data on the geological structures within mines. In this paper we want to show how the spatial relationships of complex geological structures are determined in a repository for radioactive waste in salt. Whether a discontinuity within a stratigraphic sequence can be detected depends on differences in the conductivity and permittivity of the geological units. In contrast to data treated in half-space, it is important to record and interpret the data of borehole radar measurements not only as a function of distance but also as a function of direction. The authors have developed GPR instruments and methods for interpreting directional data. Because the wave propagation velocity is known, the data can be a migrated in space by reconstructing the wave front. This allows the construction of reflection horizons that can be precisely oriented spatially. Case studies of GPR borehole measurements to locate anhydrite structures in salt mines will be used to illustrate the value of this method for efficient reconnaissance. The methods for interpreting the reflectors in terms of their geological meaning and for representing them in three-dimensions are discussed. Three-dimensional interpretation allows geologists and miners to better target their activities with greater safety.

Crosshole radar measurements were taken in 4 vertical boreholes aligned on a N-S profile. During the survey, the receiver was kept in one borehole at the extremity of the profile while the transmitter was moved along the 3 other boreholes. Using this overlapping survey geometry, several first arrival amplitudes at different transmission distances were measured for specific raypath angles. These amplitudes depend on the traveled distances and raypath angles. Several factors, such as the antenna radiation pattern, partitioning of energy at interfaces, and anisotropy of the media, explain the variations of the first arrival amplitudes with raypath angles. The antenna radiation pattern and anisotropy can be taken into account prior to, or during tomographic procedures. However, effects from partitioning at interfaces and residual amplitudes from the theoretical antenna radiation function used in data reduction, may be misleadingly introduced into a tomographic algorithm. Owing to the overlapping geometry, a correction combining these 2 factors is statistically estimated and applied to the data. The direct arrival attenuation tomograms obtained from the corrected data are more representative of the local geology.

Three-dimensional structural maps are important in optimizing the design and safe development of stopes. As mines deepen, it becomes increasingly difficult to map potentially productive horizons by drilling or geophysical sounding from the surface. Geologists develop plausible 3D ore body images from the cores of underground boreholes drilled in vertical fans from mine galleries. However the fans usually sample the rock volume too sparsely to acquire the detail needed for accurate mining. Trials in Western Australian mines have established that wideband VHF borehole radars can be used to probe the rockmass between boreholes. There is evidence that ore bodies reflect VHF radar signals both specularly and diffusely, much as the ground-air interface does when it is overflown by synthetic aperture radar (SAR). Interferometric borehole radar (InBHR) is analogous to SAR interferometry (InSAR) but it differs in certain important respects. There is also evidence of diffuse backscattering, at least from sheet-like ore bodies. This paper will examine the differences between InSAR and InBHR, and discuss the possibility of tapping into this backscatter by using interferometric methods to map both fault-hosted and other ore bodies in three dimensions.

In this paper, we propose a side looking subsurface radar system for a horizontal directional drilling machine to be used for laying power cables under the roads. The system enables to detect unknown buried objects which may be on the side of the drilling rod to prevent collisions to them. For developing such system, we propose to use slot antennas and prove the usefulness of the antennas by some experiments we have conducted. We also show the effectiveness of the system by showing images taken by the system.

This paper reports a study into the use of standard image processing techniques and measures to score and index radargrams. The study has developed from work investigating the use of neural networks to interpret sub surface radar signals. The paper details: The image processing techniques used to score the radargrams and the results of the scoring; How finite difference time domain modeling was used to generate the synthetic radargrams for the study; Introduces the simple methods used to reconcile the input to the modeling and the scores generated by the image processing. The situation modeled was that of an air filled void under a reinforced concrete slab.

Data focusing is the final processing step needed to transform GPR data into 2D and 3D images that can be directly interpreted by the NDT end-user. Focusing techniques provide the best result when the data are good and well pre-processed. Typically, the background subtraction is one of the most critical steps that might have a significant impact on the final result. Thus, we concentrated our attention on this problem in normal and special case (i.e., in presence of shallow horizontal targets), proposing some tricks to achieve the goal. In the second part of the paper, we present few 2D and 3D imaging examples, where the improvement of focusing on the final imaging result is extremely evident.

Application of conventional elevation static corrections and migration to wavefield data recorded on irregular surfaces may result in poor reconstructions of complex subsurface features. Particularly poor images may be obtained at locations where the depths to target structures are comparable to undulations in the surface topography. For example, topographic relief of only 1 - 2 m may be important for the processing of georadar data. We describe an approach that allows georadar data to be migrated directly from gently to highly irregular acquisition surfaces. When applied complicated synthetic data sets, topographically migrated images are observed to be markedly superior to those produced by two standard processing schemes. Extensive tests demonstrate that topographic migration should be considered in regions characterized by surface gradients greater than 10% (i.e., dips greater than 6 degrees). For effective topographic migration, lateral and vertical coordinates of the georadar antennas should be determined to better than 10% of the dominant georadar wavelength and velocities should be known to within 10 - 20% (e.g., 0.01 - 0.02 m/ns) of their true values.

GPR data collection in the frequency range of 3 to 66 MHz has been performed by the U.S. Air Force Research Laboratory (AFRL). To process this data into images, the relative permittivity of the medium is a key parameter since it determines the propagation velocity through the medium. Image formation using phase information returned from buried scatterers can be improved by matching the processing to the environment in which radar measurements were taken. Considering the permittivity to be an unknown scalar parameter, several images can be formed as a function of the unknown parameter leading to a choice which maximizes the sensitivity and resolution of the resulting image. In this paper we extend upon this concept to include variations of the medium that are nonhomogeneous with respect to the physical locations of receiving sensors.

To better interpret collected ground penetrating radar (GPR) data, a project is currently underway at the Virginia Smart Road. Twelve different flexible pavement sections and a continuously reinforced concrete rigid pavement section are incorporated in the road design. Thirty-five copper plates were placed at different layer interfaces throughout the pavement sections. The copper plates serve as a reflecting material and thus allow the determination of layers' dielectric constant over the GPR frequency range. An initial development of a method to calculate the complex dielectric constant of hot-mix asphalt over the frequency range of 750 to 1750 MHz using an air-coupled GPR system is presented. Utilizing GPR data, this method will be used to predict changes of the dielectric properties of the different SuperPave^TM mixes used at the Smart Road over time. The method is based on equating the overall reflection coefficient as obtained from the radar measurements with the calculated reflection coefficient using electromagnetic theory. The measured overall reflection coefficient is obtained by dividing the reflected frequency spectrum over the incident one. The theoretical overall reflection coefficient is obtained using the multiple reflection model. A Gauss-Newton method is then used to solve for the complex dielectric constant.

During summer 1998 a series of tests were conducted in Finland in order to find out how Ground Penetrating Radar (GPR) technology can be utilized at both the project and network level, when surveying the wearing course thickness of gravel roads. The second objective was to investigate the possibilities of applying dielectricity information obtained using the GPR surface reflection method when determining the quality of the gravel road wearing course. In this study GPR was tested at the project level on highway 9241 Simo in Northern Finland, where the information provided by the GPR and laboratory research was used in designing and proportioning a new wearing course. In the network level studies, performed in the maintenance areas of Kemi and Karstula in Northern and Central Finland the goal for using GPR was to inspect the condition and thickness of the wearing course and evaluate the need for additional wearing course material. The total length of the roads under survey was approximately 200 km and both a 1.5 GHz ground-coupled antenna and a 1.0 GHz horn antenna were tested in this study. The research results show that GPR can be used to measure the thickness of the wearing course, the average measuring error against reference drilling measurements being 25 mm, which is considerably larger than the error of radar measurements in paved roads. To a great extent this is due to the fact that the thickness of the wearing course varies greatly even in the road's cross-section and thus a single reference thickness does not represent the actual thickness of the area measured with the GPR. The wearing course can often get mixed up with lower layers, which makes it difficult to determine the exact layer interfaces. For this reason reference information must always be used along with the GPR measurement results. Of the two GPR antennae tested, the horn antenna proved to be the more effective in measurements. The dielectric value of the wearing course, measured using the horn antenna surface reflection method, represents well the suction properties of the wearing course. High dielectric values reflect the water sensitive and frost susceptible wearing course materials where as low values reveal the lack of binder. A quality rating of the wearing course by its dielectrics and layer thickness is also suggested. In the measuring results analysis and presentations, GIS-maps proved to be invaluable.

A GSSI SIR-8 with 1 GHz air-launched horn antennas has been modified to acquire data from a moving vehicle. Algorithms have been developed to acquire the data, and to automatically calibrate, position, process, and full waveform model it without operator intervention. Vehicle suspension system bounce is automatically compensated (for varying antenna height). Multiple scans are modeled by full waveform inversion that is remarkably robust and relatively insensitive to noise. Statistical parameters and histograms are generated for the thickness and dielectric permittivity of concrete or asphalt pavements. The statistical uncertainty with which the thickness is determined is given with each thickness measurement, along with the dielectric permittivity of the pavement material and of the subgrade material at each location. Permittivities are then converted into equivalent density and water content. Typical statistical uncertainties in thickness are better than 0.4 cm in 20 cm thick pavement. On a Pentium laptop computer, the data may be processed and modeled to have cross-sectional images and computed pavement thickness displayed in real time at highway speeds.

To address the need for developing a database of pavement layer thicknesses to support pavement management, the Florida Department of Transportation (FDOT) funded a project with the Texas Transportation Institute that developed a computer program called TERRA for analyzing Ground Penetrating Radar (GPR) data in a production environment. TERRA is an acronym for Thickness Evaluation of Roads by RAdar. It incorporates user-specified decision criteria for automated detection of layer interfaces. Tests to verify peak tracking capability demonstrated that the program is able to handle gradual or sudden changes in the patterns of the interface reflections as well as gaps in the data. Verification of the thickness predictions against core data from sites surveyed with radar showed acceptable accuracy for uncalibrated estimates of surface thickness. In particular, the average of the absolute differences between the means of predicted and measured surface thicknesses was found to be 0.30 inches. Because of the absence of measured base thicknesses, it was not possible to verify the base predictions on the sites tested. It is recommended that this be done by FDOT at a future date as part of its GPR implementation efforts.

Ground penetrating radar (GPR) has been one of widely spreading technologies in this decade. Much improvement has been achieved in devices and data processings. Main roll of GPR is to make a view of underground condition unseen to human eyes. For a good use of GPR an interpretation is crucial as well as having a good device. Interpreting work has been mostly performed in order to find and locate buried objects and to figure out geometric layer structures. The work is just a recognition of reflection. But GPR records reflect various physical phenomena. They include more information than just existence of reflectors. Complexity on records occur as a result that various physical phenomena and characteristics of layer geometry interacted. Some examples showed that theoretical speculation allows us to unveil the complexity and strangeness on records and to obtain more information on physical properties or material identification of surveyed objects.

A variety of 2-D acoustic migration algorithms are routinely applied to ground penetrating radar (GPR) array data to form images of reflecting surfaces. In a few instances 3-D migration has been performed. We demonstrate the GPR dipole radiation effects on imaging planar reflection surfaces under a 3-D acoustic Kirchhoff imaging condition. This is accomplished by analyzing migration results using synthetic GPR array data generated with a new diffraction integration method that includes interfacial dipole radiation patterns. The impact of the GPR radiation pattern is demonstrated on migration images by considering three antennas types (isotropic, x-, and y-dipoles). For all the results discussed, we use the relative dielectric permittivity for ice, and monostatic transmitter and receiver geometry. We find that an array having a 2.5:1 length-to-width (x:y) ratio and populated with isotropic elements, has a directivity of 4.8. The same array using x-oriented antenna elements has a directivity of 11; with y-oriented elements the directivity is 7. The dipole radiation pattern dominates the array factor. In migration results, when the array factor is aligned with the H-plane dipole pattern, surfaces as steep as 45 degrees are readily imaged. Conversely, when the array factor is aligned with the E-plane pattern, reflectors with dips as low as 20 degrees are difficult to image. These results stress that correct dipole orientation with-in the imaging array is vital for achieving optimal reflector images using migration techniques.

A major goal of NASA's Office of Earth Science Polar Program is to determine the mass balance of the Greenland and Antarctic ice sheets. A key variable in assessing the mass balance of an ice sheet is accumulation rate. Currently, accumulation rate is determined from ice cores and pits. There are large uncertainties in existing accumulation rate maps derived from sparely distributed ice cores and pits. There is an urgent need for developing remote sensing techniques for determining the accumulation rate. A prototype Frequency Modulated Continuous Wave (FMCW) radar system has been developed for mapping internal layers from known volcanic events in the ice. The prototype system has been designed and developed using the latest RF technologies. The system was operated from 100 to 2000 MHz, for imaging the top 200 meters of ice with high resolution. We tested this system during the 1998 and 1999 surface experiments at the North GReenland Ice core Project (NGRIP) ice camp. Our results show that internal layers were successfully mapped with high resolution down to 200 m.

A glacier consists of physical structures covering a large span of length scales. The different scales can be mapped using different radar frequencies. The bottom topography is mapped using HF frequencies (5 - 20 MHz). The internal structure is seen at UHF frequencies (100 - 500 MHz). The snow cover and firn layers can be mapped with frequencies around 1 GHz.

In 1996 and 1997 an airborne RES survey was flown in the context of the North Greenland Ice Core Project (NGRIP). At 75.10 degrees N and 40.30 degrees W a deep ice core is being drilled for palaeoclimate studies with the objective to recover an undisturbed Eemian sequence. The present survey was specially designed to determine with high lateral resolution the bed topography and the layering of internal reflectors in the vicinity around the drill site. A total of 19,000 km of profiles were flown yielding a rectangular flight pattern with side lengths of 222 km respectively 210 km on 16 flights. The spacing between two flight tracks is about 10 km for most of the area and about 2.5 km in the center of the grid. Detailed maps of ice thickness and subglacial topography have been produced. Moreover a data set was acquired that enables an independent stratigraphic control on the ice core record of NGRIP. From the map of subglacial topography and from selected profiles the bed of NGRIP can be denoted as perfectly flat particularly when compared to the region of GRIP/GISP2. There is no obvious reason, why flow disturbances eventually might have altered the stratigraphic order in the lower part of the ice sheet at least up to 30 km upstream NGRIP. On the basis of the present study NGRIP seems to be an ideally chosen drill site in order to recover an undisturbed Eemian sequence.

The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) is a radio frequency subsurface radar sounder designed to operate on the international Mars Express mission, an ESA program for the orbital and in-situ study of the subsurface, surface, ionosphere and atmosphere of the planet Mars. The Mars Express Orbiter spacecraft is developed operated and fully funded by ESA with the exception of the seven payload scientific instruments which will be used for remote observation of the red planet. According to the current ASI/NASA agreement the MARSIS instrument has an Italian PI, an U.S. Co-PI, and Co-I's from the Italy, the U.S. and other countries. There is also an U.S. Experiment Manager and an Italian Deputy Experiment Manager.

We have defined the complex bed topography for a section of a small temperate glacier using 50-MHz monostatic short-pulse radar data and a synthetic aperture array processing method. The data were collected on a 100- by 340-m array grid in the upper stem of the Gulkana Glacier of central Alaska. The array processing was based on a modified 3-D Kirchhoff migration integral and implemented with a synthetic aperture approach that uses sequences of overlapping subarrays to generate depth images in vertical planes. Typical subarray beam widths are generally less than 5 degrees at the -6-dB level, giving a flashlight-like searching capability without distorting the wavelet shape. The bed topography was constructed uscg specular reflections picked from 3-D array depth images. In some instances reflections were imaged outside the data coverage area. The bed surface dips steeply, both parallel and transverse to the direction of ice flow. The maximum observed depth is roughly 140 m. The 3-D method resolved bed dips up to 45 degrees. In regions of steepest dip, it improved depth accuracy by 36% compared it raw data, and by 15% compared with standard 2-D migration. Over 12 dB of signal-to-noise improvement and improved spatial resolution were achieved compared to raw data and 2-D migration. False bottom layering from out-of-plane arrivals, seen in the raw data and in 2-D migrations, are not observed in the 3-D array results. Furthermore, loss of bottom reflections are shown by the 3-D migration to be attributable to the dip and curvature of the reflector, and not scattering losses or signal clutter from englacial inclusions.

This paper describes a new application of Ground Penetrating Radar (GPR) in non-destructively assessing the delivered quality of bridge superstructure beams. A case history is described where GPR was used to assess the quality of 180 prestressed concrete beams in relation to the requirements specified in the engineering design. The beams analyzed in this project represent a standard design used in Queensland where several large polystyrene blocks (called 'voids') are cast internally within the deck beams to reduce the mass of the beams. GPR was used effectively to determine the finished location of these voids within the beams and identify any defects associated with the movement of the voids during manufacture of the beams. It was concluded that at least 90% of the beams were out of tolerance due to significant void movement in a vertical direction and there were significant associated defects of air cavities within the concrete, thin top and bottom flanges and longitudinal soffit cracking. Predominantly the voids had moved downwards during the concrete placement process. The accuracy of the GPR survey was determined to be +/- 5 mm where good calibration was obtained and +/- 10 mm for the global set of results of 4860 measurement points.

Much attention is being given to the challenge of detecting buried non-metallic mines and National and International programs are underway to develop more effective detection and clearance systems. Conventional metal detectors respond to the metal content of a mine, hence the minimum metal or plastic mine remains largely undetectable by current technology, particularly in areas where battlefield debris and shrapnel cause a high false alarm rate. Ground Probing Radar (GPR) offers useful performance improvements in these situations and used in conjunction with metal detector arrays can result in an improved fused performance in terms of increased signal to clutter ratio. This paper considers several aspects of the performance of GPR systems, in particular the antenna elements and arrays of antennas. Examples of the radar images of mines and the factors that influence image quality are presented.

A novel but intuitive antenna design to achieve both broad frequency bandwidth as well as good efficiency is presented. This design utilizes unfurlable folded-dipole with its length mechanically tuned to specified operational frequency. Such antenna has been proposed for subsurface sensing on Mars surface and its prototype was built and tested. The test results verified the desired bandwidth and efficiency feature.

Prior results of surface artifact collecting, test excavations, and auger sampling on an archaeological site in Barbados suggested that we experiment with GPR as a method to target areas for future study. The site is associated with village occupations of Amerindians that are dated to between approximately 2000 and 500 years ago. Archaeological features include burials, hearths, ceramic lined wells and post holes. Artifact middens contain pottery sherds, conch shells, and other marine resource debris. The site selected was located at the southern tip of Barbados and is situated on a deep stabilized surface behind a large active dune system. The soil layer consists of dry, clean quartz sand. We obtained limited ground truth at the site by hand-auguring in areas of field- identified anomalies, and by auguring control holes away from anomalies. Anomalies were almost always large diffractors such as conch shells and rocks. We used 3D software to perform standard processing enhancements and to assemble the parallel lines into three-dimensional volumes. The dimensions, distribution, and shapes of time-sliced amplitude anomalies were consistent with those of previously excavated burials, poles, and pit structures. These features would not have been obvious using conventional a profile-based GPR survey.

We have developed the 'position measurement method' to determine the GPR's position on the road by accurately measuring the distance and direction in which it has moved, as well as '3D visualization software' to compile data of cross sections and reconstruct three-dimensional structure of buried objects. With the 'position measurement method' we have developed, survey data can be obtained by operating the GPR in arbitrary directions, while maintaining a survey speed corresponding to normal walking speed. And '3D visualization software,' developed for Windows PC, has main features as follows: (1) Survey data obtained by both arbitrary and parallel line operations can be visualized three- dimensionally; (2) High speed migration processing to improve the horizontal resolution; (3) 2D placement of objects buried at various depths can be easily detected; (4) 3D structure of the buried objects can be easily extracted.

Some elements of the modern ground penetrating radar (GPR) determine its performance factor, resolution and depth of sounding. There are impulse transmitter, ultra-wide-band receiver as well as transmitting and receiver antennas. Improvement of the GPR's parameters is usually achieved by modernization of receiving circuits, antenna design, decreasing of input noises and using of complex computational algorithms for on-line and post-processing. As active element for impulse generation are widely used step recovery diodes (SRDs) or avalanche transistors. However such devices can not generate nanosecond pulses up to some hundreds volts on the antenna terminal. This work is devoted to application of drift step recovery didoes (DSRDs) in GPR transmitter design. Current drive circuit based on charge DSRD model has been computed and optimized. Investigation results for pulse generator characterized by peak power up to 5 kW and rise times as small as 2 nanosecond (ns) are reported. Application abilities of commercial power rectifier diodes in the DSRD mode are shown. Transmitter based on DSRD can operate with low impedance antennas, high repetition rate and efficiency.

The Arcolabs borehole radar system was developed to assist detailed orebody delineation particularly for mines extracting thin vein ore deposits. The probes are 32 mm and therefore fit in most common exploration and mining drillholes. The system has been successfully used at a number of mine sites to assist with ore delineation at a range of scales. Images from holes drilled alongside the extension of a massive sulphide orebody downdip from current development clearly showed the extent of the orebody and changes in thickness and dip of the orebody. The costs of these surveys were considerably less than the cost of delineation by drilling alone and the resulting image provided more detailed data which could be used to optimize the position of development. Estimates of potential savings from using the system to define the bottom of the orebody were of the order of hundreds of thousands of dollars. Images from short holes drilled at short intervals beneath the footwall of another orebody enabled a detailed wireframe of the orebody contact to be constructed. Better knowledge of the contact location helped to maximize ore extraction and minimize dilution.

In order to study the feasibility of developing a portable near-field subsurface radar, we perform numerical simulation of a multielement holographic antenna array. Spatial resolution, sensitivity and the instrumental error effects are estimated. In our model of a monochromatic or multifrequency holographic radar, a plane incident wave illuminates the object to be 'seen,' and a square N X N array of point receiver dipoles measures complex wave amplitude of the scattered field. Reconstruction algorithm represents the scattered wave as a superposition of Gaussian beams focused onto a certain 'plane of the best vision' z equals l. Their amplitudes can be found via modified Fourier transform in the antenna plane. The resulting angular spectrum, depending on the focal distance l, represents spatial density of virtual sources producing the registered field distribution. This algorithm provides maximum spatial resolution allowed by physical optics and can be easily implemented using standard FFT. Numerical simulation shows that a microwave holographic antenna has transversal resolution of about few centimeters, having high robustness with respect to the random phase errors. Two-frequency phase measurements can provide depth resolution of the same order of magnitude.

Numerical modeling of more or less realistic antennas is interesting to people working on antenna design and to people working on the processing and interpretation of radar data. They have different demands regarding the output of the model code. Our interest lies with improving scalar imaging algorithms using the coupling effects of a bi-static GPR acquisition configuration where the antennas are both close to the earth surface. They can be in each other's broadside, endfire or cross-polarization plane. We have implemented the theory for the electromagnetic radiation and scattering problem for GPR applications for straight wire antennas. The receiver antenna is identical to the source except for the excitation mechanism. The antennas are not modeled as perfect conductors but have a finite resistance distribution. To study the coupling effects between two antennas, a Neumann expansion of the integral equation for the excited currents in the antennas results in an iterative computation of the currents where each term in the expansion exactly accounts for one order of multiple scattering between the antennas. The coupling with the earth can be accounted for in the same way but can also easily included directly in the formulation.

Open-cast mining, involving severe disturbance, of shallow coal deposits has taken place in Mpumalanga, South Africa for some time with little control until recently. Current legislation requires soil investigations. The soils are agriculturally productive and merit effective rehabilitation, but several problems in this process can occur, leading to drastically reduced agricultural productivity. GPR investigation of these mine soils can help with the mapping of the depth to spoil after rehabilitation, on a significantly more cost-effective basis than traditional point observations. A field trial was carried out as part of a research project at Kleinkopje Colliery where it was shown that, despite wet conditions due to irrigation, GPR was able to map spoil depth around six times faster than augering. There is substantial scope in South Africa for GPR to make a significant contribution in this field.

Because the resolution of tomography is not high, crosshole tomography is suitable for imaging large weakly inhomogeneous bodies, but not suitable for bodies of small size, for example, thin aperture fractures. We try to use crosshole migration method to obtain underground small aperture fractures between two boreholes. Since fractures are filled with water, although the apertures of fractures are small, the electromagnetic property of fractures is very different from bedrocks. Field experiments show that reflection and diffraction from water filled fractures can be received by radar sondes. Therefore, it is possible to get images of fractures by crosshole migration. We apply the crosshole migration technique to crosshole radar data sets in frequency and time domain collected both by our research group and by USGS in Mirror Lake area, USA. By comparing the migration result of crosshole data recorded in frequency domain with USGS's results of crosshole tomography and directional single- hole measurements, we find that the migration result is consistent with USGS's results very well. Two known fracture zones are correctly imaged. The migrated section of background data illustrates two fracture zones. The difference images between migrated profile from USGS's background data and these from USGS's crosshole time-lapse data indicate that the transportation of saline tracer inside a transmissive zone can be known during the water and tracer injection and pumping. This result is also consistent with USGS's time-lapse difference-tomography results. Moreover, the detail structures inside the fracture zones could be seen from the migration profiles and the difference sections. However, differences between two results exist. This may indicate the limitation of tomography: the resolution and sensitivity of tomography are not high enough.

The ground investigations for a historical site of archaeological importance are usually a labor intensive and time consuming process. Exploratory diggings are most commonly employed to know about the buried artifacts or construction features. Many a time important features are not documented because such features are not easily accessible or the approach involves disturbance to the monument. A study was made with Ground Probing Radar (GPR) at Taj Mahal, one of the most cherished monuments of the Mughal period. The GPR techniques are comparatively new for the studies of foundation features of such monuments. In this paper, the results are presented from a GPR investigation with 100 and 200 MHz frequency antenna. Important features detected from GPR profiling near the boundary wall and on the Mausoleum floor are discussed. The location of the foundation wells and stone pinning etc. was correlated with the borewell data. Some features identified by GPR, however, could not be confirmed due to intricate location of the subsurface features. The findings show that the GPR techniques with a large spectrum of the antenna frequencies can be used to investigate the details of subsurface features at historical sites.

Ground penetrating radar datasets were collected from a variety of sites to provide three-dimensional (3D) images of coastal and eolian geomorphic environments. The images will aid in better understanding tectonically active coastlines and the internal geometry of eolian sandstones. An ancient eolian dune complex, consisting of two bedset packages with distinct truncation surfaces, was imaged at Zion National Park, Utah. The 200 MHz 3D dataset shows the internal stratigraphy with southwest dipping reflections ranging from 13 to 20 degrees. A second dataset was collected along the coastline in the southwest portion of Washington State. This 225 MHz dataset reveals the 3D structure of an erosional scarp caused by earthquake activity in the area. Results from the surveys indicate that the imaging in 3D is an effective means of analyzing internal stratigraphy of geomorphic features by allowing the user to more easily interpret spatial relationships within a dataset.

In this paper, results of GPR experiments carried out in Nalaih, Mongolia and Yakutsk, Russia will be shown. In the measurements, target is ground water and permafrost. Especially in these regions, there are special kind of permafrost structure, which are important in the study of permafrost. In Nalaih, there is 'pingo,' which is composed of several layers including permafrost in the subsurface. We applied Common Midpoint method to estimate vertical profiles. In analysis of the CMP data, we applied f - k filtering and NMO correction, which are common techniques in seismic signal processing. In our GPR data, there are reflected waves from the permafrost surface and we accurately estimated the structure of the permafrost of the pingo. In Yakutsk, Russia, there are also special structures at a few meter depth in Taiga region. We will show experiment results of GPR at the field, and we will interpret the data to detect the structure with GPR. Also we tried to compare GPR data and SAR data in Nalaih, Mongolia, and we considered interpretation of SAR.

In this report a method of frequency- and time-domain GPR signal processing is proposed for increasing the detection probability for objects with weak contrast, especially for layer boundaries with non-sharp changes of dielectric permittivity. The method consists of amplitude and phase correction either on receiver input or digitally on its output (after scaling of input signal spectrum by stroboscopic converter). Such filtration can suppress interference due to finite damping of antenna transient response (exponential decrease of signal oscillation amplitude), signal reverberations in feeder lines (constant amplitude of oscillations) and between antennas in air (t^-c decrease of amplitude). A complex coefficient is defined in frequency domain, which allows to transform the spectrum of mean signal to gauss-like spectrum. Then, in time domain after the filtration signal waveform is similar to Rieker wavelet and has almost no oscillations. This can increase the reliability of detection of weak reflections overlapped with late time oscillations of direct coupling signal.

We performed an integrated acoustic and GPR study of the Cheko Lake area (101 degrees E, 62 degrees N) during summer 1999. The GPR study aimed at imaging lake bottom and shallow sedimentary layers to plan coring of sediments coeval with the catastrophic 1908 explosion. The water of the Cheko Lake strongly attenuates radar waves. Therefore, the central and northern sectors of the lake (30 m average depth) were surveyed by means of acoustic techniques only. Integrated acoustic and GPR techniques were used in the shallow southern sector. More than 5 km of radar profiles were obtained in the lake, using 50 MHz and 100 MHz antennas. 150 meters of 200 MHz multi-fold profiles were obtained across the only accessible sectors on land. The GPR profiles processed to date successfully image discontinuities at depths greater than 700 cm. Comparison with acoustic results shows that GPR provides high resolution images of the depth range of interest (0 - 500 cm) which complement the information obtained from sub-bottom profilers and can be calibrated by the gravity cores. A deep (700 cm) flat sub-horizontal reflector, shallow (0 - 200 cm) dipping layers, sigmoidal structures and local chaotic lenses are the primary features imaged by GPR in the lake.

Finite-difference time-domain models of radar wave propagation at freshwater/saltwater transition zones indicate that a reflected event from the electrical conductivity gradient at the top of the transition zone may be detected. Ground penetrating radar surveys were used together with a suite of geophysical techniques in a reconnaissance survey to delineate the freshwater lens on the island of Key Largo, Florida, USA. In the interior of north Key Largo, the water table lies at approximately 3 m depth. There a 1 - 1.5-m thick freshwater lens overlies a 2 to 3-m transition zone to saline water. 50 MHz GPR surveys show a strong water table event followed by a weaker event that correlates with the top of the freshwater/seawater transition. Nearby cores show no lithologic discontinuities in this depth range. In lower-lying areas with minimal freshwater, an enigmatic high-amplitude high-frequency event follows the water table event closely in time. The field data indicate that reflections from the freshwater/saltwater interface may be resolved in environments with fresh water above the transition zone and with a relatively sharp conductivity gradient at the top of the freshwater/saltwater interface.

Most GPR profiles are displayed in point mode form. This gives an amplitude color coded image where waveform amplitudes are plotted according to predefined colors (forming a palette). They are similar in concept to early GPR hard copy products based on gray scale distributions but they provide grater flexibility and dynamic range for anomaly recognition. A wiggle mode trace can also be included as an overlay on the color image to assist with wavelet recognition and enhance lateral correlations. However, more subtle components of the waveform (in particular phase relationships) are often ignored. Many data reduction, image display, and signal processing algorithms used for GPR surveys have been borrowed from remote sensing, seismic and general geophysical exploration techniques. However, they have been implemented in a relatively primitive form. In particular, the advantages of correct and relevant color palette selection for point mode images have been ignored. More rational palettes are now proposed to convey amplitude features, in combination with phase information, for analysis of target properties.

An underground high voltage cable, in which pressurized mineral oil is used as an insulating medium, was known to be leaking oil at one or more locations along its 2.5 kilometer length. It was impractical and even dangerous for the most part to dig along the cable route in an attempt to find the location of this leak or leaks. It was known that a significant quantity of mineral insulating oil had left the cable and entered the soil at the site of the leak. It was decided to trial ground penetrating radar by scanning along and over the buried cable to attempt to pinpoint the site of the oil leak. Soil dielectric properties are largely determined by the moisture content so that where moisture is displaced by oil the soil dielectric properties will change. Soil stratigraphy seen using radar is due to a large extent to the variable moisture content in the layering of the soil. Where oil is dispersed through the soil, it will tend to displace moisture. This dielectric property change makes the area sufficiently anomalous so that it can be detected utilizing ground penetrating radar. This principle has now been successfully used on a number of occasions in New Zealand.

A multi-channel GPR developed to tackle a range of simultaneous, rapid applications is described. Experimental data showing beam steering results and signal-noise ratio improvements using a multi-element receiver array is presented. The results show that beam steering together with improved signal-noise ratio is feasible for GPR.

During the last five years, I have been involved in several archaeological prospecting projects carried out in China. Both high- and low-resolution GPR systems were employed in conjunction with other geophysical techniques. We have tried GPR on different type of archaeological sites, hence the archaeological targets are different in term of depth, geometry and electrical properties. The survey strategy are also different from reconnaissance survey for unknown sites to volume mapping within known sites. This paper will introduce two typical applications, the survey strategy, instrumentation, data acquisition and processing, and merits and limitation of GPR in archaeological application are also discussed.

In the present work the results of modeling and experimental results of investigation of the buried objects are given and studied using measurements of spectrum data and microwave tomography method. In the inverse problem, a complex function of space coordinates representing the normalized polarization currents, have been reconstructed. A modulus of the complex function is the image of the object under investigation. The reconstruction algorithm is based on Fourier inverse formulas. It is shown that results obtained may be applied in practical tomography setups for detection and observation of different undersurface objects.

In this paper a concept in designing an adaptive antenna for ground penetrating radar is presented along with its preliminary simulation results. The antenna considered is an array of wire dipoles arranged to form a wire bow-tie antenna. The input impedance of bow-tie antennas is known to be dependent mostly on their flare angle. For antennas situated on the ground, maximal radiation into the ground can be obtained if their input impedance is optimized with respect to the ground impedance. Bow-tie antennas can therefore be optimized to radiate maximum power into a certain type of ground by adjusting their flare angle. In a first approach, without matching the antenna to feeding line, it is found numerically that there exists a certain angle at which this antenna radiates maximal power into the ground for all types of ground. In this case, adaptation to the ground by varying flare angle is still not fully realized. In our future research, another approach will be used, in which the antenna is matched to the feeding line within the whole spectrum of input pulse in order to obtain a more effective adaptation to the ground.

For the detection of buried objects using GPR technology, it is often necessary to acquire data over a two-dimensional area. To obtain a three-dimensional image of the subsurface using such a C-scan we have to apply three-dimensional imaging methods. To avoid artifacts in the image we have to sample sufficiently in both inline and crossline direction. Generally this results in a quadratic increase of the number of data compared to acquisition along a line. Consequently, the acquisition time and costs are increased as well. Often a practical compromise is chosen such that inline spacing is kept small, but the crossline spacing is increased for faster acquisition. We have investigated the influence of the spatial acquisition geometry on the final image that is obtained after three-dimensional imaging. For that purpose, we have modeled the back scattering by a point scatterer created by the radiation of a dipole antenna on a half-space. By using a three-dimensional diffraction stack as imaging algorithm for different acquisition geometries we can observe the acquisition footprint in the image. We conclude that the crossline spacing only weakly influences the resolution in the inline direction, especially for lines at zero crossline offset to objects.

Current practice prescribes the long standing use of frequencies less than 10 MHz for GPR sounding of temperate glaciers to depths greater than about 100 m. We have obtained continuous profiles of ice depth over temperate ablation zones and have reached at least 278 m at 30 MHz on the Matanuska, 195 m at 100-MHz on the Muir and 295 m at 12 MHz on the Gulkana Glaciers of Alaska. Internal stratigraphy occurs in the Matanuska profile. Multiple bottom returns are ascribed to thrust planes and out-of-plane reflections from sloping bottoms. Inability to reach greater depths is ascribed to unfavorable bottom slopes, as verified by drilling on the Matanuska, and by beam steering studies on the Gulkana. Lateral wave clutter contaminates profiles at all frequencies and polarizations where crevasses are present. The strength of 12-MHz Gulkana bottom signals precluded the use of range gain and suggests that 500 m depth might be achieved at 12 - 30 MHz.

GPR surveys were conducted in the New Madrid seismic zone in central US -- an area used to be considered unsuitable for GPR applications. The purposes of these surveys are to correlate geological features revealed by trenching and GPR responses and consequently lending a roadway to search for subsurface paleoliquefaction features such as sand dikes and sand blows in a relatively silty and clayey country soil environment. GPR surveys using 400, 100 and 25 MHz antennas were conducted at three sites at Haynes, Arkansas, Dillarhunty, and Sikeston Ridge Missouri. Comparison with shallow shear-wave seismic surveys at the Sikeston Ridge site reveals similar subsurface features in different deformation features at different depths (10 m vs 100 m) along the western scarp of the Ridge. Detailed study to analyze GPR registration of subsurface liquefaction features will be reported at the conference.

The year 2000 is the 10th anniversary of GPR work at CUG. This paper introduced some results within these ten years. Works were carried out in more than 20 provinces and 50 or more engineering geological problems were settled in varying degrees. Most of all tasks were raised from national key projects. So the GPR technic has been rather approved by field engineers.

Slot antennas, with and without resistive covering, dipole antennas having a screen have been modeled by finite difference scheme in time domain. The following characteristics has been studied: 'front to back' ratio, field patterns for pulse radiation, coupling between transmitting and receiving antennas. An influence of the spacing between the antennas and the ground surface for soils having various dielectric constant and conductivity was studied. Optimal conductivity of the resistive covering have been found for various types of the covering of the slot antennas. Filling of the spacing between the antenna and the ground by the resistive material leads to large increase of the front to back ratio, the optimal conductivity depends on the spacing. When the antenna is covered on lateral sides, the optimal conductivity is greater. Partial filling of the spacing leads to moderate increase of the front to back ratio. Dipole antenna with a screen and resistive material between the dipole and the screen, placed at some height above the ground, provides greater front to back ratio, than the slot antenna, having the same size. Computed field patterns and other characteristics enable to understand behavior of the radiation of the antennas and are useful in designing of shielded antennas.

During May 1998, Roadscanners Oy together with the Office of Minnesota Road Research performed a series of GPR tests in Minnesota, in order to determine the level of accuracy of the GPR technology in pavement and subgrade soil testing. The project involved a total of 195 km of GPR surveys carried out in different locations throughout Minnesota. The test sections represented a range of pavement materials, structures and soils found in the state. A number of GPR tests were performed to evaluate different types of pavement defect and ascertain their causes. The results of the Minnesota GPR Project 1998 clearly show the potential benefits that GPR techniques could offer the Minnesota Department of Transportation (DOT). The results of the Mn/ROAD tests show that GPR can be applied in measuring the layer thickness of various pavement structures. The surface reflection technique can be used to determine the signal velocity of both asphalt and concrete pavement structures. Mn/ROAD surveys also revealed evidence of some previously unknown defects in test cells, e.g. stripping, voids and moisture anomalies. A good example of the benefits the GPR technique can offer in detecting stripping is the T.H. 23, T.H. 71 Willmar case, where reference data, drill cores and FWD data matched almost perfectly with the GPR data. Another notable case presented in the paper is U.S. 52, Oronoco, where defects due to differential frost heave were located.

Using standard inversion algorithm, velocity and attenuation tomograms can show artifacts which compromise interpretation. These artifacts can be due to errors in borehole trajectory measurements, medium anisotropy, T₀ (initial time) or A₀ (initial amplitude) drifts. In order to cancel these artifacts, the error sources can be introduced as unknown parameters in inversion algorithms (Hollender, 1999). In this paper, we present results obtained with crosshole radar data, recorded in a limestone quarry. Using the appropriate algorithms, all the artifacts have been cancelled and tomograms show clearly subhorizontal structures in agreement with the quarry stratification. In our data set, results do not reveal significant trajectory error, and T₀ and A₀ drifts are low. However, the presence of a velocity and attenuation anisotropy appears clearly on the tomograms. In the case of attenuation tomograms, the high anisotropy rates could be explained by the cumulative effect of the partitioning of energy due to reflection and transmission mechanisms at interfaces, and medium anisotropy.

The DFT method popular in GPR processing assumes that data is infinite outside a given interval. The selection of a finite time interval and of the orthogonal trigonometric basis over a given interval means that only those frequencies which coincide with the basis will project onto a single basis vector. The rest of the frequency set will give nonzero projections on the entire basis set [harris, 1978]. The finite data set is obtained by windowing an infinite data sequence. The assumption is that the unmeasured data is zero and this is not true. When the power of the signal is concentrated on a narrow BW this operation spreads that power into adjacent frequency regions. This phenomenon is called spectral leakage. Leakage affects power estimation, resolution, dynamic range, implementation and detectability of a sinusoidal component. Parametric methods can be used to describe the process that creates a signal. A priori knowledge is required to extrapolate the information from the input signal. This approach eliminates spectral leakage problems. Parametric methods create a model that use a number of parameters to describe the process that create the signal under observation. Adaptive filters are parametric and iterative, theses filters respond to the input by changing their model parameters. The number of samples used at the input is small, however the samples are stored in memory so that the parameters obtained from an estimate are statistically combined with those of the previous estimates. This gives an accurate reading over several iterations. To date the closed loop adaptive filters have been used more commonly in radar signal processing. The closed loop adaptive filters have a feedback factor. One of the main disadvantages of closed loop adaptive filters are firstly the need for continual optimization and secondly instability. The second little known group of adaptive filters are called open loop adaptive filters. These filters differ from open loop ADF in that they do not require feedback, the input signal is used to change the parameters of the filter. An adaptive algorithm used by an ALP in closed loop filters changes the FIR filter coefficients such that the transfer function of the adaptive filter become the inverse of that possessed by the input process. Once adapted the frequency response of the FIR filter will be unity at the frequency of the input signal and the ALP's output. The error will be at a minimal value. By comparison the frequency response of the FIR filter in an open loop configuration will be zero at the frequency of the input signal. Open loop filters are more stable than closed loops adaptive filters. A novel frequency domain open loop adaptive filter is also introduced. This filter offers more stability, does not need feed back and has increased convergence speed.

Various approaches have been suggested for velocity analysis on man-made structures, such as the evaluation of reflection amplitudes and diffraction hyperbolas, calibration using cores and multi-offset analysis with different antenna types and acquisition setups. As none of these methods can be considered best under all circumstances, a choice has to be made for each given problem. Feasibility, cost and accuracy have to be considered when making this choice. This paper describes the benefits and limits of multi-offset velocity analysis using two ground/object-coupled 1.5 GHz antennas (GSSI, Model 5100). One of these antennas is off-the-shelf, the other one was purpose-built in order to increase the possible range of offsets. Important factors such as depth of penetration, vertical resolution, offset range and the number of scans required are discussed using datasets acquired on-site and in the laboratory. The emphasis is on asphalt pavements and concrete structures. This paper aims to provide support for decisions on whether this approach is suitable for a given problem.

The LCPC (Central Laboratory of Bridges and Roads) is a state research organization, working for the state and the local authorities, involved in civil engineering. LCPC has large testing facilities such as a circular Pavement Fatigue Test Track, for researches in the road field, which is composed of several parts of different known structures. As this test site is particularly adapted for GPR investigations, we have studied a commercial GPR system for the thickness measurement of its asphalt layers. Different structures of roads have been investigated with a GSSI system. Cores have been drilled, permittivity measurements have been done. All the results are compared: cores, velocities and GPR picking measurements. A last study has consisted in avoiding calibration with cores drilling, by recording GPR signals in a CMP mode (common middle point) on the multi-layer structures. Several antennas, and frequencies, have been used in order to study the accuracy of this nondestructive testing method compared to the needs of the end-users.

Horn antennas have small direct coupling between the transmitter and the receiver antenna, and can be made with wide bandwidths. Hence they are suitable for short-distance concrete tests. Field test results are presented in the paper, which show that the S-horn antenna (defined in the text), working at the frequency band 1500 MHz to 3000 MHz, can give clear radar pictures in testing e.g., the re-bar structures within the distance range 30 cm.

This paper reports aspects of a study into the use of neural networks to interpret sub-surface radar data collected from surveys of a number of construction components containing targets such as reinforcing bars and underslab voids. The paper details the data collection and alternative synthetic data generation, the pre-processing undertaken to reduce the volume of the inputs to the neural networks, the neural network topologies investigated and presents the results of the network training and testing.

This paper describes a GPR study carried out with the aim of evaluating deterioration of concrete floors in textile factories. During some years, spillages from the production process were split onto the floor of the factory. The slow but continue action of these spillages in the concrete caused an important variation in its porosity, which could be detected by studying changes in GPR reflected pulse. A simple synthetic model was developed in order to obtain information about how the response of GPR antenna pulse is depending on changes in the porosity of concrete. We also take into account the different conditions of the factory floor at the moment (since many years ago it's been isolated from the action of the spillage). The heterogeneous conditions of the floor and the simplicity of the model used did not allow for an accurate estimation of porosity, but it was possible to map degraded areas on the floor related to changes in the reflected signal. Core drills made later confirmed in some of them a concrete porosity of up to 25%, closer to that of sand than to concrete.

Due to the radiation pattern of the GPR antennas, the amplitude of the reflection is not only dependent on the distance between the target and the antennas, but also on the angle of orientation between the antennas and this target. Alford rotation is applied to this radiation pattern of the antennas, and used to extract the location of the origin of the reflected wavefield. This information is used to improve the migration scheme. In conventional migration schemes, recorded data are migrated to all angles. In this method, instead the recorded data are migrated to certain grid points only. This makes the migration algorithm faster and more accurate. This Alford migration method is applied to synthetic data and is shown to be successful below a noise level of about 1% of the amplitude level of the data. A higher level of noise results in an inaccurate estimate of the angle to the location of the target and the signal to noise level to decrease. The result can be improved by migrating over a limited sweep of angles around the estimated angle. Application of this method to field data collected at a controlled test site has shown poor results, as there was too much noise present in the data and errors might occur due to dispositioning of the antennas.

During a ground penetrating radar (gpr) survey special attention must be paid to objects which are present above the earth surface. These objects can result in unwanted reflections in the measured data. Due to the low losses in air and the high velocity, these reflected waves can obscure the data and can make the interpretation of gpr data a difficult task. Especially in an urban area it is important to know the origin of these reflections and how to reduce the influence of these unwanted reflections. The radiation characteristics of a horizonal dipole are investigated to determine the sensitivity for reflections coming from an object which is present above the surface. Both the amplitude and polarization of the electric field play an important role. It is shown that the presence of the soil enables relatively strong reflections from vertical objects, which are present in a specific plane relative to the antennas. This analysis indicates that a reduction of the amplitude of unwanted reflections is possible by changing the acquisition parameters. A validation of these expectations is carried out by numerical modeling using a 3D modeling package for different objects present above the surface, which confirms the former expectations that the amplitude of unwanted reflections can be reduced by choosing a proper orientation of the source and receiver.

This study presents results obtained using a 3D migration algorithm on ground penetrating radar data collected with a switched antenna array. The results from the switched array are compared to similar x-y scanned data from a single pair of transmit/receive antennas. We use the Stolt wavenumber migration algorithm for 3D processing of the radar data. The migration is performed in the wavenumber domain, assuming constant wave velocity for waves traveling in the soil. This assumption gives sufficient image quality for shallowly buried objects, while retaining a low processing time. We present two data sets from a laboratory sandbox containing several buried targets: One data set was acquired as an x-y raster scan using a single pair of bow-tie transmit/receive antennas, and the other data set is taken with the new switched antenna array. With the single antenna pair, the system can resolve the size and location of buried objects to within 5 cm in dry sand. Using the antenna array, the resolution is fully maintained, but the noise level is somewhat increased. The reasons for this are differences between the transfer functions of the individual antenna elements, distortion introduced by the RF- switches, and mutual coupling effects between the antenna elements which are not yet fully calibrated.

There are may potential applications of the Ground Penetrating Radar waiting for a technology breakthrough in the direction of high resolution. We present some experiments where the requirement of very high resolution is pursued through the effective use of the synthetic aperture technique. The successful application of this technique is subject to the compliance with some essential conditions. First of all, the capacity of the system to illuminate the target with a sufficient aperture. A new non-commercial flexible stepped frequency system has been tested in the frequency range of 2 - 6 GHz. A second factor that is essential for performing a good data focusing is the accuracy of the antenna positioning system: a few millimeters precision should be ensured for the above mentioned applications. A careful design of the processing procedure is the third factor that is essential to exploit all the potential resolution of the data. Of course, the procedure should include a SAR focusing algorithm that improves the resolution and that is quite effective in clutter reduction, especially in the 3D case. Tests indicate that the real footprint of the antenna should be used to calibrate the aperture of the focusing operator because this has a positive impact on the SNR of the final image.

In this paper, the effects of receive antenna placement on image formation in a surface contact synthetic aperture radar are investigated from an experimental perspective via the analysis of high frequency ground penetrating radar data. A receive array containing 121 measurements is used to form a baseline image of subsurface features including horizontal tunnels or drifts to depths approaching 200 feet. This result is compared to images formed using far fewer spatial measurements (as few as 37 samples out of 121 measurements available) collected randomly from throughout the same field of view.

The main goal of paleoseismology is to estimate future seismic hazard through an improved characterization of past fault behavior in seismically active environments. Paleoseismological investigations provide critical knowledge about ancient earthquakes that have occurred along active faults. Such knowledge may be used to refine estimates of local and regional seismic hazard. Earthquake-related features (e.g. faults, folds and fissure fill) observed in trenches and outcrops generally exhibit complex three-dimensional (3D) geometries. Ground penetrating radar (GPR) data allow information extracted from these conventional paleoseismological observations to be extrapolated and complemented. We have conducted detailed 2D and 3D GPR surveys at various locations along the Wellington Fault in the Hutt Valley of New Zealand. Fault-related structures are seen clearly in the GPR data as offsets or abrupt terminations of laterally continuous reflections. In cross-sections and time- slices extracted from the 3D GPR data sets, sudden changes of reflection pattern determine the principal fault plane. After applying a novel topographic migration scheme to the GPR data, individual lithologic units may be mapped. Our results correlate well with observations at nearby outcrops. They show that 3D GPR surveys are capable of supplying clear subsurface images in typical paleoseismological trenching environments. GPR images may be used to guide trenching strategies aimed at features of special interest to paleoseismology.

Lava tubes are of interest because they dramatically alter the hazard assessment of volcanos in several different ways and because they have been and are potential places to live. Ground penetrating radar has been used to locate and characterize lava tubes since 1978 in Hawaii. GPR surveys have been done over hot lava tubes where the dielectric properties modeled from the radar data give an indication of temperature and the imaging provides information about geometry. GPR data have also been acquired over, inside, around, and through cold lava tubes, and between lava tubes and the surface. Such data yield information about location, size and shape of lava tubes as well as number, distribution and occurrence. Over hot tubes containing flowing lava, commercial radar systems require modification to survive the heat. Case histories from Hawaii are illustrated with data acquisition, display, processing, and modeling.

Recent interest in soils and hydrologic modeling has increased the need for information concerning the depth and movement of ground water. Ground-penetrating radar (GPR) was used eight times over a two-year period to chart water table depths and ground-water flow patterns within a 32-ha forested site in northwestern Indiana, USA. Radar imagery was correlated with depths to the water table in 16 observation wells. The velocity of propagation ranged from 0.0508 m/ns to 0.1606 m/ns at these wells. Propagation velocities were generally slower during the spring and early summer months when depths to the water table were relatively shallow. Propagation velocities were faster through dunes than through the more poorly drained interdunes. Because of the spatiotemporal variability in propagation velocities and the known complexity of soil and landform patterns, a predictive equation based on water table depths and two-way travel times was developed for each GPR survey. In this setting, the use of a predictive equation based on multiple GPR measurements over a known reflector substantially improved the accuracy of radar depth interpretations over single or averaged measurements.

The U.S. Geological Survey (USGS) operates a network of about 7,000 streamflow-gaging stations that monitor open-channel water discharge at locations throughout the United States. The expense, technical difficulties, and concern for the safety of operational personnel under some field conditions have led to the search for alternate measurement methods. Ground- penetrating radar (GPR) has been used by the USGS in hydrologic, geologic, environmental, and bridge-scour studies by floating antennas on water or mounting antennas in boats. GPR methods were developed to measure and monitor remotely the cross-sectional area of rivers by suspending a 100-megahertz (MHz) radar antenna from a cableway car or bridge at four unstable streams that drained the slopes of Mount St. Helens in Washington. Based on the success of these initial efforts, an experiment was conducted in 1999 to see if a combination of complementary radar methods could be used to calculate the discharge of a river without having any of the measuring equipment in the water. The cross-sectional area of the 183- meter (m) wide Skagit River in Washington State was measured using a GPR system with a single 100-MHz antenna suspended 0.5 to 3 m above the water surface from a cableway car. A van- mounted, side-looking pulsed-Doppler (10 gigahertz) radar system was used to collect water-surface velocity data across the same section of the river. The combined radar data sets were used to calculate the river discharge and the results compared closely to the discharge measurement made by using the standard in-water measurement techniques. The depth to the river bottom, which was determined from the GPR data by using a radar velocity of 0.04 meters per nanosecond in water, was about 3 m, which was within 0.25 m of the manually measured values.

Borehole ground penetrating radar (GPR) measurements of water content within the unsaturated zone were performed during infiltration experiments using both a uniform and point source of water at the soil surface. Horizontal GPR antenna access tubes were installed at a depth of 1 m to measure the water content within the horizontal plane underlying the surface water sources. The zero offset profile and multiple offset gather modes of data collection were used to produce velocity profiles and tomograms that were converted to water content. Time domain reflectometry (TDR) probes provided near-surface measurements of water content to complement the deeper borehole GPR data. For the point source, the water content tomograms and profiles showed that the zone of increased water content was restricted to a 1 m diameter zone, centered below the point source. For the uniform source, significant variability in water content within the studied area was observed possible due to preferential flow of water through the soil profile.

Three-dimensional imaging of ground penetrating radar data is a challenging task. Most imaging procedures are based on scalar seismic imaging algorithms. However, for electro- magnetic imaging the vectorial character of the emitted field and the radiation characteristics of the source and the receiver play an important role. In this paper a new imaging algorithm is presented, which is dedicated to the electromagnetic case. The vectorial character of the electromagnetic waves is taken into account for a monostatic fixed offset ground penetrating radar (gpr) survey, when the source and receiver are present on a dielectric medium. The forward model is described by the 3D wave field extrapolator which takes into account the vectorial character of the electromagnetic field. The imaging algorithm is based on an approximate inverse of this 3D wave field extrapolator, which is determined in the spatial Fourier domain. For a homogeneous space and a zero-offset configuration it is feasible to carry out an analytical approximation of the inverse operator. The approximate inverse of a scalar 3D wave field extrapolator is not stable, which motivates the use of a multi-component imaging algorithm. For two homogeneous halfspaces it is not feasible to carry out a similar analytical approach. However, in numerical sense the same procedure can be carried out, which has the important benefit that also the offset between the source and receiver can be taken into account. Numerical results are presented for a point scatterer in a homogeneous space, which indicates the spatial resolution which can be obtained. Imaging results of experiments are presented, which take into account the vectorial character of the measured electric field, the offset between the source and receiver and the presence of two homogeneous halfspaces.

Linear and nonlinear inversion methods have been developed to image the velocity and attenuation. In recent years, efficient ray tracing techniques and high speed computing facilities have made the application of nonlinear inversion practical on a personal computer. By combining the travel time information and the amplitude and frequency information of geophysical data such as radar data and seismic data, both velocity and attenuation can be simultaneously inverted. Ray tracing accounts for most of the computing time of the nonlinear inversion. However, the same ray tracing results can be used for both velocity and attenuation inversion, thus the simultaneous inversion does not take much longer time than velocity inversion alone. Inverted attenuation results are more accurate than those produced by ordinary straight-ray attenuation tomography due to the consideration of bending rays. Two approaches, one based on a single geophysical survey and the other on repeated surveys, are developed and tested using synthetic and field radar data. The major advantage of these two approaches is that neither of them involves estimation of source radiation pattern, receiver coupling, and geometrical spreading that are very difficult to measure accurately.

The imaging of buried objects poses the need for a dyadic Green's function for a medium stratified into above- and below-ground spaces. The perturbation field due to the existence of the object is as if radiated by equivalent currents. An integral equation is written in which the unknown is the current density. For solution by the Method of Moments, the current distribution is approximated as the weighted sum of a a set of basis functions. The Distributed Source (DS) Dyadic Green's Function is introduced to relate the vector field and basis function of directed current. This study is concerned with numerical evaluation of the DS Green's function. The function has been derived in the form of a doubly infinite integral of which the integrand contains a line singularity. In some cases evaluation of the integral presents problems of convergence. The infinite integration area has been made finite by a particular choice of basis functions. The line singularity has been eliminated by exploiting the convolution theorem. The convolution integrand contains a simple singularity which disappears under a change of variables. The DS Green's function has been evaluated without numerical difficulty. Values agree with those calculated by other methods where available.

Variations of transmitter power and instrumental time drift often observed during borehole radar surveys are not usually monitored by the commercially-available acquisition systems. These variations may create artifacts in tomograms and lead to erroneous interpretation if not taken into account. The Self- Correcting Tomographic Inversion (SCTI) is a technique that jointly recovers these source variations together with the velocity or attenuation distribution. It assumes that the transmitting time T_o and the 'source strength' A_o may be considered constant only at each transmitter position. The problem results in a linear system of equations where the usual Jacobian matrix should be augmented by sparse columns with non-null elements corresponding to the respective transmitter positions only; thus the parameter vector (slowness or attenuation coefficient distribution) can be appended with the t_o (or log A_o) values for these transmitter positions. Synthetic and survey data examples demonstrate that the conventional inversion algorithm produces artifacts mainly located along the transmitter and the receiver boreholes and towards the corners of the tomogram. The magnitude of the artifacts depends on the distance between transmitter and receiver boreholes. The SCTI technique reduces the amplitude of these artifacts while recovering the transmitter drift. Two crosshole surveys with inter-changed transmitter-receiver positions were also performed to evaluate reciprocity. The resulted tomograms are slightly different, but the overall images seem to be improved. However, the SCTI seem to diminish the discrepancy between the reciprocal values. Meanwhile, the SCTI also recovers a very suitable variation for the transmitter parameters. We have also attempted to monitor the drift of these transmitter parameters by control measurements at the ground surface at different times during the survey with different antenna separations. It shows that the variation of t_o and A_o is of the same order as resulted from the SCTI method.

In the given study the experimental results on detection and image processing of weakly scattering subsurface objects are presented. For acquisition of experimental data about scattered by the object field the 2D mechanically scanning pulse system connected to PC was used. A short rise time of a sounding pulse (< 50 ps) and corresponding wideband of a test signal have allowed to apply GPR and microwave tomography methods of experimental data processing. The obtained results allow to maintain, that both techniques of processing give ability to get the high quality images even for weakly scattering dielectric objects with the dimensions approximately 1 divided by 5 (lambda) of average wavelength of radiated pulse. Tomography allows to achieve less noisy images, though the processing in a time domain is much faster. The developed experimental methods and methods of processing are ready to practical application.

Ground penetrating radar (GPR) has been used successfully to help archaeologists locate building foundations and other artifacts of past civilizations. Yet, little has been done to help paleontologists in their search for fossilized remains. Fossilized and partially fossilized dinosaur bones are located in a sandstone outcrop at the Dinosaur Ridge Natural Landmark outside Morrison, Colorado. The bones are located within a cliff face and in two large boulders located along the road. Little work has been done to characterize the size of these bones and to study the possibility of bones located deeper within the sandstone cliff face. Mineralogical studies have shown that these bones contain approximately 15% iron oxides (Fe₂O₃) along with smaller percentages of MgO and Al₂O₃. Due to the presence of Fe₂O₃, as strong reflection is expected on the GPR record. Data have been collected along the cliff face using a Sensors and Software pulseEKKO 1000 900 MHz antenna. The area of interest measures approximately 1 meter high and 3.5 meters long. Several strong hyperbolas stand out in the raw and processed data. Velocity estimations show the depth of investigation to be greater than 1.1 meters. Data have been collected along crosslines in order to judge size and orientation of any anomalies discovered. Full waveform modeling was performed on traces showing anomalies to better characterize the dielectric permittivity and magnetic permeability. These results will be analyzed to determine what anomalies have the possibility of being dinosaur bones.

Velocity and absorption tomograms are the two most common forms of presentation of radar tomographic data. In this paper a simple transformation is developed, to convert velocity and attenuation coefficient to conductivity and dielectric constant. The approach is illustrated via application to data from the Hellyer zinc-lead-silver mine, Tasmania. The conversion to conductivity and dielectric constant was especially advantageous because mining personnel, geophysicists included, are often unfamiliar with radar velocity and absorption. Encouraging results were obtained in mapping the distribution of electrical properties between boreholes at Hellyer, illustrating the potential of radar tomography to delineate sulphide ore zones.

It is required that the locations of underground installations are made clear on the viewpoint of safety. It is very important to sufficiently investigate the position (for example, depth, horizontal position) of the pipes before the piping work is carried out. However, it is not easy to get the accurate information on the ordinary matter. Because of the size of underground prospecting system and crowded traffic problem, we often could not bring any useful equipment. Thus, the purpose of the present investigation is to miniaturize such system. And we experimentally produced a small prospecting system which could probe underground installations which were near range. The design of the small circuit with high frequency and the small antenna were mainly examined. As a result, it is shown that the object buried in the ground which is ahead at a distance of 50 cm can be prospected with high resolution.

The purpose of our investigation is to develop sounding radar for non-destructive inspection of buildings and structures designed for different uses, which can obtain high resolution radio-images representing the interior structure, objects and heterogeneities in load bearing and protecting construction. Our primary goal is to resolve problems dealing with the determination of strength of structures in service, repair and renovation of buildings.

The interaction of high-frequency electromagnetic wave-fields with a typical ground-penetrating radar (GPR) antenna is complex and its effects on the recorded data are not well understood. Further distortions of the radiation pattern and pulse shape must be expected to arise in the presence of a shielding of the antenna. To address these issues, we present a three-dimensional finite-difference approximation of Maxwell's equations that allows to model realistically the near-field radiation characteristic of a typical GPR system.

Wavelet dispersion caused by frequency-dependent attenuation is a common and significant problem in ground-penetrating radar (GPR) data. In the radar image, it is displayed as a characteristic 'blurriness' that increases with depth. Correcting for wavelet dispersion in GPR data is an important step that should be performed before either qualitative interpretation or quantitative determination of subsurface electrical properties are attempted. Over the bandwidth of a GPR wavelet, the attenuation of electromagnetic waves in many geologic materials is approximately linear with frequency. For this reason, the change in shape of a radar pulse as it propagates through these materials can be described using one parameter, Q*, which is related to the slope of the linear region. Assuming that all subsurface materials can be characterized by some Q* value, the problem of estimating and correcting for wavelet dispersion in GPR data becomes one of determining Q* in the subsurface and deconvolving its effects through the use of an inverse Q filter. A method for the estimation of Q* from GPR data based on a technique developed for seismic attenuation tomography is presented. Essentially, Q* is determined from the downshift in the dominant frequency of the GPR wavelet with time down a trace. Once Q* has been obtained, we propose an inverse Q filtering technique based on a causal, linear model for constant Q as a means of removing wavelet dispersion. Initial tests on field data indicate that this technique is very effective at enhancing the resolution of the GPR image.

A vertical borehole may pass through natural layered structures which are orthogonal or near-orthogonal to the borehole. Such structures, particularly if they are layers with a smooth surface, can be very difficult to detect with a borehole radar which has the required long range and low center frequency for remote structure detection. Methods of supplementing the radar data are discussed and include the use of an additional radar with a much higher center frequency, the use of a dielectric probe and the use of a look-ahead radar.

The Veluwe area is one of the main groundwater reservoirs in the Netherlands. The Veluwe consists of ice-pushed ridges. The ridges are reworked, mainly sandy, fluvial sediments with some dipping clay layers. Due to these dipping clay layers the sediments have an anisotropy for lateral groundwater flow. Some of these clay layers even form a complete barrier for groundwater flow. The location of these clay layers is important for the reliability of local groundwater flow models. A number of profiles were measured with Ground Penetrating Radar (GPR, 50 MHz) at three locations in the ice- pushed ridges with the aim to locate the dipping clay layers and the zones with a high anisotropy. The obtained GPR data was combined with direct observations such as groundwater levels of the phreatic aquifer, Cone Penetration Tests on the some of the pronounced dipping reflectors and local geological knowledge. For the investigation sites the following data from the radar profiles were plotted on a map: (1) the boundary on the surface between the ice-pushed- and the horizontal layered sediments, (2) the groundwater level, (3) groundwater steps, and (4) pronounced dipping reflectors. The boundary between the ice-pushed and horizontal layered sediments on the surface is the location of the transition between sediments with and without a high anisotropy for groundwater flow. The groundwater steps are locations of barriers for lateral groundwater flow, while the pronounced dipping reflectors are just indications for these barriers. A steep gradient of the water table, which is not visible on all the profiles, is an indication for a zone with a high anisotropy for lateral groundwater flow. These maps are currently being used for upgrading local groundwater flow models.

The inversion of direct arrival times is the most common technique in crosshole georadar surveying. Results of such a tomographic radar experiment can be easily contaminated by errors during data acquisition and processing. Our study of synthetic and field data shows that careful and detailed pre- processing analysis gives an impression of data quality and the factors influencing and limiting the quality for the particular field experiment. Synthetic data examples show how certain systematic errors, e.g. unrecognized borehole deviation, can be identified and distinguished from the expected real subsurface structure. However, delay problems, e.g. caused by false zero-time corrections, are often more difficult to identify, particularly in a noisy environment or in media where high velocity contrasts are present. The examples and calculations show that careful pre-inversion processing and handling of tomographic data lead to a quality increase and to more reliable tomograms.

Our research group jointly with the research group of Professor Motoyuki Sato, CNEAS (Tohoku University), conducted GPR survey in forested and forestless lands in Yakutia in August 12 - 15 1999. The aim of this survey was to test for the first time our GPR equipment on permafrost, to determine spatial dynamics of permafrost bedding depth in forested and forestless areas and to detect ice wedges in permafrost. The survey was carried out on the site about 30 km north-east of Yakutsk city. Numerous boreholes drilled in both forested and forestless areas determined permafrost bedding depth and showed that in forested areas permafrost in several spots had ice wedges more than half meter across. Measurements were made in the forest; on 'alas' (thermokarst depression) site; on the site of recent forest fire; on large forestless area with 'pingos' (round hills in 'alas' center). An attempt was made to detect 'pingo' ice kernel.

Ground penetrating radar (GPR) investigations were conducted to determine the origin of the West Prairie Mound Group. The mound group consists of thirteen low, conical, earthen mounds within Fort McCoy (central Wisconsin). Historically interpreted as PreColumbian Native American burial mounds, mounting evidence to the contrary suggests a natural origin for the mounds (e.g. no archaeological material recovered from within or near the mounds, mounds located where morphologically similar natural landforms are common, and the mounds are identified as natural landforms in local Native American oral tradition). Even so, U.S. Federal antiquities laws prohibit disturbance of these mounds and investigations to determine their true origin are limited to non-invasive techniques. Non-invasive, high resolution GPR survey methods were utilized to address the research problem. Mounds B and K were selected for detailed GPR surveys. In both cases, observed GPR reflection patterns are consistent with sandy, eolian geomorphic units common in the mound area. Moreover, no reflection patterns typical of burial disturbance or cultural practices were observed in either mound. Therefore, our analysis of Mounds B and K GPR data strongly supports the emerging interpretation that the West Prairie Mound Group is the result of natural rather than cultural processes.

This paper discusses the possible use of strapdown inertial navigation for real-time ground penetrating radar (GPR) antenna position and orientation estimation along arbitrary three-dimensional acquisition lines. Strapdown inertial navigation theory has been studied extensively in the literature for aircraft, missile and space navigation. Here, we give an overview of the theory as it applies to the antenna position and orientation problem. This includes the definition of the relevant coordinate frames and attitude parameters, a discussion of the measured acceleration and angular velocity, and a description of the four primary computational tasks pertinent to strapdown inertial navigation. These are the initial alignment of the system, the integration of angular velocity into attitude (attitude updating), the acceleration transformation and integration into velocity (velocity updating) and the integration of velocity into position (position updating). The key elements of using a low-grade versus a high-grade inertial measurement unit (IMU) are pointed out. The actual performance of a commercially available low-grade IMU is evaluated based on a series of navigation experiments. The experimental results show that the tested IMU is far from being accurate enough for completely self-contained antenna positioning and that the precise calibration for scale factors, biases and axis misalignments is vital. The observed orientation accuracy (error of less than 1 degree after 60 seconds) suggests the integration of the tested IMU with odometry, extending the applicability of the latter to environments with topography or where changing of the profile direction due to obstacles is necessary. Another possible use of low-grade IMUs might be for more sophisticated 'rubber sheeting' techniques.

In different places of Morelia, Michoacan, Mexico, there are evidences of four active geologic creep-faults system in. These events have damages (cracking and landslides) in the civil building (Garduno M., et. al, 1998; Garduno M., et. al, 1999; Lermo S., et. al., 1999). In order to find these structures in the first 10 m of depth, region where we have the influence in civil building, we carried out a geophysical study with georadar technique. We made 15 sounding in the fault zone to join the results to preliminar geologic studies in order to improve the security rules in the high risk places. In this work we show the results of three sounds with georadar, as well as the final Bidimensional Model effected with the technique of tracing of ray.

This presentation refers to the application of the Ground Penetrating Radar on two archaeological sites: Serrano and Morro Grande, situated at Araruama County, Rio de Janeiro, Brazil, with the purpose of contributing to the knowledge concerning a prehistoric indigenous culture, associated with the 'Tupinamba' that inhabited the region at prehistoric times. This research is being realized with the partnership of the Anthropology Department of the National Museum and the Geology Department, both departments pertaining to the Rio de Janeiro Federal University. The archaeological remains of the study area are mainly characterized by pottery appliance for several uses, including funeral urns, which were buried within layers of sand and clay. Several profiles were made, using a RAMAC device, with a 200 MHz frequency antenna, surrounding some partially exposed potters, in the sand quarry, at the Serrano site. The resultant radargrams conceived a response model for the archaeological and soil characteristics of the area. These radargrams are being used as correlative models for the interpretation of profiles performed at the Morro Grande site, which presents similar characteristics of the Serrano site. The generated models are intended to guide the future excavations in the archeological sites of Ri de Janeiro.

The shape and integrity of the ancient tombs is valuable data to archaeological excavation. The synthetic survey methods of ground penetrating radar, mercurometric survey and drilling with Luoyang shovels were used for the shape and integrity investigation of four Chu-tombs, which were buried in Northwest Hunan Province two thousands years ago. Firstly the holes dug by a Luoyang shovel with manpower were for gravel passage searching. Then parallel and vertical profiles to the passage were surveyed with GPR and soil mercury over the gravel pit. The reflective radar arrivals of the radargrams were used for the hollow and pit outlining of the tombs. High soil mercury anomaly and horizontal discontinuous traces indicated destroyed tombs with robbed holes.

Ground penetrating radar, 2D electric and refraction seismic methods are used to retrieve informations on geometrical, hydrogeological and chemical parameters in fluvial deposits. The results obtained with these methods give consistent informations on geometrical parameters. Indeed, the GPR interval velocities, electrical resistivities and the refraction seismic models show clearly three horizontal layers. Moreover, physical parameters are deduced from GPR and electrical data. Water content estimations of the medium are obtained from GPR data by comparing three different dielectric permittivity models for water-based porous materials: (1) an empirical model, (2) a semi-empirical fully-saturated model based on mixture theory and (3) a fully-saturated model based on the effective medium theory. Qualitative informations on water saturation are also deduced by combining two of these models. Finally, by combining water content estimations obtained from GPR interval velocities and conductivity measurements, a quantitative estimation of the salinity content of the medium is obtained. These studies show concrete applications in fluid's flow and ground contamination monitoring.

The present paper describes an adaptive range compression procedure for the compensation of the phase dispersion effects induced on low frequency radar echoes propagating through a ionized plasma, such as a planetary Ionosphere. The method is based on an equivalent model of the Ionosphere refraction index which outperforms currently available models in representing the ionosphere dispersion when the sounding frequency approaches the Ionosphere plasma frequency. The expected performance of the method is derived in the specific case of the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS), which will flight to MARS in 2003 aboard the Mars Express orbiter. Reported results indicate that the proposed algorithm gives acceptable residual distortions even when the operating frequency is very close to the ionospheric plasma frequency.

In this study, a classification method is proposed for a limited amount of ground penetrating radar data, based on a non-parametric approximation to Bayes decision probability. Ground penetrating radar is an electromagnetic sensor that detects objects both on the surface and under the surface. We use these preprocessed data for classification. The proposed study includes data enhancement, two different data reduction method that are PCA and time domain data reduction, a cepstrum analysis to extract feature and decision by k-nearest neighbor (k-NN).

The Quaternary record of the Southeastern Brazil presents several tectonic structures that are related to two main tectonic phases during Pleistocene and early to middle Holocene ages. The first phase is related to an E-W dextral transcurrent tectonic regime producing NW-SE transtensional structures. The second phase is characterized by a NW-SE extension that produced NE-SW normal faults. The Holocene sedimentary evolution is marked by an important episode of environmental instability as being related to an alluvial fan system, that are the framework of amphitheater-like headwaters and flat valley floors. This work aimed to map the tectonic signatures in GPR profiles and to establish their relationships with the stratigraphical and geomorphological evolution. To this survey it was used 50 MHz antenna frequency. The GOCAD software was used for 3D reconstruction of reflection surfaces. It was recognized a northeastern dip, NW-Se normal fault set, that are probably related to the headwater evolution due to syn-depositional E-W dextral transcurrent tectonic phase. In a site studied on a flat valley floor were mapped several NE-SW conjugate faults. These NE-SW fault sets are due to a post-depositional the NW-SE extensional tectonic phase. All of the tectonic features do not affect the upper beds marked by the shallower reflector. It documents a post-deformation depositional sequence.

The structure of coastal dunes from three different sites within Wales, UK, have been investigated using ground penetrating radar (GPR), revealing the internal structure of the dunes. GPR provides a unique insight into the internal structure of coastal dunes that cannot be achieved by any other non-destructive or geophysical technique. The profiles presented show results from surveys investigating sand thickness and distribution, and dune structure and statigraphy. Surveys at Towyn Warren map the base of the sands with their structure interpreted as a transgressive sand sheet that wedges out towards the North. Surveys at The Bennet reveal a complex internal structure of prograding units and cross-cutting erosion surfaces allowing the construction of a relative chronology for the dune. Profiles from Freshwater reveal sets of sedimentary structures including cross- stratification, dipping foresets, cut and fill troughs, bounding surfaces and erosion surfaces. These structures are interpreted in terms of the dunes evolution allowing the identification of periods of accretion and progradation, erosion, re-working, stabilization and major events in the dunes history. The water table is resolved, and the effect of saline waters on attenuation is shown.

Attenuation-difference, borehole-radar tomography was used to monitor a series of sodium chloride tracer injection tests conducted within the FSE wellfield at the U.S. Geological Survey Fractured-Rock Hydrology Research Site in Grafton County, New Hampshire, USA. Borehole-radar tomography surveys were conducted by using the sequential-scanning and injection method in three boreholes that form a triangular prism of adjoining tomographic image planes. Attenuation-difference data were inverted by using a weighted damped least-squares (WDLS) inversion method and several different solution simplicity schemes to suppress tomogram artifacts induced by the acquisition geometry, the location and magnitude of the anomaly, and noisy data. Qualitatively, flat tomograms generated by minimizing the norm of the first spatial derivative were most effective at suppressing artifacts. Although artifact suppression measures can be somewhat effective, negative consequences or artifact suppression include (1) reduction in the magnitude of the attenuation differences in the vicinity of the target anomaly and (2) blurring of the anomalies. These effects distort estimates of the location and magnitude of attenuation anomalies. In order to estimate robustly the location and magnitude of attenuation differences, areal constraints were imposed on the WDLS inversions to confine changes in attenuation to regions that are intersected by rays with large attenuation differences and bounded by rays with insignificant attenuation differences. Results from forward modeling support the application of these constraints. The resolution matrix was used to model the effects of acquisition geometry, target anomaly shape, location, and magnitude. For this study, the method of forward modeling indicates that estimates of pixel attenuation are improved by applying areal constraints to the WDLS inversions.

Borehole Radar has been identified as the most immediately applicable electromagnetic technique to delineate disruptions to gold reef in the South African DEEPMINE environment. The economically important Ventersdorp Contact Reef (VCR) has successfully been imaged over ranges of up to 95 m and with resolutions of less than a meter, using the Geosonde system with a center frequency of 60 MHz.

We performed a multi-fold GPR study at a Cretaceous-Tertiary (K-T) outcrop in limestone layers of the Peri-Adriatic carbonatic platform (Italy). Primary objective of the study was imaging of the K-T contact and mapping of localized depth variations in a general framework of homoclinical limestone layers. A secondary objective was the study of faults, fractures and cavities of interest for engineering purposes. A combination of 2-D and 3-D multifold techniques was used to image and map structural and stratigraphic features. A 200 sqm grid was surveyed with 1 meter cross-line spacing and 5 cm in- line trace interval. The K-T contact is electromagnetically transparent, and it is actually deduced from paleontologic evidence. Due to the homoclinal trend, K-T topography is reconstructed from the bedding planes bounding the contact. Fractures antithetic to bedding planes are imaged by 2-D stack and migrated profiles. Part of the fractures can be considered small transtensional faults. The results obtained provide the first geophysical evidence of small-scale transtensive deformation in the area. Curvilinear radar reflector, intersecting the homoclinal bedding planes, are imaged in faulted zones and are possibly related to limestone buildups. A fractured rock volume develops into a cavity with average estimated section of a 4 sqm.

As a result of extreme precipitation in July 1997, hundreds of landslides have developed on flysch slopes of the Carpathian mountain system in eastern part of the Czech Republic, endangering large inhabitated areas. In this situation, quick and cost-effective system for slope deformations investigation and monitoring was necessary. A geophysical prospecting system based on extensive use of GPR has been adjusted for landslides investigation, with scanning performed on longitudinal and transverse lines, completed with a limited volume of other geophysical methods: dipole electromagnetic profiling, shallow refraction seismics and vertical electrical soundings and with only very limited drilling works required for verification. After it, all information necessary for designing of slope stabilization measures was obtained. This way, it allowed to start area remediation in a short time and to limit increase of damage due to time delay.

A few field studies have noted a directional dependence in the ground-penetrating radar response. Such observations are consistent with the character of the signal transmitted from a GPR antenna into the ground under different conditions. However, the antenna orientation relative to the target geometry is seldom given much consideration in GPR survey design and execution. We use simple models to illustrate the influence of antenna orientation relative to dipping reflectors. The two fundamental responses are presented: The 'broadside' response arises when the transmitting and receiving antenna axes are parallel to the strike of the dipping feature. The 'end-fire' response is obtained when the antennas are perpendicular to the strike. Both the reflector dip and host velocity are varied. Antenna orientation relative to the target is important because of the lobate nature of the transmitted GPR signal. The signal strength is zero or almost zero at 'null points,' where the energy available for reflection is small, and any reflected energy is almost non- existent. The broadside and end-fire signals have different forms, and yield different responses to dipping features. Thus, if the angle at which a null occurs is complementary to the angle of the dip, then little or no reflection occurs.

An experimental investigation was performed to analyze the influence of the proximity of a dielectric interface on the radiation of a GPR antenna. The experimental setup consisted of two 1.5 GHz resistively loaded transmit-receive antenna pairs. Data were obtained from one transmit-receive antenna pair as it was moved from a height of 29 cm to the dielectric surface at 1 mm increments. Direct transmission data were also obtained at the second antenna pair placed on the other side of the dielectric medium. Data were obtained from three different dielectric media possessing permittivities of 5.2, 10.6, and 80. Comparison of the frequency spectra of the direct-transmission waveforms for different transmitting antenna distances from the dielectric surface revealed a slight shift towards lower frequencies when the antenna enclosure was in contact with the surface. The direct-coupled waveform between transmitting and receiving antennas inside the same enclosure varied significantly over an antenna enclosure-surface distance range of 0 to 10 cm. the changes in the direct-coupling waveform appear to be largely due to the linear superposition of: (1) the direct arrival between the transmitting and receiving antennas, and (2) the surface reflection and associated surface reflection multiples. The waveform collected by the receiving antenna adjacent to the transmitting antenna was remarkably similar to the one-way transmitted waveform recorded at the receiving antenna on the other side of the block.

A novel broad bandwidth dual-polarization GPR antenna was also developed for collecting fully polarimetric data over a wide frequency range (20 MHz to approximately 800 MHz). This new design was improved from its single-polarization version introduced by Chen (1997). The new design features improved stability and directivity over conventional surface-based GPR antennas. Such antenna is currently applied to discriminate buried UXO's from other false alarm reduction.

GPR dipole antenna patterns can be described by the interference of space and lateral waves. Because this is an interference phenomenon, antenna patterns are a function of frequency, distance, and electrical properties. Traditional far-field criteria based on dipoles in a whole-space are insufficient to describe dipole antennas on a half-space boundary. Whole-space criteria fail because they do not take into account the interference of space and lateral waves. The travel time difference between space and lateral waves increases as the angle of observation from vertical increases, or with increasing distance from the source. The result is increased interference and more abundant lobes with increasing distance and observation angle. Since GPR investigations are limited by attenuation and many environmental and engineering targets of interest are located within a few wavelengths of the antenna, asymptotic solutions do not accurately describe antenna patterns for most GPR applications. The exclusion of lateral waves in geometric optics solutions is another source of error for many GPR applications. Data were measured over a water filled tank to verify FDTD antenna pattern models. Asymptotic solutions predict H-plane peaks at an angular distance equal to the critical angle. Measured and modeled antenna patterns are broader and have peaks located at a larger angular distance, than predicted from asymptotic solutions. The peaks approach and decrease the rate of convergence toward the asymptotic solution with increasing distance from the source, and data modeled over water demonstrate that the peaks still do not converge to the asymptotic solution at a distance of 24 wavelengths. The low directivity of dipole antennas explains why out of the plane reflections are commonly observed in GPR data.

In this paper, we propose to introduce an electric field sensor using LiNbO₃ optical modulator to an array type directional borehole radar. Advantage of the sensor is accuracy of measurement of fields with no electromagnetic disturbance, no battery and small space to transfer electrical signals to optical signals. If the sensor is used as array elements of the directional borehole radar, we might accurately measure electric fields at several points, and determine directions of arrival waves with the data set. We did experiment that the sensor in a borehole is illuminated from a slot antenna as a source outside the borehole. Transmission between the transmitter and the electric field sensor in a borehole was measured, and we got array data set with the sensor. The array data was analyzed by cross-spectrum analysis, and coherence, time delay and relative amplitude among the array elements was estimated. Experimental results gave good agreement with theoretical results. This is because we could accurately measure electric fields with the optical modulator, and accuracy of the data was enough to determine directions of arrival waves in a borehole. We think that the experimental results show possibility to realize a directional borehole radar using the dipole array with an optical modulator.

A GPR for detection of buried cables and pipes is developed by Ekko Dane Production in cooperation with Aalborg University. The appearance is a 'lawn mower' model including antennas, electronics and on-line data processing. A successful result is obtained by combining dedicated hardware and signal processing. The inherent signal to clutter ratio is bad, but making measurements at many polarization angles and subsequent signal processing improves the ratio. A simple model of the polarization dependence of the scattering from the target is used. The method is improved by combining the polarization filtering with averaging over small horizontal displacements. A stepped frequency measurement system is used. The method often implies long measurement times, but this problem is overcome by development of fast RF-electronics. Standard signal processors are used for real-time data processing. Several antenna array configurations are tested and optimized for low coupling between transmitter and receiver and for a short impulse response. A large number of tests have been made for different targets, e.g. metal cables and plastic pipes filled with air or water. Tests have been made under realistic ground conditions, including sand, wet clay, pavements and grass covered soil. The results show reliable detection even when the conditions are difficult.

This paper reports on a novel application of ground penetrating radar to a longwall steering problem in the coal mining industry. The main goal of the work was to determine whether a radar-based system could be used to detect coal-rock interfaces in order to establish a suitable mining horizon within the coal seam. We investigated the feasibility of the radar unit and determined that a positive correlation exists between the radar data and known coal-rock interface geology. We also highlight some of the unique challenges encountered when attempting to develop electrical equipment that is suitable for hazardous underground coal mining environments.

We present the different aspects of the development of an HF GPR which will be devoted to the characterization of geological structures and the detection of possible water reservoirs under the form of ground ice or even of liquid water on Mars.

In this paper, the design and the modeling of an indoor impulse UWB GPR systems (1 GHz - 5 GHz), built in the scope of the HUDEM project, is presented. For an impulse UWB system, a time-domain modeling is an obvious choice. We explain how the antennas can be characterized by their normalized impulse response. By considering the antenna as a convolution operator, we get a mechanism for modeling the whole radar system as a cascade of linear responses, which gives a lot of advantages and possible application. In our research it is used to express the radar range equation in the time-domain, to optimize the antenna configuration and to tune signal- processing algorithms. The deconvolution of the signal source and antenna impulse responses is an ill posed operation. In this paper we present a method for decomposing an A-scan in a linear combination of wavelets, using the Continuous Wavelet Transformations -- by properly choosing the mother wavelet. This technique can also be used to reduce the amount of data for further processing. Finally results obtained by our UWB GPR system are shown. Advantages and shortcomings are discussed.

In the road field, the need to get information on the thickness of very thin road layers is not solved by GPR. The reason is that the devices are not able to work over several gigahertz. That is why, a research has focused on the conception of a step frequency radar technique, enable to work with very high central frequency synthetic pulses. In collaboration with the LCPC (Central Laboratory of Bridges and Roads), an ultra wide band antenna has been developed at the LEAT (Electronic, Antennas and Telecommunication Laboratory). The ultra wide band antenna, developed for roads application, forms parts of the family of the Vivaldi antennas. It has been realized in stripline technology and one obtains a bandwidth greater than one decade. In a first step, this antenna has been tested on various bituminous concrete samples, with a network analyzer. Different parameters were studied like the bandwidth, the off-set between antennas, the height, and the shape of the pulse depending to the frequencies. A second step concerns GPR dynamic measurements. An homemade software enables to record data from the network analyzer. As LCPC has large testing facilities in the road field, such as a circular Pavement Fatigue Test Track, composed of different known structures, several radar profiles have been done. Results are compared with classical GPR profiles.

We have used airborne and ground-based GPR at 400 - 500 MHz to image hidden crevasses in Antarctica. The radar antennas were either pushed in front of a snowmobile, or cantilevered from a helicopter flying at about 6 m altitude and speeds near 15 m/s. We used a high trace acquisition rate, long time ranges, and migration to show snow bridge depth, crevasse width, septums between crevasses, connecting cavities and associated folded strata in the ground-based profiles. The crevasse images are formed by the discontinuities in reflections from the stratified firn. Diffractions from crevasse walls are strongly single-sided, originate from point and linear discontinuities, and provide advance warning. Airborne recorded images are similar, but less detailed than surface images. An increased trace rate could improve airborne imaging and allow greater profile speeds.

During five austral summers, from 1994/95 until 1998/99, the Alfred Wegener Institute (AWI) carried out a large airborne radio echo sounding (RES) survey in Dronning Maud Land (DML), Antarctica. These ice thickness measurements are part of the AWI contribution to the pre-site survey for a deep ice core drill site in DML within the European Project for Ice Coring in Antarctica (EPICA). The survey encompasses more than 90000 km RES profiles over DML and the adjacent coastal area, covering more than 1 million km². The lower boundary of the ice sheet could be determined area-wide. Internal horizons occurring in the upper two thirds of the ice column can also be traced for several hundred kilometers. This work presents the latest maps of the subglacial topography of the investigated area as well as of an internal horizon.

We have obtained the first ground-penetrating radar profiles of permafrost in the Dry Valleys of Antarctica. The area has long been thought of as a possible analog for Martian conditions. We interpret deltaic glacio-fluvial outwash, the disposition of lodgement till, and eroded out-wash previously thought to be terminal moraine from 100- and 400-MHz profiles at selected sites in McKelvey, central Wright, and lower Taylor Valleys, respectively. The relative permittivity appears to range between about 4 - 5.5 , which is consistent with the dense silty and sandy gravel, mineralogy and low ice content. Maximum depth of stratigraphy profiled was about 30 m. Weak interface reflectivity may limit interpretation of maximum penetration because absorption should be low, and scarce diffractions at depth imply weak scattering at 100 MHz. Future GPR systems in the Dry Valleys and on Mars should use colinear antennas to accommodate the rocky surfaces, and lower frequencies to search for deeper reflectors such as bedrock.

A series of closely spaced parallel ground penetrating radar (GPR) profiles have been measured in an ice marginal environment in Northwest Zealand, Denmark. The measurements were performed on glaciotectonic deformed glacio-fluvial sediments in the rim of a composite ridge. The radar profiles can be differentiated into several radar facies with distinct reflection characteristics. The lithology and depositional environment of the radar facies is interpreted by correlating with information from profiles in gravel pits, geological maps and drill hole data. The recorded radar facies include glaciotectonic disturbed glacio-fluvial sediments, sediments deposited penecontemporaneous with the deformations and sediments deposited post-tectonically. Several thrust planes with dip angles between 25 degrees and 30 degrees as well as major folds and minor faults have been interpreted from the GPR data. The deformation style of the tectonised glacio- fluvial sediments is a pro-glacial thin skinned thrust complex, with associated folding. The deformations have resulted in the present ridge morphology seen in the rim of the composite ridge. On top of the deformed sediments and in front of them syn- and post-tectonic sediments are deposited, smoothing the ridge relief created by the thin skinned thrust complex. A structural geological map with dimensions of approximately 160 X 75 meters has been constructed from the GPR data revealing the extension of the individual radar facies in the thrust complex. Tectonic features like thrust planes and folds can be followed throughout the modeled area.

The River Lena draining to the Siberian Arctic is considered to be the main sediment source for the Laptev Sea. Nevertheless, for the delta of River Lena occupying an area of 28,000 km², there are many unsolved questions concerning the environmental and sedimentation history, genesis of deposits, permafrost distribution, and climatic records in the area especially for the second sandy terrace deposits in western Delta Lena. To survey the stratigraphic sequence of Lake Nikolay and its surrounding which is representative for the western Delta Lena area, radio-echo sounding (RES) with 25 MHz and 100 MHz antennae on the frozen lake and on land have been carried out in connection with drilling activities. RES measurements of the lake sediments are complemented by shallow seismic and reveal subsurface stratigraphy of the lake sediments and the bordering permafrost deposits.

Since 1985, Ground Penetrating Radar (GPR) has been increasingly used in Australia for a wide range of geotechnical and non-destructive testing (NDT) applications. Despite this, most geotechnical engineers still regard GPR as an innovative technology with low to moderate success of achieving successful engineering outcomes. Improvements can be achieved by more careful planning and laboratory testing of site materials, however, the greatest barriers to general acceptance are overselling and use of inappropriate technology by inexperienced users. A number of brief case studies of successful applications of GPR in Australia and the Pacific to geotechnical and NDT problem are included using antenna frequencies from 120 to 1400 MHz. These range from shallow bedrock mapping to depths of several meters to the detection of buried mine working beneath concrete floors which posed a significant hazard, to airport runway screening and the condition testing of tunnel and drain liners.

This paper describes development of Ground Penetrating Radar (GPR) techniques for spatially distributed measurement of soil moisture. Traditional measurement techniques are limited; most significantly they are time consuming, invasive and destructive techniques. Measurement with GPR is non-invasive and rapid. This paper investigates the relationship between a number of properties of the GPR signal and Volumetric Moisture Content (VMC). Using a series of controlled laboratory experiments the two most reliable methods were found to be the signal amplitude and amplitude spectra approaches. Significant relationships were found between maximum amplitude and VMC for a variety of earth materials and situations. Quantitative correspondence between the GPR and invasive measurements of moisture is poor due to differences in sampled area, depth of investigation and the impact of rock fragment content on the relationship between soil water and soil volumetric moisture content. In addition GPR specific errors are introduced by coupling of the radar with the ground surface, and the impact of the profile variability on the GPR signal return.

Concrete lined tunnels and pipelines commonly suffer from damage due to subsidence or poor drainage in the surrounding soils, corrosion of reinforcement if present, and acid vapor leaching of the lining. There is a need to conduct tunnel condition monitoring using non-destructive testing methods (NDT) on a regular basis in many buried installations, for example sewers and storm water drains. A wide variety of NDT methods have been employed in the past to monitor these linings including closed circuit TV (CCTV) inspection, magnetic and various electromagnetic and seismic methods. Ground penetrating radar, GPR, is a promising technique for this application, however there are few systems currently available that can provide the high resolution imaging needed to test the lining. A recently developed Australian GPR system operating at 1400 MHz offers the potential to overcome many of these limitations while maintaining adequate resolution to the rear of the linings which are typically less than 0.5 meters thick. The new high frequency GPR has a nominal resolution of 0.03 m at the center of the pulse band-width. This is a significant improvement over existing radars with the possible exception of some horn based systems. This paper describes the results of a laboratory study on a model tunnel lining using the new 1.4 GHz radar. The model simulated a concrete lining with various degrees of damage including, heavily leached sections, voids and corroded reinforcing. The test results established that the new GPR was capable of imaging subtle variations in the concrete structure and that simulated damage could be detected throughout the liner depth. Furthermore, resolution was found to exceed 0.02 m which was significantly better than expected.

The Geophysical Institute of Israel (G.I.I.) carried out a Ground Penetrating Radar -- GPR -- survey at the construction site for the administration building of the I.E.C. (The Israel Electricity Company) in the town of Ariel in the Samaria mountains of Israel. The construction workers at the site found a void in one of the pile boreholes and the GPR crew carried out a survey to detect and map the cave. The GPR data show a very clear 'cave shape' with an area of about 81m², the roof of the cave was at a depth of 5m - 7m, while the floor of the cave was at a depth of 8m - 11m. The volume estimations of the target were incorrect and the construction workers did not find any indication of the existence of the cave under the pile sites except the one prior to the GPR survey.

The comparison between geologic and radar sections shows the capability of radar to detect fractures (single or sets), karst cavities and joints of strata. Fractures are better visible when they have irregular geometry and are filled by clay or air. Sedimentary massive rocks produce lateral continuous reflections in good quality rocks and irregular reflections with diffraction hyperbolas -- in low quality sedimentary rocks. Often low quality rocks cause high attenuation of signal.

Seismic reflection processing techniques are applied routinely to georadar data. Although similarities exist between radar and seismic wave propagation, there are some significant differences (e.g., the dipole nature of georadar sources, receivers and elemental sources used to represent scattering bodies). To understand better the consequences of recording dipolar wavefields, we simulate a number of multi-component georadar data sets. These simulations are based on a weak scattering approximation, such that point heterogeneities in the subsurface can be represented by infinitesimal dipoles with moments parallel and proportional to the incident georadar wavefields. Since many subsurface structures can be modeled by appropriate suites of infinitesimal dipoles, the simulation results are quite general. On the basis of our simulations, we determine that 'pseudo-scalar' wavefields can be simulated from coincident georadar data sets acquired with two pairs of parallel source-receiver antenna, one oriented perpendicular to the other. Pseudo-scalar georadar data, which are characterized by low degrees of directionality, can be processed confidently using standard seismic processing software. To illustrate the advantages of multi-component georadar data, we combine 3D georadar data sets acquired with dual component source-receiver antenna pairs to form pseudo- scalar wavefield images.

We have developed a method to rapidly compute synthetic radar records from complex reflecting surfaces. The approach is a 3- D time domain Hemholtz-Kirchhoff (HK) representation, similar to Hilterman (1981), that includes the radiation characteristics of GPR dipoles on the surface of a uniform dielectric halfspace. Validity is established by making comparisons with published model results and by comparisons with field data. Comparison to the ray theory results of Zeng et al. (1997) show excellent agreement in reflection arrival times for pipes of various diameters. We also reproduce the non-specular reflection results of Schleicher et al. (1991), which show that large amplitude reflections can originate from the inflection points of curved surfaces. Our comparisons with field data use reflection records taken at a test site in Borden, Ontario, over horizontally oriented buried metal drums. The H-plane reflection data were collected using shielded 700-MHz dipoles. Our raw synthetic amplitude trends show reasonable agreement to the field data, but are not perfect. Using a small diameter synthetic dipole array, we show that the mismatch is most likely caused by antenna shielding effects. The versatility of the HK method is demonstrated by giving results for a number of interesting applications. These include synthetic records for crisscrossing pipes buried at various depths, reflection synthetics from a truncated cone representing the slag heaps in Daniels and Brower (1998), and reflections from a rough surface. The slag heap models demonstrate the effect of antenna polarization on reflections from sloping surfaces. Analysis of synthetic reflections from rough surfaces shows that the coda following the first impulsive arrival can be used to estimate the surface roughness. This is of interest for interpreting reflections from glacier data. Our results demonstrate that the HK method is useful in interpreting data, as well as for developing field survey strategies.

High-frequency electromagnetic wave propagation in the vicinity of boreholes is complex and can be described only partially by analytical or asymptotic methods. To improve our understanding of the governing physical processes we present a finite-difference solution of Maxwell's equations in cylindrical coordinates. This approach allows us to model the full electromagnetic wavefield associated with a typical borehole georadar experiment and to assess the adequacy of the ray-based interpretation methods currently used. We find that the nature of the medium filling the borehole or changes in the material properties along the borehole wall may have a major impact on the amplitude radiation pattern. As a result of waveguide effects, the radiation pattern of a vertical electric dipole located in a water-filled borehole is significantly distorted with respect to the corresponding reference full-space radiation pattern. Even more severe distortions of the amplitude radiation pattern may result when the emitting or receiving antenna is located near material boundaries or near the upper or lower end of the borehole.

In the near-surface environment, ground penetrating radar (GPR) sections can be difficult to interpret, even with the use of advanced processing techniques. With the application of three-dimensional, finite-difference time-domain modeling, we are able to simulate GPR wave propagation and evaluate the nature of the recorded signals. Mathematical models of the propagating electromagnetic wave are generated using a staggered, fourth-order O(2,4) finite difference scheme utilizing orthogonal, cartesian grids. Realistic antenna configurations and source signal forms are developed with practical dielectric models determining the subsurface material properties. These models are based on the superposition of single relaxation mechanisms allowing frequency-dependent, conductive, inhomogeneous, anisotropic materials to be incorporated into the scheme. To assess model performance, a series of 900 Mhz radar sections were collected over a purpose built test facility having quantifiable features and known material properties. Separate models generated from both known and estimated properties were compared to the observed data and in general, correlate well. These models provide important information on the nature of the subsurface and assist in the application of advanced processing and interpretational methods.

The electromagnetic wavefield is decomposed into up- and downgoing constituents, which allows the introduction of the one-way wave operator. Transverse scattering is taken into account by a pseudodifferential operator, the vertical slowness operator. The actual computation of the one-way wave propagator is made feasible by the introduction of the so- called generalized-screen approximation of the vertical slowness symbol. The medium is defined in terms of a background medium and a perturbation. Such a contrast formulation induces a polyhomogeneous series expansion of the vertical slowness symbol in both the magnitude and the smoothness of the medium perturbation; the addition of higher- order terms of the series expansion increases the accuracy of the one-way generalized-screen propagator. The medium parameters, dielectric permittivity and magnetic permeability, are described by Cole-Cole distributions to allow a realistic description of frequency dependent medium properties. These results are then cast into a family of fast numerical algorithms. We analyze the accuracy of the generalized-screen method in complex structures using synthetic models that exhibit significant multiple scattering. The generalized- screen method shows accuracy for wide-angle propagation as well as for the prediction of multi-pathing.

The video impulse ground penetrating radar (GPR) system for detection of small and shallow buried objects has been developed. The hardware combines commercially available components with components (e.g. antennas) specially developed or modified for being used in the system. The GPR system has been designed to measure accurately electromagnetic field backscattered from subsurface targets in order to allow identification of detected targets through solution of the inverse scattering problem. The GPR has been tested in different environmental conditions and has proved its ability to detect small and shallow buried targets.

The requirement for the destruction of anti-personnel mines is generating a need for much enhanced detection systems based upon GPR and other sensors. The paper considers the requirements for a vehicle based radar briefly describing the hardware and software. Early results are presented which show that 100% detection rates may be achieved but much additional work is required to reduce the false alarm rate. The paper includes work on one feature that allows targets to be recognized. This is based upon analyzing the natural resonances of the target using Prony's algorithm. In all cases real-time analysis is implemented.