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8th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 23 Apr 1995 - 26 Apr 1995
- Location: Orlando, Florida, Canada
- Published: 23 April 1995
21 - 40 of 104 results
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Three-Dimensional Imaging Of Underground Mine Structures Using Seismic Tomography
Authors M.J. Jackson, M.J. Friedel, D.R. Tweeton, D.F. Scott and T. WilliamsThree-dimensional seismic imaging has a number of important advantages over two-dimensional tomography, in artifact suppression and selfconsistency. However, the underdetermined or illconditioned nature of the inversion is typically more severe in three dimensions than in two. Methods for characterizing resolution and robustness are concomitantly more important for three-dimensional studies. Checkerboard resolution tests and robustness tests based on multiple inversion with different starting models provide means of evaluating the results of
travel-time inversions for two underground mine sites.
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Saltwater Intrusion: Concepts For Measurements And A Regional Characterization For Broward County, Florida
Authors Lynn Yuhr and Richard C. BensonFour basic components are necessary to properly manage our groundwater resources against saltwater intrusion;
measurement, monitoring, modeling and modification. While a discussion of the saltwater interface is presented to
provide an understanding of the hydrologic problems, this paper focuses on the first two steps in the process of
characterization; the measurements to define existing conditions of the saltwater interface and techniques for
monitoring changes in the saltwater interface over time.
A variety of techniques to measure the saltwater interface (both traditional and contemporary) are presented along
the their advantages and disadvantages. Two contemporary techniques are highlighted because of their dramatic
improvement in information which they provide: surface time domain electromagnetics (TDEM) and borehole
induction logging.
A county-wide case study is presented which utilized these contemporary techniques in Broward County, Florida.
The results of this study were used to map the saltwater interface, and identify anomalous conditions caused by
effects of head differences due to pumping, irrigation and saltwater recharge from canals as well as the presence of
“connate” saltwater in the aquifer. This regional characterization of the salhvater intrusion will be used to assess
the existing county-wide saltwater monitoring network and identify locations for future monitoring wells. The
approach for characterizing the extent of saltwater intrusion was unique and provided solid technical information
on the groundwater resources in which planning and development of the county can be based.
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Hydrogeological Investigations Of Minor Islands In Denmark
Authors K.I. Sørensen and J.P. JensenDenmark is a kingdom of islands. Denmark consists of more than 500 islands,
200 of which are inhabited, though many are smaller than 10 km2. Supplying good
quality drinking water for the inhabitants often presents major problems, some of
which are specific for the islands.
For geometrical reasons the coast-near regions of an island are a relatively larger
proportion of the total area, the smaller the island is. This means that the area, where
the proximity of the sea presents problems of salt water intrusion in the aquifers, is
relatively large, and abstraction of fresh ground water is most often precluded in these
parts, On the other hand, farming is the main occupation and means of living on the
smaller islands, so the problems with infiltration of nitrate from excess fertiliser and
pesticides related to agricultural use are very acute. For these reasons’ reports of
deteriorating water quality have appeared from many of the smaller islands.
There are many good reasons why the problem should be solved locally. The
Department of Earth Sciences has been involved in co-operative research projects with
several municipal water supplies in Denmark to find strategies for the application of
geophysical methods to solve the specific hydrogeological problems of the minor
islands, all of which are characterised by a Quatemary sedimentary geology.
An integrated use of geophysical methods has proven ifself to be very applicable
in the type of detailed hydrogeophysical investigations, which must be carried out to
provide the necessary insight into the hydrogeology of an island. This demands that
efficient and detailed methods for measurements and interpretations are developed,
and the strategic aspects of data collection and interpretation become important.
In this context we present results from the PA-CEP electrical profiling method
and the Ellog auger drilling method with undisturbed water sampling which, together
with transient electromagnetic soundings and geoelectrical soundings, can be
combined into an efficient scheme for detailed hydrogeological investigations. The
results of these investigations are the foundation for decisions on remediating
measures, sitings of new abstraction wells, and possible restrictions on the land use.
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A Comparison Of Electromagnetic Techniques Used In A Reconnaissance Of The Ground-Water Resources Under The Coastal Plain Of Isla De Mona, Puerto Rico
Authors Ronald T. Richards, Joseph W. Troester and Myrna I. MartinezAn electromagnetic reconnaissance of the ground-water resources of the coastal plain of Isla de Mona, Puerto Rico
was conducted with both terrain conductivity (TC) and transient electromagnetic (TEM) geophysical techniques.
Quantitative interpretation of the data was done using forward and inverse modeling with various starting geoelectric
models. The final geoelectric models produced by the two techniques are similar. Neither method was able to provide
useful information about the water table. The freshwater lens under the coastal plain was found to have a maximum
thickness of about 10 m near the center of the coastal plain. The lens thins toward the ocean and also thins toward the
interior of the island. This finding was not expected and indicates that the flow paths in the aquifer are not radially
symmetrical from the center of the island to the ocean. At least some of the ground water flows to the ocean by a more
circuitous and longer path. The asymmetry of the flow paths indicate that differences in hydraulic conductivity are
controlling the shape of the freshwater lens.
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Salinity And Hydrodynamics Of The Holocene And Upper Pleistocene Beneath The Louisiana Wetlands From Electrical Measurements
Authors L.D. McGinnis, M.D. Thompson, G.J. Kuecher, P.L. Wilkey and H.R. IsaacsonA conceptual hydrodynamic model in the Holocene and upper Pleistocene beneath the
Louisiana wetlands is described in terms of salinity distributions. Porewater salinity is calculated
from electrical measurements, including resistivity soundings, electric logs, and electromagnetic
profiling. Electrical measurements support the primary, basin-wide groundwater flow model;
however, the data also indicate secondary contributions from expulsion of fluids under geopressure
along active growth faults and from original waters of deposition. Expulsion of water from
growth faults has been described previously for deeper sections of the Pleistocene, but has not been
reported for the Holocene or upper Pleistocene beneath the Louisiana wetlands. Porewater
chemistry variations beneath the coastal wetlands are a consequence of the following (in order of
importance): (1) environment of deposition; (2) a basin-wide, regional flow system; (3) expulsion
from deep-seated growth faults; and (4) pore water extrusion due to compaction. Water chemistry
in Holocene clays and muds is influenced primarily by the deposition environment. In Pleistocene
sands, the chemistry is a function of the other three factors.
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Saltmap - High Resolution Airborne Em For Electrical Conductivity Profiling
Authors G.J. Street and G.P. RobertsShallow conductivity mapping using airborne electromagnetic systems has been used extensively in
Australia for environmental applications. The aim of such surveys is to define near surface
conductivity variations which can be related to dissolved salts in the groundwater. In most parts of
Australia the principal salt is naturally occurring sodium chloride (NaCl) and in many cases salt
deposits are concentrated or remobilised by the effects of man’s interaction with the environment.
To understand how these deposits are moving in the ground it is necessary to map the conductivity
variations in the near surface in three dimensions. The airborne electromagnetic system employed
must measure both at high frequency and at high sampling rates to achieve this aim. To resolve
conductivity structures at high resolution in the ground’s near surface is in some ways a more
difficult problem than to detect anomalies at great depth. A wider system bandwidth and superior
noise immunity are required and consequently greater real-time computing power. Results from the
initial surveys using SALTMAP show that most of the planned specifications of the system have
been met. The challenge for the future is to utilise the data generated in remedial environmental
work.
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The Use Of Ground Penetrating Radar For Aquifer Characterization: An Example From Southwestern British Columbia
Authors Jane Rea and Rosemary KnightTwelve kilometers of ground penetrating radar (GPR) data have been collected over the Brookswood
aquifer in southwestern British Columbia. The data have been analyzed to assess how GPR can be used to
characterize the distribution and connectivity of hydraulic units.
We have used GPR to locate the aquifer/aquitard boundary at several locations in the study area. The
electrical contrast between these two materials makes the aquifer/aquitard boundary an excellent target for GPR
surveys.
GPR was also used to reconstruct the paleo-environment of one area of the Brookswood aquifer. This was
accomplished by using a modification of the concept of architectural element analysis. Radar elements were
identified in the survey and were assigned sedimentary parameters using data from trenching and drilling in the area.
These elements were used to develop an interpretation of the paleo-environment that provides information about the
spatial distribution of hydraulic units.
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Hydrogeophysical Characterization Of Water Wells Through Geophysical Logs In Deccan Trap Of M.P., India
Authors Subhash C. Singh and G. SuryanaraynaThe western part of Madhya Pradesh particularly, Malwa
plateau region is most extensively occupied by dark greenish
black to grey, apparentlyhomogeneous looking basaltic rocks of
either A, or Paaboe type. Each flow comprises either zeolitic
vesicular basalt followed by hard massive/j.ointed fractured
basalt. Groundwater occurs in weathered mantle: joints and
fractures. Identification of hydrogeological units forming the
complex frame-work of basaltic aquifer system has been
cunsiderably made easier through the use of multi-parameter
geophysical devices of sub-surface horehole logging. The
massive part of basaltic flow which is hard and compact shows
very high resistivity (300 ohm-m to 5000 ohm-m) and low natural
gamma counts (15 cps to 40 cps) whereas t-he ves.icular part
which is filled with secondary minerals (amygdules) and the
fractured basalt show intermediate resistivity (50 ohm-m to 300
ohm-m) and natural gamma counts (40 cps to 100 cps). The inter
- trappean flow shows very low resistivity (6 to 50 ohm-m) and
very high gamma counts (100 cps to 300 cps).
The synergistic study of multi-parameter logs and .its
cross plotting followed by statistical techniques of filtering
and deconvolution have been used in the present study and
useful correlation and inferences for precise zoning of even
thin layers like redbole at deeper depths could be drawn up.
The paper h.ighlights the effective correlation between
resistivity logs and natural gamma logs so as to work out the
probable sub-surface configuration of aquifer system which will
have a major bearing on the safe and sustainable design of
groundwater abstraction structures.
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Application Of New Data Processing Techniques To Hydrogeophysical Survey Data From The Netherlands
Authors M.A. Meju and J.A.C. MeekesThe determination of aquifer characteristics from surface geoelectrical measurements is a difficult nonlinear
inverse problem. In routine data analysis, this problem can be addressed by time-consuming forward
modelling and automated iterative inversion or recently by the faster approach of direct inversion. A major
draw-back of these standard approaches is that in the absence of accurate a priori information, there is no
guarantee that the constructed model represents the true subsurface structure. A simple and effective
alternative scheme for approximate direct resistivity-depth transformation of geoelectrical data is combined
with standard numerical modelling techniques and applied to well-known transient electromagnetic and dc
resistivity survey data from the Netherlands in order to evaluate its usefulness in this geological setting.
The resulting models of the subsurface are found to be in excellent agreement with borehole lithological and
permeability distribution data and demonstrate that dc resistivity and TEM methods are an essential
combination for accurate geoelectrostratigraphic characterisation. The results also suggest that the rapid
scheme for simultaneous TEM and dc resistivity data analysis is a powerful tool for hydrogeophysical
studies in the region.
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Vertical Profiling Of Aquifer Flow Characteristics And Water Quality Parameters Using Hydrophysical’” Logging
HvdroPhvsical™ ( HpL) logging technology is a revolutionarv advancement in aquifer characterization that was
recently applied at Schofield Army Barracks, Oahu, Hawaii. The purpose of using this innovative technology was to
assess the aquifer permeability and groundwater quality to gain a quantitative understanding of groundwater flow
conditions and potential contaminant pathways. Fractured and caved zones within the boreholes precluded the use
of other techniques (e.g., inflatable packers) to obtain these data. The versatile and time saving benefits of HpL
logging provided hydrogeologic understanding of the aquifer at a cost savings from other available technologies.
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Simulation Of Airborne Electromagnetic Measurements In Three Dimensional Environments
Authors David L. Alumbaugh and Gregory A. NewmanA 3-D frequency domain EM modeling code has been implemented for helicopter
electromagnetic (HEM) simulations. A vector Helmholtz formulation for the electric fields is
employed to avoid problems associated with the first order Maxwell’s equations numerically
decoupling in the air. Additional stability is introduced by formulating the problem in terms of the
scattered electric fields which replaces an impressed dipole source with an equivalent source that
possesses a much smoother spatial dependence and is easier to model. In order to compute this
equivalent source, a primary field arising from dipole sources in a whole space must be calculated
where ever the conductivity is different than that of the background.
The Helmholtz equation is approximated using finite differences on a staggered grid. After
finite differencing, a complex-symmetric matrix system of equations is assembled and
preconditioned using Jacobi scaling before it is solved using the quasi-minimum residual (QMR)
method. In order to both speed up the solution and allow for larger, more realistic models to be
simulated, the scheme has been modified to run on massively parallel architectures. The solution
has been compared against other 1-D and 3-D numerical models and is found to produce results in
good agreement. The versatility of the scheme is demonstrated by simulating a survey over a salt
water intrusion zone in the Florida Everglades.
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1D Time Domain Electromagnetic Interpretations Over 2D / 3D Structures
By Esben AukenTime domain electromagnetic soundings have been calculated over 2D / 3D structures in a layered halfspace and
hereafter inverted using a 1D least squares time domain code. The forward calculations are done in the frequency domain
and the subsequent transform to time domain is performed using fast digital filters. The study focuses on typical
hydrogeological models. The investigated models include a resistive dyke, a resistive beam and resistive block structure with
edges with varying slopes in a conductive layered halfspace with an overburden. The 1D interpretations of the 2D / 3D
responses show that the vertical resolution is reduced and the resistivities are smeared out. The 2D / 3D responses over
models with a resistive body in a conductive host is easily fitted with the 1D models whereas it is not possible to fit the
responses from good conductors in a resistive host very well.
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Characterization And In-Field Suppression Of Noise In Hydrogeophysics.
Authors Mette S. Munkholm, Kurt I. Sørensen and Bo H. JacobsenPresent developements of hydrogeophysical methods provide us with hitherto unseen sampling density in profiling and
sounding. Transient electromagnetic sounding (TEM) data and pulled array continuous electrical profiling, PA-CEP
(Sorensen and Christensen, 1994) are among these. Common to these types of data is the possibility of simple stacking or
moving averaging to increase the signal to noise ratio due to the data redundency. Moreover, due to the volume of the raw
data the stacking must be done in the held. However, only for white Gaussian noise is simple stacking optimal. Studies have
shown that it is critical to characterize the noise with respect to frequency spectrum and statistical distribution as a design
basis for more adaptive noise suppression procedures in order to achieve reliable results.
Flexible stacking schemes for the data types are presented and we demonstrate their adaptation based on studies of the noise
characteristics for each type. Also, the special problems arising in online processing for the different stacking schemes are
addressed. The large data volume involved calls for in-field reduction of the data. This study is aimed at designing the online
processing required.
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Neural Network Interpretation Scheme For A Frequency-Domain Electromagnetic Ellipticity Surveys
Authors Ralf A. Birken and Mary M. PoultonA system of neural networks is used for the interpretation of electromagnetic ellipticity data from a frequencydomain
electromagnetic system developed at the Laboratory for Advanced Subsurface Imaging. The in-field data
interpretation consists of networks operating in mapping mode (1D) and object mode (3D, not yet implemented).
The purpose of the interpretation system is to provide a fast, approximate yet reasonable interpretation in the field
during a survey. Our approach to the neural network processing is to divide the interpretation into many parts
using several small networks. Three network paradigms were used for training, a backpropagation algorithm,
radial basis functions, and modular neural networks. We have tested the networks for a frequency range of 1kHz
to 1MHz with synthetic data and from a field survey in Wyoming.
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The Application Of Geophysics To Archaeologic Mapping Of Prehistoric, Protohistoric And Historic Sites In Western Canada
Authors Paul Bauman, Rod Heitzmann and Jack PorterIn 1799, the site of Rocky Mountain House, Alberta, stood at the southwestern corner of the
northern fur empires of the North West Company and their competition, the Hudson’s Bay
Company. It marked the endpoint of a yearly journey of up to 3,000 kilometers for the traders who
inhabited the site. Between 1799 and 1875, four forts were constructed by the two fur trade
companies. The third of these forts, which stood from 1835 until 1861, has not been excavated.
As these forts were almost entirely constructed of wood, with very little metal or stone, their
surface remains are meager. The goal of this investigation was to evaluate the utility of
geophysics as an archaeological aid in studying such historic sites in Western Canada.
Specifically, the objectives were to identify the position of the rooms and palisades of the 1835
1861 fort, and to locate burial sites associated with this and other forts. An additional objective
was to explore for prehistoric and protohistoric native campsites in the vicinity of the fort. A
challenging obstacle in describing the 1835-1861 fort using geophysics is the fact that in 1861,
the Blackfoot peoples burned the fort to the ground.
Four geophysical methods were used. Ground penetrating radar data provided the greatest detail
in describing fort construction and burial locations. The GPR data, however, would have been
of limited use if not viewed in conjunction with the information provided by total magnetic field,
magnetic gradient, and terrain conductivity plots of the particular sites. The integration of the
various methods provided an overall plan of the original construction of the 1835 fort, including
some unexpected insights into the building techniques of the period. While GPR most clearly
pinpointed several burial sites, the use of multiple instruments provided greatly increased certainty
and an increased understanding of the nature of the identified graves. Beyond being a good
example of an archaeogeophysical data set, the significance of this paper is the clarity with which
it is shown the need to integrate a number of geophysical techniques at investigations of historic
sites in Western Canada. In addition, it is evident that the spatial relationships of buildings,
burials, and palisades provided by a detailed geophysical data set can greatly enhance the overall
understanding of the activity and history of a fur trade post during its active life.
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The Geophysical Discovery Of A Second World War Battlefield In Central Crete During Construction Activities By A Building Company. The Solution To A Major Environmental Problem.
Authors St.P. Papamarinopoulos, M.G. Papaioannou, P. Stefanopoulos and X. BafitisDuring the initial steps of preparation of a ten hectares piece of land for building purposes in central
Crete a bomb was discovered accidentally. The Laboratory of Geophysics accepted a request by the
company and carried out differential magnetic, and ground penetrating radar measurements.
In spite of the environmental noise produced by the tratIic and the function of nearby radio station
emitting at 80 MHz, it became possible to apply a normalization and filtering technique in the
instruments and successfully locate a large variety of war remains from 1 to 4m depths. Depth
estimates of the explosives were obtained by modeling with 2-112 D theoretical bodies and later by
object delineation using Euler’s homogeneity equation.
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Geophysical Investigation For The Location Of A Historic Heiau Kawaihae, Hawaii
Authors Jose L. Llopis and Michael K. SharpThere currently is an awareness in Hawaii to preserve historic sites and the culture of ancient Hawaii.
One area of cultural significance, Pu’ukohola Heiau National Historic Site, is located in Kawaihae on the
northwest coast of Hawaii (Figure 1). The site is administered by the U.S. Department of the Interior’s
National Park Service (NPS). A heiau is a massive stone structure which was used as a temple by the ancient
Hawaiians.
The Pu’ukohola Heiau is the primary structure associated with the founding of the Kingdom of Hawaii.
The last major heiau was built in 1791 by Kamehameha the Great to honor, regain the favor, and enlist the
services of his family war-god, Ku-ka-ili-moku. An Englishman, John Young, reported that Kamehameha
offered 11 human sacrifices at the dedication of the heiau. The principal offering was the body of Keoua Kuahu’ula,
Kamehameha’s only serious rival for the control of the island of Hawaii. With his war temple built
and acceptable to the war-god, Kamehameha conquered Maui, Lanai, and Molokai islands in 1794 and Oahu in
1795. With the successful conquest of Oahu, Kamehameha founded the Kingdom of Hawaii. Kauai remained
independent until 1810, when it joined the Kingdom by mutual consent to forestall invasion by Kamehameha.
Following the death of Kamehameha in 1819, the traditional religion was abandoned. The carved
wooden images of Pu’ukohola Heiau were discarded and its thatched temple houses, prayer tower and altar
destroyed. Today, there are two intact stone structures, or heiaus, that can be visited at the Pu’ukohola Heiau
National Historic Site. One structure is about 200 ft long and 100 ft wide and the other about 275 ft long and
50 ft wide. A third, smaller structure, measuring approximately 10 ft by 10 ft, has historically been reported to
exist at the site but its exact location is unknown. Some local residents claim that the missing heiau is located
in the bay just a few tens of yards offshore from the site while others maintain that it is buried somewhere
onshore near the shoreline.
A geophysical investigation was performed at the Pu’ukohola Heiau National Historic Site during the
period 11-18 August 1993 in order to locate a purported “shark heiau” in the vicinity of the Kawaihae Boat
Harbor construction project, South Kohala, Island of Hawaii. This was performed as part of Section 106,
National Historic Preservation Act of 1966, as amended, compliance, pursuant to implementing regulations
contained in 36 CFR 800, for the proposed construction at Kawaihae Harbor. NPS persoMe desired to noninvasively
determine the location of the shark heiau; the heiau will then presumably be investigated and
protected. The geophysical investigation was conducted by personnel of the U.S. Army Engineer Waterways
Experiment Station (WES) at the request of the U.S. Army Engineer Division, Pacific Ocean.
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Buried In The Basement - Geophysics Role In A Forensic Investigation
Authors Scott F. Calkin, Richard P. Allen and Michael P. HarrimanMrs. Pearl Bruns of South Portland, Maine was reported missing in August 199 1. The search for Mrs. Bruns
went on for thirteen months. Evidence from various forensic techniques and interviews suggested a remote
possibility that Mrs. Bruns may have been interred in the dirt basement (approximate 3.5 foot crawlspace) of her
residential home. In July 1992, the Maine State Police contacted ABB Environmental Services inquiring about
the use of geophysical methods which could detect shallow graves. Based on site conditions and law
enforcements’ desire not to tear the home from its foundation to dig up the cellar, ground-penetrating radar
(GPR) was chosen to screen for the presence of a shallow grave. Considering the target was approximately 5
feet long and 1.5 feet in width, a one by one foot survey grid was conducted in September 1992 using a GSSI
System III GPR unit equipped with a 500 MHz transducer. A strong reflector (approximately 3 feet below the
basement surface) was profiled throughout the survey area. A test pit revealed the reflector represented an
oxidized, cemented sand which could not be penetrated with hand tools. However, in one comer of the
basement next to a foundation wall, GPR data indicated the reflector was conspicuously absent. Mrs. Brims,
wrapped in plastic bags and bound by the wrists and ankles, was found buried 2.5 feet below the basement
surface at this location. Her husband, Mr. William Bruns was arrested and charged with murder. Mr. Bruns
plead guilty to manslaughter in April 1994 and is serving a twenty year prison sentence.
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Use Of Bistatic Allofrequency Antennas In Ground-Penetrating Radar (Gpr) Investigations
More LessShielded monostatic transducers used in ground-penetrating radar investigations
(GPR) provide good results in probing subsurface features. Use of bistatic (paired) isofrequency
transducers can improve survey results. Bistatic antennas transmitting and receiving
at the same center frequency (iso-) can reduce ‘ringing” produced by initial contact
of a vertically incident radar pulse with highly conductive surface material. Selection
of a suitable antenna separation can improve capture of reflected pulses that would
be lost using a monostatic system. What is reported here is the use of a pair of antennas
having different center frequencies (allo-), with the higher frequency receiver serving as
a filter for the lower frequency transmitter. Impulse radar units transmit and receive
broad bandwidth pulses. Lower frequency antennas usually transmit pulses with higher
power, allowing specific frequencies to penetrate deeper into geologic media. In the
zone of frequency overlap, sufficient energy will be reflected back to the higher
frequency receiver to permit higher resolution of targets at greater depth.
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Ultra-Wideband Antenna Design For Gpr Application
Authors Chris Thompson and Bibhas DeWe have been developing an ultra-wideband antenna design for use in Ground Penetrating Radar
applications. Adapted from a patented antenna intended for use in dielectric permittivity well logging (De
and Nelson (1992a)), the antenna is small (3cm by 3cm aperture) and has a wide bandwidth (10’s MHz to
1 Ghz useable range). Initial tests indicate that the basic antenna is compatible with current commercial
digital instruments, although relatively inefficient compared to conventional dipole antennae. Reasonable
quality field data were recorded which are comparable to dipole data but lower amplitude. Our ultimate
goal is to design a small, wideband antenna with superior insulation from the air half space. Such an
antenna is required for GPR site assessments at urban and culturally noisy sites.
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