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9th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 28 Apr 1996 - 02 May 1996
- Location: Keystone, Colorado, USA
- Published: 28 April 1996
41 - 60 of 134 results
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Monitoring Dnapl Pumping Using Integrated Geophysical Techniques
Authors Robin L. Newmark, William D. Daily, Kevin R. Kyle and Abelardo L. RamirezThe removal of DNAPL during pumping has been monitored using integrated in situ
geophysical techniques. At Hill Air Force Base in Utah, a free-product DNAPL plume
(consisting predominantly of TCE) is pooled in water-wet soil on a thick clay aquitard.
Groundwater pumping at Operable Unit 2 (OU 2) began in 1994; to date, nearly 30,000
gallons of DNAPL have been recovered from the site. From September, 1994 through
September, 1995, changes in the basin during DNAPL pumping were monitored using an
integrated geophysical system. Fiber optic sensors and neutron logs verify the presence of
DNAPL in the vicinity of three boreholes which form a cross section from the perimeter of
the basin to its center. Cross borehole electrical resistance tomography (ERT) images the
changes in formation electrical properties due to the removal of DNAPL, extending the
understanding of DNAPL removal between the boreholes. During pumping, electrical
resistivities decreased; we suggest that these decreases are directly caused by the reduction
in DNAPL. During ground water pumping, water with relatively low resistivity replaces
some of the DNAPL pockets as the highly insulating DNAPL is removed. The results
suggest that, as DNAPL is pumped from a nearby well, product slowly drains along the
top of an aquitard and into the pump well, where it collects.
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Fractures, Fluid Flow And In Situ Stress Indicators In Shallow Sedimentary Rocks At The Proposed Wake/Chatham Low Level Nuclear Waste Disposal Site, North Carolina
Authors Colleen A. Barton and Colleen A. BartonRecent analyses of borehole data recorded in relatively deep crystalline rock show a significant
correlation between critically-stressed fractures (that is, fractures optimally-oriented to the stress
field for frictional failure) and hydraulic conductivity (Barton et al. 1995). In this study, we
examine the relationship between fracture orientation, fluid flow and in situ stress using data from
detailed analyses of fracture geometry, precision temperature logs that indicate localized fluid flow
and in-situ stress indicators recorded in sediments at relatively shallow depths. We have conducted
this study to determine if a correlation exists between in situ stress and fluid flow in the shallow
crust similar to that found at depth in crystalline rock.
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Geophysical Characterization Of A Fractured-Bedrock Aquifer And Blast-Fractured Contaminant-Recovery Trench
Authors J.W. Lane, F.P. Haeni, Susan Soloyanis, Gary Placzek, J.H. Williams, C.D. Johnson, M.L. Buursink, P.K. Joesten and K.D. KnutsonBorehole- and surface-geophysical methods were used to characterize the hydrogeology and the effects of
blast fracturing an in-situ recovery trench in a contaminated fractured-bedrock aquifer. The recovery trench is located
at the former fire-training area of Loring Air Force Base in Aroostook County, Maine. Borehole-geophysical
methods, used in six wells at the site, included video, acoustic televiewer, heat-pulse flowmeter under nonpumping
and low-rate pumping conditions, natural gamma, electromagnetic induction, tluid temperature and conductivity,
caliper, deviation, and borehole radar. Borehole radar was used in a single-hole reflection configuration with
directional and non-directional 60-MHz (megahertz) antennas and in a cross-hole tomography configuration with 22-
MHz antennas. One surface-geophysical method, azimuthal square-array direct-current resistivity, also was used.
Geophysical surveys were conducted before and after blast fracturin, 0 the recovery trench. Integrated
interpretation of the geophysical data collected before blasting indicates that most transmissive fractures are steeply
dipping and are oriented northeast and southwest. Analysis of azimuthal square-array-resistivity data indicates that
the secondary porosity of the fractured-bedrock aquifer is about I percent. The borehole-geophysical data and crosshole
radar tomography data indicate that more fractures are present in the upper 20 to 25 m (meters) of bedrock than
in bedrock below this depth. Interpretation of the geophysical data collected after blast fracturing the recovery trench
indicates that the blast created an intensely fractured zone about 3 m wide, 26 m deep, along the 50-m length of the
recovery trench. Blast-induced porosity in the recovery trench is estimated from the borehole-radar data to be 13.5+ 5
percent at the midpoint of the trench, decreasin, u to 7.3+ 6 percent at the northwestern end. Post-blast effects on the
hydrology of the area adjacent to the recovery trench include (1) a decline in static water levels, (2) order-ofmagnitude
increases in upward flow in two wells, (3) reversal of flow directions in two wells, (4) order-of-magnitude
increases in the estimated transmissivity of three wells, and (5) an estimated increase in aquifer secondary porosity to
2 percent near the trench. The increase in secondary porosity is estimated on the basis of azimuthal square-array
resistivity data collected over the recovery trench and cross-hole tomography collected parallel to but outside the
trench. These effects are consistent with increased porosity and permeability in the blast-fractured recovery trench
and with increased fracture transmissivity near the recovery trench. The increased fracture transmissivity resulted
from an apparent hydraulic cleaning that occurred when water was ejected out of wells near the trench during the
blast.
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Subsurface Utility Engineering: Utility Detection Methods And Applications
More LessThe nation’s infrastructure continues to grow as a result of population growth and the proliferation of new
technologies. New technologies include the replacement of copper communication cables with fiber optics. In
addition, the deterioration and replacement of existing structures have expanded activity in the infrastructure industry.
The “footprint” of new construction often conflicts with existing infrastructure. When this existiug infrastructure is
hidden from view (e.g., buried), it is often discovered in the construction phase of a project. During this phase, the
costs of con&t resolution and the potential for catastrophic damages are the highest.
Existing underground utilities and then related structures constitute a significant portion of this infrastructure. They
create inefficiencies and risks on projects. The majority of these inefIicieucies and risks result from inaccurate,
incomplete, and/or out-of-date information on the existence and location of existing subsurface utilities, In the past,
utilities were rarely a high priority. However, the costs of these risks are becoming high enough that priorities are
changing.
Many surface geophysical methods exist that are useful in identifying and characterizing underground utilities.
Utilities as near surface structures often interfere with the interpretation of data for deeper structures, soils,
contaminants, and so forth. Therefore. in cases such as brown field sites, military bases, etc., it becomes necessary to
first apply appropriate surface methods to identify and characterize the existing utilities so that then influence on
other data can be ascertained. Subsequent mapping and data management accrues other benefits. This practice is
gaining momentum in a field called subsurface utility engineering.
Subsurface Utility Engineering has been a program focus for federal agencies such as the IJSDOT. DOE, NSF,
NTSB and others. Additionally, professional organizations such as AXE and SAME are educating their members
about how the application of surface geophysics can reap benefits in identifying and mapping utilities for engineering
and environmental purposes.
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Sensor Evaluation Study For Use With Towed Arrays For Uxo Site Characterization
Authors J.R. McDonald and Richard RobertsonThe Naval Research Laboratory is developing a Multi-sensor Towed Array Detection System
(MTADS) with support from the DOD Environmental Security Technology Certification Program (ESTCP).
In this effort we seek to extend and refine ordnance detection technology to more efficiently characterize OEW
sites, identifying nonferrous and smaller items, distinguishing ordnance from clutter and analyzing clustered
targets to identify and locate individual targets within complex target fields. Our evaluation shows that these
goals are best met by combining magnetic and electromagnetic sensors. We report on field studies at a prepared
test range of commercial sensors in arrays in various configurations and including; Cesium vapor
magnetometers in single sensor and gradiometric configurations, fluxgate gradiometers, proton procession
magnetometers, and electromagnetic pulsed induction sensors. The advantages and disadvantages of each
technology and their applicability based upon survey requirements is discussed. We also discuss recommended
data densities including horizontal sensor spacings, survey speeds, sensor heights and make recommendations
about the appropriate use of gradiometers and active sensors.
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The Probability Of Magnetic Or Electromagnetic Detection Of A X+-Gallon Drum As A Function Of Line And Station Spacing
By David ButlerA simplified elliptical footprint of a %-gallon drum for electromagnetic and magnetic detection as a function
of depth is defined. The signal-to-noise ratio for field measurements is used to scale this ellipse. For a given
ellipse, the probability of detection at various line and station spacings is calculated.
Representative numbers indicate that with a line spacing equal to the major axis of the ellipse and a station
spacing equal to the minor axis, the probability of detection of a 1:2 (minor:major axis) ellipse by at least one
station is 0.66, but only 0.12 for the recording of two anomalous values.
Compound probability enters the problem if more than one target is present. If location rather than detection
is the goal, more that one anomalous station is required. If the number of stations is proportional to cost,
location or characterization will certainly increase the costs. This paper provides information to disqualify
specifications tendered by procurement departments who often request badly aliased surveys.
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The Combined Use Of Magnetic And Electromagnetic Sensors For Detection And Characterization Of Uxo
Authors Bruce Barrow, Nagi Khadr, Robert DiMarco and Herbert H. NelsonData has been collected on a test field of inert UXO with both a Geometries 822A total field
magnetometer and a Geonics EM61 pulsed, electromagnetic induction sensor. This study
allows comparison of the two instrument’s detection capabilities. While the EM61 as
currently configured is not as sensitive as the 822A in terms of depth of detection, it does
detect objects of interest down to IO-l.5 feet, as well as detecting non-ferrous materials.
While the location, depth, and size of single UXO targets are readily estimated from
magnetic measurements, it is not as clear what can be done with an electromagnetic sensor
that will synergistically add to the capability of the magnetic sensor. Based on laboratory
measurements, electromagnetic sensors may be capable of size estimation based on their
temporal response. For frequency domain instruments such as the EM31, this involves
measuring the phase angle response. For time domain instruments such as the EM61, this
mvolves recording the time decaying response. This size estimation is not affected by
remnant magnetization and also reflects the size of individual objects in a collection of
obiects. Because the spatial response of an electromagnetic sensor involves the relative
geometry of the transmitter, the object, and the receiver, it is expected to be sensitive to
obiect orientation. Measurements made on large elongated UXO in different orientations
confirm this.
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Delineation Of Pipeline River Crossing Using Cable And Pipe Locator With Real-Time Differential Gps
Authors B.S. Waddington and M. MaxwellThe location and depth of cover over pipeline river crossings must be checked periodically to ascertain that
the pipeline remains undisturbed and adequately covered. We have developed a technique to determine
pipeline plan location and depth of cover utilizin, Q a combination of electromagnetic detection and
echosounding with real-time navigation, in this case differential GPS. The technique offers an alternative
to acoustic location methods where small pipe size or the presence of acoustically opaque sediments
prevent pipe detection. In addition, the technique can be used in fast-flowing rivers or in heavy marine
traffic where anchoring is an unlikely option. We have successfully applied the method to locate and
profile a 168 mm steel pipeline crossing under the Fraser River, near Vancouver, Canada.
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Sasw Test In Location Of Buried Objects
Authors Nenad Gucunski, Vahid Ganji and Mohamad H. MaherThe ability to detect underground objects is of significant importance in certain aspects of civil
(geotechnical) and environmental engineering. A number of geophysical techniques have shown excellent
results in location of certain types underground obstacles (anomalies). The Spectral-Analysis-of-Surface-
Waves (SASW) method is a seismic nondestructive technique, that has so far been typically used in the
evaluation of elastic moduli and layer thicknesses of layered systems, like soils and pavements. One of
the assumptions of the test is that the system tested consists of infinite homogeneous layers of a constant
thickness. This assumption is violated whenever heterogeneity of the system exists due presence of buried
objects and cavities, presence of discontinuities, like pavement edges [Sheu et al. (1988)], variation of
layer thicknesses, etc. The problem is of special importance in SASW testing of pavements in an urban
environment, where obstacles like utility conduits, subways, and foundation structures cause wave
reflections that can affect significantly test results.
The effects of anomalies on propagation of elastic waves have been examined by a number of
authors. Cooper and Ballard (1988) reported a distinct travel time increase during refraction surveying in
soil with voids present close to the surface. Belesky and Hardy (1986) report successful implementation
of reflection survey in deep cavity detection, but significant difficulties in identification of shallow
cavities. On the other hand, Haupt (1977), Dravinsky (1983) and Curro (1983) demonstrated numerically
and experimentally that surface waves are sensitive to anomalies close to the surface. Recently Al-Shayea
et al. (1994) demonstrated experimentally that results of the SASW test are affected by underground
objects. They showed that an underground cavity artificially created in a homogeneous sand layer can
cause significant decrease in the phase velocity of the Rayleigh wave in a broad frequency range. Later,
numerical simulations by Gucunski et al. (1996a and 1996b) confirmed findings of Al-Shayea et al.
(1994). The following paragraphs discuss the most important findings on the effects of underground
obstacles on the Rayleigh wave dispersion obtained from the SASW test, and the application of the test
in detection of buried objects.
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Gpr In Forensic And Archeological Work: Hits And Misses
More LessGround-penetrating radar has been used successfully in the location of human
remains, both at archeological sites and in forensic work involving the discovery of I
clandestine graves. Forensic searches have occurred in subsoil burials, as well as burials
under concrete floor slabs. Not all investigations yield buried remains, however, and we
must separate out cases where bodies are not found because none is buried there, and
cases where the radar fails to detect the buried remains.
Witnesses can give faulty or misleading testimony leading to wild gooses chases in
otherwise credible cases. Investigators not familiar with the availability of noninvasive
geophysical search methods may try massive excavations that seriously disturb the
ground surface, and then call in someone to do GPR.
Physico-chemical characteristics of the subsoil can dramatically influence the length
of time skeletal remains persist in the ground, acid, well drained soils will cause loss of
identifiable remains over decades to centuries. At other sites, circulating mineral-rich
groundwater can impregnate the bony remains, yielding a more solid GPR target. Most
New England burials were made in deposits of stratified drift, which is a resistive and
almost ideal GPR medium; on the other hand it is an acid, well drained environment.
Burials using stone crypts (e.g., some 18th and 19th century US burials) will be
easily detected because the stone cover and an underlying air space will provide
dielectric contrasts recognizable on a GPR scan. Articles of clothing may also provide a
good GPR target when a body search is being conducted.
Recent clandestine burials yield near surface conductive anomalies that prevent radar
depth penetration below the body and appear as a signal loss whiteout. Once conductive
body fluids begin diffusing away, the skeleton and clothing articles provide point targets
that can be detected with radar.
Key words: ground-penetrating radar, human remains,
archaeology, forensics.
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Location Of Mohegan Burial Grounds Using Gpr
Authors Roelof Versteeg, Jeffrey Bendremer and John LaneFort Shantok is a national Historic Landmark and one of the most important and sacred historical sites d
the Mohegan Tribe, which recently repossessed the site. While the Mohegan Tribe is strongly interested in
a detailed characterization of the site, there is a strong pi&em for using non invasive tools. One of the
parts of the sites that needed to be characterized was a small cemetery. On this cemetery (where the gmve
markers have been removed and whem no surface indications of the graves remain) a pseudo 3D radar set
was collected. The time slices generated from this dataset give signatures which are strongly suggestive cf
time which can be expected from graves. The results from this data (and from follow up work) will be used
to remark the graves and the cemetery.
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Magnetic Viscosity Of Baked Clays And The Possibility Of Its Use In The Location Of Buried Ceramic Objects
Authors N.O. Kozhevnikov and S.P. NikiforovElectromagnetic (EM) methods have been used in archaeology since about 1960. The
study of soil electrical conductivity plays a significant part in archaeological surveying, as in
the case for any superficial exploration. That is why one of the most useful prospection
instrument still in use today is the inductive soil conductivity meter: surveys can be carried out
almost as fast as the operator can walk, making this among the fastest ground geophysical
methods now available. Metal detectors. which work on a similar principle. are frequently used
to search for ancient metallic objects not yet completely oxidized and to sort out modern cultural
pollution from magnetic anomalies deriving from older sources such as hearths (Wynn, 1986).
I_Jse of Slingram EM systems with carefully designed spatial and frequency parameters
now permits archaeologists to obtain both electrical conductivity and magnetic susceptibility
data at the same time without having to establish physical contact with the ground (Tabbagh, 1986).
As EM techniques were becoming more and more sophisticated, it has been found that
secondary magnetic field is affected not only by conductivity and susceptibility but by magnetic
viscosity of earth’s upper layers as well. C. Colani and M.J. Aitken studying archaeological
sites in England revealed that magnetic viscosity of soil influences substantially EM data
obtained with pulse metal detector ( 1966). The effects of soil magnetic viscosity on transient
electromagnetic methods (TEM) were also observed and reported by Buselli ( 1982). In 1985 the
soil magnetic viscosity has been found to produce TEM anomalies measured at some sites in
Western Pri bai kalje (Vakhromeev and Kozhevni kov, 1988).
Being measured in the time domain magnetic viscosity manifests itself in the slowly
decaying transients (Colani and Aitken, 1966: Buselli, 1982: Vakhromeev and Kozhevnikov,
1988). In frequency domain magnetic viscosity gives rise to the imaginary part of magnetic
susceptibility and to the dependence of its real part on frequency (Tabbagh, 1986:
Kozhevnikov and Snopkov, 1990). In either case the interpretation of EM data without
regard for magnetic viscosity results in soil conductivities too high when compared to actual.
If an object to be investigated is well conductive. magnetic viscosity effects are small as compared
with those produced by eddy currents. However, when studying resistive media magnetic
viscosity effects become dominant.
It has been found that for the most part the magnetic viscosity of soils is caused by
relaxation of superparamagnetic (SPM) particles (Buselli, 1982). Recall that superparamagnetlsm
is a property exhibited by single domain (SD) particles of ferro - and ferrimagnetic materials. In
contrast to large particles which consist of many domains, in the small one a multidomain
structure is impossible and thus the whole particle is a single domain. In SD particles the
response to an applied field is a rotation of the magnetization rather than domain wall
movement (Parkinson. 1983 ).
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Recommendations For A The Creation Of A National Organization Of Geophysicists Dedicated To Providing Assistance To The Law Enforcement Community
By John R. DewInvestigations requiring the location of human remains or underground caches are rare on a state or local level. Crime scenes requiring a search for human remains are complex and especially of great media interest. Because of infrequent need, however, most law enforcement organizations do not maintain a state of readiness enabling them to provide an adequate response to process these crime scenes.
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The Scientist As An Expert Witness
Authors G. Clark Davenport and Miles MadorinThe work environment of a scientist is characterized by orderliness and control. A scientist is
trained to think reflectively and in logical sequences; his or her success as a professional is
measured by the rigor with which he or she follows methodological processes to gather and
evaluate data. But how well do these skills translate to other, less well controlled, work
environments where the scientist may be called upon to provide technical expertise?
One such environment is the courtroom, where a scientist may be called upon to assist the court,
counsel and fact-finder by way of expert testimony or other assistance. In this instance, a scientist
is faced with a work environment characterized by seemingly random events, which follow a
course of Byzantine rules and procedures which defy common sense. Witness questioning does
not allow the luxury of thoughtful consideration, but demands immediate responses and facilitates
spontaneous dialogs. And while science is an objective assessment of data, a trial is an adversary
proceeding, where each side is motivated by subjective considerations. not necessarily in a
collegial fashion.
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Monitoring Of A Controlled Lnapl Spill Using Ground-Penetrating Radar
Authors David L. Campbell, Jeffrey E. Lucius, Karl J. Ellefsen and Maryla Deszcz-PanUsing ground penetrating radar (GPR), we monitored a controlled low-density non-aqueous
phase liquid (LNAPL) gasoline spill at a test facility at Oregon Graduate Institute, near Portland OR. The
results were different from some reported for uncontrolled gasoline spills, in which the gasoline apparently
blurs the contrast in dielectric permittivity that usually exists at the top of the saturated zone (SZ), so that
GPR reflections from the SZ are subdued. Instead, at OGI we saw a SZ reflection almost everywhere, but
this reflection was brighter (higher amplitude) under the spill. The bright spots grew and spread as the spill
progressed. We explain this effect by noting that sand grains above the SZ were quite moist, so that values
of relative dielectric permittivity (RDP) were relatively high there. As the spilled gasoline displaced this
interstitial moisture, RDP values dropped, leading to a GPR high velocity layer and concomitant bright spots.
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Imaging Pvc Gas Pipes Using 3-D Gpr
Authors J. Bradford, M. Ramaswamy and C. PeddyOver the years, many enhancements have been made by the oil and gas industry to improve the quality of seismic
images. The GPR project at GTRI borrows heavily from these technologies in order to produce 3-D GPR images of PVC
gas pipes. As will be demonstrated, improvements in GPR data acquisition, 3-D processing and visualization schemes yield
good images of PVC pipes in the subsurface.
Data have been collected in cooperation with the local gas company and at a test facility in Texas. Surveys were
conducted over both a metal pipe and PVC pipes of diameters ranging from i/z in. to 4 in. at depths from 1 ft to 3 ft in
different soil conditions. The metal pipe produced very good reflections and was used to fine tune and optimize the
processing run stream. It was found that the following steps significantly improve the overall image:
1) Statics for drift and topography compensation
2) Deconvolution
3) Filtering and automatic gain control
4) Migration for focusing and resolution
5) Visualization optimization
The processing flow implemented is relatively straightforward, simple to execute and robust under varying
conditions. Future work will include testing resolution limits, effects of soil conditions, and leak detection.
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Modeling The Gpr Response Of Leaking, Buried Pipes
Authors Michael H. Powers and Gary R. OlhoeftUsing a 2SD, dispersive, full waveform GPR modeling program that generates complete GPR response
profiles in minutes on a Pentium PC, the effects of leaking versus non-leaking buried pipes are examined. The
program accounts for the dispersive, lossy nature of subsurface materials to GPR wave propagation, and accepts
complex functions of dielectric permittivity and magnetic permeability versus frequency through Cole-Cole
parameters fit to laboratory data. Steel and plastic pipes containing a DNAPL chlorinated solvent, an LNAPL
hydrocarbon, and natural gas are modeled in a surrounding medium of wet, moist, and dry sand. Leaking fluids are
found to be more detectable when the sand around the pipes is fully water saturated. The short runtimes of the
modeling program and its execution on a PC make it a useful tool for exploring various subsurface models.
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Recent Improvements In Ground Penetrating Radar Antenna Design
Authors Paul R. Hague and Eugene BogatyrevGeophysical Survey Systems, Inc.(GSSI) has developed several new antenna designs to expand and improve its
subsurface investigation capabilities. These antennas operate in the 16 - 80 MHz range, and at center frequencies of
200 MHz, 400 MHz, 1 GHz and 2 GHz. These new antennas significantly expand the range of available
frequencies with which we can profile the near-subsurface.
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Near Surface Applications Of Borehole Radar
Authors E.W. Gilson, J.D. Redman, J. Pilon and A.P. AnnanBorehole radar (BHR) measurements, collected adjacent to a landfill site, demonstrate the useful
application of this technique in understanding the near surface (upper 30m) hydrogeological conditions.
The stratigraphy consists of relatively uniform ice-contact sand deposits, with the water table at a depth
of 16.5 m. Zero offset gathers provide a simple technique for defining stratigraphy, water content and
contaminate delineation, Multiple offset gathers, before and during a water injection experiment,
demonstrate that velocity tomograms can image water content changes on the order of 0.5 percent.
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Radar Tomography For Cavities Detection
Authors Stefano Valle and Luigi ZanziPreliminary tests on laboratory models have enabled us to provide some guidelines for traveltime ray
tomography with GPR applied to civil engineering problems, specifically to find voids in pillars, walls and
structures. The width of the Fresnel zone and the source and receiver locations are the limits to resolution
capability. For crosshole geometry a criterion to know resolution capability, based on detectable wavenumbers,
is analytically derived.
Acquisition and reconstruction parameters (source and receiver location, operating frequency, measurement
number, acquisition time, slowness grid) are discussed and optimized with tomographic experiments on some
models drilled expressly to produce voids. Tomography is solved by SVD, experimenting both regular and
irregular gridding. An iterative procedure for noise reduction is proposed to improve the solution. A sort of
black and white tomography is also applied to explore the actual limits of straight ray approximation. For
crosshole geometry a wavenumber decomposition of the problem is proposed and the benefits discussed.
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