- Home
- Conferences
- Conference Proceedings
- Conferences
24rd EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 10 Apr 2011 - 14 Apr 2011
- Location: Charleston, USA
- Published: 10 April 2011
1 - 20 of 190 results
-
-
Previous Excavations and Geophysical Discoveries at a Prehistoric Earthwork Site in Western Michigan
Authors Laura Sherrod, Jan Brashler and Donald GaffGeophysical surveying was performed during the summer of 2010 at the South Flats Earthwork Site (20MU2) located in Muskegon County, Michigan. This prehistoric earthwork site is a circular feature of raised earth material located in a present-day young oak forest. the enclosure is approximately 25-30m in diameter, has a width of 4m around the perimeter where the ground relief is altered approximately 0.5m. It is located within the Muskegon State Game Area on a bluff overlooking the Muskegon River. the site was first excavated by the Michigan archaeologist George Quimby in 1937 and has been only moderately disturbed by anthropogenic sources since that time. Recent excavation was performed in 2006 by a team of researchers from Grand Valley State University. This field work clarified the results and aided in the Interpretation of the records kept of the 1937 excavation. Additionally, the recent excavations increased overall knowledge of the role that earthwork structures played in the cultures of the time.
Due to the site location on State-owned land, excavation is restricted. Ground penetrating radar and magnetometer surveys were applied at this site to provide an image of the subsurface and facilitate further development of cultural Interpretations. Soil composition is predominantly sandy making ground penetrating radar a very effective geophysical tool. Previous excavation units and other recent anthropogenic disturbances are clearly visible in the geophysical results. the earthwork structure itself is identifiable through the ground penetrating radar images and several small-scale geophysical features aid in site Interpretation. Results from the surveys provide insight into the prehistoric use of earthworks structures and illustrate the complicated nature of interpreting geophysical surveys at previously excavated sites.
-
-
-
Overview of the Workshop On Monitoring and Failure Detection in Earthen Embankments
Authors Craig Hickey and James SabatierThe Homeland Security Presidential Directive 7 of May 7, 2007, classified dams and levees as one of the 18 critical infrastructure and key resource sectors. these networks of dams and levees are vital to the security, national economic security, public health or safety of the United States. the U.S. National inventory of Dams currently lists more than 80,000 dams in the USA. Preliminary estimates by the National Committee on Levee Safety indicate there may be more than 100,00 miles of levees across the United States. Due to the extent of the embankment system and the high cost of failure, rapid, low-cost, highly reliable inspection and monitoring technologies are needed. A workshop was held at the US Army Corps of Engineers Waterways Experiment Station 9-12 February 2009 to explore the state-of-the-art in inspection and monitoring, identify technologies that might be applied in the near term, and to define a roadmap for research investment. in this presentation we will provide an overview of the results of the workshop. (Workshop sponsored by the US Army Research office and the USDA-ARS.)
-
-
-
A Comprehensive validation of the Skytem System
Authors Esben Auken, Nikolaj Foged, Kurt Sorensen, Anders Vest Christiansen and Max HalkjaerAccuracy and stability of data from airborne electromagnetic systems is an issue addressed in numerous publications and conference presentations. We have recently done a comprehensive and well documented comparison of data from ground based measurements and repeated SkyTEM lines from different altitudes.
the ground based test line was made on the National Danish Test Site and consists in two perpendicular lines each of a length of 1.0 km. On each of these lines 25 soundings with a 40x40 m2 TEM system was made. the TEM system measures the first time gate in 8 micro sec from begin of ramp and was prior to the measurements calibrated at the test site.
Comparing Inversion results form the SkyTEM and the groundbased data shows that the model repeatability of the SkyTEM system is excellent in both the same altitude and in different altitudes. Also, there are no directional problems, i.e. it does not matter in which direction the lines are flown. the agreement to the groundbased reference sections is also very good, showing that the SkyTEM-system yields data of same high quality as the groundbased system.
A validation of the SkyTEM system at the data level was set up to examine the responses gate by gate, which, among other things, rules out the equivalent model issue. the different comparisons in the data space show that the SkyTEM system repeats the test lines equally good in different altitudes, and the agreement to the ground based responses is very good and in general within the data standard deviation of 5%.
the validation serves as a quality assurance of the high-precision modeling of the SkyTEM system, together with the robust processing and Inversion scheme developed for the data. the validation of the SkyTEM system now set the standard for the data quality expected for any airborne system to qualify for the Danish national groundwater mapping effort.
-
-
-
Application of an Artificial Neural Network for Airborne Magnetic Data Discrimination
Authors Jeannie Norton, Les Beard and Jacob SheehanArtificial neural networks (ANN) are computational constructs that attempt to mimic the workings of the human brain with respect to the brain’s ability to detect patterns. ANNs can be trained to determine which class an object belongs to based on selected inputs. the objective of this work was to develop and apply an artificial neural network to discriminate ordnance from non-ordnance based on input derived from airborne magnetic data. A training set was constructed for the ANN from existing data acquired over known items: ordnance, exploded fragments, and non-ordnance. the goal was to be able to predict whether the source of a magnetic anomaly was produced by ordnance. the output classes fell into one of two categories. Either the item of interest was unexploded ordnance (UXO) or it was not unexploded ordnance (non-UXO). This latter category included geology, fragments from exploded ordnance, and non-ordnance items. the low-altitude magnetic data were inverted for source parameters (depth, magnetic moment, and orientation) to generate various parameters that served as input to the ANN. using this training data set, weighting coefficients were computed. the reliability of the ANN was verified and validated using a subset of data with known solutions that were not included in the original training set, and the ANN successfully reduced the number of false positives. in the original assessment of this dataset the analytic signal was to prioritize the anomalies and resulted in a ratio of false positives to true items of 42:75 at 50% target detection and 74:150 at 100% detection. using the ANN on this same dataset the ratio of false positives to true items was improved 5:75 at 50% detection and 68:150 at 100% detection. the use of this ANN will improve the efficiency of the airborne data through enhanced target picking and reduced sampling and excavation costs.
-
-
-
New Generation TDR for Identifying and Characterizing Engineering Properties of Soils
Authors Vincent Drnevich, Majdi Najm and Sochan JungRecent work indicates that Time Domain Reflectometry (TDR), using signatures from currently available probes and equipment can be processed to identify soil type and determine water content and dry density. Several characteristics of the signatures in addition to the apparent dielectric constant and bulk electrical conductivity have been identified to support these determinations. the presentation will identify these characteristics, give the development of the process, and demonstrate their use for a variety of soils and compaction conditions. Implications will be provided for extension of the method to field applications for geotechnical/transportation construction control of soils.
-
-
-
Characterizing Mississippi River Levee Segments using Soils and Geologic Data
Authors Khaled Hasan, James Aanstoos, Majid Mahrooghy, Lalitha Dabbiru and Joseph DunbarApproximately 150 miles of levees in the Lower Mississippi River valley bordering Mississippi, Arkansas and Louisiana are being studied to determine their vulnerability to slough slide failure and sand boil development. the study is designed to use Synthetic Aperture Radar (SAR) imagery from both aerial and satellite platforms as its primary investigative tool. Images have been acquired with NASA’s airborne UAVSAR imaging at L-band and DLR’s satellite borne TerraSAR-X imaging at X-band. Currently multi-faceted analysis of the acquired images is in progress by several of our team members and the results look promising. to aid the image analysis effort we are also looking at the physical processes of slides and sand boil formation which are highly influenced by subsurface movement of water which in turn is controlled by textural properties of the soil and sediments beneath. to characterize levee segments having unique soil and sediment condition with respect to water transmissivity, soil and geologic data have been collected from NRCS-USDA and USACE respectively. GIS analyses of the textural and geomorphic characteristics of these data have allowed classification of the levee into several zones where water transmission properties may make them more susceptible to failure than other areas. in these zones highly sandy soils on the riverside of levee allows water to move to the levee where clay rich soils restrict lateral flow, creating conditions where the water could move upward to weaken the levee segment. A majority of the known slide events occur in these zones, which supports this inference. the spatial distribution of these slide events also suggests that geomorphic features such as ridge and swale and ox-bow lakes tend to have a geographic association with these events. Vegetation patterns indicative of repaired slides derived from TerraSAR-X images also coincide with these zones based on soil criteria.
-
-
-
Restoring a National Treasure: Recovering Airborne Geophysical Data from Antiquated Data Tapes for Geosurv Iraq
Authors David Smith, Benjamin Drenth, Jared Abraham and Janan SaffoThe State Company of Geological Survey and Mining (GEOSURV) is the ministry in Iraq responsible for the development of natural and mineral resources. As part of a Department of Defense initiative by the Task force for Stabilization and Business Operations in Iraq, the U.S. Geological Survey partnered with GEOSURV scientists to modernize GEOSURV’s geophysical capabilities. the objectives of the geophysical component were two-fold: train GEOSURV personnel in the use of state-of-the-art data processing techniques; and recover digital data from a 35-year old tape archive so that GEOSURV can use it to guide their exploration program. This talk focuses on the data recovery effort.
A national aeromagnetic and radiometric survey was flown in 1974 by Compagnie General de Geophysique (CGG). the data were of excellent quality, as evident from the detailed paper contour maps that were originally produced. A comparable survey today would cost millions of dollars. the digital data were stored on 9-track magnetic tapes. Over time, as computing equipment evolved, GEOSURV lost the capability to access the data on the tapes. GEOSURV agreed to convey the tape archive to the USGS for possible data recovery. We worked closely with a company near Denver, Colorado that specializes in reading old magnetic tapes using legacy equipment, in this case a 1970’s vintage Raytheon mainframe computer with original Kennedy tape drives. After a lengthy cleaning and conditioning process, the company managed to read Information from the tapes in the original EBCDIC format. the USGS converted the data to standard ASCII and painstakingly corrected innumerable data errors caused by drop-outs and bit-flips, achieving in the end 99.999 percent recovery. the data were imported into Geosoft Oasis montaj for filtering, gridding, and mapping. the final total field anomaly map is superior to the original magnetic field contour maps, as it reveals structural features not previously detected. GEOSURV can now access the CGG survey data and utilize it to benefit the economic development of Iraq. the money saved by not re-surveying the entire country can be redirected for field Investigations of targets of economic importance.
-
-
-
Detecting Graves in a Lime Marl Environment: A Comparison of Soil Resistivity and Ground Penetrating Radar Methods
Locating unmarked graves is frequently necessary in older cemeteries that have poor or no records. Such is the case for a cemetery located on the fort Hood Army Base. the base is located in central Texas and is home to more than 2,000 archeological sites of varying ages. the goal of our Investigation was to determine if unmarked graves were present at a particular site. the Tools utilized to reach this goal were a soil resistivity meter and a Ground Penetrating Radar (GPR) system. the existing headstones indicate the cemetery was active at least from 1871 through 1964. However, it is suspected that the cemetery was used prior to 1871. Soils at the site consist of thin loam overlying limey clay. the Walnut formation (Cretaceous) crops out at the site and consists of lime marl with layers of fossiliferous limestone. the survey area was approximately sixty meters by fifty meters. Resistivity measurements were made using the Wenner array with an A-spacing of one meter and a transect spacing of two meters. the GPR system utilized a 270 MHz antenna with half meter transect spacing. Resistivity data indentified areas believed to be disturbed, but not at a scale useful for locating specific graves. GPR successfully located eighty-four percent of the marked graves. GPR also identified nine anomalies consistent with graves that were not marked. Data indicates that specific graves are not identifiable in a lime marl environment using soil resistivity alone. the use of GPR greatly enhanced the ability to identify individual graves, both marked and unmarked.
-
-
-
Combining Tomography and Reverse Time Migration for Improved Near Surface Seismic Imaging
Authors Nedra Bonal and Lewis BartelSeismic traveltime Tomography is often used to attain velocity structure images but cannot resolve complex structures due to smoothing requirements in processing. Furthermore, imaging at depth may be restricted due to limited raypath density below a reflecting boundary. Consequently, imaging lateral discontinuities (e.g. steep dips, buried boulders) or beneath seismically reflective boundaries common in near surface environments can be difficult. Additionally, reflected signals of interest are regularly combined with direct arrivals so removing direct arrivals to observe only reflected signals is not possible. Reversed-time migration (RTM) uses the complete wave equation, making it possibly more accurate than the ray approximation Kirchhoff migration algorithm frequently used in Tomography. Furthermore, RTM can process arrivals from multiple waves and steep slopes. Though computationally expensive, multi-core machines commonly used today can process small data sets typical of near surface projects. We present an example of imaging below a seismically reflective boundary using Tomography followed by RTM. Tomography results show reflective layers at 10 and 17 meters below the ground surface. Most P-wave energy is reflected from these layers with little to no energy reflected from the deeper perched aquifer of interest. the Tomography results are used as the starting point for the high-quality velocity model required to produce an accurate image from the RTM method. the resulting RTM image has strong reflectors between 60-70 meters deep, which correspond with expected depth and range of the perched aquifer. Additionally, there appears to be a break in the continuity at a distance of x = 75 meters for depths in excess of 55 meters. This break may be related to the connection of the perched aquifer to the regional groundwater system, which is expected in this area. the case presented shows this two-step approach results in imaging complex structures and deeper depths than Tomography alone.
Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin company, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
-
-
-
Monitoring Tree Roots over Time with GPR
By John ButnorFor over ten years, ground-penetrating radar (GPR) has been used in a variety of applications to detect tree roots, quantify their spatial distribution, and to estimate root diameter and biomass. Most surveys are performed once, offering a point-in-time assessment of root parameters. My own approach has been to link a small destructive sample using soil cores to GPR data collection, allowing direct comparison of target and acquired signal. All collection parameters (range, gain, dielectric, etc.) are held constant, since the data are collected over the course of a day or two, there is minimal temporal variation. for measures spread out over a longer period of time, differences in soil moisture, water usage, and drainage patterns will likely play havoc with root resolution and parameter estimation, making time series comparisons (months to years) problematic unless such environmental “noise” can be accounted for.
to better understand seasonal variation in root detection, several 20 m transects were established in a 25 year-old balsam fir (Abies balsamea) plantation in South Burlington, Vermont. the transects were located on a deep sandy loam and were scanned 20 times with a 1500 MHz antenna between March and November 2010 using identical settings. A reference transect was created by horizontally inserting 8 mm aluminum rods into undisturbed soil at several depths to accurately measure signal velocity and variation with depth. Soil moisture ranged from 7% to 32% creating dielectric values from 6 to 23. After processing to reduce clutter and isolate root biomass, the radargrams were analyzed with image analysis to quantify the area occupied by roots. Preliminary results are encouraging; GPR data (area) under one tree were compared to soil moisture and dielectric values for 20 different days. Though variation in GPR data was large (order of magnitude) over the season, it was exponentially related to both soil moisture (R2 0.48) and soil dielectric (R2 0.81).
-
-
-
Seismic Refraction Shootout: Using Ray-Based Tomographic Inversion
Authors Nedra Bonal and Leiph PrestonRay-based Tomographic Inversion is a common technique used to process first-arrival travel times into structural images of the earth. We propose to use a 3-dimensional ray-based travel-time Tomographic Inversion program to obtain a velocity model from the synthetic data for the Seismic Refraction Shootout session at the SAGEEP 2011 meeting. Our code uses a ray-tracing scheme to calculate travel times for the forward problem and an iterative inverse procedure to find incremental changes in model parameters that optimally fit travel-time residuals (observed minus calculated) subject to model smoothness constraints. We first calculate the ray paths by following the finite-difference (eikonal) travel-time gradient from source to receiver to compute travel time residuals and fill the matrix of partial derivatives. We then solve for perturbations in slowness by conjugate gradient least squares. Due to regularization requirements in Tomographic processing, resolution of the data is important to consider especially for complex structures. Resolution tests (checkerboard tests) will be conducted on the data to aide in the Interpretation of the results of the tomogram. Standard error analysis tests (jackknife tests) will also performed on the Tomography model to obtain error estimates.
Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin company, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
-
-
-
The Development of a 2-Dimensional Microtremor Survey Method Based on Spac Method using Sequential Linear Arrays
Authors Takaho Kita, Koichi Hayashi and Haldun BingolThe demand to quickly and economically obtain S-wave velocity profiles in geotechnical and seismic engineering fields has been increasing recently. in order to satisfy this need, many types of surface wave methods have been developed and have become widespread. It is, however, not easy to find survey methods which rapidly provide cross sections of the shear-wave velocities at depths of greater than about 30m. in order to overcome this limitation, we have developed a new 2-dimensional microtremor survey method based on the SPAC method using sequential linear arrays. We call this survey method “2-Dimensional Linear Array Microtremor Survey (2D-LAMS) Method”. We applied this new method to field surveys and evaluated the results. Consequently, we confirmed that the cross sections of the shear-wave velocities obtained by this new method were consistent with the cross sections obtained by such conventional geophysical survey methods as 2D-MASW, seismic reflection surveys and electrical resistivity surveys. the 2-Dimensional Linear Array Microtremor Survey Method has advantages in terms of the depths of Investigation in comparison with MASW. in addition, this method is less susceptible to ambient noises when compared with the other conventional survey methods.
-
-
-
Nuclear Magnetic Resonance (NMR) Properties of Unconsolidated and Unsorted Materials Under Low-Field and Mid-Field Conditions
Authors Kathryn Martin, Ryan North, Jason McKenna and Yaoguo LiFailing dams and levees experience changes in porosity, permeability, and water content. Surface nuclear magnetic resonance (sNMR) may allow direct and noninvasive detection of water distribution in these dams and levees. in particular, the T2 response is dependent upon such hydrologic parameters as porosity and permeability that in turn affect water content. the properties of sNMR make it a potentially good technique for monitoring dams and levees. However, a better understanding of the NMR response to the subsurface under the conditions associated with leaky dams and levees is required to fully develop this approach. Though NMR measurements are routinely performed on unsaturated materials in the petroleum industry, these measurements are typically used to detect the locations of water or hydrocarbons in well sorted consolidated rock. Also, most laboratory measurements performed to date utilize a magnetic field that is much higher than the earth’s field, which is used for sNMR. Thus, there is a need to characterize the NMR response of materials typically used in dam and levee construction under the low-field condition and variable water saturations. A typical earthen dam is constructed of an impermeable clay core covered with a less impermeable layer of gravel, sand, and clay sized particles. Due to a lack of sorting and the wide distribution of grain sizes these sediments are typically unsaturated. We have carried out a series of laboratory sample measurements using a low-field and a mid-field performed on unsaturated, unsorted, and unconsolidated samples that are analogous to the permeable layer of dams so that we can better understand the sNMR responses under the conditions of a leaky dam. using spherical glass beads we prepared samples of varying porosities and permeabilities. We then performed both T2 and T2* lab measurements on the saturated samples using the low-field lab equipment. We then performed T2 measurements using mid-field laboratory equipment. these measurements were inverted to estimate the T2 time constantdistribution. Parallel to the saturated measurements, we repeated the same set of measurements on the gravity drained samples thereby simulating a naturally occurring condition of partial saturation. in this talk, we will present preliminary results obtained from these measurements.
-
-
-
Assessment of the Cooperative Source Concept for Single Target Classification using EM63 Metal Detector
Authors Alfonso Benavides and Mark E. EverettThe objective is to assess UXO risk reduction capabilities of a new cooperative source concept. the basic requirement is to develop cost-effective technologies to discriminate munitions of various types from the wide range of non-hazardous items buried in the ground. Classification techniques based on diagnostic target attributes such as principal axis polarizabilities have made significant progress in recent years. However significant limitations remain due to the limited Information content on available sensors. Current development of EMI devices is based on adding transmitters or receivers. Our approach makes use of Geonics EM63 metal detector and a cooperative source. Cooperative source is an object of regular shape and known composition that operates synergistically with a conventional EMI transmitter to illuminate a buried target from a wide range of azimuth positions. the method is based on the mutual inductive coupling between the cooperative source and a buried target after both have been illuminated by the transmitter. Data obtained consists of EMI transients as a function of the cooperative source position. Datasets are dimension-reduced by extracting feature vectors based on the moments of the EMI transients. the feature vectors are loaded into an unsupervised statistical classifier, which in our case is based on a merge self—organizing map (MSOM). Upon output, the primary target is classified as either a target—of—interest (toI), warranting further attention, or else an item not of interest (non—toI) requiring no further attention. Preliminary results show that mutual coupling between cooperative source and target is measurable and strongly dependent on the geometry and orientation of the target, resulting in extraordinarily rich dataset. Unsupervised MSOM learning shows feature vectors clustering from which a-posteriori toI classification can be performed.
-
-
-
Geophysical Investigations at a Potential Mass Grave Site in Bethlehem, Pa
Authors Charles Messler, Laura Sherrod and James HigginsDuring the winter of 1918-19 there was an outbreak of Spanish influenza in Bethlehem, PA. the city was based around the steel industry and had seen a large surge in production and therefore population during the First World War. the outbreak is documented to have claimed nearly two hundred lives, although the accuracy of this number has been questioned by some. Those hardest hit were the poor working class. This group of immigrant workers had few or no relatives living in the area, and thus no one available to make funeral arrangements. the task was appointed to the city, or done through the church of the deceased. Records from this time period are incomplete, but there is evidence that suggests a mass burial during the epidemic on South Mountain in Bethlehem. Geophysical surveying (GPR and magnetometer) was performed in the summer of 2010 at St. Michael’s Cemetery located in South Bethlehem, Lehigh County Pennsylvania. the section of the cemetery surveyed is 19m by 13m and located on the south end of the cemetery. the land was used by St. Michael’s Roman Catholic Church from the mid 19th through the early 20th centuries. the area surveyed is of particular interest because of the time period in which it was used. Grave markers show that a large number of burials took place during the Spanish influenza Outbreak of 1918-19. the terrain is sloped and marked by many physical obstructions. Due to vandalism, topography, and vegetation many of the grave markers are broken, shifted, or completely missing. A three dimensional dataset was created to image the subsurface burials.
-
-
-
Monitoring the Spatial and Temporal Evolution of the Self-Potential Field Produced By Pumping in a Fractured Aquifer
Authors Aaron DesRoches and Karl ButlerSelf potential (SP) signals associated with groundwater flow through a fractured aquifer system were continuously monitored on the surface around a pumping well in the hydrogeologically complex Springdale well field, near Sussex, New Brunswick, Canada. the objective was to investigate whether anticipated azimuthal anisotropy in groundwater flow would be reflected in the SP anomaly expected to develop on surface. SP data were measured over a 40 by 70 m area using an irregular array of 34 non-polarizing Pb-PbCl2 electrodes referenced to a remote electrode placed 170 m away. SP data were logged at 3 second intervals using a high input impedance (20 Gohms) datalogger connected to the electrodes through a custom-built 36-channel passive filter box used to attenuate noise at frequencies higher than ~ 1 Hz. the pumping well operated for 300 minutes at a flow rate of 8 L/sec, generating drawdowns of 1.4 m in the pumping well and 1.0 m in a monitoring well 27 m away. SP increased monotonically during pumping with clear anomaly amplitudes ranging from ~ 1 to 8 mV amongst the 34 electrodes. Linear regression of the drawdown in the monitoring well versus SP of an adjacent electrode provides an apparent streaming potential correlation coefficient of -3.36 mV/m used to calculate the approximate drawdown over the field of the SP array. This drawdown approximation assumes a homogeneous and isotropic aquifer. Time-lapse contour maps illustrate the progression and intensification of the SP field over the study area, with signal variations greatest to the northwest through to the southwest; unlike a radially symmetric pattern one would expect in an isotropic, homogeneous aquifer. This study has revealed that SP signals generated during pumping tests have the potential to rapidly identify variations in the self-potential field associated with groundwater flow and aquifer drawdown.
-
-
-
Classification of UXO By Principal Dipole Polarizability
By Karl KapplerData acquired by multiple-transmitter, multiple-receiver time-domain electromagnetic instruments show great potential for determining the geometry and composition of near surface conductive targets. Here is presented analysis of data from one such system; the Berkeley Unexploded-ordnance Discriminator (BUD) system. BUD multi-static data matrices data are succinctly reduced to obtain magnetic dipole polarizability tensors for each time gate. When viewed over all time gates, the projections of the data onto the principal polar axes yield so-called polarizability curves. these curves are especially well suited to discriminating anomalies corresponding to objects of rotational symmetry from those of irregularly shaped objects. the curves have previously been successfully employed as library elements in a pattern recognition scheme aimed at discriminating harmless scrap metal from dangerous intact unexploded ordnance. However, previous polarizability-curve matching methods have only been applied at field sites which are known a priori to be contaminated by a single type of ordnance, and furthermore, the particular ordnance present in the subsurface was known to be large. Thus signal amplitude was a key element in the discrimination process. the work presented here applies feature-based pattern classification techniques to BUD field data where more than 20 categories of object are present, spanning a broad range of sizes. Data from a calibration grid at the Yuma, AZ proving ground are used in a cross validation study to calibrate the pattern recognition method. the resultant method is then applied to the Yuma Blind Test Grid data. Results indicate that when lone UXO are present and SNR is reasonably high, Polarizability Curve Matching successfully discriminates UXO from scrap metal when a broad range of objects are present.
-
-
-
Intergrated Well-Log, VSP, and Surface Seismic Analysis of Near-Surface Glacial Sediments: Red Lodge, Montana
Authors Jingqiu Huang, Robert Stewart, Joe Wong and Carlos MontanaWe conducted a series of geophysical surveys to characterize a glacial bench deposit and underlying strata near Red Lodge, Montana. Well logs and VSP data were acquired in a PVC-cased, 115m deep borehole. the multi-offset VSP was undertaken using surface sources (an accelerated weight drop and sledge hammer) with a hydrophone string and downhole, wall-clamping, 3-component geophone. the well logs included measurements of conductivity, radioactivity (gamma ray), temperature, and sonic velocity. Sonic and VSP velocities range from 1500m/s in the very near surface to 3000m/s at 85m depth. A distinct black clay (with high conductivity, high gamma ray, and low velocity) is penetrated at 85m. High-resolution 2D and 3D seismic surveys, using a sledge hammer source, show a number of reflectors to about 150ms two-way traveltime. An 80ms seismic reflection correlates to the 85m interface (via the composite or L-plot with well log, synthetic seismograms, and VSP processed to a corridor stack). Various other reflections in the VSP and surface seismic data are interpreted to represent glacial deposit layers and water zones (from the perforation logs).
-
-
-
High Resolution Eri Evaluation of injectate used to Remediate a Dry Cleaning Site, Jackson, Tennessee
Authors Todd Halihan, Stuart McDonald and Phil PateyA former dry cleaning site in Jackson, Tennessee has undergone remediation to treat TCE and PCE impacted soil beneath the site. the dry cleaning operation closed in 1977. in 2002, a series of Injections were made at the site including corn syrup, vegetable oils, and Simple Green®. in 2004, approximately 200 cubic yards of soil was excavated and the bottom of the excavation covered with sodium lactate. in 2009, the site was characterized using high resolution electrical resistivity imaging (ERI) and follow up confirmation soil borings that targeted anomalies detected via the geophysical work. the results indicate an extremely conductive (< 1 ohm-m) vadose zone downgradient from the Injection wells, and extremely resistive areas (> 10,000 ohm-m) near the Injection area. Sample data indicate that the electrically resistive zones in the subsurface contain moderate to high concentrations of undegraded dry cleaning compounds, and the electrically conductive areas are believed to represent zones of degradation. Specifically, due to the extreme conductivity values detected, the chemical composition, and the dominant vadose zone location of the conductive zones, these are interpreted as likely areas of biological activity generated by the injected amendments to the site.
-
-
-
MRS Tests in Eastern Canada - Coping with Magnetite Dissemination
From late 1990s to early 2000s several MRS (Magnetic Resonance Sounding) missions in Europe and Southern Africa have shown the appropriateness of the MRS technique for groundwater studies. However MRS tests in Eastern Canada in 2003, did not show significant NMR responses over shallow, saturated, clean sand targets. Upon examination, it was found that disseminated magnetite was likely the cause of high magnetic gradients at the scale of water containing pores. This was later confirmed at the Rice U. NMR lab (Hirasaki, personal communication 2004).
the 2003 tests were documented in a paper with a recommendation to focus on T2 rather than T2*. Thanks to IRD, a spin echo mode of MRS survey was implemented on a light version MRS tool: NUMISLITE. This implementation was field tested in August 2008 over most of the sites tested in 2003. Field NMR spin echo responses were observed over these sites. All the tested sites represented shallow aquifers.
in the mean time numerical modeling of the field-scale spin echo mode was developed at IRD, Grenoble, France.
in a subsequent MRS mission - summer 2010 - a full power MRS tool (NUMISPLUS) was used to demonstrate that no spurious surface effects were observed during the 2008 tests. Sites in the same geological environment, with magnetite dissemination, were systematically investigated with aquifers at least 10 m below surface. Also a key site made in 2008 was repeated to insure instrumental integrity of the procedure. Clear NMR spin echo responses were observed at all the tested sites.
As a side issue, field data acquisition was also modified to allow acquiring MRS data at locations where the Larmor frequency is an harmonic of the local power line frequency.
All in all, the MRS technique is gradually improving toward a maturity status.
-