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20th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 01 Apr 2007 - 05 Apr 2007
- Location: Denver, Colorado, USA
- Published: 01 April 2007
1 - 50 of 164 results
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Post-Tsunami Helicopter-Borne Electromagnetics Along The Coasts Of Aceh, Indonesia
Authors B. Siemon, A. Steuer, U. Meyer and H.J. RehliAfter the earthquake and the tsunamievent on December 26, 2004, the Indonesian and German governments decided to set up a project that was dedicated to reinstall the public life of the people in the coastal region of Aceh Province, Indonesia. As the tsunami waves caused large scale coastal saltwater intrusions and destroyed thousands of shallow drinking water wells, the focal point was the water assessment in coastal areas of Aceh about nine months after the tsunami. The target areas are: Banda Aceh / Aceh Besar, the west coast between the towns of Calang (Aceh Jaya) and Meulaboh (Aceh Barat), and Sigli on the northeast coast. A helicopterborne survey including fivefrequency electromagnetics (HEM), magnetics and gammaray
spectrometry was conducted by the BGR airborne group from August to October 2005. The northernmost survey area, Banda Aceh / Aceh Besar, comprises a 20 km by 50 km wide area that was surveyed within four weeks. The HEM survey revealed coastal saltwater occurrences caused by the tsunami, deep saltwater occurrences up to several kilometres inland, and several potential freshwater occurrences. Several requests for information on the geological/hydrogeological situation at sites for planned water wells were successfully evaluated.
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Case Study Of A Rapid Response Underwater Search For A Tow Missile
More LessIn Mid July 2006 the USAESCH began searching for a prototype TOW missile using underwater EM61 and magnetometer sensors. The missile was lost in Indian Creek, on Redstone Arsenal in Alabama, and its flight motor was needed to analyze telemetry data. More than three weeks of searching with analog detectors proved fruitless. Believing digital mapping techniques would be easy, we quickly learned that variable current, confined operating areas and bottom obstructions will wreak havoc on the best of plans. Even anomaly marking and recovery proved a challenge in current and zero visibility. Urgency required rapid prototyping of a submersible housing for the EM61 sensor and our initial design placed the coil 0.3m below the water surface while allowing survey speeds of up to three knots. Four conventional missiles and assorted debris were detected using this configuration in shallow waters. In deeper areas we ballasted the housing for bottom-towing but repeated entanglement in sunken trees necessitated a new approach. A dual-sensor magnetometer array was towed at a constant depth of one meter in waters up to 3.5 meters deep and anomalies as small as one-gallon welding rod containers were found. The prototype missile was recovered in early August.
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Integrated Geophysical Investigation For The Vulnerability Assessment Of Earthen Levee
More LessIntegrated geophysical investigation was undertaken to assess the vulnerability of earthen levees to flooding and earthquake. The tested geophysical methods involved multi-channel surface wave dispersion measurement (MASW), capacitively coupled (CC) resistivity measurement, multi-frequency electromagnetic (EM) survey, and high-resolution seismic reflection survey using S-wave type Land Streamer. Because these methods required no fixing of sensors on the levee surface, high performance on field measurement work could be accomplished. The CC resistivity as well as EM survey successfully reconstructed resistivity profiles along levees, and delineated anomalously high or low resistivity zones within or beneath the levee body. The MASW method mapped shear wave velocity structures along levees, and clearly imaged relatively high or low velocity zones in the levee body. High-resolution seismic reflection surveying delineated the layered structure in the levee and in the underlying foundation sediments. Integrated investigations of resistivity and shear wave velocity structure remarkably highlighted the potentially permeable zones in the levee body as high resistivities and intermediate to low S-wave velocity areas. As a result, the geophysical methods effectively delineated the unexpectedly heterogeneous structure in the body of the levee, and the comprehensive investigation approach is shown to be helpful for the vulnerability assessment of levees through interpreting geophysical anomaly identified by means of integrated surveying.
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Analysis Of Naturally Occurring False Alarms At A Uxo Test Site On Jefferson Proving Ground
More LessThe detection and discrimination of UXO can be limited by small scale geologic anomalies that exhibit similar responses, both in spatial extent and amplitude, to real ordnance. These anomalies are referred to as naturally occurring false alarms (NOFA). During the Jefferson Proving Ground 4 (JPG4) demonstrations in 1996, a number of NOFA were identified in total field magnetic data with one being quite large. To explain the causes of these NOFA, in-situ magnetic susceptibility measurements were made over the anomalies as well as the collection of soil samples up to a meter deep. The soil samples have been analyzed for mineralogy and the magnetic susceptibility, as well as frequency dependence of susceptibility, have been measured in the laboratory. A number of the NOFA also exhibited reversed polarity which would mean that they probably quite shallow anomalies. A number of these NOFA have been modeled to determine their remnance. The results of all of these analyses lead to the conclusion that the large magnetic anomaly is due to mineral transport and deposition along two converging ephemeral streams.
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Electromagnetic Induction (Emi) Coil Sensitivity Maps For Evaluating Coil Designs And Configurations Used In The Geophysical Detection Of Unexploded Ordnance (Uxo)
Authors Neha Jain, Dr. Lloyd S. Riggs and Bob SelfridgeThis paper summarizes efforts to develop and test a software tool for evaluating electromagnetic transmitter coil designs and configurations used in the geophysical detection of unexploded ordnance (UXO). In particular, we are interested in evaluating the detection and discrimination potential of Wide-Area Transmitter and Multi-Transmitter (WAT-MT) sensor systems. The effort is directed toward developing a better understanding of the capabilities and limitations of WAT-MT sensor systems. A Matlab computer code has been developed that maps sensor response to a standardized infinitesimal object in a static field. These plots take in full account of both the transmitter and receiver coil shapes with no explicit consideration of target characteristics. The software allows the user to obtain sensitivity as well as streamline plots. Streamline plots are preferred over sensitivity plots when one is interested in visualizing the direction of the magnetic field due to the transmitter and/or receiver coil. A combination of streamline and sensitivity plots provides good insights into the overall capabilities of a particular coil configuration and also allows one to objectively compare competing designs. Measurements with the Geonics Ltd EM-61 and EM-63 will be compared with sensitivity plots in order to validate the WAT-MT software tool.
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Emi Detection And Discrimination Of Uxo Using An Array Of Fluxgate Magnetic Sensors
Authors Michael W. Asten and Andrew C. DuncanWhile existing technologies have proved successful in establishing the location of metal objects and scrap, additional measurements are required in order to discriminate shape and size of targets. The advantages of a fluxgate magnetometer as the sensor in EMI metal detection are established in a series of observed profiles over dummy UXOs, and a related set of modeling studies. A series of model studies was conducted to establish what improvement in target orientation information could be achieved with single or multiple vector fluxgate sensors compared with commercial conventional single-component single-sensor systems. The model studies use a novel fast approximation for a permeable prism which is capable of modeling the non-linear or frequencydependent magnetic properties of steel objects. The model studies show that when the target size is known, the use of a single vector sensor delivers an order of magnitude greater accuracy in location in 3D space and orientation of the target, compared with the use of vertical-component only data in conventional metal detectors. When the target size is unknown, a single vector sensor can produce accurate location, but is likely to produce unstable orientation estimates. We conclude that an array of receiver sensors is preferable. Comparison of a single vector sensor versus an array of three vector sensors in model studies shows that the array of three vector sensors has the advantage of delivering accurate and stable estimates of both location and orientation of the target, even when target dimensions are unknown.
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Berkeley Uxo Discriminator (Bud)
Authors Erika Gasperikova, J. Torquil Smith, H. Frank Morrison and Alex BeckerThe Berkeley UXO Discriminator (BUD) is an optimally designed active electromagnetic system that not only detects but also characterizes UXO. The system incorporates three orthogonal transmitters and eight pairs of differenced receivers. It has two modes of operation: (1) search mode, in which BUD moves along a profile and exclusively detects targets in its vicinity, providing target depth and horizontal location, and (2) discrimination mode, in which BUD, stationary above a target, from a single position, determines three discriminating polarizability responses together with the object location and orientation. The performance of the system is governed by a target size-depth curve. Maximum detection depth is 1.5 m. While UXO objects have a single major polarizability coincident with the long axis of the object and two equal transverse polarizabilities, scrap metal has three different principal polarizabilities. Our results clearly show that there are very clear distinctions between symmetric intact UXO and irregular scrap metal, and that BUD can resolve the intrinsic polarizabilities of the target. The field survey at the Yuma Proving Ground in Arizona showed excellent results within the predicted sizedepth range.
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Applications Of A Robotic Multi-Sensor Uxo Detection Platform
More LessTo reduce the cost of site characterization and cleanup, it is critical to implement new technologies capable of improved detection and discrimination of Unexploded Ordnance (UXO). Digital geophysical mapping and improved physics-based discrimination have led to reduced false alarm rates. Despite these improvements, current UXO technologies still have difficulty finding small UXO that are approximately the same size as most clutter objects, and challenges remain in adequately discriminating objects during a single detection/discrimination pass. In this study, we present the results of testing a multi-sensor Electromagnetic Induction (EMI) and Ground Penetrating Radar (GPR) array system originally developed for landmine detection. Our current advanced ordnance detection system integrates sensor arrays, highly accurate global and local positioning, and on-board target detection/classification software on the front loader of a semi-autonomous robotic platform. We focus on the analysis of features from two-dimensional EMI array data collected in a controlled test pit as well as multi-sensor EMI and GPR data collected during field tests on a range. High resolution steppedfrequency synthetic aperture GPR data yield images of small UXO and supporting information for discrimination against small clutter objects. Experiments with new EMI coil configurations and timedomain processing indicate potential for enhanced discrimination.
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Trend Removal And Detection Of Overlapping Magnetic Field Anomalies By Wavelet Analysis
Total magnetic field data measured for geophysical exploration purposes comprise the superposition of the effects of all underground magnetic sources. Usually the targets in magnetic
exploration are small, shallow buried bodies, and their magnetic field is superimposed on the regional field that arises from larger and/or deeper source or sources located further away. Sometimes inaccurately removed core fields or large scale topographic features also give rise to regional components. The regional field is generally smooth, adding a trend to the data. The estimation and subtraction of this trend field yields the residual field that corresponds to the target sources. Evidently, the reliability of the interpretation of the residual field depends on the correct estimation of the regional field. In this work the regional-residual separation in the wavelet domain is performed with the aid of the discrete wavelet transformation (DWT) realized with the use of compactly supported wavelets (Daubechies, 1990) with two or three vanishing moments. These wavelets are orthogonal to first or second order polynomials. This means essentially that the regional field (usually represented by a first or second order polynomial) is invisible to the wavelets and thus the regional field is almost entirely hidden in the coefficients of the coarser level of the wavelet transformation. However, in the realization of the DWT as decimated and periodized, the periodic assumption produces some non-zero contribution in a few detail coefficients. Therefore the suppression of all detail coefficients degrades the calculated regional field. To avoid such a distortion we can process a relatively large symmetrical extension of the
data sequence from both sides. Alternatively, we can use an internal model for the polynomial field that controls the separation. Because of the spectral overlap, the approximation of the regional field contains some of the energy of the residual field. We can tackle this problem by analyzing the reconstructed approximation of the regional field in a proper new wavelet basis (with the same number of vanishing moments) and repeating the separation procedure. The choice of the model is empirical; thus it depends on the interpreter’s experience. The wavelet that concentrates the energy of the regional field in the low-resolution coefficients and spreads the energy of the residual field in the high-resolution coefficients gives best results. A good choice of
wavelet pairs for the first order model is the Db4 and the triangular biorthogonal wavelet. For the second order model, the combination of the Db6 and Villasenor2 wavelets gives a very good separation. The proposed method preserves the signal’s features and has the ability to detect the possible local variations of the regional field. The same method can be used for the detection of overlapping magnetic field anomalies. Although the method may have application in more general settings we are mostly focused on archaeological geophysics, a fact that limits the kind of regional-residual problems which occur in certain ways.
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Ground-Penetrating Radar For Urban Archaeological Mapping
More LessUrban settings, which are one of the most challenging areas for archaeological near-surface geophysical mapping, can benefit from the use of ground-penetrating radar. The GPR method has the ability to focus energy downward and therefore can potentially map buried features within the clutter of pipes, trenches and other typical urban materials. In addition, GPR can map buried stratigraphy in three-dimensions, which allows stratigraphic analysis of buried deposits. When amplitude slice-maps are produced in various horizontal levels in the ground they can show changes in land usage by building period, making GPR maps analogous to excavation levels over many depths used in traditional archaeological excavations.
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Geophysical Investigation To Locate Buried Structures At The Site Of An 18Th Century House
Authors Jutta Hager, Joshua King and Robert A.S. BullerIn 2005 Hager GeoScience, Inc. (HGI) conducted a geophysical investigation at the site of a 1703 house outside Boston, Massachusetts. The structure, one of the oldest surviving First Period
houses in the United States, is located on a ¾-acre former colonial farm property that reportedly included several outbuildings, including at least one timber-framed barn. HGI performed the
investigation using a GSSI GEM-300 multifrequency terrain conductivity profiler and SIR-3000 GPR system with 400-MHz antenna. The survey located a primary target near the reported location of a former timber-framed barn, as well as a less well-defined target elsewhere on the site. Excavation of the primary target revealed an unmortared fieldstone foundation wall and a trash pit extending from just below the ground surface to the cemented till floor of the structure. The less well-defined target proved to be a natural feature consisting of bouldery till beneath outwash sands and gravels.
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Summary Of New Developments In Tdr For Soils
Authors Vincent P. Drnevich and Robert L. NowackTime Domain Reflectometry (TDR) is a method to determine the electromagnetic properties of soils and recent research indicates that TDR is an increasingly powerful tool to assess the engineering properties of soils. There were symposia and workshops on this topic held in 1994 and 2001 at Northwestern University and one in September 2006 at Purdue University. The authors were among the organizers of TDR 2006: 3rd International Symposium and Workshop on Time Domain Reflectometry for Innovative Soils Applications (TDR 2006) at Purdue University on September 17-20, 2006. There were five keynote presentations and thirty-five paper presentations with much discussion among the more than 70 researchers and practitioners from agricultural engineering, agronomy, electrical engineering, geotechnical engineering, soil science, and soil physics. The five themes were: 1) TDR Calibration in Challenging Media, 2) Geotechnical Applications of TDR, 3) Innovations, Challenges, and Future Opportunities, 4) TDR Probe Design and Selection, and 5) Hydrologic Applications of TDR. Papers to TDR 2006 are available free of charge on line at https://engineering.purdue.edu/TDR. This paper presents highlights of some interesting papers to TDR 2006. Items to be discussed include: effects of geometrical and interfacial factors on effective permittivity, improved methods for volumetric water contents for pavement bases and subgrades, cone penetrometers to measure permittivity and conductivity, a new TDR source signal that is non dispersive, and soil texture characterization from TDR waveforms. Unfortunately only a few of the many excellent papers could be highlighted. The paper concludes with a quotation from the presentation of G. Clarke Topp, the acknowledged father of modern TDR for soil moisture measurement.
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Geophysical Location, Identification, And Characterization Of Archaeological Structures Of The Jornada Mogollon People At The Three Rivers National Petroglyph, New Mexico
Authors Jaime O. Hincapié and Diane I. DoserWe present preliminary results of an ongoing study regarding the application of shallow geophysical methods to archeological sites using a unique combination of geophysical techniques. This approach adds precision, greater spatial resolution, and time efficiency. In 1976 a group of archaeologists discovered and reconstructed prehistoric structures at the Three Rivers National Petroglyph Site, New Mexico. The area is covered by dense vegetation and, moreover, it is often occupied by cattle and tunnel-digging, den-building mammals, which destroy both surface and subsurface features that could indicate centers of past human activity. The 1976 excavations successfully made use of magnetometry to help locate structures of interest. In the 30 years that
followed no further geophysical investigations were conducted, although periodic mapping of surface features and excavations continued. Between December 2005 and December 2006, a new set of geophysical campaigns were carried out at the site, in order to locate new structures. The surveys included ground conductivity, magnetometry (including gradiometry), and ground penetrating radar (GPR). We first used conductivity and magnetic gradiometry to delineate anomalies that could represent structures, followed by GPR. As of October 2006, three areas have been targeted as suspicious, and one of them represents an adobe structure that is currently being excavated. Further reconnaissance studies were carried out throughout December 2006.
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Gpr Survey Of The Japanese Imperial Family Tombs In Miyazaki: Application Of Gpr Overlay Analysis
Authors Dean Goodman, Hongo Hiromichi, Noriaki Higashi and Yasushi NishimuraA method is developed to create comprehensive 2D images of subsurface structures which are not level buried in the ground. The method, referred to as overlay analysis, uses desired portions of a complete time slice dataset where the relative-strongestreflectors are synthesized into single 2D images. The method is advantageous over simple thick slices since individual time slice components can be weighted independently in the compositing process. Successful implementation of overlay analysis is shown for the discovery of a destroyed 5th century burial moats surrounding the Japanese Imperial Family Burial Tombs in Kyushu.
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Grade Estimation At Cvrd Inco’S Canadian Sulphide Mines
Authors Glenn M. McDowell, Andrew D. Mackie and Mark PalkovitsThe paper provides an overview of grade estimation at CVRD Inco Limited’s (CVRD Inco) Canadian sulphide mines. The main Ni grade estimation technique used is blasthole conductivity. This
technique is applicable in zones where the sulphide is sufficiently well connected to provide eddy current responses in inductive conductivity probes. In zones where the sulphide content is low (less than 25-30%) and the degree of sulphide connectivity is insufficient to cause reliable eddy current responses in inductive conductivity probes, magnetic susceptibility is being employed to enhance Ni grade estimation. In these zones, magnetic susceptibility complements conductivity-based grade estimation
because of the monoclinic or magnetic pyrrhotite content of the sulphide. Additional techniques being investigated for grade estimation and discrimination between chalcopyrite-rich and pyrrhotite-rich mineralization include resistivity, natural gamma and density. The paper concludes with a summary of the nuclear-based PGNA (Prompt Gamma Neutron Activation) technique. This is a more direct grade determination technique that employs a neutron generator and gamma detectors. The resulting gamma ray spectra contain information about elemental concentrations including Ni, Cu, Co, Fe, S, Si, Ca, Al, etc.
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Groundwater And Environmental Applications Of Advanced Geophysical Logging Tools: Geochemical And Magnetic Resonance Tool Reviews
Authors Ned Clayton and Wendy WempeHigh-quality data and highly-skilled technical analysis are the keys to good decision-making about groundwater resource management and environmental site assessment issues. Typical water well geophysical logs are used qualitatively in the groundwater industry to identify potential changes in lithology and/or water quality. Advanced logging technologies, on the other hand, are used quantitatively to constrain aquifer properties, define aquifer heterogeneity, and determine water quality, leading to improved aquifer characterization, more accurate flow modeling, and more reliable fluid transport modeling. Two advanced logging technologies are particularly valuable to the groundwater and environmental industries: (1) electronic pulsed neutron geochemical logs and (2) nuclear magnetic resonance logs. This paper introduces the physical principles of these two advanced logging technologies and their respective applications.
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Borehole Logging As An Aid In The Design Of A Subsurface Pump Station
Authors Mario Carnevale and Jutta HagerThe Combined Sewer Overflow (CSO) Project in Providence, RI consists of a 16,000-foot-long TBM rock tunnel connecting to an 117x61x68-foot pump cavern 300 feet in the sedimentary rocks of the Providence Formation. An important consideration related to the pump cavern construction was the presence and potential angle of intersection of the pump cavern ceiling and/or walls with a highly deformed and friable graphitic shale unit, since this could have major impacts on worker safety and, therefore, the amount of structural support required. To gain a better understanding of bedrock conditions and discontinuities at the pump cavern location, the Project drilled and cored two deep rock boreholes for acoustic televiewer and caliper logging.
Data from the borehole logging were correlated with core descriptions in order to characterize the orientations and stratigraphic positions of discontinuities in the proposed pump cavern ocation. Based on the results of these analyses, the pump cavern was moved from its original proposed location.
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Cross-Borehole Flow Tests And Insights Into Hydraulic Connections In Fractured Mudstone And Sandstone
More LessCross-borehole flow tests provided insights into hydraulic connections in fractured and dipping mudstone and sandstone that were consistent with the lithostratigraphic and structural framework of a VOC-contaminated bedrock research site in west-central New Jersey. Two cross-borehole flow tests were completed. Each test involved measurement and analysis of transient flow in a newly installed deep corehole with a long open interval during short-term pumping and recovery in an adjacent shallow well with a short open interval. The cross-borehole flow test in the mudstone identified a hydraulic connection through a dipping fractured bed between the pumped interval in the well and a flow zone at an intermediate depth in the corehole. The presence of a hydraulic connection between the pumped well and the corehole was not obvious because the water-level response in the corehole was dominated by a shallow zone of high transmissivity, which was hydraulically isolated from the pumped interval. In the sandstone, the cross-borehole flow test identified a hydraulic connection along dipping fractured beds as well as a connection to a deep high-angle fracture that cuts across bedding. These results suggest that application of cross-borehole flow tests at other contaminated fractured-bedrock sites could provide insights into hydraulic connections useful the design and implementation of monitoring and remediation programs.
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Systematic Errors In Resistivity Measurement Systems
Authors Douglas La Brecque, William Daily and Paula AdkinsThe greatest obstacles in achieving higher resolution of electrical resistivity tomography (ERT) data are systematic errors that result from the non-ideal nature of measurement systems or
procedures. Systematic errors are correlated to the system functions and cannot be removed by data averaging. This paper discusses a number of sources of systematic errors including:
Errors in the system gains or calibration of voltage and current monitors, Leakage and coupling in multiplexers, cables and wires, and Electrode aging and impedance effects. Of particular concern are leakage currents within the types of cable used on sites in the past. These errors were found to be larger than expected. It is also important to investigate errors related to the electrodes used in ERT in part since errors such as the cable leakage depend partly on electrode impedance and in part as errors arise from the electrode themselves. There is no simple, clear relation between electrode errors and such factors as material type, history of use, and waveform time/frequency. Preliminary results indicated that the best electrodes were copper-copper sulfate even when they are used as both transmitters and receivers. The best, simple metal electrodes were welding steel.
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Efficient 2.5D Resistivity Modelling Using A Quadtree Discretization
Authors Robert A. Eso and Douglas W. OldenburgWe explore methods for improving the numerical efficiency to solutions of the 2.5D resistivity forward problem. By employing a quadtree structured mesh discretization, fewer model cells are
required in the solution and the volume of interest is easily extended so that zero-flux boundary conditions are satisfied. When these alterations are combined with matrix factorization methods we generate a computationally expedient solution to the 2.5D DC resistivity forward problem. A fast and accurate forward modelling forms the foundation of an inversion. Here we illustrate this by carrying out an inversion on a simulated data set.
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Enhancing Model Reliability From Tem Data Utilizing Various Multiple Data Strategies
Authors Ruizhong Jia and R.W. GroomOver fifteen years, we have developed and utilized forward and inversion techniques to interpret electromagnetic data collected with various commercial systems. A wide range of survey configurations have been utilized including in-loop and outside-loop measurements with both moving and fixed source configurations and with arbitrary location and orientation of receivers. A variety of different inversion strategies have been developed based on either overdetermined or underdetermined approaches utilizing approaches similar to those that other researchers have adopted. These algorithms have been used extensively in a range of applications including mining exploration and groundwater applications. This experience leads us to the belief that a more comprehensive approach must be taken to ensure reliable results. We have developed inversion algorthms that simultaneously incorporate data from both multiple data components or multiple data locations. Incorporating various data into an inversion process provides better signal-to-noise ratios within the inversion. Applying the inversion on carefully selected data that contain information about different geological structures may enhance the resolution of the inverted models and result in more meaningful models. In this paper, we begin by performing an underdetermined Occam inversion on synthetic data simulated with the configurations where the receiver is inside a transmitter loop (in-loop) or outside a transmitter loop (outside-loop). The inversion technique essentially generates smooth models that fit the data within a prescribed tolerance. We built synthetic layered earth models to generate impulse responses plus Gaussian noise upon which we ran inversion. Specifically, we built the first layered earth model by inserting a conducting layer into a relatively resistive host medium. Our inversion results of this model show that the inversion on either the in-loop data or the outside-loop data can resolve the conducting layer. Further, a joint inversion of both the in-loop and the outside-loop data leads to an
improved inversion model. Our second synthetic layered earth model was built by adding a thin conducting overburden to the first model. In this case, our inversion results show that the in-loop data may resolve the top overburden layer better than the outside-loop data. However, the inversion on the inloop data did not resolve the basement, that is, the lower half-space. Moreover, the application of inversion on the outside-loop data may detect the lower half-space, and a joint inversion of both the inloop and the outside-loop data gives rise to an overall improved model with enhanced resolution of both shallower and deeper layers. In short, we utilized synthetic examples to demonstrate that the inversion on the in-loop data tend to resolve the top layers better than the inversion on the outside-loop data while the outside-loop data may see the deeper structures better than the in-loop data, and inverting both the in-loop and the outside-loop data simultaneously may lead to layered earth models of enhanced resolution. We also performed a overdetermined least-squares inversion on a ground data set with a large loop from the Hornby Bay basin in western Nunavut of Canada.
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An Examination Of Frequency Domain And Time Domain Hem Systems For Defining Spatial Processes Of Salinisation Across Ecologically Important Floodplain Areas: Lower Murray River, South Australia
Authors A. Fitzpatrick, T.J. Munday, V. Berens and K. CahillFloodplains play an important role in catchment hydrology, representing a zone in which groundwater is shallow, and groundwater - atmosphere interactions through evapotranspiration (ET) are more pronounced. Spatial patterns in evapotranspiration develop due to the variable distribution and type of floodplain sediments, patterns of vegetation type, floodplain elevation and geometry. Where groundwater is saline, as in the lower River Murray in South Australia, evapotranspiration concentrates salt and can lead to floodplain salinisation, vegetation dieback or health decline. Modelling these systems can assist our understanding of which areas of vegetation are at high risk from salinisation in order to target them for management. However, models of this scale require detailed data for parameter population and validation. Geophysical, particularly electrical, methods have the potential to provide detailed spatio-temporal information on the distribution of salinity in soils and groundwater, thereby assisting our understanding of floodplain processes that characterise the lower River Murray, in South Australia. In this paper we review this potential, and examine the relative merits of high resolution airborne electromagnetic technologies, and consider the relative performance of the RESOLVE frequency domain helicopter EM (FDHEM) and the SkyTEM time domain helicopter EM (TDHEM) systems for defining variations in near surface conductivity and sediment salt load across the Bookpurnong Floodplain. Results from coincident surveys are reviewed as are strategies for the inversion of these data. Data are examined against available borehole information including sediment chloride content and groundwater conductivity.
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A New Radiomagnetotelluric Device For Environmental Geophysics Operating In The Frequency Range From 10 Khz – 1 Mhz
Authors Bülent Tezkan and Alexander SaraevRadiomagnetotelluric (RMT) is one of the newest and innovative methods of applied geophysics. Military and civilian radio stations broadcasting in the frequency range between 10 kHz and 1 MHz are used as transmitters. Information about the conductivity distribution of the earth can be derived from 1 m to 100 m downwards. A new RMT device was developed which can record time series of electric and magnetic fields in a wide frequency range of 10 kHz to 1 MHz. Transfer functions were determined by spectral analysis using a newly developed processing software. The observed transfer functions in the field are the first ones worldwide in a frequency range above 300 kHz and lead to a better resolution of the shallow structure. RMT measurements were carried out in Ukraine using the new device. The main aim of this field survey is the mapping of kerosene contamination close to a military area. RMT transfer functions and their interpretation by 2D inversion calculations will be demonstrated.
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Soil Texture From Tdr Waveform Analysis
Authors Carlos E. Zambrano, Vincent P. Drnevich, Xiong Yu and Robert NowackThe dispersive electromagnetic (EM) behavior of soils is strongly related to the mineralogy, soil structure, and pore fluid characteristics. However, time domain reflectometry (TDR) measurements (TDR waveforms) are predominantly used for soil water content and dry density estimation. These two parameters are calculated based on empirical equations that relate them to the soil dielectric permittivity (Ka) and the bulk electric conductivity (ECb). Ka and ECb are obtained in the time domain from few data points of the TDR waveform, disregarding most of the acquired data (usually 2048 data points) that reflects the EM response of the material over a broad frequency range. The complexity of the soil-water interaction in the presence of a time-varying EM field, and the presence of a non-transverse propagation mode in the TDR system limit the characterization of soils by dielectric spectroscopy. This paper presents a semi-empirical method for soil texture identification based on an integrated numerical and experimental analysis of the effect of the EM soil dispersive behavior on TDR waveforms. Evaluation of TDR tests conducted at 20°C on sands, silts, and clays using tap water at different water contents and dry densities shows that a simple time-domain signal processing of the first reflection from the probe section captures the effects of the EM soil-water interaction. Considering that the coefficients of the TDR empirical equations for soil water content and dry density estimation are
soil-type dependent, the developed method allows self-calibrating the TDR system. The result of this work provides the basis for making the TDR technique a tool not only for water content and dry density estimation, but also for soil characterization.
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Mapping Fracture Zones In The Dry Creek Experimental Watershed Using Seasonal Time Lapse Ert Measurements
Authors Troy R. Brosten, Carlyle R. Miller, Partha S. Routh and James P. McNamaraFour temporal electrical resistivity tomography (ERT) surveys were conducted within Dry Creek Basin, Idaho, to refine hydrologic models of the catchment that describes subsurface architecture. The repeatability of the data acquired during two dry conditions (October 2005 and July 2006) and two wet conditions (December 2005 and April 2006) support an investigation of time lapse change of the electrical conductivity and its relation to hydrologic conditions. Inversion of the ERT measurements illustrate conductive anomalies within the transverse profiles (perpendicular to the stream) and are likely caused by pore fluid in fracture zones within the Idaho Batholith aquifer region. These anomalies are more localized in the profile collected und er dry conditions (July and October) compared to the profiles gathered during water-saturated conditions (December and April). The conductive anomalies in December and April are attributed to increased water input into the geohydrological system through precipitation that dilutes the local conductive minerals within the fracture zones. A persistently conductive fracture zone on the south facing slope explains an unknown water pathway evident in previously developed hydrologic groundwater models.
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Use Of Two-Dimensional Resistivity Imaging To Optimize High Capacity Well Locations For Some Of Indiana'S New Ethanol Plants
More LessRecent demand for high groundwater yield at a number of Indiana's newest ethanol plant sites has made it necessary to call on the use of extensive geophysical surveys to locate optimal water well locations in order to maximize groundwater yields. Use of geophysics to complement more traditional searches for groundwater is uncommon. But, the demand for relatively high volumes of groundwater has forced the groundwater professionals to maximize aquifer yields. Principally two-dimensional resistivity imaging has been used to accomplish the task at hand. A variety of geologic settings have been encountered and both unconsolidated and fractured bedrock aquifers have been considered. A high degree of success has been realized using this method relative to the use of fracture trace analysis and intuition. Perhaps an order of magnitude or better yield has been realized, and therefore both the cost of well drilling and the time required to locate adequate aquifer material have been greatly reduced - and has made the siting of large capacity ethanol plants possible in some difficult areas.
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Combined Straightforward Inversion Of Resistivity And Induced Polarization Sounding Data
Authors Sri Niwas and Pravin K. GuptaStraightforward Inversion Scheme (SIS) developed by the authors for 1D interpretation of resistivity sounding data is used in a combined fashion for interpreting the Schlumberger configuration time-domain induced polarization (IP) sounding data. For this purpose a formulation based on dynamic dipole theory is presented. The test examples presented validate the use of SIS. The proposed scheme would complement the resistivity interpretation with special reference to shaly sand formations.
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Electric Log Analysis Of Precambrian Igneous And Metamorphic Rocks In The St. Francois Mountians, Missouri
More LessElectric log, core, and optical petrographic analysis of a metamorphosed and deformed PreCambrian-aged rhyolite effusive event identified 2 litho-facies and effected characterization of the
rock deformation. Single-point resistance (SPR) and spontaneous potential (SP) electric logs identified the ubiquitous clay seams and localized dikes. The igneous/metamorphic rocks had naturally elevated gamma emissions; consequently, natural gamma (NG) logging was useless in the identification of clay seams. However, NG logs proved useful in the identification of dikes, which had readings of less than 150 cps. The SPR/SP suite also identified intrusive black zones, characterized as martite by thin section analysis, within the rhyolite. Acoustic televiewer (AT) logs identified a conjugate shear fracture set with the main fracture set bearing a strike of N35oW and dip 80oNW or SE. The minor fracture set trends N35oE and dips 80oNE or SW. Thirty percent of the fractures logged are horizontal suggesting a vertically upward stress relief consistent with granite emplacement. Porous zones within the rhyolite porphyry and contiguous with fractures appear to be the result of subsurface potassium feldspar phenocryst weathering and erosion. These zones are invisible to SPR, SP, and NG tools. Much of the feldspars within the rhyolite porphyry show weathering to kaolinite. Erosion and mobilization of the kaolinite is putatively considered to be the causative agent for the deposition of clay in the horizontal fracture sets.
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Monitoring Resins Injection With 3D Electrical Resistivity Tomography (Ert) Using Surface And Multi-Borehole Electrode Arrays
Authors Federico Fischanger, Gianfranco Morelli, Douglas LaBrecque and Marco OcchiInjection of polyurethane resins has recently become a widespread technique to improve the geotechnical characteristics of shallow soils for homogenization and consolidation purposes.
A patent-pending methodology for the in-situ design and monitoring of these injections is illustrated. The technique was applied, over almost one year, in more than eighty (80) building
restoration sites with the acquisition of Electrical Resistivity Tomography (ERT) data sets summing more than 750 thousand measurements. Cross-borehole and surface arrays of electrodes are selected on case-by-case criteria. In particular for surface arrays, an innovative approach is illustrated for the use of L-shaped, Cshaped or “loop” electrode arrangements, that gives the possibility to work around the external walls of buildings in a sort of non-destructive manner. Specific sequence generation for innovative geometries of electrodes, 3D inversion of collected
data-sets, selection of the main parameters affecting ERT resolution (mesh, topography, roughness, noise estimate, etc.) are described. The technique reveals to be very useful both in giving information on the state of building foundations before injection (type, depth, continuity, etc.) and in describing the dynamic modification of the soil and its correlation with geotechnical parameters, resistivity and chargeability.
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Application Of Geophysical Methods For Geotechnical Engineering In Portugal
Authors Chen Yuxin, Carlos Dinis da Gama and Xie QiangThe role of geophysics in geotechnical engineering is considered for Portugal. In the developing period since 70’s, geophysics has mainly contributed to the investigation of new projects such as tunnels, dams and high-rise buildings. In the coming sustainable era, geophysics must be used for increasing safety and quality for human life. Some of the geophysical methods applied to geotechnical engineering are briefly described. Application examples of geophysics to investigations for disaster prevention, maintenance of existing constructions and soil and groundwater pollutions are also presented to demonstrate their role in geotechnical engineering. Future topics in this field for geophysics and geophysicists are also discussed.
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Site Investigation In Urban Tunnelling Using Hr Seismic Reflection Survey: A Case Study
Authors Mario L. Rainone, Patrizio Torrese and Raffaele MadonnaTunnel planning and construction is a very complex and difficult task due to non homogeneous contacts between surface deposits and the bedrock, soil and rock properties, fractured zones and hydraulic conditions. Furthermore, the possibility of running into a thick filling material body, especially in urban areas, enhances dangers and further expenses. Subsoil geophysical exploration is a very useful tool to improve prognosis and to reduce risk and probability of damaging infrastructures and surface buildings. This note presents an application of a shallow reflection seismic survey aimed at a site investigation for an urban tunnelling program undertaken in a complex geotechnical environment. Time cross-sections and depth sections are discussed and compared with geognostic data. The opportunity of comparing the obtained results before and after a jet-grouting treatment, that was carried out due to the presence of poor lithological conditions, enabled to assess the effects of ground improvement on subsoil seismic imaging.
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An Algorithm For Waveform Inversion Of Crosswell Radar Data
Authors Karl J. Ellefsen, Aldo T. Mazzella, Craig W. Moulton and Jeffrey E. LuciusAn algorithm for waveform inversion of crosswell radar data has been developed and implemented. The algorithm is based on an objective function that has two terms: One term measures
the misfit between the calculated data and the observed data, both of which are in the frequency domain. The other term measures the deviation between the current model and the starting model. Because the objective function is non-linear, it is minimized iteratively using conjugate direction and line search methods. The waveform inversion is tested with a model that is homogeneous, except for a small heterogeneity in the center. The estimated models have prominent anomalies that correspond to the heterogeneity in the original model and also have side-lobes that are adjacent to the prominent anomalies. Both the vertical and the horizontal resolutions improve as the wavelength decreases and are always better than the corresponding resolutions obtained with traveltime tomography. The vertical resolution is always better than the horizontal resolution.
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Instantaneous Spectral Analysis: Time-Frequency Mapping Via Wavelet Matching With Application To 3D Gpr Contaminated Site Characterization
Authors John H. Bradford and Yafei WuIn recent years it has been demonstrated that time-frequency analysis, or spectral decomposition, can differentiate small-scale features associated with hydrocarbon reservoirs in seismic reflection data. Similar reflectivity anomalies are sometimes induced in ground-penetrating radar (GPR) data by electric property variations caused by groundwater contaminants that are often below the conventional resolution of the signal. Isolating and mapping discreet components of the time-frequency spectrum using spectral decomposition can highlight details of a contaminant distribution. The windowed fourier transform was an early approach to spectral decomposition, however wavelet based approaches have superior time localization properties. Here, we give the wavelet matching spectral decomposition algorithm we developed at the Houston Advanced Research Center in the mid 1990s. In a 3D GPR dataset acquired at the former Wurtsmith AFB, MI, the time-frequency attributes image details of a hydrocarbon plume not resolved by conventional instantaneous attributes or GPR AVO attributes.
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The Application Of Image Processing And Analysis Algorithms To Complex Gpr Datasets
By Jan FranckeIn suitable environments, ground penetrating radar (GPR) offers the highest resolution representation of the shallow subsurface available in the geophysical toolbox. Potential applications of
the technology have burgeoned over the last 30 years from academic and archeological pursuits by a handful of researchers to the myriad of industries and environments of today. Regardless of the current commonality of GPR, the approaches used for data processing and interpretation, based primarily on reflection seismics, have persisted. Although the analogy between acoustic and electromagnetic wave reflection profiling is valid, GPR can yield raw data which are orders of magnitude richer in detail. Recent advents in rapid sampling circuitry and large multi-channel arrays have rendered the traditional approach of manually discerning point reflectors or horizons insufficient. Rather than being relegated to the onfines of seismic reflection processing, this paper explores a novel approach to the processing and analysis of GPR data by considering radar profiles as raster images. Image processing methods, commonly employed in microscopy, industrial quality control, forensics and radiology, offer the ability to extract subtle textural or reflector orientation variations, enhance or subdue various temporal or spatial frequencies, and automatically detect targets based on image morphology. This approach to data processing may offer GPR researchers and practitioners the ability to extract dramatically more detailed and consistent information from profiles which were previously under-interpreted.
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A Simple New Georadar Survey Method For Bathymetric Profiling Over White Water Rapids
Authors J.-L. Arsenault, R. Paul, R. Reid and J. CardinA major hydroelectric project of Hydro-Québec (Rupert River Diversion) required geophysical investigations at the location of future sites where weirs and cofferdams will be constructed. The
engineers required accurate information of the rock profile and the bathymetry for adequate designs. These data were not accessible from conventional geotechnical and geophysical investigations methods in dangerous river rapids. An innovative bathymetric method, using the georadar technology was then set up and successfully used by Geophysics GPR International.
A SIR 3000 system (from GSSI) was used for its lightness and energy autonomy. The use of the 1.5 GHz antenna was dedicated to the water surface topography measurements, which were necessary for the accurate seismic refraction calculations, as well as for the aerial georadar bathymetric surveys. A 270 MHz antenna was suspended to a steel cable crossing the river, for the bathymetric measurements. Both antennas were located in 3D with a dynamic laser total station, and all the further calculations used the three information sources together to correctly extract the accurate water surface topography as well as the first bathymetric estimation. A special methodology was finally applied to correct the raw bathymetric results, taking into account the effect of the white water effects.
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Application Of Frequency Response Towards Travel-Time Tomography For Detecting Soil Disturbance
Authors Arvin M. Farid, Akram N. Alshawabkeh and Carey M. RappaportSoil disturbance evaluation can be used as an indirect tool to detect buried objects, which is in turn of interest in forensic and security applications to local police departments, the Federal Bureau of Investigation and the Department of Homeland Security. Heterogeneity and variations in soil stratigraphy due to finite size rocks and boulders, etc. may be mistaken with disturbed zones. Besides, even uniform precipitation can affect the nonuniform environment unevenly and locally. The moisture difference is the key to creation of dielectric property contrast between disturbed and undisturbed zones. The research on the sandy soil in the pilot scale facility of Northeastern University (referred to as SoilBED) has shown that the disturbance effect may fade by vibrations or after cyclic drainage and recharge due to precipitation over time and up to some extent, but this effect is minimal. Cross-Well Radar (CWR) and Ground Penetrating Radar (GPR) are among the most promising potential detection techniques. The SoilBED facility is used to experimentally simulate the problem along with other numerical and analytical simulations. To study and evaluate the feasibility of disturbance detection using radar-based geophysical techniques, PVC-cased borehole monopole antennas were installed on a circle around the area suspected to be disturbed. Then, cross-tomography measurements are collected and images of the disturbed zone were reconstructed. Obviously, CWR may not be the erfect tool to evaluate soil disturbance over a large area, but can be employed to study the potential of using radarbased techniques to detect soil disturbance. The results can be used for detection of other anomalies, such as tunnels, landmine, etc.
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Electrical Resistivity Tomography (ERT) as a Tool for Monitoring Moisture Dynamics in Soil Filled Containers
Authors Oliver Mohnke, K. Prokoph and U. YaramanciThe multidisciplinary research group INTERURBAN (DFG 409) has been formed to investigate the dynamics of water and solutes at urban locations with particular attention to the spatial heterogeneity, the organic soil substance, and soil-biological transformation processes in the unsaturated zone. The geophysical subproject GEO aims at the development of a noninvasive conception to map the water distribution and the water dynamics on small scales. The outcome of several field studies [1, 2] points at the importance of the heterogeneous spatial distribution of small (≤ dm) patchy hydrophobic areas for the transport of water and matter through preferential flow in soils. In this respect soil animals, e.g. earthworms, modulate the composition of the soil solution in time and have a species-specific impact on the release pattern of nutrients and pollutants from plant litter and soil [3, 4]. A feasibility study was carried out to assess the possibilities and limitations of small scale ERT to monitor the 3D dynamics of water repellent zones in the presence of soil fauna activity.
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Gravity And Gpr Investigations For The Hydrogeologic Determination Of Aquifer Properties
Authors John F. Kick, Doria L. Kutrubes, Melanie Denham and Katie DowtyA sole-source aquifer supplying potable water to over 100,000 people in eastern Massachusetts was evaluated using gravity and GPR survey techniques to characterize the aquifer’s hydrogeologic properties. Limited boring information within the approximately 19.6 million square foot area of the site indicated that bedrock ranged from 0 to over 100 feet below grade. Because traditional seismic techniques would likely have failed to image the deep bedrock valley beneath the heavily industrialized and developed western portion of the survey area, a gravity survey was conducted to determine bedrock topography and the aquifer’s saturated thickness. Ground penetrating radar (GPR) helped determine water table depth and characterize stratigraphy. GPR signal penetrated a maximum of 20 to 40 feet using the 200 MHz and 100 MHz antennas, respectively , less in paved areas where road salt was present. GPR determined hat watertable was relatively shallow throughout the site, typically 7 to 12 feet below grade, and only 1 to 2 feet within the flood plain of the Neponset River.
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Microwave Dielectric Measurements For Soil Density And Moisture Content Inference In Engineering Applications
Authors Arvin M. Farid, Akram N. Alshawabkeh and Carey M. RappaportSoil is a material of interest in a number of disciplines such as geotechnical, environmental, military and agricultural engineering. Precise knowledge of dielectric properties of soil provides
information about the interactions between the soil and applied electromagnetic (EM) fields. Detecting anomalies of interest in heterogeneous soil media without enough information about the background media is very challenging, if not impossible. Dielectric properties are considerably intricate, can exhibit frequency dependent behavior, and correlate with many physical and chemical properties. Measuring dielectric properties can therefore be used to estimate those physical and chemical properties, if the correlation between the dielectric properties and other physical and chemical properties is well investigated and understood. In this study, laboratory measurements and theoretical modeling of dielectric properties of sandy soils are carried out. Dielectric property measurements are executed using a minimally invasive cross-borehole microwave measurement technique. An in-situ technique to measure dielectric properties of a sandy soil at different densities and moisture contents, and their frequency dependence over a wideband of frequency (0.4 GHz to 2.2 GHz) is implemented and evaluated. Then, the correlation between variations of dielectric and physical properties of the soil (e.g. density and water content) is studied. Dielectric mixing models were used to ascertain these correlations as a forward model for future inversion. Finally, a comparison between the forward model and experimental results was undertaken to seek the level of agreement.
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Investigation Of The Electromagnetic Properties Of Magnetite As A Function Of Grain Size
Authors Brianne D. Hamm, David E. Stillman and Gary R. OlhoeftGround-penetrating radar (GPR) can be used to find subsurface water on Mars. The electromagnetic properties of the soil, specifically dielectric permittivity and magnetic permeability, strongly affect the depth of penetration of GPR. Attenuation of electromagnetic waves is higher in soils with high magnetic permeability and dielectric permittivity values. Previous research suggests that the electromagnetic properties of magnetite, a mineral present in the global Martian dust layer, may vary with grain size at low frequencies. In this paper these properties were measured at radar frequencies to determine whether grain size will affect GPR. The measurements indicated that grain size has an effect on these properties. Dielectric permittivity decreased with decreasing grain size, while magnetic permeability increased with decreasing grain size. The time constant of the magnetic relaxation also increases with decreasing grain size. The
changes in dielectric permittivity are small and will have little effect on GPR results. However, the changes in magnetic permeability and the time constant of magnetic relaxation will have a larger effect. These results indicate that grain size should be taken into account when interpreting GPR data obtained on Mars.
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Burried-Channel Imaging Using P- And Sh-Wave Shallow Seismic Reflection Techniques, Examples From Manitoba, Canada
Buried channels are erosive sedimentary features that can possibly be formed by sub-glacial melt-water circulation. The size of these channels is very variable with widths up to several kilometers and depths from few meters up to several hundreds of meters. Their coarse-gravely, sandy sediment fills act as reservoirs which can be important sources of water or occasionally gas.
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Marine Resistivity As A Tool For Characterizing Zones Of Seepage At Lake Lacawac, Pa
Authors Matthew J. Heaney, Jonathan E. Nyquist and Laura E. ToranThe groundwater-surface water exchange zones of lakes and streams are dynamic and difficult to characterize. The spatial variability of seepage zones makes them hard to locate using traditional point sampling methods. The goal of this project is to use marine resistivity to identify potential zones of groundwater discharge and recharge, providing focus for point measurements. Multiple resistivity surveys were conducted at Lake Lacawac, a small, glacially formed lake in northeastern Pennsylvania. One target for these surveys was the resistivity contrast between groundwater and surface water. Another target was resistivity contrasts created by geologic heterogeneities that control groundwater discharge into the lake. Two types of surveys were conducted using a SuperSting® resistivity system. In a continuous resistivity profile, a multi-electrode cable was towed parallel to shore to look for spatial variability in resistivity around the lake. A second resistivity array was laid on the lake bottom perpendicular to the shoreline to examine how resistivity varied with distance from shore. The results of these surveys
suggested several lithology changes both along the shoreline and with distance from shore. Seepage meters were used to provide ground truth about interpreted areas of seepage.
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Noise Cancellation And Low-Snr 2D/3D Imaging Methods For Multi-Channel Surface Nmr Groundwater Investigations
More LessMulti-channel surface NMR instrumentation and software, developed in the United States, has been applied to investigate 2D and 3D hydrology at various locations in the Western US. Two new multi-channel processing techniques, reference coil-based noise cancellation and T2*-weighted porosity imaging, are shown to increase effective signal to noise ratios by an order of magnitude or more. These effective SNR gains enable multi-coil surface NMR to produce useful and reliable images when the post-averaged SNR is less than 1, and at locations where
previous single-coil surface NMR investigations have failed. Experimental results are presented for recent field studies conducted in Nebraska, Minnesota, Iowa and Washington.
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Magnetotellurics: What You Need To Know
By Ted AschInvestigation and development of ground water resources are a continuing and increasingly important issue for local and national governments. As the depths to fresh water resources increase, geophysical techniques that are most sensitive to depth ranges from 10 m to 800 m, such as controlledsource audio magnetotellurics (CSAMT), e.g., Geometric’s STRATAGEM® system, have become increasingly useful. Magnetotellurics (MT) and Audio-Magnetotellurics (AMT) have been successfully utilized to delineate fresh and saline water, lithology, and subsurface geologic structures that impact ground water flow. However, it has become apparent that while more and more practitioners are using MT/CSAMT, sometimes successfully and sometimes not, their training and knowledge of the basic magnetotelluric technique has not kept pace with their use. The purpose of this talk is to present a primer on how to set up a field survey (TM vs. TE modes) and what to look for when recording AMT data. Discussion focuses on what constitutes good signals, bad signals, effects from lightning, and cultural noise effects (usually power lines and actively pumping water wells and pipe lines), and how to mitigate these effects. MT and AMT are examples of geophysical techniques that can be used to help map subsurface geology and effectively support hydrogeologic investigations. However, magnetotelluric surveying, as with most geophysical methods, works best when it is integrated into a omprehensive geophysical investigation.
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Research On Dispersion Curves Of Masw
Authors Yinhe Luo, Jianghai Xia, Jiangping Liu, Yixian Xu and Qingsheng LiuThe multichannel analysis of surface wave (MASW) method has been effectively used to determine near-surface shear (S)-wave velocity and map bedrock. Estimating the S-wave velocity profile from Rayleigh-wave measurements is straightforward. A three-step process is required to obtain S-wave velocity profiles: acquisition of a multiple number of multichannel records along a linear survey line by use of the roll-along mode, extraction of dispersion curves of Rayleigh waves and inversion of dispersion curves for an S-wave velocity profile for each shot gather. A pseudo-2D S-wave velocity section can be generated by aligning 1D S-wave velocity models at the midpoint of each spread. This process implies that the extracted dispersion curve is only determined by the geophysical structure within the geophone spread and not affected by the source geophysical structure. In this paper, dispersion curves of synthetic dataset by fixing the receiver spread and changing the source location are calculated to testify the assumption of MASW. Results demonstrate that the dispersion curves are affected by the whole acquisition system including source and receiver spread structure.
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Surface Wave Testing To Investigate The Nature Of Roller Determined Soil Stiffness
Authors Nils Ryden and Michael A. MooneyContinuous compaction control (CCC) with instrumented vibratory roller compactors is an effective tool to estimate the relative soil stiffness over the complete area of a construction site.
However, research is still needed to extract roller measured stiffness values directly comparable with pavement design parameters and laboratory measurements. In this study we have used surface wave testing over a compacted subgrade along with CCC to study the influence depth of the roller measured stiffness value. Results show that shear wave velocity with depth profiles can be useful to study the influence depth of roller measured stiffness values.
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Seismic Investigations In Residential Area Liquefied By Mid Niigata Prefecture Earthquake
Authors Koichi Hayashi, Masahito Tamura, Neagu Cristian, Yasuaki Kikuchi, Katsuaki Ando and Yoshiyuki ItoA surface-wave method and a seismic refraction method were applied to residential area liquefied by the Mid Niigata Prefecture Earthquake in order to evaluate the applicability of seismic investigations to a liquefaction potential evaluation. The result of the analysis agreed with actual liquefaction damage. A liquefaction potential analysis by shear-wave velocity obtained from the surface-wave method was carried out. Groundwater level estimated by the seismic refraction method also agreed with that of monitoring wells. The shear-wave velocity and the groundwater level are important factors in the liquefaction potential evaluation. The result implies that the seismic investigations enable us to evaluate the liquefaction potential from the surface nondestructively.
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Tdr For Compaction Control Of Granular Materials With Large Particle Sizes
Authors Aaron C. Evans and Vincent P. DrnevichCompaction of soil is typically controlled by specifying water content during placement to achieve a desired dry density. Earlier work at Purdue University provided the means of applying Time
Domain Reflectometry (TDR) technology to compaction control by relating dielectric constant and bulk electrical conductivity determined from TDR with water content and dry density. With time, modifications and new means of applying the technology have been developed and applied, becoming the basis for an ASTM Standard Method of Test (ASTM D6780-2005). However, presently there has been limited study in the use of TDR for the compaction control of granular materials containing large particle sizes. This paper examines the effects of the large particle sizes on accurately determining water content and dry density with the use of the Purdue TDR Method. Testing consisted of lab calibration and field testing. Aggregates tested included Indiana Aggregate Specification 53 (a densely graded aggregate) and 08 (a uniformly graded aggregate), in both crushed stone and gravel forms. This paper explores the effect of spike insertion and its disturbance to the sample, the effect of large particles on the TDR waveform and the determination of the dielectric constant and bulk electrical conductivity, and lab
calibration and field testing considerations for compaction control.
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Delineation Of An Old Coal Mine In An Urban Environment With Surface Wave Seismics Using A Landstreamer And Laterally Constrained Inversion
Authors Roger Wisén, Mattias Lindén and Mats SvenssonPrior to the site investigation for a tunnel below Helsingborg, southern Sweden, a surface wave seismic investigation was made to delineate an old coal mine. The mine as described in old literature has an area of about 6 acres and each layer of coal has a height of less than one m; however, the exact location and status is unclear. The sedimentary geological setting consists of fill, quaternary deposits, shale, coal and sandstone. The mine, or alternatively the coal, is found at 10 m depth between a layer of shale and a layer of soft sandstone. The seismic measurements were made along two crossing profiles, located on the walkways covered with gravel, in the area where the mine is expected. The measurement system was a landstreamer with 24 4.5 Hz geophones, a Geometrics Geode and a shotgun. The vs models clearly show increasing velocities with depth with a low velocity layer at 10 m depth. The results correlate well with the expected geology and results from geotechnical drillings that indicate an open mine in parts of the area; however, the low velocity layer is mainly due to the soft sandstone and does not seem to be strongly affected by the presence of the open mine.
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Application Of The Wiener Filter To Total-Field Magnetic Data For Uxo Detection
Authors Todd Meglich, Yaoguo Li and Leonard R. PasionThe detection of UXO in magnetic environments continues to be a difficult task. In these environments identified geophysical anomalies may either be metallic objects (UXO) or of a geologic
origin. Current techniques such as bandpass filtering are sometimes inadequate by themselves in highly magnetic environments where the spatial wavelengths associated with the background geology are comparable to, or overlaps with, those of UXO anomalies. The Wiener filter assumes that the collected field data is a summation of the desired signal and the background response and the two components are not correlated. We develop a procedure based on the Wiener filter to separate geologic responses from UXO signals. Application of the Wiener filter involves the estimation of a transfer function defined by the ratio of signal and data power spectra. We have developed an iterative approach to estimate the transfer function using the power spectra of signal and geologic noise from the measured field data set and limited forward modeling of UXO anomalies. This approach is demonstrated by applying it to synthetic data examples and field data from Helena, Montana.
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