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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 - 100 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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Alltem Uxo Detection Sensitivity And Inversions For Target Parameters From Yuma Proving Ground Test Data
ALLTEM is a multi-axis electromagnetic induction system designed for unexploded ordnance (UXO) applications. It uses a continuous triangle-wave excitation and thus measures target step
response rather than the more common impulse response. In May, 2006, we operated ALLTEM over the Army’s UXO Calibration Grid and Blind Test Grid at the Yuma Proving Ground (YPG), Arizona. The system multiplexed through all three orthogonal (Hx, Hy, and Hz axes) transmitting loops and recorded a total of 19 different transmitting (Tx) and receiving (Rx) loop combinations. This was accomplished while in continuous motion with a spatial data sampling interval, after waveform averaging, of 15 cm to 20 cm. ALLTEM records data at a constant 100 kilosamples/s rate at 24-bit precision rather than in a small number of time gates. Maps produced from differences between early- and late-time unfiltered signal amplitudes are of
high quality, but exhibit ground response and system thermal drift effects. We find that by exploiting the high density of the time-series data to digitally filter the data and by moving the early- time pick to 275 μs, late enough that the step response of an analog low-pass filter has settled, instead of the 75 μs early time we had previously used, we can produce amplitude difference data and maps that are almost free of ground response and system drift effects while retaining good sensitivity to UXO. The improvement in the signal-to-noise ratio (SNR) greatly enhances the ability to detect small or deep targets and also produces more consistent inversion results from ALLTEM data. An inversion algorithm has been developed and applied to data from various sets of the available 19 Tx-Rx combinations over a number of targets. We present results that show that the inversion algorithm produces accurate parameters for some known targets in the Calibration Grid. This suggests that it is possible to obtain good multi-axis system target inversions from moving platform data even with some position “noise.”
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Tools For Assessing Geophysical Survey Data Quality
Authors Raye Lahti, David D. Tyrer, Mark Blohm, Ken Valder and Philip SirlesGeophysical investigations for munitions and explosives of concern (MEC) are conducted principally using magnetic or electromagnetic geophysical methods. These data collection methods
require that geophysical measurements are accurately tagged to a ground location. A number of simple and advanced survey methods have been used, ranging from “wheel mode” to global positioning system (GPS) methods. Advantages and limitations of each positional survey type have been evaluated and selected depending upon survey requirements and site conditions. This paper discusses geophysical surveys that were acquired at Vandenberg Air Force Base (AFB) to assess the potential presence of MEC within existing housing areas. The project scope required evaluation of geophysical systems that are proven effective in the detection of potential subsurface MEC. Additional requirements included sub-meter accuracy and “survey grade” location equipment. Following our testing of sensor technology and location equipment we selected off the shelf systems including the Geonics EM61 MK2 and Leica real-time kinematic (RTK) global positioning (GPS) technology. The nature of the terrain, vegetation, and the housing units provided numerous sources of interference. The survey was further complicated by multi-path interference, and unsuitable GPS satellite coverage, a result of low satellite number (nSat) and high position dilution of precision (PDOP) during significant portions of the work day. To address these difficulties, several unique data management tools were developed at the project outset. As a result, high-quality positional data were identified and used in the final data assessment. This paper provides a brief overview of the project, the instrumentation and procedures employed.
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High-Accuracy Positioning For Geophysical Target Characterization
More LessGeophysical technologies for supporting ordnance and explosive waste remediation have focused on the problems of detecting, locating, and mapping the presence of underground objects. Experience has shown that the majority of underground objects detected by these systems presents no safety hazard and do not need to be excavated. Researchers have shown a likelihood of being able to characterize buried targets via sophisticated imaging and inversion algorithms that require high-accuracy positioning systems coupled with high-fidelity geophysical sensor technologies. ENSCO has developed and demonstrated an integrated, self-contained, local-area, high-precision inertial navigation technology that provides sub-centimeter positioning accuracy over areas of a couple of square meters. The technology has been integrated with a Geonics EM-61HH and also demonstrated with a Geometrics G-858. Positioning accuracy has been verified using an independent method. In addition to 3-D position, the velocity and attitude of the sensor are also provided. The prospect of effective target characterization should be realizable with this addition of improved position data.
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Inversion-Based Uxo Discrimination: Utilizing The Magnetic Multipole Response
Authors David Sinex, Yaoguo Li and Don YuleWe investigate the feasibility of using information about quadrupole and higher-order magnetic moments in UXO discrimination based on total-field magnetic data. Current state-of-practice only
utilizes the dipole moment, yet there is coherent signal present in the residuals of many inversions. Part of the residual is due to multipole moments such as the quadrupole and octupole. We approximate the response of a compact source body using both dipole and quadrupole moments. Synthetic models resembling UXO and non-UXO targets, with induced magnetization distributions obtained from integral equation solutions, are used to examine the nature of the multi-pole responses. We decompose the full response of the models into separate dipole, quadrupole, and higher-order moment responses. Analyses indicate that the field due to quadrupole and other higher-ordered moment responses can be as large as 10% of the dipole response. Based on this understanding, we developed a new approach to UXO discrimination by using a weighted ratio of residual over dipole field. The ratio yields a measure of the strength of the higher-order moments relative to the dipole and indicates the possibility of an irregular shaped non-UXO item. Extensive simulation and application to field data sets show that this new
discrimination criterion is viable with currently available magnetic data from UXO clearance.
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Identification Of Uxo With Surface Magnetic Charges On A Sphere
Authors N. Lhomme, L. Pasion and D.W. OldenburgDiscrimination of buried unexploded ordnance (UXO) with electro-magnetic sensors requires robust predictive models to correctly interpret data recorded at the surface. Shubitidze et al. have recently suggested a representation of the Electromagnetic Induction (EMI) response of a metallic object by using a model of Normalized Surface Magnetic Charges (NSMC) distributed on a spheroidal surface enclosing the target. Their results suggest that the Total Normalized Magnetic Charge (TNMC), the integral of NSMC over the spheroid, can be used to identify the object. The interpretation however is much simpli ed by using a sphere. Theoretical considerations show that the scattered eld of a spherical object is purely dipolar. The associated NSMC istribution is uniform on a sphere and the TNMC is directly related to the magnetization tensor and sphere radius. These concepts have impacted upon our approach where we estimate the charge distribution on the surface of the sphere by solving a linear inverse problem. An additional bene t of using a sphere instead of a spheroid is that it is no longer necessary to specify the orientation parameters of the buried object. Azimuth and dip are instead revealed in the recovered surface charge distribution. We nd that this formulation helps develop a robust NSMC that has potential for practical discrimination of UXO. We demonstrate our approach by using Geonics EM63 data collected at the USACE-ERDC test stand in Vicksburg, MS.
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Combined Nsmc And Pseudo-Spectral Finite-Difference Method For Inverting A Buried Object Location
Authors F. Shubitidze, B. Barrowes, K. O’Neill, I. Shamatava and J.P. FernándezThere is a wide-range of different inverse scattering methodologies (single and double dipole models, the standardized excitation approach (SEA), the normalized surface magnetic charge model (NSMC), etc) currently being used or developed for discrimination of UXO from non-UXO items. In order to utilize these approaches, first the buried object’s location and orientation have to be inverted, which usually is done by solving a time consuming, ill-posed inverse-scattering problem. In order to avoid the standard ill poised inversion procedure for location and orientation, here the NSMC is combined with a pseudo-spectral finite different (PSFD) method for inverting for the location of the buried object. In the NSMC model, over the entire magneto-quasi static regime, the scattered magnetic field outside the object is reproduced mathematically by equivalent magnetic charges. The amplitudes of the NMC, which is proportional to the primary field, are determined directly from measurement data. At the end the integrated total NSMC is employed for discriminating objects of interested from nonhazardous items. Note that the model takes into account the scatterer’s heterogeneity as well as near- and far-field effects. In addition, the NSMC that are distributed on a surface conformal to the measurement surface, can be used to extend the EMI magnetic field above the measurement surface and to generate spatially distributed monostatic as well as bi-static data. In this paper, a buried object’s location is determined by first extending the secondary measured magnetic field from xoy surface at z=h height to its parallel surface at z=h+dz/2 height. Then the PSFD method is employed in the curl and divergence free Maxwell’s equations to find the scattered magnetic field everywhere below the measurement xoy surface at z=h height, inside the observation volume. From the
distribution of this calculated magnetic field the buried object’s location is estimated. To demonstrate the applicability of the combined NSMC and PSFD algorithm, several numerical tests are presented.
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Processing Techniques For Improving Target Identification In Uxo Investigations With Noisy Tdem Data
Authors Darrell B. Hall and John W. DickersonHigh noise levels due to terrain, culture, and geologic sources are often unavoidable in UXO investigations. Higher noise levels increase costs due to increased 'no find' responses, and reduce
confidence that sources have not been obscured. To improve target identification in noisy TDEM data sets, several processing techniques were compared using evaluation plots with known sources or intrusively investigated data sets. A model for separating noise it into a component that correlates between individual time gate responses, and one that does not, is discussed. Techniques examined for identifying and reducing noise include power-law decay model misfit, time gate sums, and a noise suppression filter based on decay profiles. All of these approaches show potential benefits for reviewing data sets and improving target selection.
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Effects Of Intra-Inversion Filtering On The Accuracy Of Uxo Magnetic Dipole Inversions Using Standardized Test Site Data
Authors R.M. René and Ki Young KimMagnetic dipoles are modeled by inversion of magnetic data from surveys designed to detect and identify unexploded ordnance (UXO) and clutter (non-UXO). Such surveys facilitate excavation of UXO while leaving clutter in place. Some clutter can be identified by non-dipolar anomalies or by a large deviation of the dipole’s orientation from the direction of the earth’s field. The latter is an indication of remanence, which is typically destroyed by impact of UXO projectiles. Inversion may be hindered by geologic noise and overlapping dipole fields of neighboring UXO and clutter not modeled simultaneously with the target field. Inversions with and without intra-inversion filtering (IIF) are applied to magnetic anomalies in MTADS data from the Aberdeen Proving Ground, Maryland. These results are compared to ground truth. Small-window, peak-only, trough-only, single- and multi-swath, flag-node, and all-node inversions are tested. In flag-node inversions, only those nodes of a regular grid nearest to measurement stations are used. For very shallow sources, all-node and flag-node inversions may yield significantly different results. For IIF inversions, gapped gradient-nulling (GGN) and edgeadaptive gapped gradient-nulling (EAGGN) high-pass filters are tested. Significant improvements in accuracy of results are demonstrated for IIF inversions.
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Gravity Gradients Over A Simple Two-Dimensional Structure: Interval Gradients Redux
More LessBack in the days before “full tensor gravity gradiometers” were available and the in vogue topic for potential fields papers, there was a rich and extensive literature discussing gravity gradients from the perspective of interval (finite difference) gradients from gravity measurements or from derivative filter transformations of gravity maps. In fact, the very first issue of Geophysics (1936) had an intriguing article by H. M. Evjen, “The Place of the Vertical Gradient in Gravitational Interpretations.” Measurement of the interval vertical gradient involves painstaking measurements with gravimeters and towers or tripods (Figure 1), while the horizontal gradients are calculated from “closely-spaced” surface gravity measurements. The excellent tutorial article by Saad (2006) discusses the attributes of true or differential gravity gradients for structural definition and filtering. Similar discussions of the attributes of interval gravity gradients are presented by Hammer and Anzoleaga (1975), Butler (1984a, 1995), and others (many listed in the reference lists of the preceding papers).
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Microgravity Mapping Of Karst Conduits Within The Woodville Karst Plain Of North Florida
Authors Ronald D. Kaufmann and Rodney S. DeHanThe Woodville Karst Plain (WKP) is a major geomorphic subdivision of the Gulf Coastal Lowlands in the Florida Panhandle. Its unique karstic geology renders it highly interactive with surface waters, thus vulnerable to pollution from the various activities on land and in near-shore coastal waters. Like many areas of coastal Florida, the WKP has also been “discovered” by developers and, as a result, is facing a population influx and associated activities that are threatening the long term integrity of the entire ecosystem. The WKP is characterized by major recharge areas, large conduits, cavities, caves, sinkholes, and karst windows along with some of the most spectacular springs in the United States, if not the world. The characterization of these karst features is a necessary step towards the development of conceptual, analytical and numerical models capable of forecasting and evaluating the impact of natural and manmade events; thus helping the effort to manage and protect these natural systems. As part of the regional characterization effort of the WKP, we used microgravity to identify conduits in areas of the watershed that are inaccessible to cave divers. Initially, microgravity data were acquired over known locations of previously-mapped conduits to prove and calibrate the method in this particular geology and quantify the expected anomalies of typical conduits. Following that initial test, over 12 linemiles of microgravity data were acquired across a large portion of the WKP. The survey lines were located between sources of wastewater discharge and the location of a major spring system downgradient of these sources. This reconnaissance survey identified gravity anomalies consistent with those identified over the control locations. We conclude that microgravity surveys, especially when complimented by dye tracing studies, can provide accurate characterization of karstic geology to improve the development of models that can be used by decision makers to better protect and manage watersheds and ecosystems in complex karst settings.
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Geophysical Technologies To Image Old Mine Works
Authors Kanaan Hanna and Jim PfeifferZapataEngineering, Blackhawk Division performed geophysical void detection demonstrations for the US Department of Labor Mine Safety and Health Administration (MSHA). The objective was to advance current state-of-practices of geophysical technologies for detecting underground mine voids. The presence of old mine works above, adjacent, or below an active mine presents major health and safety hazards to miners who have inadvertently cut into locations with such features. In addition, the presence of abandoned mines or voids beneath roadways and highway structures may greatly impact the performance of the transportation infrastructure in terms of cost and public safety. Roads constructed over abandoned mines are subject to potential differential settlement, subsidence, sinkholes, and/or catastrophic collapse. Thus, there is a need to utilize geophysical imaging technologies to accurately locate old mine works. Several surface and borehole geophysical imaging methods and mapping techniques were employed at a known abandoned coal mine in eastern Illinois to investigate which method best map the location and extent of old works. These methods included: 1) high-resolution seismic (HRS) using compressional P-wave (HRPW) and S-wave (HRSW) reflection collected with 3-D techniques; 2) crosshole seismic tomography (XHT); 3) guided waves; 4) reverse vertical seismic profiling (RVSP); and 5) borehole sonar mapping. In addition, several exploration borings were drilled to confirm the presence of the imaged mine voids. The results indicated that the RVSP is the most viable method to accurately detect the subsurface voids with horizontal accuracy of two to five feet. This method was then applied at several other locations in Colorado with various topographic, geologic, and cultural settings for the same purpose. This paper presents the significant results obtained from the geophysical investigations in Illinois (Hanna, et al, 2006).
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Evaluation Of Three-Dimensional Electrical Resistivity Array Types For Optimal Detection Of Voids In Karstic Limestone
Authors James D. Prikryl, Ronald N. McGinnis and Ronald T. GreenElectrical resistivity imaging provides a non-destructive means for detecting the presence of karst features (e.g., caves, solution cavities, and sinkholes) in limestone terrains. To statistically improve delineation of three-dimensional (3-D) heterogeneities, such as caves, a true 3-D electrical resistivity survey using a 3-D interpretation model can be used. When conducting 3-D resistivity investigations in karst terrains, a common problem is determining which of the existing electrode configurations will respond best to material changes in the subsurface, and provides the needed depth and resolution for accurate void delineation. In this study, 3-D electrical resistivity measurements were collected over the site of Dead Deer Cave in Bexar County, Texas, using various electrode configurations (i.e., dipole-dipole and pole-dipole). The entrance to Dead Deer Cave is a pit that connects to a series of vertical and horizontal solution cavities that have
been surveyed to a depth of approximately 30 m. The pit has been filled in with rock and dirt, concealing its exact location. Results of 3-D numeric modeling of the resistivity measurements at Dead Deer Cave indicate that the pole-dipole array configuration provided the needed depth and resolution for locating the cave entrance as well as the shafts and passages that are beneath the surveyed area.
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The Use Of Ground Penetrating Radar To Evaluate The Location And Formation Of Sinkholes Associated With A Retention Pond
Authors Craig C. Schuettpelz, Dante Fratta and David J. HartDevelopment and construction over karst often leads to unintended results. In this case study, a retention pond was built in a new subdivision to capture surface runoff and add appeal for potential homeowners. However, water never rose to the proposed level and has drained suddenly and frequently since construction in the year 2000. The failure of the retention pond to perform as designed is due to the presence of carbonate bedrock beneath the site. The bedrock, the Prairie du Chien dolomite, is highly weathered and prone to many relatively small sinkholes. Geophysical surveys were proposed to evaluate the subsurface conditions and to determine the extent of sinkholes below the pond shorelines in an attempt to propose engineering solutions to the problem. Four geophysical surveys were performed: ground penetrating radar (GPR), seismic reflection and refraction, electromagnetics (EM), and subbottom profiling. Although all methods provided subsurface information, the GPR surveys were most useful to site characterization. The GPR surveys show evidence of severely disturbed soil in the subsurface that is associated with sinkhole formation. These surveys help delineate the areas around the retention pond that may produce additional sinkholes and failure and will help to focus remediation efforts.
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Advances In Air-Coupled Lamb Wave Scanning
Authors Alex Gibson, Nils Ryden and John S. PopovicsImpact-echo is an effective method for the nondestructive evaluation of in-situ concrete members and has progressively developed over the past 20 years. This study outlines recent advances in the adoption of microphone-based signal acquisition in order to perform rapid non-contact impact echo scanning, in the context of the recently proposed Lamb wave dispersion hypothesis. Various challenges associated with noise control, data acquisition, processing and imaging are addressed. Data obtained from scanning a control slab over a range of source-receiver separations are presented alongside results from traditional point-by-point impact-echo testing. Potential applications of this method include rapid thickness profiling of large structures and
identification of flaws in concrete pavements, reinforced concrete pipes, bridge decks, as well as quality assurance of grouting in post-tensioning tendon ducts.
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Application Of Probabilistic Approach To The Solution Of Inverse Problems In Nondestructive Testing And Engineering Geophysics
Authors Rambod Hadidi, Nenad Gucunski and Ali MaherInterpretation of geophysical data often requires the solution of an inverse problem or simply, inversion. Inverse problem is a problem where the observed data is used to infer the characteristics of the system under investigation. There are two general approaches to the solution of inverse problems, deterministic and probabilistic approaches. Traditionally, in engineering geophysics, inversion is carried out using a deterministic approach, where a single set of results is identified as the interpretation outcome. In complex inverse problems, the deterministic solution process is often guided by an interpreter, who uses his information, experience, or judgment to guide the process. The deterministic approach to the solution of inverse problems implicitly assumes that the uncertainties in data and quantitative models are negligible. However, this assumption is not valid in many applications and, consequently, obtaining a single set of results does not provide a complete picture in terms of quantifying the effects of data and/or theoretical uncertainties on the obtained solution. In this paper, a general probabilistic approach to the solution of inverse problems is introduced, which offers the framework required to obtain uncertainty measures and to include some a priori information in the solution process. A technique for the evaluation of the probabilistic solution using Monte Carlo Markov Chains (MCMC) with Neighborhood Algorithm (NA) approximation is introduced and explained. Finally, the application of the presented approach in the health monitoring of transportation infrastructure using non-destructive testing (NDT) is illustrated.
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Seismic Modeling of a Rising Mine Water Table
Authors Dirk Orlowsky and Bodo LehmannIn former deep coal mining areas in Germany the mine water table is regulated by a water pump system such that the drinking water at the earth’s surface is not influenced. Nevertheless, in the next years it is planned to reduce the pumping rate in selected areas or to stop the pumps completely. Thus, the mine water table will rise and will effect the hydrogeologic situation at the earth’s surface. To minimise or to avoid critical changes it will be necessary to determine the effects of a rising mine water table in advance. For a detailed forecast the exact depth of the mine water table has to be monitored during the rising process. For the modelling of possible changes at the earth’s surface using the so called box model (Eckart et. al., 2003), a finite element model of the hydrogeologic situation in the Ruhr Area
has been developed. To observe the depth of the mine water table usually old shafts or exploration drill holes are used at selected locations. Nevertheless, there are to less observation stations for a detailed modelling of the complete Ruhr Area so that additional observation locations are needed. To avoid the construction of expensive and complicated drill holes down to more than 1000 m depth an alternative technique to monitor the rising of the mine water table could be the time-lapse seismic (TLS) which is routinely used to monitor the effects of the exploitation of oil and gas deposits.
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Stresses Analysis Of The Area Between Aswan And Red Sea Hills, Egypt Using Magnetic And Anisotropy Techniques
Authors Ahmed Saleh and Mahmoud MekkawiThe aim of the present study is to obtain the stress direction using magnetic anisotropy and aeromagnetic interpretations. Representative sixty oriented rock samples have been collected from five sites in the study area. The rocks magnetic properties and magnetic anisotropy analysis have been determined for all the studied samples. The interpretation clearly defined magnetic lineation at all site and anisotropy of magnetic susceptibility (AMS) parameters. The stress direction of the studied area has been determined using magnetic anisotropy and aeromagnetic analysis. The specific objective of the aeromagnetic interpretation is to establish the trend and depth of the structural configuration of the basement rocks.. Horizontal gradient could
to delineate deep sources and enabled tracing several faults that are mainly striking in the E-W direction. Eular deconvolution method has been applied to the aeromagnetic data and provided fast information about depth and trends of the shallower subsurface structures. In agreement with results from AMS interpretation has been estimated and the present stress direction results agree with the geological and tectonic information in Red Sea and Aswan areas. Keyword: magnetic anisotropy, aeromagnetic interpretation and stresses analysis.
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Combining Multiple Seismic And Ground Penetrating Radar Techniques To Analyze Geologic Controls Of Riparian Meadow Complexes In The Central Great Basin, Nevada Usa
Riparian meadow systems in the Central Great Basin are of interest because they support the majority of ecosystem diversity in the region. The riparian meadows are highly dependent upon
groundwater levels, thereby making them vulnerable to fluctuations. These systems are actively degrading due to incision of the streams, resulting in a lowered water table and modification of the associated ecosystems. Geologic controls, such as bedrock geometry and sediment variability, are important in the meadows because of their control on the overall system. The current hypothesis is that the sediments associated with side-valley alluvial fans and fault-related bedrock steps interact to constrict ground water flow. Seismic reflection data and seismic refraction tomography data were collected to analyze bedrock structure and topography from 10 to 80 meters depth, while ground penetrating radar (GPR) data were collected to determine the stratigraphic variability in the upper 10 meters. These data were integrated to provide a comprehensive interpretation of the upper 80 meters of the subsurface. Seismic reflection data were processed to identify the bedrock surface. This surface was then correlated with the seismic refraction tomography to extend the bedrock surface across the meadow complexes. The large
volume of GPR data were interpreted by classifying radar facies based on the characteristics of the radar reflectors. These facies (in conjunction with borehole information) confirm and extend areas of alluvial fan related sediment distribution. Integration of these three geophysical techniques is advantageous because they provide more information than could be obtained with the individual techniques.
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3-D Electrical Resistivity Imaging (Eri) Of A Potential Mine Stoop
More Less3-D electrical resistivity imaging (ERI) survey of a recently and twice-repaired sinkhole at a site in Chester County, PA reveals a small localized opening in the top of rock suggestive of a potential sinkhole throat. The area is underlain by carbonate rocks prone to sink activity. It is also located fairly close to the Wheatley Mine District, a series of lead, zinc, and copper mines that date back to the 1800's, and that have operated periodically up until the 1920's. Re-fined imaging of the 3-D data shows that the small opening is a top of rock expression of an inclined, cylindrical-shaped structure that looks like a mine stoop. The approximately 3 meter wide opening is associated with a linear depression in the rock surface that may represent a haul road and/or man-made drainage to control storm-water runoff. The proximity of the site to the former mining district, coupled with the mine-like structure observed in the 3-D data strongly suggest that ground failure was not triggered by sink activity but rather by a mine collapse.
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Defeat The Dragon: Coal Fires Between Self Ignition And Fire Fighting
Authors Manfred W. Wuttke, Stefan Weßling and Winfried KesselsSpontaneous coal fires in near surface coal seams are a worldwide recognized problem. They are destroying coal as a resource and emit climate relevant gases like CO2 both in considerable amounts. While the extinction of such fires is a most desirable goal, the estimation of the actual input of greenhouse gases into the atmosphere is of great interest especially in the context of the Kyoto protocol as such values are needed as baseline for the Clean Development Mechanism policies. Under the framework of the Sino-German Coalfire research project we develop numerical models of such coal fires. The aim of our calculations is first to understand the governing physical and chemical processes that are relevant for the whole combustion process. Based on such gained insights we study the coal fire spreading along the seams for typical situations. From these scenario calculations we can deduce informations needed to support the CDM baseline estimation and to assess the progress of fire extinguishing efforts like water injection and surface covering to dissipate the heat and suffocate the fire. We present case studies using the finite-element-code ROCKFLOW applied to realistic geometries based on field observations in the Shenhua Group Coal Mining Area Wuda (Inner Mongolia, PR China).
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Geophysical Investigation Of The Success Dam Foundation: An Overview
Authors Lewis E. Hunter, Michael H. Powers, Seth Haines, Theodore Asch and Bethany L. BurtonSuccess Dam is a zoned earth-fill embankment located about 70 miles northeast of Bakersfield, CA. Stability analyses indicate that there is a potential for large-scale deformation of the dam during relatively low levels of earthquake shaking. At least three earthquakes in the past 150 years, and prior to dam construction, are believed to have been large enough to create a dam failure. To better understand material behavior, the U.S. Army Corps of Engineers has been investigating properties of the dam and its foundation. This includes extensive field explorations and detailed engineering studies using a variety of analytical techniques to estimate the response of the dam and foundation to earthquake shaking. Although a large amount of data have been acquired since 1992, these data are largely point data from borings. A geophysical investigation was designed to provide a continuous image of the foundation toe. This investigation employed direct-current (DC) resistivity, seismic refraction tomography (P- and S-wave), audio-magnetotellurics (AMT), and self-potential (SP). The purpose of the DC resistivity and seismic refraction tomography was to produce 2-D imagery across the foundation to investigate depth to bedrock and the occurrence of beds potentially susceptible to liquefaction. DC resistivity was used to look at the conductivity relationships in the subsurface. The resistivity data produced a higher-resolution image relative to seismic refraction tomography, which looks at compressional and shear properties of the material. AMT was applied to look considerably deeper (several 100s of m) in order to confirm depth to bedrock and investigate for deep faults. The goal of this paper is to provide technical background on the site and to highlight how these data have been used by the engineers in redesigning the new dam. Specific details on the geophysical methods are presented by the co-authors in two other papers in this session (Asch et al., 2007; Powers et al., 2007).
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Using Airborne Electromagnetic Data To Construct A Sediment Textural Model And Salt Budget For Use In Hydrogeological Applications: A Case Study From New South Wales, Australia
More LessThis paper reports on the research to quantify salt budgets and sediment and saprolite textures in a sub-catchment of the Lachlan Catchment, NSW. Data were obtained from airborne electromagnetic (AEM), ground and borehole electromagnetic (EM) data, and laboratory petrophysical and geochemical studies. Algorithms have been derived from statistical relationships between AEM conductivity data, down-hole induction logs and petrophysical attributes. These algorithms are then used in ArcGIS™ software to model the salt budgets and textural distribution model.
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Detection Of Subsurface Diesel Contamination Using Electromagnetic Induction Geophysical Techniques
Authors Jeffrey S. Cooper and Song JinDelineating the extent of petroleum hydrocarbon spills/plumes in subsurface soil and groundwater is typically done by soil boring and installation of monitoring wells. These methods are labor intensive and expensive. Site heterogeneity tends to introduce errors. In this study, we investigated electromagnetic induction survey as an alternative technique to map the extent of subsurface hydrocarbons in a nondestructive, noninvasive way. This study was designed to demonstrate the effectiveness and accuracy of such a survey in its response to subsurface diesel contamination. Geophysical surveys were undertaken at two mining sites near Gillette, Wyoming, using a EM34-XL™ unit. Samples from monitoring wells at the two sites were
correlated to the survey results for validation. Data from the survey well matched the readings from sample analysis. Results from this study indicate that electromagnetic induction surveys could be an effective tool in mapping the subsurface petroleum contaminants.
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Electrical Resistivity Imaging To Monitor A Simulated Leak From An Underground Storage Tank At A Radiological Waste Facility
Authors Brian D. Cubbage, Dale F. Rucker, Marc T. Levitt and Shawn M. CalendineAn electrical resistivity survey was performed during a simulated leak near an underground storage tank, located on the Hanford Site in eastern Washington. The resistivity data collection involved eight surface arrays oriented along orthogonal lines and 41 steel cased wells completed in the vadose zone in the S Tank Farm. The monitoring included three phases to determine the effects of fluid migration: (1) pre leak to establish baseline conditions, (2) mid leak using surface arrays, and (3) post leak survey, conducted several weeks after the cessation of the injection, to determine the simulated leak’s migration.
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Case Study: Resistivity Variation With Biodegradation In A Refinery Oil Dump In Brazil
Authors Guilherme P. Castilho, Daniel F.S. Maia and Maria C. PessoaThe geoelectrical response of an oil contaminated site has been the focus of several scientific studies over the last years, mainly when considering the time-related changes of the oil physical
properties such as it's resistivity due to bacterial degradation. The site under study is located at an oil refinery in Brazil and was used as hydrocarbonate residue dump until two decades ago. An environmental diagnostic request was made by the refinery owner in order to investigate the contamination extension and to plan the area remediation. The contaminated region presented an electrical resistivity two orders of magnitude below the normal background for the area. These results combined with TPH (Total Petroleum Hydrocarbon) levels analysis confirmed previously made laboratory measurements that asserted the decrease in electrical resistivity with biodegradation.
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Integrated Geophysical Approach For Mapping An Active Landslide In Himalaya: A Case Study
Authors Rambhatla G. Sastry, Suman K. Mondal, Param K. Gautam and Ashok K. PachauriA gravimetric survey was carried out over an active landslide area, followed by 2D multielectrode resistivity surveys in order to understand the present landslide in terms of failure surfaces and
predict its future behavior. Preliminary gravity survey has delineated a number of failure surfaces or faults within the active landslide zone and its neighboring area. The electrical resistivity profiles were conducted across the inferred faults lines for confirmation and for deciphering subsurface lithology.
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Wide Area Assessment Of Munitions-Contaminated Sites
Authors H.H. Nelson and A.M. AndrewsIn response to a recent Defense Science Board Task Force report and Congressional direction, the Environmental Security Technology Certification Program initiated a Wide Area Assessment Pilot Program in 2005 with demonstrations at three Formerly Used Defense Sites. In 2006, the Pilot Program was expanded to include three additional sites with different characteristics. All data collection, interpretation, and validation efforts have been completed at five of the sites and data collection and analysis is ongoing at the former Camp Beale in CA. In this paper we briefly describe the technologies used in the demonstrations, present an overview of the survey data collected during the demonstrations, discuss the validation activities undertaken, and close by drawing conclusions on the applicability of this process to other potentially-contaminated sites.
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Determination Of Soil Magnetic Susceptibility From Electromagnetic Induction Measurements
Authors Ryan E. North and Janet E. SimmsKnowledge of the magnetic susceptibility of soils is of primary importance in three subsets of geophysics: archaeology, landmine detection and unexploded ordnance detection. Current methodology involves making a number of in-situ point measurements or collecting soil samples at point locations for later laboratory analysis. Magnetic susceptibility data would be more useful if it could be measured at a higher spatial density, both horizontally and vertically. The long term goal of this project is to invert electromagnetic induction (EMI) data to determine the spatial distribution of magnetic susceptibility. As an initial study, in-situ magnetic susceptibility measurements were collected with three instruments (ZH Instruments SM-30, Geonics EM38B and Bartington MS2 D & F) at two meter spacing along a 100 meter transect. Surface soil samples were collected at each location and analyzed in the laboratory with the Bartington MS2B. Electrical resistivity data (AGI SuperSting R8) and EMI data (DualEM-4S, Geonics EM31 & EM38B, and Geophex GEM-2) were also collected along the line. The question to be answered is, can in-phase EMI data be used as a proxy for magnetic susceptibility point measurements or will a more advance inversion model be required to extract this information.
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Airborne And Ground-Based Electromagnetic Investigation Of The Freshwater Potential In Tsunami-Hit Areas Of Northern Sumatra
Authors Annika Steuer, Bernhard Siemon and Detlef EberleThe earthquake and the tsunami event on December 26th, 2004, damaged the freshwater supply system in the coastal areas of northern Sumatra. Therefore, the German-Indonesian HELicopter Project ACEH (Siemon et al. 2007) was initiated to assist the Indonesian Government in their efforts to plan and realize a sustainable reconstruction of community infrastructure (like freshwater supply) by providing geophysical and hydrogeological data serving as a base for spatial planning. After two successful airborne geophysical surveys funded by the Federal Institute for Geosciences and Natural Resources (BGR) and conducted by the BGR airborne group on the north coast near the city of Banda Aceh and along the west coast between the towns of Calang and Meulaboh from August to October 2005, Coca Cola Foundation Indonesia (CCFI) funded an additional survey on the north-east coast around the town of Sigli (Figure 1).
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Contaminants Evaluation As Indicators Of Water Quality In Ago-Iwoye, Southwestern, Nigeria
More LessThe study evaluates some functional parameters of well water in a densely populated university town, Ago-Iwoye, South-western, Nigeria. Well water samples were collected at ten sites across the town. Analysis of the presence of Coliform count, Salmonella count, standard plate count, physicochemical properties (14 elements and 2 physical parameters) as indicators of water contaminants in the wells in the study area were carried out on the water samples. 40 % of the well samples were contaminated with coliform while 20% were contaminated with salmonella indicating the source of contamination (fecal contaminant). Further analysis revealed that most of the wells have their mineral values within the tolerant level according to WHO standard, however the two most toxic chemicals from the recommendations of WHO were identified in wells 2,3,5 and 10 with values exceeding tolerant level of 0.05 mg/l for lead and 2.56mg/l value for nitrate in well 2.Results confirm the presence of bacteria growth of such samples, highly dangerous to life. Also wells 2, 4, & 8 were contaminated with excess concentration of Iron (Fe) mineral which could make the water tasty and have bacteria growth while wells 1, 2, 3, & 7 have excess concentrations of Copper (Cu) mineral which could cause a stringent taste.
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Twenty Years Of Progress In Electromagnetic Exploration For Near-Surface Geophysics
More LessProgress in electromagnetic exploration for engineering and environmental investigations is characterized by development and adaptation in practice of three technologies. New metods now extensively employed are, terrain conductivity meters for shallow electrical conductivity profiling, time domain electromagnetic soundings in the dept range from about 30 m to 1,500 m and time domain electromagnetic profiling for detecting small buried metal objects. The relatively rapid acceptance of these technologies in engineering practice appears the result of merging of several factors, such as the existence of a solid theoretical foundation, instrument manufacturers who developed instrumentation specific for needs in engineering and environmental studies, and professionals willing to introduce new technologies in practice.
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Two Decades Of Near-Surface Seismology Progress
Authors Don W. Steeples and Rick MillerShallow seismic methods have matured noticeably over the two decades since the first SAGEEP was held in 1988. At that time, the world’s scientific literature contained no more than a dozen refereed papers on shallow (less then 30 meters deep) reflection, but now there are hundreds of such examples. Analysis of surface waves was done with two-channel seismic systems in the 1980’s, whereas seismographs with dozens of recording channels are used today. Even refraction, the shallow-seismic method in use for nearly three quarters of a century, has undergone evolutionary change over the past two decades as tomographic methods have become available for near-surface geophysical applications. Much of the improvement in shallow seismic methods is related to the revolution in microelectronics and the associated several orders of magnitude decrease in computational costs, while developments in sources, seismographs, computers, and methods have all played a role to differing degrees. In many cases, the concepts and methods have been around for decades, but only recently has the computing power been available to put these into play in a cost-effective way. Clearly, advances in microprocessorbased technology have been the primary catalyst for growth in number and diversity of shallow seismic applications as well as the significant improvements in overall data quality.
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Compressional And Shear Wave Seismic Refraction Tomography At Success Dam, Porterville, California
Authors Michael H. Powers, Seth Haines and Bethany L. BurtonSuccess Dam is an earthen embankment located near Porterville, Calif., and is of interest due to earthquake-related collapse potential. In order to characterize the geologic setting of the current dam and to help guide planning for a replacement dam, the U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, has undertaken a multi-method geophysical investigation of the site. The seismic component of this investigation consists of three transects, each with compressional (P) and horizontally polarized shear (S) wave coverage. Along each transect, we calculated tomographic velocity models of P-wave velocity (Vp) and S-wave velocity (Vs). These velocity models agree with available well information and show the transition from unconsolidated sediment at the surface to consolidated sedimentary rock to crystalline basement at depth. Weak zones such as soft sand in the upper sediments and highly weathered/fractured rock are manifested as low-velocity zones. Because Swave velocity is closely tied to engineering properties such as shear strength, low-velocity zones in the S-wave velocity models are of particular interest. We identify several zones of concern using calculated Vp/Vs ratios and Poisson’s ratio; these results will be used to guide future plans at the site.
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Engineering And Environmental Applications Of The Potential Field Methods Of Geophysics.
More LessGravity and magnetic methods are potential field methods and used for a wide range of applications and scales in geosciences. Traditionally, they have been used for regional, large scale investigation of geological structure, such as basement relief and fault structure delineation. Despite the initial contribution of gravity methods to oil/petroleum exploration by detection and mapping of salt domes, “gravity data” is viewed primarily as a “reconnaissance tool in oil exploration” and “to provide constraints in seismic interpretation.” (quotes from Telford et al.,
1990) A familiar, smaller-scale (higher resolution) application of the gravity and magnetic methods is for ore body detection and mapping. The key geological factor required for
application of the gravity and magnetic methods is lateral variation in physical properties of subsurface materials. If the only variation in physical properties is in the vertical direction, such
as is the case for horizontally layered, homogeneous strata, the gravity and magnetic methods are applicable only for confirmation of the uniformity and lack of anomalous conditions.
Engineering and environmental (near-surface) applications of the gravity and magnetic methods were limited prior to the 1960's. Equipment developments and the emergence of new
classes of high priority applications have brought about a resurgence of interest in the potential field methods of geophysics and the development of high-resolution, high-accuracy field
procedures. The new classes of applications can be summarized as environmental (hazardous and toxic waste site assessments), archaeological, abandoned mine lands reclamation, cavity and tunnel detection and mapping, site investigations in karst areas, seismotectonic investigations, and other specialized problems. The gravity and magnetic methods are noted for two facts, one positive and the other somewhat negative: (1) the methods, which rely on measurement of variation in a naturally occurring potential fields, are fundamentally non-invasive and nondisturbing; (2) the interpretation of survey results is complicated by the fundamental, inherent nonuniqueness or ambiguity of source determination. The inherent ambiguity of gravity and
magnetic interpretation often requires the exercise of more geological insight and constraining direct information, such as from boreholes, for quantitative interpretation than required by many
of the other geophysical methods (although in fact interpretation of all geophysical survey results involves varying degrees of nonuniqueness and ambiguity). For purely qualitative, anomaly
mapping applications, the gravity and magnetic methods often can be used when other geotechnical methods are not effective. And, with apologies for not including other near-surface
geophysical methods that are legitimately potential field methods, e.g., direct current resistivity and self-potential, this paper only addresses gravity and magnetic methods and their engineering and environmental applications.
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Adventures In Seeing The Unseen – From Borehole To The Moon
More LessIn 1967, I met Prof. David W. Strangway, who introduced me to geophysics as a freshman at MIT. From then to now, I’ve had a lot of fun doing geophysics in my head, on the computer, in the lab, and in the field. Two of the geophysical methods that I use the most are nonlinear complex resistivity (NLCR) and ground penetrating radar (GPR). I have advanced the state of the art in both, but hardly claim to be a pioneer, as both techniques were pioneered before I was born. I am honored to be invited to give this paper. This is a personal account and perspective on the applications of NLCR and GPR to environmental and engineering applications that barely scratches the surface of what has been accomplished by the geophysical community in the past more than 20 years.
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‘In The Land Of The Blind A One-Eyed Man Is King’
More LessBorehole geophysics has grown from analog/digital hybrid technology to fully digital tools with the implementation of modern PC technology over the last two decades. New logging hardware is ‘smarter’ and easier to use, more sophisticated, and smaller. At the same time, post-acquisition software has become more advanced allowing for more quantitative log analysis to be performed faster. Despite this advancement, modern hardware and software has not matured enough to meet the expectation of industry and to insure quality data and solutions without experienced personnel. The human factor is complicated by a ‘graying’ of the work force and loss of experience at a time of increased demand. Education of a new younger work force is the single biggest issue facing the industry today. Education needs to include an understanding of the specifications, algorithms and limitations of the hardware and software as well as a better understanding of the physical sciences (geology, hydrology, etc.). Only then will the industry and personnel understand ‘Why log?’ or how to apply borehole geophysics and what type of type of information that is needed from the logs. Lastly, the new work force needs to be able to integrate borehole geophysical data with the other available information such as laboratory analysis,
geologic information, hydrologic information, etc. to constrain and optimize underdetermined solutions.
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Great Expectations – Geophysics And Geotechnics
More LessHow could 20 years have passed since the first SAGEEP and the groundwork that conference laid for the formation of the Environmental and Engineering Society? Looking back is an interesting and sometimes informative exercise and in this situation, it provides for this “pioneer” a reassuring hope for the future.
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From Polaroid Film To Data Acquisition Systems And Field Laptops
By F.P. HaeniThe theme of this paper is captured in a paragraph written by one of the early environmental geophysicsts and one of the founders of EEGS - John Greenhouse - in the Leading Edge (Greenhouse, 1991). In his article, John is documenting the rising interest in the field of environmental studies, including hydrogeology and geophysics, by students at the University of Waterloo during the 1980s and describing the emerging field of environmental geophysics. It is during this time period that the seeds were planted for the formation of a new organization that would represent this new breed of scientist. “Finally, is it appropriate to talk about fun? In this growing field there are few megaprojects, few specialists. One must do almost everything oneself, run magnetometers, seismic reflection, radar, process data, massage clients, advertise, write reports, juggle books… you name it. What a pleasure to see the rise of a grass roots geophysical industry where all hands are dirty, where responsibility comes early, where ingenuity, perseverance and luck must compliment technical skills. It’s reminiscent of the stories we read in THE LEADING EDGE of pioneer days in the oil industry. What a contrast to the specialized jobs that so many in the geophysical profession put up with, jobs conducted from the tenth floor of office buildings in London, Houston or Calgary. Environmental geophysics is fun and it is relevant; Students should be told that.”
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Shallow Seismic Reflection Methods For The Delineation And Hydrogeological Characterization Of Buried Eskers In Eastern Ontario
Authors Susan E. Pullan, André J.-M. Pugin and James A. HunterThe surficial deposits of Eastern Ontario include a series of buried and/or confined glacial features, such as esker and fan deposits, which are currently the primary municipal drinking water source for a number of towns and villages. The Geological Survey of Canada is conducting a field program using shallow seismic reflection profiling to delineate the three-dimensional structure of the buried eskers and the surrounding basin stratigraphy
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Comparison Of Compressional And Shear Wave Seismic Reflection Methods For Characterizing Aquifer Stratigraphy At The Former Fort Ord, California
More LessAt the former Fort Ord, in Monterey County, California, contamination threatens an aquifer that provides drinking water for local communities. Assessment and remediation of contamination requires accurate hydrological modeling, which in turn requires a thorough understanding of aquifer stratigraphy. In order to help guide remediation efforts, the U.S. Geological Survey has undertaken seismic re ection surveys at the site, testing both compressional (P) and horizontally polarized (SH) waves. Sledgehammer-source SH data show re ections from interfaces up to approximately 60 m deep which correspond with the major boundaries between aquifers and aquitards. In contrast, P wave data show only the re ection from the water table at approximately 30 m depth. The interpreted SH-wave images agree with available well information, constrain the geology for groundwater models, and provide guidance for future geophysical studies. These favorable results demonstrate the effectiveness of SH re ection methods for imaging unconsolidated aquifer layers.
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Principle And Application Of 4D Microgravity Survey For Engineering Purpose, Case Example: Groundwater Level Lowering And Subsidence In Residential Area Of Jakarta
Authors Wawan G.A. Kadir, Djoko Santoso and Susanti AlawiyahBouguer gravity anomaly derived from observed gravity in the surface reflects all of possibilities of subsurface density change relating to their volume in its lateral and depth variation. In the time-lapse microgravity anomaly, gravity value is observed more than one measurement at certain time period. The difference between both gravity measurements, called as time-lapse microgravity, represents subsurface density contrast and station elevation change. Hence, in the area undergoing surface subsidence and high ground water exploitation, the elevation change and the ground water lowering could be a target of microgravity survey with resolution which depends on gravimeter used and its applied correction. As a case example, three (3) times of gravity measurements had been conducted in the residential area of 2 x 1 km2 with 4 to 6 months period between two (2) measurements. 168 gravity stations were carried out in the area with 50 – 100 m station spacing. In order to investigate subsidence and ground water lowering of the area, gravity gradient and water-pass elevation measurements were also used to support advance analysis. The survey result shows that all of the area undergoes subsidence with 15 cm average rate per year and more than 20 cm per year in the west part of the area. The rate of subsidence was influenced by season with the highest rate is in the dry season. In addition, it was identified the existence of ground water level lowering, sea water intrusion and compaction zone in the east part of the area.
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Evaluating The Feasibility Of Artificial Recharge Sites Using High Resolution Electrical Methods Near Victorville, California
Authors John R. Jansen, Lance Eckhart, Anna Garcia and Ted L. PowellArtificial recharge and water augmentation are important aspects of many groundwater management programs. The subsurface must be understood in reasonable detail to design an efficient
and effective artificial recharge system. Often the cost to collect this data by drilling alone is prohibitively high. When properly applied, geophysical methods can provide subsurface information at a much lower cost. Geophysical data provides more complete coverage and can be used to target drilling efforts toward the most important areas. This presentation illustrates a recent project where geophysical methods were used to help a water agency design a testing program to develop an artificial recharge project. The Mojave Water Agency (MWA) was studying the feasibility of storing water in the unconsolidated material of the Oro Grande Wash due to its thick unsaturated zone and coarse-grained soils that allow for rapid infiltration, as well as its proximity to the California Aqueduct. A test boring installed in 2003 encountered an unexpected thick sequence of clay and silt above the water table. The presence of these fine-grained deposits could potentially impair the ability of the area to store and produce water and forced MWA to collect more data to test the conceptual model of the recharge system. A geophysical survey was used to collect subsurface information over an area of several square miles in an efficient and economic manner. Nine electrical resistivity resistivity profiles and 34 time domain electromagnetic soundings were collected to map the grain size of the soil to depths of over 1,000 feet. The results of the geophysical survey indicated that the subsurface geology was more
complex than originally expected. The deeper sediments are clay rich and poorly suited to recharge the aquifers used by the local municipal well fields. The shallow coarser grained sediments could be used to store water. However, the volume of water that could potentially be stored and recovered with a dedicated well field has yet to be determined. A modeling study of the recharge system is currently being conducted to determine if an economic system can be developed. Other areas are also under consideration.
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The Applicability Of Dc Resistivity Imaging To Investigating The Feedback Mechanism Between Water Quality And Transpiration Beneath Circular Islands In The Okavango Delta, Botswana: A Case Study Of Thata Island
Authors Loago N. Molwalefhe and Elisha M. Shemang2-D Resistivity Survey was carried out in the Thata Island, one of the numerous circular islands in the Okavango Delta to investigate the mechanism governing the interactions between surface water, vegetation and groundwater. Seven profiles were laid across the island and the imaging results indicate that the centre of the island has very low resistivities (less than 10 ohm-m), while outside the island margins resistivity values increase laterally. This lateral resistivity zoning responds to shallow groundwater chemistry below the islands; high solutes load inside and the presence of fresh water outside the islands. Results of borehole to surface resistivity imaging in the island indicate a sinking blob of saline water to depths of 60 m. Groundwater salinities below the island range from 11.7g/l from outside the fringe to 122g/l at the centre of the island. Beyond the depth of 60m, the groundwater salinity drops to about 0.33 g/l at the centre of the island. Depth to water table in all the boreholes is less than 3 m below ground level. Results of the lateral and down-hole imaging as well as water salinity values show a migrating plume of high salinity groundwater from the surface of the island invading a relatively deeper low-density fresh groundwater environment.
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Electrical Characterization Of Success Dam In Porterville, California
Authors Ted Asch, Bethany L. Burton, Michael H. Powers, Brian Rodriguez and Paul BedrosianAn integrated geophysical investigation of Success Dam, near Porterville, California, evaluated the foundation of a proposed new dam and delineated zones of underground water seepage. In fall 2005, the U.S. Geological Survey (USGS) conducted seismic refraction tomography, direct current (DC) resistivity, self-potential (SP), and audio-magnetotelluric (AMT) surveys of the
base of the current Success Dam. The seismic refraction tomography delineated alluvium and bedrock and mapped the bedrock surface. The DC resistivity survey delineated more electrically
conductive zones (ground water) and less conductive (unsaturated) zones within the alluvium. The DC survey also mapped resistive bedrock and indicated subsurface displacement east of the
spillway. Interpretation of self-potential data confirmed the fault by modeling it as a sheet flow source. A repeat SP survey, performed along the dam face in June 2006 during the high water levels, indicated much stronger seepage along the eastern end of the dam. The AMT survey provided corroborating evidence of the conductive zones representing water in unconsolidated materials. Integration of the geophysical information has helped resolve ambiguities and brought out subtleties in data sets that might have been overlooked if another data set with similar, but physically different, information were not present. These geophysical investigations have been successful in characterizing variations in lithology and geologic structure that should be of assistance to the designers of the new Success Dam under development.
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Mapping Salt-Loads Of The Murray River, Australia, Using Airborne And In-River Electromagnetic Methods
Authors A. Fitzpatrick, T.J. Munday, V. Berens, M.A. Hatch and A.L. TelferSalinity in the River Murray and in adjacent floodplains of south-central Australia, has important environmental, economic and social consequences. Methods to monitor the temporal state of river and particularly river-groundwater interactions, have been in place for many years now. However, few have the capacity to define variability at a resolution appropriate for developing effective salinity management strategies, such as salt interception schemes. The use of geophysical methods for rapid high resolution mapping of river sediments has been successfully trialed in Australia, particularly using the “in stream” NanoTEM, a time domain ground EM system, deployed in a boat with the transmitter and receiver towed behind on a rigid floating boom. More recently, tests have been conducted using two different helicopter EM systems; a frequency domain EM system (FDHEM) and a time-domain EM system (TDHEM). Comparisons between conductivity-depth sections derived from the “in stream” NanoTEM and the airborne datasets suggest that the different approaches are comparable. This paper examines the potential of using the FDHEM RESOLVE system as basis for mapping reaches of the river that contribute to elevated salt loads in the Murray River to the south east of Mildura in Victoria. The advantages of the airborne systems become more apparent when data coverage and acquisition costs are considered, particularly in a situation where a parallel swath approached is
employed. This entails the acquisition of adjacent lines of EM data along the centre and along the margins of the river. We suggest this approach provides for a better understanding of recharge and discharge processes and links between the floodplain and the main-river channel. Compared with data acquired along the river alone, this study demonstrated our ability to use Helicopter EM data to map losing and gaining (from a salt load perspective) stretches of the river and to provide insight into which parts of the groundwater-floodplain system were significant contributors to river salt loads. The rapid acquisition of airborne EM data makes these systems more suited to providing temporal snapshots of a river-floodplain environment during dramatic climatic events, such as flooding. In the Murray basin this may assist our understanding of how salt stores are mobilised during such occasions.
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Improved Mapping Of Conductive Clays And Groundwater Salinity Using Attitude-Corrected Helicopter-Borne Em
Authors G. Hodges, T. Munday, A. Heydorn and A. FitzpatrickThe interpretation of airborne electromagnetic (AEM) data has always assumed that the systems maintain a fixed geometry and attitude relative to the earth during survey. However, recent testing has demonstrated that the systems commonly experience significant vertical and horizontal offsets and rotations during flight. Failure to take account of variations in the observed conductivity induced by these movements have limited the potential for AEM systems to accurately resolve shallow conductive features that are often the target in environmental applications.
We present some initial results on the effects of variations in EM bird attitude on the observed response from the RESOLVE FDHEM system, in a recent study conducted in South Australia. Bird attitude was measured using three-antenna GPS array mounted on a boom at the front of the bird during survey. The intent of the survey was to define the thickness and extent of near surface, conductive clays as part of a saline water disposal management strategy being developed by the South Australian State Government. These clays have a significant influence on the rates of groundwater recharge in the study area, and the accurate definition of clay thickness was required as an input into a groundwater recharge model, which in turn was used to determine salt flux to the Murray River system from planned and extant disposal basins in the area. It has been shown that correction for normal changes in bird attitude in relatively smooth terrain
does create a small but measurable change to the HEM data amplitudes, but virtually no measurable change to the apparent resistivity. However, when precision results are desired for inversion of the data, where the amplitude of the response is the most sensitive parameter to the depth to target layers, the geometric correction may be necessary.
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After The Helicopter Is Gone: Investigating Anomalies In Stream-Axis Em Data From The Colorado River, Texas
Authors Jeffrey G. Paine and Edward W. CollinsOngoing investigations of salinization along the upper Colorado River, Texas present an opportunity to integrate results from a stream-axis airborne geophysical survey, well drilling and sampling, and groundand borehole-geophysical surveys. Airborne electromagnetic induction (EM) measurements along 437 km of river and tributary stream axes identifi ed discrete salinized streambed segments, including several near oil fi elds. An initial round of monitor wells verifi ed groundwater salinization in one of the oil fi elds, but did not adequately delineate salinization nor identify specifi c salinity source areas. Subsequent ground and borehole geophysical surveys complemented airborne EM and well data by establishing lateral and vertical salinization bounds, discovering possible salinity source areas, and determining optimal locations for additional monitor wells.
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Spatio-Temporal Monitoring Of Floodplain Environments Using Electromagnetic Methods: A Scaled Approach To Understanding Surface Water- Groundwater Interactions On The Chowilla Floodplain, South Australia
Authors T.J. Munday, I. Overton, A. Fitzpatrick, K. Cahill, V. Berens, M. Hatch and R.C. BrodieGeophysical methods are used in Australia to provide detailed spatial information to help predict the impact of current and future irrigation developments, the design of salt interception schemes and protection of floodplain values. RESOLVE frequency domain helicopter electromagnetic data were acquired over the Chowilla Floodplains, in the Lower Murray region of southern Australia, to provide detailed baseline data on the spatial distribution of near-surface salt stores and materials in the floodplain and their relationship with in-river salinity. Degradation across the floodplain and wetlands has resulted primarily from a significant reduction in flood events, and overgrazing. Restoration of the floodplain will involve the reduction of salinity flow from groundwater into the river and increasing H87environmental flows across the floodplain. Conductivity models predicted from HEM data help identify local recharge and discharge areas,
and links with river salinity. The baseline data provided by the airborne data are used with high resolution ground EM surveys including EM31 and time-domain EM, over targeted areas. Ground methods can be repeated, to monitor affects of artificial flooding designed to restore vegetation health. Similarly the combination of airborne and ground data, allows piezometers to be effectively targeted with the resulting information interpreted within the context of the baseline conductivity structure defined form airborne data.
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The Effect Of Lateral Inohomogeneities On The Interpretation Of Shallow Refraction Seismic Data (Lateral Effects Problem)
More LessLateral effects problem deals with the effect of the lateral changes along the upper refracting interfaces on the lower refractors. The recorded traveltime curve from the lower refractors usually has pseudo number of inflection points and traveltime elements. An increase or decrease in the number of the traveltime elements along the traveltime curve is a result of these lateral variations. Linear traveltime elements are defined as linear segments with the same slope and consequently the same apparent velocity. Such traveltime curves cannot be explained directly by most of shallow refraction seismic interpretation methods. To identify this problem two traveltime parameters are used. These are layer reciprocal time and the apparent refractor velocity. Reversed profiling technique is essential. The ray tracing technique is used in this study to compute the synthetic traveltime curves of first arrivals. Surprisingly, this problem is rarely discussed in literature, and if ever, it is often without suggestions for interpretation, so the name lateral effects is used to define it.
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Design Of Linear Phase Iir Filters With Application To Processing Of Seismic Data
By H.A. MansourIt is possible to design FIR filters with exact linear phase, however high orders are required. Typical group delay specifications can be met with approximately linear-phase IIR filters of lower
order, resulting increased processing speed. In this paper, a lower order linear phase IIR filter is designed from a corresponding FIR one via model reduction techniques. Also, the effects of linear phase FIR and IIR filtration on acquired seismic signals are demonstrated. It is found that the filtration effects are similar, with IIR filter order of only one- half that of FIR, which recommends the changing of FIR filters chain in NRIAG (National Research Institute of Astronomy and Geophysics) digital seismic stations by their alternatives IIR.
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