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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
21 - 40 of 164 results
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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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