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Near Surface 2011 - 17th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 12 Sep 2011 - 14 Sep 2011
- Location: Leicester, UK
- ISBN: 978-90-73834-15-6
- Published: 12 September 2011
121 - 127 of 127 results
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Estimating the Effect of Temperature, Density and Water Content on Waste Electrical Resistivity
Authors R. Clement, S. Moreaux and T. GüntherOne of the bioreactor concepts is based on waste moisture optimisation to increase biogas production and accelerate biodegradation to reduce post closure operation and possible impact on the environment. Measuring moisture content of landfilled waste is a difficult task due to the complexity of sensor implementation during landfilling of waste and the weak representativeness of punctual data. Among all the techniques available electrical resistivity tomography proves since many years its potential It proved its ability to evaluate leachate recirculation network performance by showing the zones subjected to electrical resistivity variations. Nevertheless, electrical resistivity is influenced by many physical parameters and no single relationship with volumetric water content was yet established for municipal solid waste (MSW).The aim of this study was to evaluate the effect of temperature, density and water content on electrical resistivity of waste samples in laboratory.
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Wind and Rain Induced Noise on Reflection Seismic Data
By E. NørmarkSeismic noise induced by wind and rain has been monitored as function of rain intensity and wind speed. Noise samples are compiled and characterized. The present results suggest that landstreamer data are more sensitive to noise induced by wind compared to data recorded by planted geophones. Both planted geophones and geophones mounted on sledges are sensitive to noise induced by rain and show approximately the same noise level but with different characteristics. In order to demonstrate the consequences of wind- and rain-induced noise, different noise levels are simulated on vibroseismic data. Data samples illustrate the influence of noise at certain wind speeds and rain intensities on correlated and stacked data. Noise from rain, recorded by geophones mounted on sledges, is mainly visible as localized events, caused by the individual rain drops. Even with moderate to heavy rain, relatively few events of short duration are present compared to quiet periods in between. This can be useful in developing a noise suppression method reducing noise from rain on uncorrelated vibroseismic data. The method requires that several sweeps are carried out at each source location. The performance of the noise suppression method is tested on data, where noise has been imposed.
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Seismo-acoustic Emission in Near-zone of Powerful Vibrator
Authors Y.I. Kolesnikov and E.A. HogoevThe results of the full-scale experiment on the study of vibrations influence on seismo-acoustic emission in near-zone of powerful 40-ton vibrator are presented. It is shown that after vibration sessions lasting a few tens of minutes the gradual increase of energy of microseisms takes place. After ending of the vibrations energy of microseisms begins to decrease. Data processing using the algorithm of seismic emission tomography justifies the endogenous nature of microseisms initiated by powerful vibrations.
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SAGEEP1 Multi-elevation Calibration of Frequency Domain Electromagnetic Data
Authors B.J. Minsley, G. Hodges, B.D. Smith and J.D. AbrahamThe ability to make quantitative inferences about subsurface properties is an important component of interpreting frequency domain electromagnetic (FDEM) data. Systematic data errors caused by imperfect instrument calibration can lead to inversion artifacts or, in some cases, best-fit models that are inconsistent with the measured data. Factory and inflight internal system calibrations have helped to reduce, though not always eliminate, calibration errors in modern FDEM systems. A number of methods have been developed to calibrate data after it has been acquired, but these are primarily based on having auxiliary information about subsurface properties from well logs or ground-based geophysical surveys, which are not always available and may have inaccuracies of their own. In this work, we propose a new strategy for calibrating FDEM data that does not rely on prior knowledge of the subsurface structure. This calibration procedure involves acquiring multiple datasets along a single calibration line at several different survey elevations at the beginning of a survey. Calibration parameters, consisting of gain, phase, and bias correction factors for each frequency, are derived by requiring that data from the multiple survey elevations must be consistent with the same earth model at each location along the line. This is accomplished by simultaneously inverting the multi-elevation data for an earth model at each location along the profile along with a single set of calibration parameters. This joint inversion strategy recovers the combination of earth models and calibration parameters that are optimally consistent with the multi-elevation data. The derived calibration parameters are then applied to the survey data, and the calibration procedure can be repeated as necessary to correct for system drift.
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SAGEEP2 Assessing Water Storage Changes on the Field Scale Combining Superconducting Gravimeter Observations with a Hydro-logical Model
Authors B. Creutzfeldt, A. Güntner, H. Wziontek and B. MerzInformation on water storages is crucial for many different applications, like agricultural production, groundwater recharge or transport of contaminants. Limitations of observation techniques and high spatio-temporal variability make the estimation of water storage challenging, especially for deeper zones. Temporal gravimeter observations are significantly influenced by water storage changes (WSC) at the field scale and hence may provide valuable information about the state of the hydrological system. In this study, we assess the benefit of temporal gravimeter measurements as an integral signal for hydrological application by evaluating a hydrological model using residuals time series of a superconducting gravimeter (SG). A simple conceptual model is used to estimate local WSC in the snow, soil, unsaturated saprolite, and saturated aquifer storage. The model is calibrated and evaluated against SG data on the one hand and several groundwater and/or soil moisture data on the other. The model is validated against independently estimated WSC derived from a state-of-the-art lysimeter. The results show that using an SG as calibration constraint improves the model results substantially in terms of predictive capability and variation of the behavioral model runs in comparison to classical hydrological point measurements. Gravity measurements integrate over different hydrological storage components and the sampling volume is several orders of magnitude larger than that for the point measurements. The general problem of specifying the internal model structure or individual parameter sets can, however, not be solved with gravimeters alone. Additionally, the results show that also WSC in the deep vadose zone contribute significantly to the hydrological cycle, so SG might provide a tool to continuously and non-invasively monitor WSC also in this zone.
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SAGEEP3 Multi-scale Monitoring of Ecohydrological Processes Using Electrical Resistivity Tomography
Authors R.L. van Dam, D. Hyndman, A. Kendall, K. Diker, B. Christoffersen and S. SaleskaHydrogeophysics is a growing discipline that holds significant promise to help elucidate details of dynamic processes in the near surface, built on the ability of geophysical methods to measure properties from which hydrological and geochemical variables can be derived. For example, bulk electrical conductivity is governed by, amongst others, interstitial water content, fluid salinity, and temperature, and can be measured using a range of geophysical methods. In many cases, electrical resistivity tomography (ERT) is well suited to characterize these properties in multiple dimensions and to monitor dynamic processes, such as water infiltration and solute transport. In recent years, ERT has been used increasingly for ecosystem research in a wide range of settings; in particular to characterize vegetation-driven changes in root-zone and near-surface water dynamics. This increased popularity is due to operational factors (e.g., improved equipment, low site impact), data considerations (e.g., excellent repeatability), and the fact that ERT operates at scales significantly larger than traditional point sensors. Current limitations to a more widespread use of the approach include the high equipment costs, and the need for site-specific petrophysical relationships between properties of interest. In this presentation we will discuss recent equipment advances and theoretical and methodological aspects involved in the accurate estimation of soil moisture from ERT results. Examples will be presented from two studies in a temperate climate (Michigan, USA) and one from a humid tropical location (Tapajos, Brazil).
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SAGEEP4 Integrating Hydrology and Geophysics to Evaluate the Impact of Artificial Recharge on Groundwater in Rural India
Authors S. Moysey, D. Matz, S. Gangrade, M. Choudhary, C. Guha and R. RavindranathThe monsoonal climate of India coupled with the complex geology and low storage capacity of the Deccan basalts contribute to water scarcity in central India during the dry season. One of the primary tools proposed to manage this problem is the artificial recharge of runoff captured during the monsoon to enhance groundwater availability throughout the year. One common approach for artificial recharge is the construction of small dams to generate percolation ponds, as exemplified by a small reservoir in the Salri watershed of Mahdya Pradesh, India. We use this specific example to illustrate how the integration geophysical and hydrologic data can be used to understand the influence of the dam on groundwater in the watershed. Electrical resistivity and electromagnetic induction surveys are used to assist in developing a geologic conceptual model for the watershed consisting of a thick sequence of basalt flows overlain in the lowland portion of the watershed by weathered basalt and alluvium for a depth of up to 10m. This geologic model has guided our understanding of the local flow system. A shallow flow system in the near-surface weathered basalts and alluvium is the primary source of water for agriculture. In contrast, vertical variability in the competent basalt flows is expected to create a highly anisotropic flow system with high horizontal permeability and low vertical permeability. As a result, the geophysical data help to form a conceptual model where the dam primarily impacts the shallow aquifer and has limited impact on deeper regional flow systems. To assess this hypothesis and quantify the impact of the dam on the overall hydrology of the watershed a hydrologic monitoring program was implemented. By integrating the geophysically-based conceptual model with this hydrologic data we are able to provide a quantitative assessment of the role of the dam within the watershed.
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