1,720,967 research outputs found
Tracking contaminant transport using time-lapse geophysics: A review on applications of electrical methods
No full textSource depth estimation of self-potential anomalies by spectral methods
No full textSpectral analysis of the self-potential (SP) field for geometrically simple anomalous bodies is studied. In particular, three spectral techniques, i.e. Periodogram (PM), Multi Taper (MTM) and Maximum Entropy (MEM) methods, are proposed to derive the depth of the anomalous bodies. An extensive numerical analysis at varying the source parameters outlines that MEM is successful in determining the source depth with a percent error less than 5%. The application of the proposed spectral approach to the interpretation of field datasets has provided depth estimations of the SP anomaly sources in very good agreement with those obtained by other numerical methods
Self-Potential data inversion through a Genetic-Price algorithm
No full textA global optimization method based on a Genetic-Price hybrid Algorithm (GPA) is proposed for identifying the source parameters of self-potential (SP) anomalies. The effectiveness of the proposed approach is tested on synthetic SP data generated by simple polarized structures, like sphere, vertical cylinder, horizontal cylinder and inclined sheet. An extensive numerical analysis on signals affected by different percentage of white Gaussian random noise shows that the GPA is able to provide fast and accurate estimations of the true parameters in all tested examples. In particular, the calculation of the root-mean squared error between the true and inverted SP parameter sets is found to be crucial for the identification of the source anomaly shape. Finally, applications of the GPA to self-potential field data are presented and discussed in light of the results provided by other sophisticated inversion methods
Electrokinetic component of the self-potential for complex aquifer system characterization
No full textThe study focuses on the analysis of the electrokinetic component of the self-potential (SP), which may be associated to the diagenetic processes that control the hydrogeological behaviour of widespread pyroclastic lithostratigrafic unit in saturated conditions. In silica rocks, such a component is usually associated with the drag of the excess of positive charges resulting in a positive electrical potential in the groundwater flow direction. With regard to the most important and widespread pyroclastic formation of Southern Italy (i.e. Campanian Ignimbrite), this study points out that an inversion of the charge carrier's sign can be observed in presence of zeolitc zones and quaternary ammonium compounds. An example of this occurrence is here presented with reference to an area characterized by high antropic impact and periodic flooding events, where SP, resistivity and hydrogeological surveys were performed. An integration of the SP data with the hydrogeophysical model of the pyroclastic-alluvial aquifer, allowed to individuate diagenetic processes, which likely modify the hydrogeological behavior of the intercalated ignimbrite unit and control the contaminant propagation. Finally, some hints on groundwater contamination emerge from a preliminary study on the correlation between the residual map of the SP anomalies and the measured redox potential
High-resolution spectral analysis methods for self-potential data inversion
No full textIn the last few decades, the spectral analysis approach has been successfully applied for depth estimation of gravity and magnetic anomaly sources by analyzing the signal power distribution as a function of spatial frequencies. In the present work, application of high-resolution spectral methods is proposed for inversion of self-potential (SP) data. In particular, Periodogram Method (PM), Maximum Entropy Method (MEM) and Multi Taper Method (MTM) are used to invert synthetic SP data generated by cylinder and sheet sources. From analysis, MEM was found to be better in providing more accurate estimates of the source depth as compared to PM and MTM. Finally, the application of the proposed methods to field data is presented and the estimated depths are compared with those obtained by other numerical methods
A comparative analysis of SP data inversion by spectral, tomographic and global optimization approaches
No full textSelf-Potential (SP) fields are natural fields that originate from various forcing mechanisms related to electrical, hydraulic, chemical and thermal gradients. Due to the complexity of the source mechanisms, inversion of SP data is not easy and motivates the development of suitable techniques depending on application field, which ranges from engineering and geotechnical investigations to geothermal and mineral explorations. In this work, quantitative interpretations of self-potential data are given when SP anomaly sources can be modelled by simple polarized bodies whose parameters have to be determined. In particular, a comparative analysis is performed for the solutions of three different methods based on highresolution spectral analysis, tomographic approach and global optimization, respectively. The efficiency of each technique has been tested by finding depth, polarization angle and shape factor of the anomaly source on synthetic data generated by simple geometrical structures (like sphere, horizontal and vertical cylinder and inclined sheet) and on field examples. The study shows limits and potentialities of the investigated methods and suggests hybrid algorithms as suitable tools for an accurate and full characterization of the anomaly source
Self-Potential data inversion through the integration of spectral analysis and tomographic approaches
No full textAn integrated approach to interpret Self-Potential (SP) anomalies based on spectral analysis and tomographic methods is presented. The Maximum Entropy Method (MEM) is used for providing accurate estimates of the depth of the anomaly source. The 2-D tomographic inversion technique, based on the underground charge occurrence probability (COP) function, is, then, used to fully characterize the anomalous body, as the MEM is not helpful in delineating the shape of the anomaly source. The proposed integrated approach is applied for the inversion of synthetic SP data generated by geometrically simple anomalous bodies, such as
cylinders and inclined sheets. This numerical study has allowed the determination of mathematical relationships between zero lines of the COP distributions, the polarization angles and the positions along the profile of the causative sources, which have been of great help for interpreting the related SP anomalies. Finally, the analysis of field examples shows the high potential applicability of the proposed integrated approach for SP data inversion
Time evolution of self-potential anomaly sources due to organic contaminant transport by different data inversion approaches
No full textThe infiltration of organic contaminants in the subsoil may cause major effect on groundwater quality. The employ of realtime monitoring of physical and/or chemical parameters as well as of simulation modelling has proved an useful tool for predicting the underground solute transport (Cassiani and Binley, 2005). Among the commonly used geophysical methods in hydrology, the electrical methods have proved the most effective techniques for detecting soil and/or groundwater pollution due to changes in soil electrical properties resulting from biodegradation processes (Ntarlagiannis et al., 2016 and references therein). In particular, this work is focused on modelling of the transport of olive oil mill wastes (OOMWs) by using different inversion approaches of selfpotential (SP) data acquired at different times in a pilot study area (i.e. an evaporation pond of OOMWs) located in western Crete (Greece). Specifically, five SP datasets acquired from May to July 2014 along a profile located about 15 m from Keritis river have been analyzed. Quantitative interpretations of selected SP anomaly sources, likely related to zones with contamination from OOMWs, are attempted by using simple polarized source models whose parameters have to be determined. In particular, three different methods based on high resolution spectral analysis, tomographic approach and global optimization, respectively, have been used to estimate the time evolution of the source depth. A validation of the obtained results has been provided by comparison with the electrical resistivity distributions coming from time-lapse resistivity tomography surveys performed along the SP measurement profile
Multi-methodological geophysical approach for contamination detection in a high flood risk area (southern Italy)
No full textDue to very fast industrial growth and urbanization, problems of environmental contaminations are growing rapidly. The soil and groundwater pollution is one of the most important concerns that have received attention at local, regional and global levels because of their impact on public health. The use of geophysical techniques is of great help for environmental studies because they not only give the localization of polluted areas, but also provide an estimate of the extent of contamination, through the determination of the most likely contaminated volumes. To identify possible soil and groundwater contamination, integrated analysis of resistivity, chargeability and self-potential data has been performed in a survey area located in the town of Castel San Giorgio (Salerno, Italy) in the western basin of Solofrana river valley. This area is periodically affected by flooding induced by severe or significant rainfall, which cause the river to overflow and contribute to potential soil and groundwater contamination by heavy metals discharged from the tanning plants operating in the upper part of the valley
Application of self-potential method for monitoring the contamination from Olive oil mills' waste (OOMW)
No full textThe self-potential (SP) method is one of the oldest geophysical method which measures the distribution of natural electric potential at the ground surface. Integrated electrical resistivity tomography (ERT) and self-potential techniques are often used to identify groundwater flow direction and possible soil and groundwater contamination. In the present study, the results of ERT and SP measurements are analyzed to characterize a site in western Crete contaminated from olive oil mill waste (OOMW). The production of olive oil is one of the major economic importance in Mediterranean region, particularly in Greece which is the third country (worldwide) in olive-oil production with Island of Crete contributing more than 30% of the total olive oil production in Greece. The production procedure of olive oil generates large volumes of OOMW, which pose serious environmental problems due to their high organic load and rich in inorganic constituents. The OOMWs are usually disposed in poorly constructed shallow evaporation ponds, which often results into overflow or leaking of wastewaters, hence, polluting soil and groundwater. The high electrical conductivity and the high concentration of phenolic compounds are the main features that make OOMWs detectable by means of geoelectric prospecting methods. In the study area, five self-potential surveys from May to July 2014 were carried out along an ERT profile by using the fixed base configuration. The SP field data have been analyzed by using the 2D tomographic approach bas ed on the charge occurrence probability (COP) function and spectral methods. Taking into account the electrical resistivity distribution from the ERT tomography, COP maps are interpreted to provide temporal information about self-potential sources and their possible correlations with contamination from OOMW
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