2-Dimensional soil and vadose-zone representation using an EM38 and EM34 and a laterally constrained inversion model

Soil Research ◽  
2009 ◽  
Vol 47 (8) ◽  
pp. 809 ◽  
Author(s):  
J. Triantafilis ◽  
F. A. Monteiro Santos
Keyword(s):  
Electrical Conductivity ◽  
Vadose Zone ◽  
Root Zone ◽  
Clay Content ◽  
Inversion Algorithm ◽  
Near Surface ◽  
Particle Size Fractions ◽  
Murray Darling Basin ◽  
Full Solution ◽  
Soil Particle Size Fractions

The network of prior streams and palaeochannels common across the Riverine Plains of the Murray–Darling Basin act as conduits for the redistribution of water and soluble salts beneath the root-zone. To improve scientific understanding of these hydrological processes there is the need to better represent and map the connectivity and spatial extent of these physiographic and stratigraphic features. Groundbased electromagnetic (EM) instruments, which measure bulk soil electrical conductivity (σa), have been used widely to map their areal distribution across the landscape. However, methods to resolve their location with depth have rarely been attempted. In this paper we employ a 1-D inversion algorithm with 2-D smoothness constraints to predict the true electrical conductivity (σ) at discrete depth increments using EM data. The EM data we use include the root-zone measuring EM38 and the deeper sensing EM34. We collected EM38 data in the vertical (EM38v) and horizontal (EM38h) dipole modes and EM34 data in the horizontal mode and coil spacing of 10, 20, and 40 m (respectively, EM34-10, EM34-20, and EM34-40). In order to compare and contrast the value of the various EM data we carried out multiple inversions using different combinations, which include: independent inversions of (i) EM38 (root-zone) and (ii) EM34 data (vadose-zone), and in combination using (iii) EM38v, EM38h, and EM34-10 (near-surface), and (iv) all 5 EM datasets (regolith) available. The general patterns of σ are shown to compare favourably with the known pedoderms, physiographic, and stratigraphic features and soil particle size fractions collected from calibration cores drilled across the lower Macquarie Valley study area. In general we find that the EM38 assists in resolving root-zone variability, specifically duplex soil profiles and physiographic features such as prior streams, while the use of the EM34 assists in resolving the stratigraphic nature of the vadose-zone and specifically the likely location of palaeochannels and subsurface anomalies that may indicate the location of good quality groundwater and/or clay aquitards. In this case, our potential to use σ to predict clay content is limited by the non-linearity of the cumulative functions. In order to improve on the non-linearity of our inversion we need to develop a full solution of the forward problem.

Resolving the spatial distribution of the true electrical conductivity with depth using EM38 and EM31 signal data and a laterally constrained inversion model

Soil Research ◽  
2010 ◽  
Vol 48 (5) ◽  
pp. 434 ◽  
Author(s):  
J. Triantafilis ◽  
F. A. Monteiro Santos
Keyword(s):  
Electrical Conductivity ◽  
Spatial Distribution ◽  
Vadose Zone ◽  
Root Zone ◽  
Joint Inversion ◽  
Geophysical Methods ◽  
Exchange Capacity ◽  
Saturated Soil ◽  
Cotton Field ◽  
Inversion Algorithm

The ability to map the spatial distribution of average soil property values using geophysical methods at the field and district level has been well described. This includes the use of electromagnetic (EM) instruments which measure bulk soil electrical conductivity (σa). However, soil is a 3-dimensional medium. In order to better represent the spatial distribution of soil properties with depth, various methods of inverting EM instrument data have been attempted and include Tikhonov regularisation and layered earth models. In this paper we employ a 1-D inversion algorithm with 2-D smoothness constraints to predict the true electrical conductivity (σ) using σa data collected along a transect in an irrigated cotton field in the lower Namoi valley. The primary σa data include the root-zone measuring EM38 and the vadose-zone sensing EM31, in the vertical (v) and horizontal (h) dipole modes and at heights of 0.2 and 1.0 m, respectively. In addition, we collected σa with the EM38 at heights of 0.4 and 0.6 m. In order to compare and contrast the value of the various σa data we carry out individual inversions of EM38v and EM38h collected at heights of 0.2, 0.4, and 0.6 m, and EM31v and EM31h at 1.0 m. In addition, we conduct joint inversions of various combinations of EM38 σa data available at various heights (e.g. 0.2 and 0.4 m). Last we conduct joint inversions of the EM38v and EM38h σa data at 0.2, 0.4, and 0.6 m with the EM31v and EM31h at 1.0 m. We find that the values of σ achieved along the transect studied represent the duplex nature of the soil. In general, the EM38v and EM38h collected at a height of 0.2, 0.4, and 0.6 m assist in resolving solum and root-zone variability of the cation exchange capacity (cmol(+)/kg of soil solids) and the electrical conductivity of a saturated soil paste extract (ECe, dS/m), while the use of the EM31v and EM31h at 1.0 m assists in characterising the vadose zone and the likely location of a shallow perched-water table. In terms of identifying an optimal set of EM σa data for inversion we found that a joint inversion of the EM38 at a height of 0.6 m and EM31 signal data provided the best correlation with electrical conductivity of a saturated soil paste (ECp, dS/m) and ECe (respectively, 0.81 and 0.77) closely followed by a joint inversion of all the EM38 and EM31 σa data available (0.77 and 0.56).

Transformation of VLF data into apparent resistivities and phases

Geophysics ◽  
1999 ◽  
Vol 64 (5) ◽  
pp. 1393-1402 ◽  
Author(s):  
Mehran Gharibi ◽  
Laust B. Pedersen
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Large Scale ◽  
Low Cost ◽  
Real Data ◽  
Geological Structure ◽  
Direct Estimate ◽  
Horizontal Magnetic Field ◽  
Near Surface ◽  
Full Solution

In the VLF method, the ratio between the vertical and the horizontal magnetic field or the total magnetic field anomaly is measured to detect localized changes in electrical conductivity contrasts. Although the VLF technique has probably been the most popular electromagnetic (EM) tool for mapping near‐surface geological structures in a large scale for the past few decades because of the low cost and speed with which surveys can be carried out, the measurements themselves do not give a direct estimate of electrical conductivity. A fast iterative method has been developed to estimate the impedance or apparent resistivity and phases from measurements of the magnetic components at the surface of a 2-D geological structure. From Maxwell’s equations in E-polarization, a relation was derived between the horizontal and vertical components of the magnetic field. A full solution has been obtained by making use of the fact that the secondary horizontal and vertical magnetic fields are of internal origin and form a Hilbert transform pair. Synthetic and real VLF data have been used to evaluate the performance and limitation of the method. Using synthetic and real data, one can achieve a full recovery of the E-polarization impedance as long as the length of the profile is sufficiently long. A number of precautions must be taken to ensure reliable estimation of impedance results.

Fast resistivity/IP inversion using a low‐contrast approximation

Geophysics ◽  
1996 ◽  
Vol 61 (1) ◽  
pp. 169-179 ◽  
Author(s):  
Les P. Beard ◽  
Gerald W. Hohmann ◽  
Alan C. Tripp
Keyword(s):  
Inversion Algorithm ◽  
Forward Solution ◽  
Near Surface ◽  
Low Contrast ◽  
Volume Integral Equation ◽  
Strike Direction ◽  
Resistivity Model ◽  
Resistivity Inversion ◽  
Full Solution ◽  
End Corrections

By computing only the diagonal terms of the volume integral equation forward solution of the 3-D DC resistivity problem, we have achieved a fast forward solution accurate at low to moderate resistivity contrasts. The speed and accuracy of the solution make it practical for use in 2-D or 3-D inversion algorithms. The low‐contrast approximation is particularly well‐suited to the smooth nature of minimum structure inversion, since complete forward solutions may be computationally expensive. By using this approximate 3-D solution as the forward model in an inversion algorithm, and by constraining the resistivities and polarizabilities along any row of cells in the strike direction to be held constant, we effect a fast 2-D resistivity inversion that contains end corrections. Because the low‐contrast solution is inaccurate for cells near the electrodes, we employ a full solution to compute the response of the near‐surface when the near‐surface environment is substantially different from the host rock. This response is stored and used in the iterative resistivity inversion in conjunction with the approximate solution. Once an adequate estimated resistivity model has been found, derivatives from this model are used with Seigel’s formula to compute the inverse solution to the linear polarizability problem in a single iteration.

A spatially constrained 1D inversion algorithm for quasi-3D conductivity imaging: Application to DUALEM-421 data collected in a riverine plain

Geophysics ◽  
2011 ◽  
Vol 76 (2) ◽  
pp. B43-B53 ◽  
Author(s):  
Fernando Acácio Monteiro Santos ◽  
John Triantafilis ◽  
Kira Bruzgulis
Keyword(s):  
Electromagnetic Induction ◽  
Clay Content ◽  
Agricultural Systems ◽  
Stream Channel ◽  
Inversion Algorithm ◽  
Vertical Extent ◽  
Murray Darling Basin ◽  
Imaging Application ◽  
Em Induction ◽  
Conductivity Imaging

The efficient use of water in irrigated agricultural systems is of increasing importance given the changes in climatic patterns currently being experienced in the irrigated areas of the Murray-Darling Basin (MDB) in Australia. In previous research, electromagnetic (EM) induction instruments have been used to map the distribution of the clay content in those areas. However, describing their vertical extent and connectivity with groundwater tables or stratigraphic features such as paleochannels has not been studied adequately. One of the reasons for the paucity of research is the lack of suitable instrumentation or software to invert apparent conductivity (σa) data. The aim of this research is to demonstrate how DUALEM-421 equipment, which operates using electromagnetic induction theory, can be used to map not only the areal distribution of a prior stream channel but its vertical extent by inputting the data into a 1D spatially constrained algorithm for quasi-3D conductivity imaging. We discovered how the inversion of the apparent electrical conductivity, measured in the horizontal (HCP) and perpendicular (PRP) arrays, characterizes the Quaternary alluvial clays which dominate the riverine plain of the lower Gwydir valley, and indicates the location and extent of a prior stream channel and its sediments across Auscott Midkin field 11. We found the calculated conductivity values favorably represent the known stratigraphy of these physiographic units. Our results suggest the prior stream channel may be interconnected with a more extensive paleochannel.

scholarly journals An evaluation of water quality at Sandhill Wetland: implications for reclaiming wetlands above soft tailings deposits in northern Alberta, Canada

2021 ◽  
Author(s):  
Jeremy A. Hartsock ◽  
Jessica Piercey ◽  
Melissa K. House ◽  
Dale H. Vitt
Keyword(s):  
Water Quality ◽  
Electrical Conductivity ◽  
Surface Water ◽  
Water Chemistry ◽  
Water Quality Monitoring ◽  
Total Alkalinity ◽  
Near Surface ◽  
Water Quality Guidelines ◽  
Quality Guidelines ◽  
Annual Water

AbstractThe experimental Sandhill Wetland is the first permanent reclamation of a composite tailings deposit, and annual water quality monitoring is of specific interest for evaluating and predicting long-term reclamation performance. Here, we present water chemistry monitoring data obtained from Sandhill Wetland (years 2009–2019) and compare results to twelve natural reference wetlands and to environmental quality guidelines for Alberta surface waters. By comparing water quality at Sandhill Wetland and natural sites to established guidelines, we can begin to document the natural background water quality of wetlands in the region and examine if guideline exceedances are seen in natural undisturbed environments, or appear only at active reclamation sites. At Sandhill Wetland the dominant ions in near-surface water were bicarbonate, sulfate, chloride, sodium, calcium, and magnesium. Since the first growing season concentrations for these ions have increased annually, causing concurrent increases in electrical conductivity. In year 2019, water chemistry at Sandhill Wetland was most comparable to regional saline fens, systems that exhibit elevated electrical conductivity and high sodicity. Near-surface water at Sandhill Wetland exceeded water quality guidelines for three substances/properties (dissolved chloride, iron, and total alkalinity) in the most recent year of monitoring. The saline fen natural sites also exceeded water quality guidelines for the same chemical substances/properties, suggesting guideline exceedances are a norm for some natural wetland site types in the region. Of note, in each year of monitoring at Sandhill Wetland, dissolved organic compounds evaluated in sub- and near-surface water were below detection limits.

A hybrid regularization scheme for the inversion of magnetotelluric data from natural and controlled sources to layer and distortion parameters

Geophysics ◽  
2012 ◽  
Vol 77 (4) ◽  
pp. E301-E315 ◽  
Author(s):  
Thomas Kalscheuer ◽  
Juliane Hübert ◽  
Alexey Kuvshinov ◽  
Tobias Lochbühler ◽  
Laust B. Pedersen
Keyword(s):  
Transfer Functions ◽  
Homogeneous Distribution ◽  
Stable Configuration ◽  
Inversion Algorithm ◽  
Magnetotelluric Data ◽  
Data Set ◽  
Near Surface ◽  
Minimum Solution ◽  
Magnetic Transfer ◽  
Distortion Parameters

Magnetotelluric (MT), radiomagnetotelluric (RMT), and, in particular, controlled-source audiomagnetotelluric (CSAMT) data are often heavily distorted by near-surface inhomogeneities. We developed a novel scheme to invert MT, RMT, and CSAMT data in the form of scalar or tensorial impedances and vertical magnetic transfer functions simultaneously for layer resistivities and electric and magnetic galvanic distortion parameters. The inversion scheme uses smoothness constraints to regularize layer resistivities and either Marquardt-Levenberg damping or the minimum-solution length criterion to regularize distortion parameters. A depth of investigation range is estimated by comparing layered model sections derived from first- and second-order smoothness constraints. Synthetic examples demonstrate that earth models are reconstructed properly for distorted and undistorted tensorial CSAMT data. In the inversion of scalar CSAMT data, such as the determinant impedance or individual tensor elements, the reduced number of transfer functions inevitably leads to increased ambiguity for distortion parameters. As a consequence of this ambiguity for scalar data, distortion parameters often grow over the iterations to unrealistic absolute values when regularized with the Marquardt-Levenberg scheme. Essentially, compensating relationships between terms containing electric and/or magnetic distortion are used in this growth. In a regularization with the minimum solution length criterion, the distortion parameters converge into a stable configuration after several iterations and attain reasonable values. The inversion algorithm was applied to a CSAMT field data set collected along a profile over a tunnel construction site at Hallandsåsen, Sweden. To avoid erroneous inverse models from strong anthropogenic effects on the data, two scalar transfer functions (one scalar impedance and one scalar vertical magnetic transfer function) were selected for inversion. Compared with a regularization of distortion parameters with the Marquardt-Levenberg method, the minimum-solution length criterion yielded smaller absolute values of distortion parameters and a horizontally more homogeneous distribution of electrical conductivity.

Computer Application in Geosciences: Imaging of the Subsurface by Structural Coupled Inversion of Potential Field Data

2014 ◽  
Vol 644-650 ◽  
pp. 2670-2673
Author(s):  
Jun Wang ◽  
Xiao Hong Meng ◽  
Fang Li ◽  
Jun Jie Zhou
Keyword(s):  
Potential Field ◽  
Field Data ◽  
Gravity Data ◽  
Computer Application ◽  
Magnetic Data ◽  
Imaging Method ◽  
Inversion Algorithm ◽  
Constant Property ◽  
Near Surface ◽  
Potential Field Data

With the continuing growth in influence of near surface geophysics, the research of the subsurface structure is of great significance. Geophysical imaging is one of the efficient computer tools that can be applied. This paper utilize the inversion of potential field data to do the subsurface imaging. Here, gravity data and magnetic data are inverted together with structural coupled inversion algorithm. The subspace (model space) is divided into a set of rectangular cells by an orthogonal 2D mesh and assume a constant property (density and magnetic susceptibility) value within each cell. The inversion matrix equation is solved as an unconstrained optimization problem with conjugate gradient method (CG). This imaging method is applied to synthetic data for typical models of gravity and magnetic anomalies and is tested on field data.

Shallow Magnetic Induction Measurements for Delineating Near-Surface Hot Groundwater Sources in Alaskan Geothermal Areas

1983 ◽  
Vol 105 (2) ◽  
pp. 156-161 ◽  
Author(s):  
T. E. Osterkamp ◽  
K. Kawasaki ◽  
J. P. Gosink
Keyword(s):  
Electrical Conductivity ◽  
Magnetic Induction ◽  
Hot Springs ◽  
Measured Temperature ◽  
Conductivity Data ◽  
Induction Method ◽  
Near Surface ◽  
Saline Groundwater ◽  
Geophysical Surveys ◽  
Conductivity Anomalies

Variations in the electrical conductivity of a soil and water system with temperature and salt concentration suggest that a soil containing hot and/or saline groundwater may be expected to have a higher conductivity compared to a cooler and/or less saline system. Temperature and conductivity surveys were carried out at Pilgrim Springs, on the Seward Peninsula, and at Chena Hot Springs, near Fairbanks, to test the use of a magnetic induction method (which measures electrical conductivity) for delineating near-surface hot groundwater sources in geothermal areas surrounded by permafrost. Comparison of the temperature data and conductivity data from these surveys demonstrates that the conductivity anomalies, as measured by the magnetic induction method, can be used to define the precise location of hot groundwater sources in these geothermal areas with the higher temperatures correlating with higher values of conductivity. Magnetic induction measurements of conductivity can also be used to define the lateral extent of the thawed geothermal areas (used for calculating the stored energy) in permafrost terrain. The utility of these magnetic induction measurements of conductivity for reconnaissance geophysical surveys of geothermal areas is that a much greater density of data can be obtained in a shorter time in comparison with shallow temperature measurements. In addition, it is simpler, cheaper and easier (physically) to obtain the data. While conductivity anomalies can result from other than hot and/or saline groundwater, these conductivity data, when coupled with a few measured temperature profiles and groundwater samples, should result in reliable reconnaissance level geophysical surveys in Alaskan geothermal areas.

scholarly journals Using Multivariate Geostatistics to Assess Patterns of Spatial Dependence of Apparent Soil Electrical Conductivity and Selected Soil Properties

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Glécio Machado Siqueira ◽  
Jorge Dafonte Dafonte ◽  
Montserrat Valcárcel Armesto ◽  
Ênio Farias França e Silva
Keyword(s):  
Electrical Conductivity ◽  
Soil Properties ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Clay Content ◽  
Data Sets ◽  
Soil Electrical Conductivity ◽  
Multivariate Geostatistics ◽  
Northwestern Spain

The apparent soil electrical conductivity (ECa) was continuously recorded in three successive dates using electromagnetic induction in horizontal (ECa-H) and vertical (ECa-V) dipole modes at a 6 ha plot located in Northwestern Spain. One of the ECadata sets was used to devise an optimized sampling scheme consisting of 40 points. Soil was sampled at the 0.0–0.3 m depth, in these 40 points, and analyzed for sand, silt, and clay content; gravimetric water content; and electrical conductivity of saturated soil paste. Coefficients of correlation between ECaand gravimetric soil water content (0.685 for ECa-V and 0.649 for ECa-H) were higher than those between ECaand clay content (ranging from 0.197 to 0.495, when different ECarecording dates were taken into account). Ordinary and universal kriging have been used to assess the patterns of spatial variability of the ECadata sets recorded at successive dates and the analyzed soil properties. Ordinary and universal cokriging methods have improved the estimation of gravimetric soil water content using the data of ECaas secondary variable with respect to the use of ordinary kriging.

scholarly journals Real-time monitoring of nitrate transport in the deep vadose zone under a crop field – implications for groundwater protection

2016 ◽  
Vol 20 (8) ◽  
pp. 3099-3108 ◽  
Author(s):  
Tuvia Turkeltaub ◽  
Daniel Kurtzman ◽  
Ofer Dahan
Keyword(s):  
Real Time ◽  
Water Table ◽  
Vadose Zone ◽  
Land Surface ◽  
Agricultural Land ◽  
Root Zone ◽  
Isotopic Signature ◽  
Nitrate Transport ◽  
Mass Migration ◽  
Crop Field

Abstract. Nitrate is considered the most common non-point pollutant in groundwater. It is often attributed to agricultural management, when excess application of nitrogen fertilizer leaches below the root zone and is eventually transported as nitrate through the unsaturated zone to the water table. A lag time of years to decades between processes occurring in the root zone and their final imprint on groundwater quality prevents proper decision-making on land use and groundwater-resource management. This study implemented the vadose-zone monitoring system (VMS) under a commercial crop field. Data obtained by the VMS for 6 years allowed, for the first time known to us, a unique detailed tracking of water percolation and nitrate migration from the surface through the entire vadose zone to the water table at 18.5 m depth. A nitrate concentration time series, which varied with time and depth, revealed – in real time – a major pulse of nitrate mass propagating down through the vadose zone from the root zone toward the water table. Analysis of stable nitrate isotopes indicated that manure is the prevalent source of nitrate in the deep vadose zone and that nitrogen transformation processes have little effect on nitrate isotopic signature. The total nitrogen mass calculations emphasized the nitrate mass migration towards the water table. Furthermore, the simulated pore-water velocity through analytical solution of the convection–dispersion equation shows that nitrate migration time from land surface to groundwater is relatively rapid, approximately 5.9 years. Ultimately, agricultural land uses, which are constrained to high nitrogen application rates and coarse soil texture, are prone to inducing substantial nitrate leaching.

Sign in / Sign up

Export Citation Format

Share Document