Enhancing the Resolving Ability of ERT for Imaging Saltwater Intrusion through Improvements in Inversion Methods: A Laboratory and Numerical Study

Geophysics ◽  
2021 ◽  
pp. 1-65
Author(s):  
Meredith Goebel ◽  
Rosemary Knight ◽  
Seogi Kang
Keyword(s):  
Saltwater Intrusion ◽  
Reference Model ◽  
Numerical Study ◽  
A Priori ◽  
Geophysical Methods ◽  
Resistivity Tomography ◽  
Porosity And Permeability ◽  
Priori Information ◽  
High Level

Mapping and monitoring of saltwater intrusion are critical to the sustainable management of groundwater in coastal aquifers around the world. Increasingly, geophysical methods, such as electrical resistivity tomography (ERT), have been used to address these needs. We identified methods for the inversion of ERT data that would most accurately map the location and geometry of an intrusion wedge. This was accomplished using both laboratory and synthetic experiments, with the classic representation of an intrusion wedge perpendicular to the coast. The laboratory experiments allowed us to collect ERT data on a saltwater intrusion wedge in an environment where we had supporting data that provided (1) the distribution of salinity within the tank with which to verify our inversion results, (2) the resistivity, porosity and permeability of the porous medium, and (3) the transform between resistivity and salinity. The synthetic experiments allowed to explore issues of specific interest related to the presence of lithologic heterogeneity at a field site: the role of lithologic heterogeneity in introducing complexity both the resistivity-salinity relationship and the geometry of the saltwater intrusion wedge. We found that using a reference model with a good approximation of the wedge to inform the inversion greatly improved the ability of the resulting resistivity profile to map the wedge. Where there was no, or limited lithologic heterogeneity, a parametric approach, which constrained the range of possible solutions by solving for a sharp interface between the saltwater and freshwater regions, was very effective at capturing the wedge location and geometry. Where there was lithologic heterogeneity, a hybrid between the parametric and informed inversion approaches was most effective, resolving the wedge with a high level of accuracy with little a priori information.

scholarly journals The Analysis Of The Students’ Difficulty in Memorizing English Vocabulary in Elementary School

2018 ◽  
Vol 1 (1) ◽  
Author(s):  
Dewi Ulya Mailasari
Keyword(s):  
Elementary School ◽  
Intrinsic Motivation ◽  
Subject Matter ◽  
Qualitative Method ◽  
A Priori ◽  
Motivational Factors ◽  
Main Role ◽  
High Level ◽  
Compulsory Subject

<p class="05IsiAbstrak">This article describes the students’ difficulty in memorizing English vocabulary in Integrated Islamic Elementary School (SDIT) Amal Insani Jepara.  This study uses a descriptive qualitative method. The result denotes that students have difficulties in memorizing vocabulary including there is no visible intrinsic motivation from students, considering English as just another compulsory subject. In addition to the factors of integration and talent, it seems that attitudinal and motivational factors take the main role of the difficulties of students of SDIT Amal Insani in remembering English vocabulary. Students with a high level of intelligence coupled with high enthusiasm, because there is a reward from the teacher, easy to remember vocabulary as well as remembering other subject matter. Students with a priori and low motivation attitude find it difficult to remember the vocabulary that has been given.</p>

scholarly journals Retrieval of Canopy component temperatures through Bayesian inversion of directional thermal measurements

2009 ◽  
Vol 6 (2) ◽  
pp. 3007-3040 ◽  
Author(s):  
J. Timmermans ◽  
W. Verhoef ◽  
C. van der Tol ◽  
Z. Su
Keyword(s):  
Sensitivity Analysis ◽  
Surface Temperature ◽  
A Priori ◽  
Inversion Method ◽  
Success Rates ◽  
Brightness Temperatures ◽  
Ill Posed ◽  
Priori Information ◽  
The Individual ◽  
High Level

Abstract. In remote sensing evapotranspiration is estimated using a single surface temperature. This surface temperature is an aggregate over multiple canopy components. The temperature of the individual components can differ significantly, introducing errors in the evapotranspiration estimations. The temperature aggregate has a high level of directionality. An inversion method is presented in this paper to retrieve four canopy component temperatures from directional brightness temperatures. The Bayesian method uses both a priori information and sensor characteristics to solve the ill-posed inversion problem. The method is tested using two case studies: 1) a sensitivity analysis, using a large forward simulated dataset, and 2) in a reality study, using two datasets of two field campaigns. The results of the sensitivity analysis show that the Bayesian approach is able to retrieve the four component temperatures from directional brightness temperatures with good success rates using multi-directional sensors (ℜspectra≈0.3, ℜgonio≈0.3, and ℜAATSR≈0.5), and no improvement using mono-angular sensors (ℜ≈1). The results of the experimental study show that the approach gives good results for high LAI values (RMSEgrass=0.50 K, RMSEwheat=0.29 K, RMSEsugar beet=0.75 K, RMSEbarley=0.67 K), but for low LAI values the measurement setup provides extra disturbances in the directional brightness temperatures, RMSEyoung maize=2.85 K, RMSEmature maize=2.85 K. As these disturbances, were only present for two crops and can be eliminated using masked thermal images the method is considered successful.

scholarly journals Seismic Constrained Gravity Inversion: A Reliable Tool to Improve Geophysical Models Away from Seismic Information

Geosciences ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 467
Author(s):  
Daniele Sampietro ◽  
Martina Capponi
Keyword(s):  
High Resolution ◽  
Gravity Field ◽  
A Priori ◽  
Geophysical Methods ◽  
Real Life ◽  
Gravity Inversion ◽  
Seismic Surveys ◽  
Real Model ◽  
Gravity Fields ◽  
Priori Information

The exploitation of gravity fields in order to retrieve information about subsurface geological structures is sometimes considered a second rank method, in favour of other geophysical methods, such as seismic, able to provide a high resolution detailed picture of the main geological horizons. Within the current work we prove, through a realistic synthetic case study, that the gravity field, thanks to the availability of freely of charge high resolution global models and to the improvements in the gravity inversion methods, can represent a valid and cheap tool to complete and enhance geophysical modelling of the Earth’s crust. Three tests were carried out: In the first one a simple two-layer problem was considered, while in tests two and three we considered two more realistic scenarios in which the availability on the study area of constraints derived from 3D or 2D seismic surveys were simulated. In all the considered test cases, in which we try to simulate real-life scenarios, the gravity field, inverted by means of an advanced Bayesian technique, was able to obtain a final solution closer to the (simulated) real model than the assumed a priori information, typically halving the uncertainties in the geometries of the main geological horizons with respect to the initial model.

scholarly journals Retrieval of canopy component temperatures through Bayesian inversion of directional thermal measurements

2009 ◽  
Vol 13 (7) ◽  
pp. 1249-1260 ◽  
Author(s):  
J. Timmermans ◽  
W. Verhoef ◽  
C. van der Tol ◽  
Z. Su
Keyword(s):  
Sensitivity Analysis ◽  
A Priori ◽  
Inversion Method ◽  
Success Rates ◽  
Brightness Temperatures ◽  
Single Temperature ◽  
Ill Posed ◽  
Priori Information ◽  
The Individual ◽  
High Level

Abstract. Evapotranspiration is usually estimated in remote sensing from single temperature value representing both soil and vegetation. This surface temperature is an aggregate over multiple canopy components. The temperature of the individual components can differ significantly, introducing errors in the evapotranspiration estimations. The temperature aggregate has a high level of directionality. An inversion method is presented in this paper to retrieve four canopy component temperatures from directional brightness temperatures. The Bayesian method uses both a priori information and sensor characteristics to solve the ill-posed inversion problem. The method is tested using two case studies: 1) a sensitivity analysis, using a large forward simulated dataset, and 2) in a reality study, using two datasets of two field campaigns. The results of the sensitivity analysis show that the Bayesian approach is able to retrieve the four component temperatures from directional brightness temperatures with good success rates using multi-directional sensors (Srspectra≈0.3, Srgonio≈0.3, and SrAATSR≈0.5), and no improvement using mono-angular sensors (Sr≈1). The results of the experimental study show that the approach gives good results for high LAI values (RMSEgrass=0.50 K, RMSEwheat=0.29 K, RMSEsugar beet=0.75 K, RMSEbarley=0.67 K); but for low LAI values the results were unsatisfactory (RMSEyoung maize=2.85 K). This discrepancy was found to originate from the presence of the metallic construction of the setup. As these disturbances, were only present for two crops and were not present in the sensitivity analysis, which had a low LAI, it is concluded that using masked thermal images will eliminate this discrepancy.

Composite distribution inversion applied to crosshole tomography

Geophysics ◽  
1995 ◽  
Vol 60 (5) ◽  
pp. 1283-1294 ◽  
Author(s):  
James D. Clippard ◽  
Douglas H. Christensen ◽  
Richard D. Rechtien
Keyword(s):  
Least Squares ◽  
Reference Model ◽  
A Priori ◽  
Ideal Point ◽  
Stable Solution ◽  
Parameter Estimates ◽  
Point Spread Functions ◽  
Priori Information ◽  
Damped Least Squares ◽  
Composite Distribution

Crosshole tomography requires solution of a mixed‐determined inverse problem and addition of a priori information in the form of auxiliary constraints to achieve a stable solution. Composite distribution inversion (CDI) constraints are developed by assuming parameters are drawn from a composite distribution consisting of both normally and uniformly distributed parameters. Nonanomalous parameter estimates are assumed to be Gaussian while anomalous parameters are assumed uniform. The resulting constraints are sensitive to anomaly volume and are an alternative to the usual constraints of minimizing [Formula: see text] solution length or some measure of roughness. Damped least‐squares inversion, which minimizes solution length, distributes anomalous signal through poorly resolved areas to produce in attenuated and smoothed anomalies. Similar regularization methods, such as smoothness or flatness constraints, also degrade small spatial wavelength features and produce diffuse images of distinct anomalies. CDI constraints preserve small spatial wavelength features by encouraging small amplitude anomalies to assume the value of the reference model and by allowing truly anomalous parameter estimates to assume whatever value minimizes prediction error without incurring additional penalty. CDI tomograms are characterized by nearly ideal point‐spread functions, suggesting the possibility of better quantitative parameter estimates than are produced using most existing methods. CDI tomograms of both synthetic and field data are shown to produce less diffuse images with more accurate anomaly amplitude estimates than damped least‐squares methods. The CDI algorithm is potentially applicable to nontomographic inversion problems.

A systematic, science-driven approach for predicting subsurface properties

2020 ◽  
Vol 8 (1) ◽  
pp. T167-T181
Author(s):  
Kelly Kathleen Rose ◽  
Jennifer R. Bauer ◽  
MacKenzie Mark-Moser
Keyword(s):  
Language Processing ◽  
A Priori ◽  
Basin Scale ◽  
Porosity And Permeability ◽  
Priori Information ◽  
Efficient Exploration ◽  
Well Data ◽  
Ideal Framework ◽  
Discontinuous Data

As human exploration of the subsurface increases, there is a need for better data- and knowledge-driven methods to improve prediction of subsurface properties. Present subsurface predictions often rely upon disparate and limited a priori information. Even regions with concentrated subsurface exploration still face uncertainties that can obstruct safe and efficient exploration of the subsurface. Uncertainty may be reduced, even for areas with little or no subsurface measurements, using methodical, science-driven geologic knowledge and data. We have developed a hybrid spatiotemporal statistical-geologic approach, subsurface trend analysis (STA), that provides improved understanding of subsurface systems. The STA method assumes that the present-day subsurface is not random, but is a product of its history, which is a sum of its systematic processes. With even limited data and geologic knowledge, the STA method can be used to methodically improve prediction of subsurface properties. To demonstrate and validate the improved prediction potential of the STA method, it was applied in an analysis of the northern Gulf of Mexico. This evaluation was prepared using only existing, publicly available well data and geologic literature. Using the STA method, this information was used to predict subsurface trends for in situ pressure, in situ temperature, porosity, and permeability. The results of this STA-based analysis were validated against new reservoir data. STA-driven results were also contrasted with previous studies. Both indicated that STA predictions were an improvement over other methods. Overall, STA results can provide critical information to evaluate and reduce risks, identify and improve areas of scarce or discontinuous data, and provide inputs for multiscale modeling efforts, from reservoir scale to basin scale. Thereby, the STA method offers an ideal framework for guiding future science-based machine learning and natural language processing to optimize subsurface analyses and predictions.

Simultaneous use of electrostatic quadrupole and GPR in urban context: Investigation of the basement of the Cathedral of Girona (Catalunya, Spain)

Geophysics ◽  
2000 ◽  
Vol 65 (2) ◽  
pp. 526-532 ◽  
Author(s):  
Michel Dabas ◽  
Christian Camerlynck ◽  
Pere Freixas i Camps
Keyword(s):  
A Priori ◽  
Geophysical Methods ◽  
Limited Area ◽  
Urban Context ◽  
Northern Spain ◽  
Geophysical Investigation ◽  
Combined Use ◽  
Priori Information ◽  
Ground Penetrating ◽  
Electrostatic Quadrupole

There is a growing demand for nondestructive geophysical investigation in archaeology, especially in an urban context. This is a result of taking our heritage more seriously than in the past. Since excavations are possible only over a very limited area, any a priori information brought by geophysical methods can help to focus these excavations. The classical geophysical methods used in archaeology (resistivity, magnetism) are not applicable in an urban context with problems of accessibility and inherent electromagnetic noise. The potential of the combined use of ground‐penetrating radar (GPR) and electrostatic (ES) quadrupole data is demonstrated in the investigation of the floor of the cathedral of Girona in northern Spain. A 1.3 × 1.3 m electrostatic quadrupole was towed continuously over a set of parallel profiles to produce a resistivity map for a 20 × 60 m area. A set of resistive anomalies corresponds with known structures (probably graves). The largest observed anomalies appear to be related to foundations of former buildings. A set of 450-MHz GPR profiles were collected and common midpoint (CMP) soundings were performed to convert from time to depth. The time slice centered at 14 ns (at 0.9-m depth) shows anomalies similar to those in the resistivity map. Two different physical properties are measured (electrical resistivity and a reflectivity coefficient that is mainly a function of the contrast in dielectric permittivity); both methods may be sensitive mainly to the water content in the volume under investigation. The improved confidence in an interpretation obtained by combining these two sets of data enables us to infer the location and geometry of the Romanesque building which stood previously on the site of the present cathedral of Girona. Excavations support the interpretation.

scholarly journals Archaeological investigations in the shallow seawater environment with electrical resistivity tomography

2021 ◽  
Author(s):  
Kleanthis Simyrdanis ◽  
Nikos Papadopoulos ◽  
Jung-Ho Kim ◽  
Panagiotis Tsourlos ◽  
Ian Moffat
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
A Priori ◽  
Simulation Models ◽  
Burial Depth ◽  
Electrode Arrays ◽  
Resistivity Tomography ◽  
Priori Information ◽  
Target Characteristics ◽  
Special Environment

This work explores the applicability and effectiveness of electrical resistivity tomography in mapping archaeological relics in the shallow marine environment. The approach consists of a methodology based on numerical simulation models validated with comparison to field data. Numerical modelling includes the testing of different electrode arrays suitable for multi-channel resistivity instruments (dipole–dipole, pole–dipole, and gradient). The electrodes are placed at fixed positions either floating on the sea surface or submerged at the bottom of the sea. Additional tests are made concerning the resolving capabilities of electrical resistivity tomography with various seawater depths and target characteristics (dimensions and burial depth of the targets). Although valid a priori information, in terms of water resistivity and thickness, can be useful for constraining the inversion, it should be used judiciously to prevent erroneous information leading to misleading results. Finally, an application of the method at a field site is presented not only for verifying the theoretical results but also at the same time for proposing techniques to overcome problems that can occur due to the special environment. Numerical and field electrical resistivity tomography results indicated the utility of the method in reconstructing off-shore cultural features, demonstrating at the same time its applicability to be integrated in wider archaeological projects.

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