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Physical Sciences and Mathematics Commons™
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- Keyword
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- Ground penetrating radar (3)
- Arctic streams (1)
- Contamination (1)
- Fourier transforms (1)
- Geophysical signal processing (1)
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- Georadar (1)
- Geostatistics (1)
- Ground water flow (1)
- Groundwater (1)
- Hyporheic zone (1)
- Inversion (1)
- Lake (1)
- Partial differential equations (1)
- Radiative transfer (1)
- Random processes (1)
- Sand (1)
- Sediments (1)
- Self-potential (1)
- Stratigraphy (1)
- Stream solute transport (1)
- Terrestrial electricity (1)
- Thermocline (1)
- Tomography (1)
- Tracers (1)
- Transient storage (1)
- Water pollution (1)
- Wave equations (1)
Articles 1 - 9 of 9
Full-Text Articles in Physical Sciences and Mathematics
Imaging Thermal Stratigraphy In Freshwater Lakes Using Georadar, John H. Bradford, Cody R. Johnson, Troy Brosten, James P. Mcnamara, Michael N. Gooseff
Imaging Thermal Stratigraphy In Freshwater Lakes Using Georadar, John H. Bradford, Cody R. Johnson, Troy Brosten, James P. Mcnamara, Michael N. Gooseff
CGISS Publications and Presentations
Thermal stratification exerts significant control over biogeochemical processing in freshwater lakes. Thus, the temporal and spatial distribution of the thermal structure is an important component in understanding lake ecosystems. We present the first reported observations of lake thermal stratification from surface based georadar measurements acquired over two small freshwater lakes. This method is very useful because it can provide rapid acquisition of 2D or 3D lotic stratification.
Tomography Of The Darcy Velocity From Self-Potential Measurements, A. Jardani, A. Revil, A. Bolève, A. Crespy, J.-P. Dupont, Warren Barrash, Bwalya Malama
Tomography Of The Darcy Velocity From Self-Potential Measurements, A. Jardani, A. Revil, A. Bolève, A. Crespy, J.-P. Dupont, Warren Barrash, Bwalya Malama
CGISS Publications and Presentations
An algorithm is developed to interpret self-potential (SP) data in terms of distribution of Darcy velocity of the ground water. The model is based on the proportionality existing between the streaming current density and the Darcy velocity. Because the inverse problem of current density determination from SP data is underdetermined, we use Tikhonov regularization with a smoothness constraint based on the differential Laplacian operator and a prior model. The regularization parameter is determined by the L-shape method. The distribution of the Darcy velocity depends on the localization and number of non-polarizing electrodes and information relative to the distribution of the …
Incorporating Geostatistical Constraints In Nonlinear Inverse Problems, T. C. Johnson, Partha S. Routh, Tom Clemo, Warren Barrash, William P. Clement
Incorporating Geostatistical Constraints In Nonlinear Inverse Problems, T. C. Johnson, Partha S. Routh, Tom Clemo, Warren Barrash, William P. Clement
CGISS Publications and Presentations
In this paper we present a method of incorporating semivariogram constraints into nonlinear inversion problems. That is, we describe a method of sampling the space of inverse solutions that honor a specified semivariogram or set of semivariograms and also explain a set of state data. The approach can be considered a method of conditional simulation where model conditioning is based upon state data (as opposed to parameter data). The difference between this approach and other simulation approaches is that the simulation is posed as an optimization problem with the joint objective of matching the semivariograms and honoring the state data. …
Instantaneous Spectral Analysis: Time-Frequency Mapping Via Wavelet Matching With Application To Contaminated-Site Characterization By 3d Gpr, John H. Bradford, Yafei Wu
Instantaneous Spectral Analysis: Time-Frequency Mapping Via Wavelet Matching With Application To Contaminated-Site Characterization By 3d Gpr, John H. Bradford, Yafei Wu
CGISS Publications and Presentations
Spectral decomposition, by which a time series is transformed from the 1D time/amplitude domain to the 2D time/spectrum domain, has become a popular and useful tool in seismic exploration for hydrocarbons. The windowed, or short-time Fourier transform (STFT) was one early approach to computing the time-frequency (t-f) distribution. This method relies on the user selecting a fixed time window, then computing the Fourier spectrum within the time window while sliding the window along the length of the trace. The primary limitation of the STFT is the fixed window which prevents either time localization of high frequency components (if …
Transient Storage As A Function Of Geomorphology, Discharge, And Permafrost Active Layer Conditions In Arctic Tundra Streams, Jay P. Zarnetske, Michael N. Gooseff, Troy R. Brosten, John H. Bradford, James P. Mcnamara, W. Breck Bowden
Transient Storage As A Function Of Geomorphology, Discharge, And Permafrost Active Layer Conditions In Arctic Tundra Streams, Jay P. Zarnetske, Michael N. Gooseff, Troy R. Brosten, John H. Bradford, James P. Mcnamara, W. Breck Bowden
CGISS Publications and Presentations
Transient storage of solutes in hyporheic zones or other slow-moving stream waters plays an important role in the biogeochemical processes of streams. While numerous studies have reported a wide range of parameter values from simulations of transient storage, little field work has been done to investigate the correlations between these parameters and shifts in surface and subsurface flow conditions. In this investigation we use the stream properties of the Arctic (namely, highly varied discharges, channel morphologies, and subchannel permafrost conditions) to isolate the effects of discharge, channel morphology, and potential size of the hyporheic zone on transient storage. We repeated …
Frequency-Dependent Attenuation Analysis Of Ground-Penetrating Radar Data, John H. Bradford
Frequency-Dependent Attenuation Analysis Of Ground-Penetrating Radar Data, John H. Bradford
CGISS Publications and Presentations
In the early 1990s, it was established empirically that, in many materials, ground-penetrating radar (GPR) attenuation is approximately linear with frequency over the bandwidth of a typical pulse. Further, a frequency-independent Q* parameter characterizes the slope of the band-limited attenuation versus frequency curve. Here, I derive the band-limited Q* function from a first-order Taylor expansion of the attenuation coefficient. This approach provides a basis for computing Q* from any arbitrary dielectric permittivity model. For Cole-Cole relaxation, I find good correlation between the first-order Q* approximation and Q* computed from linear fits to the attenuation coefficient …
Modified Kubelka-Munk Equations For Localized Waves Inside A Layered Medium, Kasper Van Wijk
Modified Kubelka-Munk Equations For Localized Waves Inside A Layered Medium, Kasper Van Wijk
CGISS Publications and Presentations
We present a pair of coupled partial differential equations to describe the evolution of the average total intensity and intensity flux of a wave field inside a randomly layered medium. These equations represent a modification of the Kubelka-Munk equations, or radiative transfer. Our modification accounts for wave interference (e.g., localization), which is neglected in radiative transfer. We numerically solve the modified Kubelka-Munk equations and compare the results to radiative transfer as well as to simulations of the wave equation with randomly located thin layers.
A Field Comparison Of Fresnel Zone And Ray-Based Gpr Attenuation-Difference Tomography For Time-Lapse Imaging Of Electrically Anomalous Tracer Or Contaminant Plumes, Timothy C. Johnson, Partha S. Routh, Warren Barrash, Michael D. Knoll
A Field Comparison Of Fresnel Zone And Ray-Based Gpr Attenuation-Difference Tomography For Time-Lapse Imaging Of Electrically Anomalous Tracer Or Contaminant Plumes, Timothy C. Johnson, Partha S. Routh, Warren Barrash, Michael D. Knoll
CGISS Publications and Presentations
Ground-penetrating radar (GPR) attenuation-difference tomography is a useful tool for imaging the migration of electrically anomalous tracer or contaminant plumes. Attenuation-difference tomography uses the difference in the trace amplitudes of tomographic data sets collected at different times to image the distribution of bulk-conductivity changes within the medium. The most common approach for computing the tomographic sensitivities uses ray theory, which is well understood and leads to efficient computations. However, ray theory requires the assumption that waves propagate at infinite frequency, and thus sensitivities are distributed along a line between the source and receiver. The infinite-frequency assumption in ray theory leads …
Physical Modeling And Analysis Of P-Wave Attenuation Anisotropy, Kasper Van Wijk
Physical Modeling And Analysis Of P-Wave Attenuation Anisotropy, Kasper Van Wijk
CGISS Publications and Presentations
Anisotropic attenuation can provide sensitive attributes for fracture detection and lithology discrimination. This paper analyzes measurements of the P-wave attenuation coefficient in a transversely isotropic sample made of phenolic material. Using the spectral-ratio method, we estimate the group (effective) attenuation coefficient of P-waves transmitted through the sample for a wide range of propagation angles (from 0° to 90°) with the symmetry axis. Correction for the difference between the group and phase angles and for the angular velocity variation help us to obtain the normalized phase attenuation coefficient A governed by the Thomsen-style attenuation-anisotropy parameters εQ and δQ. …