scholarly journals Reflection waveform inversion of ground-penetrating radar data for characterizing thin and ultrathin layers of nonaqueous phase liquid contaminants in stratified media

Geophysics ◽  
2015 ◽  
Vol 80 (2) ◽  
pp. H1-H11 ◽  
Author(s):  
Esther Babcock ◽  
John H. Bradford
Keyword(s):  
Thin Layer ◽  
Ground Penetrating Radar ◽  
Waveform Inversion ◽  
Contaminated Site ◽  
Data Sets ◽  
Nonaqueous Phase Liquid ◽  
Near Surface ◽  
Reflection Data ◽  
Phase Liquid ◽  
Ground Penetrating

Accurately quantifying thin-layer parameters by applying a targeted reflection waveform inversion methodology to ground-penetrating radar (GPR) reflection data may provide a useful tool for near-surface investigation and especially for contaminated site investigation where nonaqueous phase liquid (NAPL) contaminants are present. We implemented a targeted reflection waveform inversion algorithm to quantify thin-layer permittivity, thickness, and conductivity for NAPL thin ([Formula: see text] dominant wavelength [Formula: see text]) and ultrathin ([Formula: see text]) layers using GPR reflection data. The inversion used a nonlinear grid search with a Monte Carlo scheme to initialize starting values to find the global minimum. By taking a targeted approach using a time window around the peak amplitude of the reflection event of interest, our algorithm reduced the complexity in the inverse problem. We tested the inversion on three different synthetic data sets and four field data sets. In all testing, the inversion solved for NAPL-layer properties within 15% of the measured values. This algorithm provides a tool for site managers to prioritize remediation efforts based on quantitative assessments of contaminant quantity and location using GPR.

2-D ray‐based tomography for velocity, layer shape, and attenuation from GPR data

Geophysics ◽  
1999 ◽  
Vol 64 (5) ◽  
pp. 1579-1593 ◽  
Author(s):  
Jun Cai ◽  
George A. McMechan
Keyword(s):  
Ground Penetrating Radar ◽  
Synthetic Data ◽  
Covariance Matrices ◽  
Sensitivity Matrix ◽  
Near Surface ◽  
Reflection Data ◽  
Value Decomposition ◽  
Ground Penetrating ◽  
Density Resolution ◽  
Velocity Layer

Tomographic inversion for near‐surface structure from multioffset ground‐penetrating radar (GPR) reflection data is implemented. The model is parameterized as layers with constant velocity and constant attenuation. The solution is divided into two parts. First, the velocity and shape of each layer are estimated from the observed reflection traveltimes; then using this geometry and the corresponding ray paths, the attenuation of each layer is estimated from the observed relative amplitudes. Solution of both tomographic problems is performed by singular value decomposition of the sensitivity matrix (to compute information density, resolution, and covariance matrices as well as the solution). Tests on synthetic data, for which the solution is known, show that the algorithm converges efficiently to the neighborhood of the correct solution. Inversion of multichannel field data in a GPR line from a fluvial/eolian environment produces a model that is consistent with structural images and velocity estimates obtained independently by traditional common‐midpoint processing.

Viscoacoustic crosswell imaging using asymptotic waveforms

Geophysics ◽  
2001 ◽  
Vol 66 (3) ◽  
pp. 861-870 ◽  
Author(s):  
Henk Keers ◽  
Don W. Vasco ◽  
Lane R. Johnson
Keyword(s):  
Waveform Inversion ◽  
Data Sets ◽  
Saturated Sand ◽  
Nonaqueous Phase Liquid ◽  
Forward Algorithm ◽  
Data Set ◽  
Sensitivity Functions ◽  
Phase Liquid ◽  
Water Saturated ◽  
Q Values

We present a method to invert viscoacoustic waveforms. The waveform inversion is based on a new forward algorithm for waves propagating through viscoacoustic media. The algorithm represents the wavefield in terms of a summation over nonstationary raypaths. The amplitudes at the caustics are computed correctly. The inclusion of nonstationary raypaths makes it possible to compute sensitivity functions for both velocity and attenuation. The sensitivity functions lead to a linearized formulation of the waveform inversion. The inversion is applied to two 2-D data sets that previously had been matched using only velocity. The first data set consists of crosswell data obtained from a tank filled with a water‐saturated sand. The second data set was obtained after injecting a nonaqueous‐phase liquid into the tank. The inclusion of attenuation significantly improves the fit to the data, especially in the case of the second experiment. A misfit reduction of 80% was obtained, whereas the misfit reduction after inversion for velocity only was 40%. The Q values obtained for the two experiments (Q = 60–100 before the injection and Q = 10–20 in the second experiment) fall within the range predicted by other experiments.

Quantifying the ground-penetrating radar response to ultrathin layers of nonaqueous phase liquid contaminants

2015 ◽  
Vol 3 (4) ◽  
pp. SAB23-SAB31 ◽  
Author(s):  
Esther Babcock ◽  
John Bradford
Keyword(s):  
Layer Thickness ◽  
Ground Penetrating Radar ◽  
Groundwater Resources ◽  
Physical Models ◽  
Radar Signal ◽  
Nonaqueous Phase Liquid ◽  
Resolution Limit ◽  
Ultrathin Layers ◽  
Phase Liquid ◽  
Ground Penetrating

Contamination of groundwater resources is a worldwide problem that threatens human health. Characterizing the type, location, and quantity of the contamination is the first step toward successful site remediation. Ground-penetrating radar (GPR) is one geophysical tool that provides information that may be used to derive the location and quantity of nonaqueous phase liquid contaminants (NAPLs). Because of the large contrast between the dielectric permittivity of water and NAPL, GPR is sensitive to areas in which NAPL displaces pore water. We have used numerical and physical models to investigate the GPR response to ultrathin layers of dense NAPL (DNAPL) trapped at a sand/clay interface. We have defined ultrathin as one-tenth of a wavelength [Formula: see text] or less at the dominant frequency of the radar signal. The numerical and physical models were in good agreement and both found an increase in reflection strength of 10% or more with partially DNAPL-saturated layer thicknesses as low as [Formula: see text]. The reflection strength generally increased with DNAPL-layer thickness reaching a 61% increase with a layer thickness of [Formula: see text]. These results were especially pertinent to field investigations because they were often limited to lower frequency radar ([Formula: see text]) and NAPL accumulations may lie well below the conventional [Formula: see text] radar resolution limit.

scholarly journals Integrating Geophysical and Photographic Data to Visualize the Quarried Structures of the Roman Town of Bassianae

2021 ◽  
Vol 13 (12) ◽  
pp. 2384
Author(s):  
Roland Filzwieser ◽  
Vujadin Ivanišević ◽  
Geert J. Verhoeven ◽  
Christian Gugl ◽  
Klaus Löcker ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Urban Infrastructure ◽  
Aerial Photographs ◽  
Surface Model ◽  
Data Sets ◽  
Buried Structures ◽  
Archaeological Prospection ◽  
Ground Penetrating ◽  
Geophysical Prospection ◽  
Strong Agreement

Large parts of the urban layout of the abandoned Roman town of Bassianae (in present-day Serbia) are still discernible on the surface today due to the deliberate and targeted quarrying of the Roman foundations. In 2014, all of the town's intramural (and some extramural) areas were surveyed using aerial photography, ground-penetrating radar, and magnetometry to analyze the site's topography and to map remaining buried structures. The surveys showed a strong agreement between the digital surface model derived from the aerial photographs and the geophysical prospection data. However, many structures could only be detected by one method, underlining the benefits of a complementary archaeological prospection approach using multiple methods. This article presents the results of the extensive surveys and their comprehensive integrative interpretation, discussing Bassianae's ground plan and urban infrastructure. Starting with an overview of this Roman town's research history, we present the details of the triple prospection approach, followed by the processing, integrative analysis, and interpretation of the acquired data sets. Finally, this newly gained information is contrasted with a plan of Roman Bassianae compiled in 1935.

Migration‐based traveltime waveform inversion of 2-D simple structures: A synthetic example

Geophysics ◽  
2001 ◽  
Vol 66 (3) ◽  
pp. 845-860 ◽  
Author(s):  
François Clément ◽  
Guy Chavent ◽  
Susana Gómez
Keyword(s):  
Least Squares ◽  
Waveform Inversion ◽  
Domain Of Attraction ◽  
Optimization Methods ◽  
Data Sets ◽  
Seismic Reflection Data ◽  
Prestack Migration ◽  
Reflection Data ◽  
Full Wave ◽  
The Time Domain

Migration‐based traveltime (MBTT) formulation provides algorithms for automatically determining background velocities from full‐waveform surface seismic reflection data using local optimization methods. In particular, it addresses the difficulty of the nonconvexity of the least‐squares data misfit function. The method consists of parameterizing the reflectivity in the time domain through a migration step and providing a multiscale representation for the smooth background velocity. We present an implementation of the MBTT approach for a 2-D finite‐difference (FD) full‐wave acoustic model. Numerical analysis on a 2-D synthetic example shows the ability of the method to find much more reliable estimates of both long and short wavelengths of the velocity than the classical least‐squares approach, even when starting from very poor initial guesses. This enlargement of the domain of attraction for the global minima of the least‐squares misfit has a price: each evaluation of the new objective function requires, besides the usual FD full‐wave forward modeling, an additional full‐wave prestack migration. Hence, the FD implementation of the MBTT approach presented in this paper is expected to provide a useful tool for the inversion of data sets of moderate size.

Imaging the internal structure of trunks via multiscale phase inversion of ground-penetrating radar data

2021 ◽  
pp. 1-53
Author(s):  
Lei Fu ◽  
Lanbo Liu
Keyword(s):  
Dielectric Constant ◽  
Internal Structure ◽  
Ground Penetrating Radar ◽  
Phase Inversion ◽  
Multiscale Approach ◽  
White Oak ◽  
Near Surface ◽  
Oak Tree ◽  
Ground Penetrating ◽  
Constant Distribution

Ground-penetrating radar (GPR) is a geophysical technique widely used in near-surface non-invasive detecting. It has the ability to obtaining a high-resolution internal structure of living trunks. Full wave inversion (FWI) has been widely used to reconstruct the dielectric constant and conductivity distribution for cross-well application. However, in some cases, the amplitude information is not reliable due to the antenna coupling, radiation pattern and other effects. We present a multiscale phase inversion (MPI) method, which largely matches the phase information by normalizing the magnitude spectrum; in addition, a natural multiscale approach by integrating the input data with different times is implemented to partly mitigate the local minimal problem. Two synthetic GPR datasets generated from a healthy oak tree trunk and from a decayed trunk are tested by MPI and FWI. Field GPR dataset consisting of 30 common shot GPR data are acquired on a standing white oak tree (Quercus alba); the MPI and FWI methods are used to reconstruct the dielectric constant distribution of the tree cross-section. Results indicate that MPI has more tolerance to the starting model, noise level and source wavelet. It can provide a more accurate image of the dielectric constant distribution compared to the conventional FWI.

Joint full-waveform GPR and ER inversion applied to field data acquired on the surface

Geophysics ◽  
2021 ◽  
pp. 1-77
Author(s):  
diego domenzain ◽  
John Bradford ◽  
Jodi Mead
Keyword(s):  
Ground Penetrating Radar ◽  
Joint Inversion ◽  
Waveform Inversion ◽  
Shallow Groundwater ◽  
Computational Domain ◽  
Alluvial Deposits ◽  
Subsurface Structures ◽  
Full Waveform ◽  
Stable Source ◽  
Ground Penetrating

We exploit the different but complementary data sensitivities of ground penetrating radar (GPR) and electrical resistivity (ER) by applying a multi-physics, multi-parameter, simultaneous 2.5D joint inversion without invoking petrophysical relationships. Our method joins full-waveform inversion (FWI) GPR with adjoint derived ER sensitivities on the same computational domain. We incorporate a stable source estimation routine into the FWI-GPR.We apply our method in a controlled alluvial aquifer using only surface acquired data. The site exhibits a shallow groundwater boundary and unconsolidated heterogeneous alluvial deposits. We compare our recovered parameters to individual FWI-GPR and ER results, and to log measurements of capacitive conductivity and neutron-derived porosity. Our joint inversion provides a more representative depiction of subsurface structures because it incorporates multiple intrinsic parameters, and it is therefore superior to an interpretation based on log data, FWI-GPR, or ER alone.

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