Target-oriented interferometric tomography for GPR data

Geophysics ◽  
2007 ◽  
Vol 72 (3) ◽  
pp. J1-J6 ◽  
Author(s):  
Sherif M. Hanafy ◽  
Gerard T. Schuster
Keyword(s):  
Velocity Model ◽  
Estimation Accuracy ◽  
Real Field ◽  
Near Surface ◽  
Interferometric Technique ◽  
Traveltime Tomography ◽  
Transit Times ◽  
The Difference ◽  
Tomography Method ◽  
Ground Penetrating

An interferometric form of Fermat’s principle and traveltime tomography is used to invert ground-penetrating radar (GPR) data for the subsurface velocity distribution. The input data consist of GPR traveltimes of reflections from two buried interfaces, [Formula: see text] (reference) and [Formula: see text] (target), where the data are excited and recorded by GPR antennas at the surface. Fermat’s interferometric principle is then used to redatum the surface transmitters and receivers to interface [Formula: see text] so the associated reflection traveltimes correspond to localized transit times between interfaces [Formula: see text] and [Formula: see text]. The overburden velocity model above interface [Formula: see text] is not required. The result after tomographic inversion is a high-resolution estimate of the velocity between interfaces [Formula: see text] and [Formula: see text] that does not depend on the velocity model above interface [Formula: see text]. A motivation for introducing interferometric traveltime tomography is that typical layer-stripping approaches will see the slowness error increase with depth as the layers are inverted. This suggests that near-surface statics errors are propagated and amplified with depth. In contrast, the interferometric traveltime tomography method largely eliminates statics errors by taking the difference between reflection events that emanate from neighboring layer interfaces. Slowness errors are not amplified with depth. However, the method is sensitive to the estimation accuracy for the geometry of the reference interface. Both synthetic and real field data are used successfully to validate the effectiveness of this interferometric technique.

Early arrival waveform tomography on near-surface refraction data

Geophysics ◽  
2006 ◽  
Vol 71 (4) ◽  
pp. U47-U57 ◽  
Author(s):  
Jianming Sheng ◽  
Alan Leeds ◽  
Maike Buddensiek ◽  
Gerard T. Schuster
Keyword(s):  
Ground Truth ◽  
Velocity Model ◽  
Frequency Method ◽  
Near Surface ◽  
Good Convergence ◽  
Traveltime Tomography ◽  
Early Arrival ◽  
Synthetic Test ◽  
Waveform Tomography ◽  
Tomography Method

We develop a waveform-tomography method for estimating the velocity distribution that minimizes the waveform misfit between the predicted and observed early arrivals in space-time seismograms. By fitting the waveforms of early arrivals, early arrival waveform tomography (EWT) naturally takes into account more general wave-propagation effects compared to the high-frequency method of traveltime tomography, meaning that EWT can estimate a wider range of slowness wavenumbers. Another benefit of EWT is more reliable convergence compared to full-waveform tomography, because an early-arrival misfit function contains fewer local minima. Synthetic test results verify that the waveform tomogram is much more accurate than the traveltime tomogram and that this algorithm has good convergence properties. For marine data from the Gulf of Mexico, the statics problem caused by shallow, gassy muds was attacked by using EWT to obtain a more accurate velocity model. Using the waveform tomogram to correct for statics, the stacked section was significantly improved compared to using the normal move-out (NMO) velocity, and moderately improved compared to using the traveltime tomogram. Inverting high-resolution land data from Mapleton, Utah, showed an EWT velocity tomogram that was more consistent with the ground truth (trench log) than the traveltime tomogram. Our results suggest that EWT can provide supplemental, shorter-wavelength information compared to the traveltime tomogram for both shallow and moderately deep seismic data.

Random objective waveform inversion of surface waves

Geophysics ◽  
2020 ◽  
Vol 85 (4) ◽  
pp. EN49-EN61
Author(s):  
Yudi Pan ◽  
Lingli Gao
Keyword(s):  
Objective Function ◽  
Surface Waves ◽  
Waveform Inversion ◽  
Velocity Model ◽  
Initial Model ◽  
S Wave ◽  
Data Set ◽  
Near Surface ◽  
Synthetic Test ◽  
Ground Penetrating

Full-waveform inversion (FWI) of surface waves is becoming increasingly popular among shallow-seismic methods. Due to a huge amount of data and the high nonlinearity of the objective function, FWI usually requires heavy computational costs and may converge toward a local minimum. To mitigate these problems, we have reformulated FWI under a multiobjective framework and adopted a random objective waveform inversion (ROWI) method for surface-wave characterization. Three different measure functions were used, whereas the combination of one measure function with one shot independently provided one of the [Formula: see text] objective functions ([Formula: see text] is the total number of shots). We have randomly chose and optimized one objective function at each iteration. We performed a synthetic test to compare the performance of the ROWI and conventional FWI approaches, which showed that the convergence of ROWI is faster and more robust compared with conventional FWI approaches. We also applied ROWI to a field data set acquired in Rheinstetten, Germany. ROWI successfully reconstructed the main geologic feature, a refilled trench, in the final result. The comparison between the ROWI result and a migrated ground-penetrating radar profile further proved the effectiveness of ROWI in reconstructing the near-surface S-wave velocity model. We also ran the same field example by using a poor initial model. In this case, conventional FWI failed whereas ROWI still reconstructed the subsurface model to a fairly good level, which highlighted the relatively low dependency of ROWI on the initial model.

3D seismic traveltime tomography imaging of the shallow subsurface at the C O2 SINK project site, Ketzin, Germany

Geophysics ◽  
2009 ◽  
Vol 74 (1) ◽  
pp. G1-G15 ◽  
Author(s):  
Sawasdee Yordkayhun ◽  
Ari Tryggvason ◽  
Ben Norden ◽  
Christopher Juhlin ◽  
Björn Bergman
Keyword(s):  
Velocity Structure ◽  
Velocity Model ◽  
Geological Structure ◽  
Seismic Survey ◽  
Storage Site ◽  
Near Surface ◽  
Shallow Subsurface ◽  
Traveltime Tomography ◽  
Reflection Seismic ◽  
Reflection Data

A 3D reflection seismic survey was performed in 2005 at the Ketzin carbon dioxide [Formula: see text] pilot geological-storage site (the [Formula: see text] project) near Berlin, Germany, to image the geological structure of the site to depths of about [Formula: see text]. Because of the acquisition geometry, frequency limitations of the source, and artefacts of the data processing, detailed structures shallower than about [Formula: see text] were unclear. To obtain structural images of the shallow subsurface, we applied 3D traveltime tomography to data near the top of the Ketzin anticline, where faulting is present. Understanding the shallow subsurface structure is important for long-term monitoring aspects of the project after [Formula: see text] has been injected into a saline aquifer at about [Formula: see text] depth. We used a 3D traveltime tomography algorithm based on a combination ofsolving for 3D velocity structure and static corrections in the inversion process to account for artefacts in the velocity structure because of smearing effects from the unconsolidated cover. The resulting velocity model shows low velocities of [Formula: see text] in the uppermost shallow subsurface of the study area. The velocity reaches about [Formula: see text] at a depth of [Formula: see text]. This coincides approximately with the boundary between Quaternary units, which contain the near-surface freshwater reservoir and the Tertiary clay aquitard. Correlation of tomographic images with a similarity attribute slice at [Formula: see text] (about [Formula: see text] depth) indicates that at least one east-west striking fault zone observed in the reflection data might extend into the Tertiary unit. The more detailed images of the shallow subsurface from this study provided valuable information on this potentially risky area.

A comparison of phase inversion and traveltime tomography for processing near-surface refraction traveltimes

Geophysics ◽  
2009 ◽  
Vol 74 (6) ◽  
pp. WCB11-WCB24 ◽  
Author(s):  
Karl J. Ellefsen
Keyword(s):  
Standard Deviation ◽  
Phase Inversion ◽  
Small Scale ◽  
Complex Frequency ◽  
S Wave ◽  
Near Surface ◽  
Residual Standard Deviation ◽  
Wave Refraction ◽  
Traveltime Tomography ◽  
The Difference

With phase inversion, one can estimate subsurface velocities using the phases of first-arriving waves, which are the frequency-domain equivalents of the traveltimes. Phase inversion is modified to make it suitable for processing traveltimes from near-surface refraction surveys. The modifications include parameterizing the model, correcting the observed phases, and selecting the complex frequency. This modified phase inversion is compared to traveltime tomography. For two comparisons using computer-simulated traveltimes, the difference between the estimated and correct models, the residual mean, and the residual standard deviation are smaller for the phase inversion than they are for the traveltime tomography. For a comparison using field data from an S-wave refraction survey, both methods estimate models that are consistent with the known geology. Nonetheless, the phase-inversion model includes small-scale features in the bedrock that are geologically plausible; the residual mean and the residual standard deviation are smaller for the phase inversion than they are for the traveltime tomography.

Crosshole reflection imaging with ground-penetrating radar data: Applications in near-surface sedimentary settings

Geophysics ◽  
2020 ◽  
Vol 85 (4) ◽  
pp. H61-H69
Author(s):  
Niklas Allroggen ◽  
Stéphane Garambois ◽  
Guy Sénéchal ◽  
Dominique Rousset ◽  
Jens Tronicke
Keyword(s):  
Ground Penetrating Radar ◽  
Field Data ◽  
Electromagnetic Property ◽  
Velocity Model ◽  
Radar Data ◽  
Near Surface ◽  
Velocity Models ◽  
Reflection Image ◽  
Detailed Interpretation ◽  
Ground Penetrating

Crosshole ground-penetrating radar (GPR) is applied in areas that require a very detailed subsurface characterization. Analysis of such data typically relies on tomographic inversion approaches providing an image of subsurface parameters. We have developed an approach for processing the reflected energy in crosshole GPR data and applied it on GPR data acquired in different sedimentary settings. Our approach includes muting of the first arrivals, separating the up- and the downgoing wavefield components, and backpropagating the reflected energy by a generalized Kirchhoff migration scheme. We obtain a reflection image that contains information on the location of electromagnetic property contrasts, thus outlining subsurface architecture in the interborehole plane. In combination with velocity models derived from different tomographic approaches, these images allow for a more detailed interpretation of subsurface structures without the need to acquire additional field data. In particular, a combined interpretation of the reflection image and the tomographic velocity model improves the ability to locate layer boundaries and to distinguish different subsurface units. To support our interpretations of our field data examples, we compare our crosshole reflection results with independent information, including borehole logs and surface GPR data.

scholarly journals Ray-tracing traveltime tomography versus wave-equation traveltime inversion for near-surface seismic land data

2017 ◽  
Vol 5 (3) ◽  
pp. SO11-SO19
Author(s):  
Lei Fu ◽  
Sherif M. Hanafy
Keyword(s):  
Wave Equation ◽  
Ray Tracing ◽  
Water Table ◽  
Seismic Data ◽  
Velocity Model ◽  
Water Table Depth ◽  
Seismic Survey ◽  
Near Surface ◽  
Traveltime Tomography ◽  
Initial Starting

Full-waveform inversion of land seismic data tends to get stuck in a local minimum associated with the waveform misfit function. This problem can be partly mitigated by using an initial velocity model that is close to the true velocity model. This initial starting model can be obtained by inverting traveltimes with ray-tracing traveltime tomography (RT) or wave-equation traveltime (WT) inversion. We have found that WT can provide a more accurate tomogram than RT by inverting the first-arrival traveltimes, and empirical tests suggest that RT is more sensitive to the additive noise in the input data than WT. We present two examples of applying WT and RT to land seismic data acquired in western Saudi Arabia. One of the seismic experiments investigated the water-table depth, and the other one attempted to detect the location of a buried fault. The seismic land data were inverted by WT and RT to generate the P-velocity tomograms, from which we can clearly identify the water table depth along the seismic survey line in the first example and the fault location in the second example.

Estimation of the spatial distribution of fluid permeability from surface and tomographic GPR data and core, with a 2‐D example from the Ferron Sandstone, Utah

Geophysics ◽  
2002 ◽  
Vol 67 (5) ◽  
pp. 1505-1515 ◽  
Author(s):  
William S. Hammon ◽  
Xiaoxian Zeng ◽  
Rucsandra M. Corbeanu ◽  
George A. McMechan
Keyword(s):  
Spatial Distribution ◽  
Fluid Transport ◽  
Velocity Model ◽  
Borehole Data ◽  
Permeability Model ◽  
Depth Migration ◽  
Traveltime Tomography ◽  
Fluid Permeability ◽  
Ground Penetrating ◽  
Kirchhoff Depth Migration

Reservoir analogs provide detailed information that is applicable to fluid transport simulations but that cannot be obtained directly from reservoirs because of inaccessibility. The Ferron Sandstone of east‐central Utah is an analog for fluviodeltaic reservoirs; its excellent outcrop exposures are ideal for detailed study. Ground‐penetrating radar (GPR) data were collected in and between two cored boreholes and are used to build a 2‐D fluid permeability model in four steps. First, an anisotropic GPR propagation velocity model is obtained from traveltime tomography between two boreholes and between each borehole and the earth's surface. Second, the geometry of the sedimentological features is imaged by prestack Kirchhoff depth migration of constant‐offset GPR data acquired along a line between the two holes at the earth's surface. Third, a background permeability is assigned to each layer by interpolating the geometrical average of the measured permeabilities in each sedimentological element. Finally, the spatial distribution of flow baffles and barriers is estimated by calibrating the instantaneous amplitude and frequency of the surface GPR data associated with the mudstone layers in the boreholes via cluster analysis. The result is an integrated model that contains GPR velocity, lithology, and fluid permeability distributions. Low GPR velocities correspond to mudstones with low permeability. The main mudstone layers (potential barriers and/or baffles to fluid flow) do not appear to be continuous between the boreholes, which means that interpretations based on borehole data alone would overestimate element continuity and thereby underestimate effective permeability.

A Layer-cell Tomography Method for Near-surface Velocity Model Building Using First Arrivals

2020 ◽  
Vol 177 (9) ◽  
pp. 4161-4175
Author(s):  
Yukai Wo ◽  
Hua-Wei Zhou ◽  
Hao Hu ◽  
Jingjing Zong ◽  
Yinshuai Ding
Keyword(s):  
Model Building ◽  
Velocity Model ◽  
Surface Velocity ◽  
Near Surface ◽  
Layer Cell ◽  
Velocity Model Building ◽  
Tomography Method

Joint refraction traveltime tomography and migration for multilayer near-surface imaging

Geophysics ◽  
2019 ◽  
Vol 84 (6) ◽  
pp. U31-U43
Author(s):  
Yihao Wang ◽  
Jie Zhang
Keyword(s):  
High Velocity ◽  
Velocity Structure ◽  
Joint Inversion ◽  
Velocity Model ◽  
Surface Velocity ◽  
Inversion Method ◽  
Near Surface ◽  
Traveltime Tomography ◽  
First Arrival ◽  
Migration Method

In near-surface velocity structure estimation, first-arrival traveltime tomography tends to produce a smooth velocity model. If the shallow structures include a weathering layer over high-velocity bedrock, first-arrival traveltime tomography may fail to recover the sharp interface. However, with the same traveltime data, refraction traveltime migration proves to be an effective tool for accurately mapping the refractor. The approach downward continues the refraction traveltime curves and produces an image (position) of the refractor for a given overburden velocity model. We first assess the validity of the refraction traveltime migration method and analyze its uncertainties with a simple model. We then develop a multilayer refraction traveltime migration method and apply the migration image to constrain traveltime tomographic inversion by imposing discontinuities at the refraction interfaces in model regularization. In each subsequent iteration, the shape of the migrated refractors and the velocity model are simultaneously updated. The synthetic tests indicate that the joint inversion method performs better than the conventional first-arrival traveltime tomography method with Tikhonov regularization and the delay-time method in reconstructing near-surface models with high-velocity contrasts. In application to field data, this method produces a more accurately resolved velocity model, which improves the quality of common midpoint stacking by making long-wavelength static corrections.

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