Unified multi‐depth‐level field decomposition          下载免费PDF全文

Niels Grobbe  Joost van der Neut  Evert Slob  Kees Wapenaar  Carlos Almagro Vidal  Guy Drijkoningen 《Geophysical Prospecting》2016,64(2):361-391

Wavefield decomposition forms an important ingredient of various geophysical methods. An example of wavefield decomposition is the decomposition into upgoing and downgoing wavefields and simultaneous decomposition into different wave/field types. The multi‐component field decomposition scheme makes use of the recordings of different field quantities (such as particle velocity and pressure). In practice, different recordings can be obscured by different sensor characteristics, requiring calibration with an unknown calibration factor. Not all field quantities required for multi‐component field decomposition might be available, or they can suffer from different noise levels. The multi‐depth‐level decomposition approach makes use of field quantities recorded at multiple depth levels, e.g., two horizontal boreholes closely separated from each other, a combination of a single receiver array combined with free‐surface boundary conditions, or acquisition geometries with a high‐density of vertical boreholes. We theoretically describe the multi‐depth‐level decomposition approach in a unified form, showing that it can be applied to different kinds of fields in dissipative, inhomogeneous, anisotropic media, e.g., acoustic, electromagnetic, elastodynamic, poroelastic, and seismoelectric fields. We express the one‐way fields at one depth level in terms of the observed fields at multiple depth levels, using extrapolation operators that are dependent on the medium parameters between the two depth levels. Lateral invariance at the depth level of decomposition allows us to carry out the multi‐depth‐level decomposition in the horizontal wavenumber–frequency domain. We illustrate the multi‐depth‐level decomposition scheme using two synthetic elastodynamic examples. The first example uses particle velocity recordings at two depth levels, whereas the second example combines recordings at one depth level with the Dirichlet free‐surface boundary condition of zero traction. Comparison with multi‐component decomposed fields shows a perfect match in both amplitude and phase for both cases. The multi‐depth‐level decomposition scheme is fully customizable to the desired acquisition geometry. The decomposition problem is in principle an inverse problem. Notches may occur at certain frequencies, causing the multi‐depth‐level composition matrix to become uninvertible, requiring additional notch filters. We can add multi‐depth‐level free‐surface boundary conditions as extra equations to the multi‐component composition matrix, thereby overdetermining this inverse problem. The combined multi‐component–multi‐depth‐level decomposition on a land data set clearly shows improvements in the decomposition results, compared with the performance of the multi‐component decomposition scheme.  相似文献   

Developments in triaxial testing technique     

Franklin  John A.  Hoeck  Evert 《Rock Mechanics and Rock Engineering》1970,2(4):223-228

Summary A simple triaxial cell is described together with details of the technique employed for triaxial testing. Triaxial strength results for 254 specimens of eight rock types are tabulated.

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Zusammenfassung Ein einfaches Triaxial-Prüfgerät wird, zusammen mit Einzelheiten des experimentellen Verfahrens, beschrieben. Ergebnisse dreiachsiger Festigkeitsprüfung sind für 254 Proben aus acht verschiedenen Gesteinsarten in Tabellen wiedergegeben.

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Résumé Un appareil triaxial simple est décrit avec des détails sur la technique expérimentale. Des résultats de résistance triaxiale pour 254 échantillons pris parmi huit types de roche sont donnés.

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With 2 Figures  相似文献   

Reply to Comment on ‘Aspects of 1D seismic modelling using the Goupillaud principle’ by E. Szaraniec1     

Evert Slob  Anton Ziolkowski 《Geophysical Prospecting》1994,42(1):85-87

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Effects of humic substances on Fe(II) sorption onto aluminum oxide and clay     

Ying Zhu  Jingjing Liu  Omanjana Goswami  Ashaki A. Rouff  Evert J. Elzinga 《Geochemical transactions》2018,19(1):3

We studied the effects of humic substances (HS) on the sorption of Fe(II) onto Al-oxide and clay sorbents at pH 7.5 with a combination of batch kinetic experiments and synchrotron Fe K-edge EXAFS analyses. Fe(II) sorption was monitored over the course of 4 months in anoxic clay and Al-oxide suspensions amended with variable HS types (humic acid, HA; or fulvic acid, FA) and levels (0, 1, and 4 wt%), and with differing Fe(II) and HS addition sequences (co-sorption and pre-coated experiments, where Fe(II) sorbate was added alongside and after HS addition, respectively). In the Al-oxide suspensions, the presence of HS slowed down the kinetics of Fe(II) sorption, but had limited, if any, effect on the equilibrium aqueous Fe(II) concentrations. EXAFS analyses revealed precipitation of Fe(II)–Al(III)-layered double hydroxide (LDH) phases as the main mode of Fe(II) sorption in both the HA-containing and HA-free systems. These results demonstrate that HS slow down Fe(II) precipitation in the Al-oxide suspensions, but do not affect the composition or stability of the secondary Fe(II)–Al(III)-LDH phases formed. Interference of HS with the precipitation of Fe(II)–Al(III)-LDH was attributed to the formation organo-Al complexes HS limiting the availability of Al for incorporation into secondary layered Fe(II)-hydroxides. In the clay systems, the presence of HA caused a change in the main Fe(II) sorption product from Fe(II)–Al(III)-LDH to a Fe(II)-phyllosilicate containing little structural Al. This was attributed to complexation of Al by HA, in combination with the presence of dissolved Si in the clay suspension enabling phyllosilicate precipitation. The change in Fe(II) precipitation mechanism did not affect the rate of Fe(II) sorption at the lower HA level, suggesting that the inhibition of Fe(II)–Al(III)-LDH formation in this system was countered by enhanced Fe(II)-phyllosilicate precipitation. Reduced rates of Fe(II) sorption at the higher HA level were attributed to surface masking or poisoning by HA of secondary Fe(II) mineral growth at or near the clay surface. Our results suggest that HS play an important role in controlling the kinetics and products of Fe(II) precipitation in reducing soils, with effects modulated by soil mineralogy, HS content, and HS properties. Further work is needed to assess the importance of layered Fe(II) hydroxides in natural reducing environments.  相似文献   

A Comparison of Strategies for Seismic Interferometry   总被引：2，自引：0，他引：2  

Roel Snieder  Masatoshi Miyazawa  Evert Slob  Ivan Vasconcelos  Kees Wapenaar 《Surveys in Geophysics》2009,30(4-5):503-523

The extraction of the response from field fluctuations excited by random sources has received considerable attention in a variety of different fields. We present three methods for the extraction of the systems response that are based on cross-correlation, deconvolution, and the solution of an integral equation, respectively. For systems that are invariant for time-reversal the correlation method requires random sources on a bounding surface only, but when time-reversal invariance is broken, for example by attenuation, a volume distribution of sources is needed. For this reason the correlation method is not useful for diffusive or strongly attenuating systems. We provide examples of the three methods and compare their merits and drawbacks. We show that the extracted field may satisfy different boundary conditions than does the physical field. This can be used, for example, to suppress surface-related multiples in exploration seismology, to study the coupling of buildings to the subsurface, and to remove the airwave in controlled source electromagnetics (CSEM).  相似文献   

Review paper: Virtual sources and their responses,Part II: data‐driven single‐sided focusing          下载免费PDF全文

Kees Wapenaar  Jan Thorbecke  Joost van der Neut  Evert Slob  Roel Snieder 《Geophysical Prospecting》2017,65(6):1430-1451

In Part I of this paper, we defined a focusing wave field as the time reversal of an observed point‐source response. We showed that emitting a time‐reversed field from a closed boundary yields a focal spot that acts as an isotropic virtual source. However, when emitting the field from an open boundary, the virtual source is highly directional and significant artefacts occur related to multiple scattering. The aim of this paper is to discuss a focusing wave field, which, when emitted into the medium from an open boundary, yields an isotropic virtual source and does not give rise to artefacts. We start the discussion from a horizontally layered medium and introduce the single‐sided focusing wave field in an intuitive way as an inverse filter. Next, we discuss single‐sided focusing in two‐dimensional and three‐dimensional inhomogeneous media and support the discussion with mathematical derivations. The focusing functions needed for single‐sided focusing can be retrieved from the single‐sided reflection response and an estimate of the direct arrivals between the focal point and the accessible boundary. The focal spot, obtained with this single‐sided data‐driven focusing method, acts as an isotropic virtual source, similar to that obtained by emitting a time‐reversed point‐source response from a closed boundary.  相似文献   

Metal contamination and filtering in soil from an iron (magnetite) mine–smelter complex in the critical Hudson Highlands watershed,New York     

Sivajini Gilchrist  Alexander E. Gates  Matthew Gorring  Evert Jan Elzinga 《Environmental Earth Sciences》2011,63(5):1029-1041

Organic material in metal contaminated soils around an abandoned magnetite mine–smelter complex in the critical Highlands watershed protects the groundwater and surface water from contamination. Metals in these waters were consistently below local and national water standards. Two groups of soil types cover the area: (1) Group A disturbed metal-rich soils, and (2) Group B undisturbed organic soils. Chromium and nickel were more elevated than other metals with Cr more widespread than Ni. In Group A, Cr correlated strongly with sesquioxides in the lower horizons (Fe₂O₃: r = 0.74, p < 0.025; Al₂O₃: r = 0.92, p < 0.005). In Group B, Cr correlated strongly (r = 0.96, p < 0.005) with soil organic matter (SOM) in the O-horizons. Ni–Cr (Group A: 52 and 70% in O- and lower horizons, respectively; Group B: ~100% in both horizons) and V–Cr correlations (78% only in Group A lower horizons) suggest similar retention mechanisms for these elements. Average soil \textpH_\textCaCl2 {\text{pH}}_{{{\text{CaCl}}_{2} }} for both groups ranged between 3.65 and 5.91, suggesting that soil acidity is determined by organic acids and solubility of Al³⁺ releasing H⁺ ions. SOM and sesquioxides contribute significantly to creating naturally occurring filtration systems, removing metals, and protecting water quality. High Ca, Fe, and Ti in Group A soils suggest slag and ash were mixed into the soils. Some low-Cr sources include magnetite, slag, and ash (100, 100 and 200 mg/kg, respectively). Constant ZrO ₂ :TiO ₂ ratios in the lower soils indicate soil formation from breakdown of underlying tailing rocks, contributing Cr to these layers.  相似文献   

Synthesis of all known analytical permittivity reconstruction techniques of nonmagnetic materials from reflection and transmission measurements     

Gorriti  A.G. Slob  E.C. 《Geoscience and Remote Sensing Letters, IEEE》2005,2(4):433-436

This letter shows that all published analytical reconstruction formulas for the permittivity of a nonmagnetic material from the measured total reflection and transmission responses-the Nicolson-Ross, Weir, and Stuchly-Matuszewsky equations-are equal to either the impedance or propagation methods. We also show that the measured total reflection and transmission are independent measurements and hence allow for simultaneous and unique reconstruction of the complex electric permittivity, including conductivity, and the complex magnetic permeability.  相似文献   

The Third GABLS Intercomparison Case for Evaluation Studies of Boundary-Layer Models. Part B: Results and Process Understanding   总被引：1，自引：1，他引：0  

Fred C. Bosveld  Peter Baas  Gert-Jan Steeneveld  Albert A. M. Holtslag  Wayne M. Angevine  Eric Bazile  Evert I. F. de Bruijn  Daniel Deacu  John M. Edwards  Michael Ek  Vincent E. Larson  Jonathan E. Pleim  Matthias Raschendorfer  Gunilla Svensson 《Boundary-Layer Meteorology》2014,152(2):157-187

We describe and analyze the results of the third global energy and water cycle experiment atmospheric boundary layer Study intercomparison and evaluation study for single-column models. Each of the nineteen participating models was operated with its own physics package, including land-surface, radiation and turbulent mixing schemes, for a full diurnal cycle selected from the Cabauw observatory archive. By carefully prescribing the temporal evolution of the forcings on the vertical column, the models could be evaluated against observations. We focus on the gross features of the stable boundary layer (SBL), such as the onset of evening momentum decoupling, the 2-m minimum temperature, the evolution of the inertial oscillation and the morning transition. New process diagrams are introduced to interpret the variety of model results and the relative importance of processes in the SBL; the diagrams include the results of a number of sensitivity runs performed with one of the models. The models are characterized in terms of thermal coupling to the soil, longwave radiation and turbulent mixing. It is shown that differences in longwave radiation schemes among the models have only a small effect on the simulations; however, there are significant variations in downward radiation due to different boundary-layer profiles of temperature and humidity. The differences in modelled thermal coupling to the land surface are large and explain most of the variations in 2-m air temperature and longwave incoming radiation among models. Models with strong turbulent mixing overestimate the boundary-layer height, underestimate the wind speed at 200 m, and give a relatively large downward sensible heat flux. The result is that 2-m air temperature is relatively insensitive to turbulent mixing intensity. Evening transition times spread 1.5 h around the observed time of transition, with later transitions for models with coarse resolution. Time of onset in the morning transition spreads 2 h around the observed transition time. With this case, the morning transition appeared to be difficult to study, no relation could be found between the studied processes, and the variation in the time of the morning transition among the models.  相似文献   

Software provides Window to the Stars     

Robert Izzard  Evert Glebbeek 《Astronomy& Geophysics》2006,47(4):4.28-4.29

Robert Izzard and Evert Glebbeek demonstrate the working of their user-friendly stellar modelling tool, Window to the Stars.  相似文献