Point‐spread functions for interferometric imaging          下载免费PDF全文

Kees Wapenaar 《Geophysical Prospecting》2015,63(5):1033-1049

Interferometric redatuming is a data‐driven method to transform seismic responses with sources at one level and receivers at a deeper level into virtual reflection data with both sources and receivers at the deeper level. Although this method has traditionally been applied by cross‐correlation, accurate redatuming through a heterogeneous overburden requires solving a multidimensional deconvolution problem. Input data can be obtained either by direct observation (for instance in a horizontal borehole), by modelling or by a novel iterative scheme that is currently being developed. The output of interferometric redatuming can be used for imaging below the redatuming level, resulting in a so‐called interferometric image. Internal multiples from above the redatuming level are eliminated during this process. In the past, we introduced point‐spread functions for interferometric redatuming by cross‐correlation. These point‐spread functions quantify distortions in the redatumed data, caused by internal multiple reflections in the overburden. In this paper, we define point‐spread functions for interferometric imaging to quantify these distortions in the image domain. These point‐spread functions are similar to conventional resolution functions for seismic migration but they contain additional information on the internal multiples in the overburden and they are partly data‐driven. We show how these point‐spread functions can be visualized to diagnose image defocusing and artefacts. Finally, we illustrate how point‐spread functions can also be defined for interferometric imaging with passive noise sources in the subsurface or with simultaneous‐source acquisition at the surface.  相似文献   

A Simple Analytical Formula for the Leakage Flux Through a Perforated Aquitard          下载免费PDF全文

Matthijs Bonte  Willem Jan Zaadnoordijk  Kees Maas 《Ground water》2015,53(4):638-644

In this methods note, we present a simple analytical formula to quantify the steady‐state leakage flux (Q) over a perforated aquitard. The flux depends on the aquitard thickness (D), the radius of the perforation (R), the hydraulic conductivity of the material inside the perforation (k_fill), the conductivities of the overlying and underlying aquifers (k₁ and k₂, respectively), and the head difference between the two aquifers (ΔH): This equation assumes an aquitard separating two homogeneous and infinite aquifers (R ? aquifer thickness) in which radial flow to and from the perforation occurs, with no other recharge or discharge boundaries near the perforation. The flux through a perforation in a hypothetical case study with D = 10 m, k₁ = 10 m/d, k₂ = 20 m/d, R = 0.072 m, and ΔH = 1 m ranges between less than 1 mL/d if the hole is backfilled with bentonite (k_fill = 10^?4 m/d), to several liters per day if the perforation is backfilled with sand from the overlying aquifer (k_fill = 10 m/d), to several m³/d if the perforation forms an open conduit (k_fill = 10⁵ m/d). The leakage fluxes calculated with this model agree well with those calculated using a numerical model (MODFLOW).  相似文献   

Two‐dimensional controlled‐source electromagnetic interferometry by multidimensional deconvolution: spatial sampling aspects     

Jürg Hunziker  Evert Slob  Yuanzhong Fan  Roel Snieder  Kees Wapenaar 《Geophysical Prospecting》2012,60(5):974-994

We use numerically modelled data sets to investigate the sensitivity of electromagnetic interferometry by multidimensional deconvolution to spatial receiver sampling. Interferometry by multidimensional deconvolution retrieves the reflection response below the receivers after decomposition of the fields into upward and downward decaying fields and deconvolving the upward decaying field by the downward decaying field. Thereby the medium above the receiver level is replaced with a homogeneous half‐space, the sources are redatumed to the receiver level and the direct field is removed. Consequently, in a marine setting the retrieved reflection response is independent of any effect of the water layer and the air above. A drawback of interferometry by multidimensional deconvolution is a possibly unstable matrix inversion, which is necessary to retrieve the reflection response. Additionally, in order to correctly separate the upward and the downward decaying fields, the electromagnetic fields need to be sampled properly. We show that the largest possible receiver spacing depends on two parameters: the vertical distance between the source and the receivers and the length of the source. The receiver spacing should not exceed the larger of these two parameters. Besides these two parameters, the presence of inhomogeneities close to the receivers may also require a dense receiver sampling. We show that by using the synthetic aperture concept, an elongated source can be created from conventionally acquired data in order to overcome these strict sampling criteria. Finally, we show that interferometry may work under real‐world conditions with random noise and receiver orientation and positioning errors.  相似文献   

Bifurcation modelling in a meandering gravel–sand bed river     

Kees Sloff  Erik Mosselman 《地球表面变化过程与地形》2012,37(14):1556-1566

The Rhine bifurcation at Pannerden forms the major distribution point for water supply in the Netherlands, distributing not only water and sediment but also flooding risks and navigability. Its morphological stability has been a concern for centuries. We present experiences from more than two decades of numerical morphological modelling of this bifurcation with a gravel–sand bed and a meandering planform. Successive computations have shown the importance of upstream approach conditions, the necessity to include physical mechanisms for grain sorting and alluvial roughness, and the need to assume a thicker active layer of the river bed than is suggested by laboratory flume experiments using a constant discharge. The active layer must be thicker in the model to account for river bed variations due to higher‐frequency discharge variations that are filtered out in morphological modelling. We discuss limitations in calibration and verification, but argue that, notwithstanding these limitations, 2D and 3D morphological models are valuable tools, not only for pragmatic applications to engineering problems, but also for revealing the limitations of established knowledge and understanding of the relevant physical processes. The application of numerical models to the Pannerden bifurcation appeared to reveal shortcomings in established model formulations that do not pose particular problems in other cases. This application is therefore particularly useful for setting the agenda for further research. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Seismic interferometry,intrinsic losses and Q‐estimation*     

Deyan Draganov  Ranajit Ghose  Elmer Ruigrok  Jan Thorbecke  Kees Wapenaar 《Geophysical Prospecting》2010,58(3):361-373

Seismic interferometry is the process of generating new seismic traces from the cross‐correlation, convolution or deconvolution of existing traces. One of the starting assumptions for deriving the representations for seismic interferometry by cross‐correlation is that there is no intrinsic loss in the medium where the recordings are performed. In practice, this condition is not always met. Here, we investigate the effect of intrinsic losses in the medium on the results retrieved from seismic interferometry by cross‐correlation. First, we show results from a laboratory experiment in a homogeneous sand chamber with strong losses. Then, using numerical modelling results, we show that in the case of a lossy medium ghost reflections will appear in the cross‐correlation result when internal multiple scattering occurs. We also show that if a loss compensation is applied to the traces to be correlated, these ghosts in the retrieved result can be weakened, can disappear, or can reverse their polarity. This compensation process can be used to estimate the quality factor in the medium.  相似文献   

Understanding and managing the morphology of branches incising into sand-clay deposits in the Dutch Rhine Delta     

Kees SLOFF  Ary VAN SPIJK  Esther STOUTHAMER  Arjan SIEBEN 《国际泥沙研究》2013,28(2):127-138

In the Rhine-Meuse delta in the south-western part of the Netherlands,the morphology of the river branches is highly dependent on the erodibility of the subsoil.Erosion processes that were initiated after closure of the Haringvliet estuary branch by a dam(in 1970),caused a strong incision of several connecting branches.Due to the geological evolution of this area the lithology of the subsoil shows large variations in highly erodible sand and poorly erodible peat and clay layers.This study shows how the geological information can be used to create 3D maps of the erodibility of the sub-soil, and how this information can be used to schematize the sub-soil in computational models for morphological simulations.Local incisement of sand patches between areas with poorly erodible bed causes deep scour holes,hence increasing the risk on river-bank instability(flow slides) and damage to constructions such as groynes,quays,tunnels, and pipelines.Various types of mathematical models,ranging from 1D(SOBEK) to quasi-3D(Delft3D) have been applied to study the future development of the river bed and possible management options.The results of these approaches demonstrate that models require inclusion of a layer-bookkeeping approach for sub-soil schematization, non-uniform sediment fractions(sand-mud),tidal and river-discharge boundary conditions,and capacity-reduction transport modeling.For risk-reducing river management it has been shown how the development of the river bed can be addressed on a large scale and small scale.For instance,the use of sediment feeding and fixation of bed can be proposed for large-scale management,while monitoring and interventions at initiation of erosion can be proposed as response to small-scale developments that exceed predefined intervention levels.  相似文献   

Harmonization of land-use scenarios for the period 1500�C2100: 600?years of global gridded annual land-use transitions, wood harvest, and resulting secondary lands     

G. C. Hurtt  L. P. Chini  S. Frolking  R. A. Betts  J. Feddema  G. Fischer  J. P. Fisk  K. Hibbard  R. A. Houghton  A. Janetos  C. D. Jones  G. Kindermann  T. Kinoshita  Kees Klein Goldewijk  K. Riahi  E. Shevliakova  S. Smith  E. Stehfest  A. Thomson  P. Thornton  D. P. van Vuuren  Y. P. Wang 《Climatic change》2011,109(1-2):117-161

In preparation for the fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC), the international community is developing new advanced Earth System Models (ESMs) to assess the combined effects of human activities (e.g. land use and fossil fuel emissions) on the carbon-climate system. In addition, four Representative Concentration Pathway (RCP) scenarios of the future (2005?C2100) are being provided by four Integrated Assessment Model (IAM) teams to be used as input to the ESMs for future carbon-climate projections (Moss et al. 2010). The diversity of approaches and requirements among IAMs and ESMs for tracking land-use change, along with the dependence of model projections on land-use history, presents a challenge for effectively passing data between these communities and for smoothly transitioning from the historical estimates to future projections. Here, a harmonized set of land-use scenarios are presented that smoothly connects historical reconstructions of land use with future projections, in the format required by ESMs. The land-use harmonization strategy estimates fractional land-use patterns and underlying land-use transitions annually for the time period 1500?C2100 at 0.5°?×?0.5° resolution. Inputs include new gridded historical maps of crop and pasture data from HYDE 3.1 for 1500?C2005, updated estimates of historical national wood harvest and of shifting cultivation, and future information on crop, pasture, and wood harvest from the IAM implementations of the RCPs for the period 2005?C2100. The computational method integrates these multiple data sources, while minimizing differences at the transition between the historical reconstruction ending conditions and IAM initial conditions, and working to preserve the future changes depicted by the IAMs at the grid cell level. This study for the first time harmonizes land-use history data together with future scenario information from multiple IAMs into a single consistent, spatially gridded, set of land-use change scenarios for studies of human impacts on the past, present, and future Earth system.  相似文献   

Seabirds and chronic oil pollution: self-cleaning properties of gulls, Laridae, as revealed from colour-ring sightings     

Camphuysen KC 《Marine pollution bulletin》2011,62(3):514-519

Mystery oil spills off the Dutch coast affected colonial, adult Lesser Black-backed Gulls prior to and within the breeding season. From colour-ringed individuals, it was demonstrated that most oiled birds survived and were clean within a few weeks and often bred successfully. Further evidence of self-cleaning properties of Larus-gulls is provided from a long-term colour-ringing project (1984-2009). In total 46 birds were reported ‘oiled’, two died, but the majority cleaned itself and survived for up to 20 years after being oiled. From colour-ring data and 30 years of beached bird surveys (1980-2010) it is demonstrated that the effects of chronic oil pollution is larger in winter than in summer; a reflection of seasonal differences in exposure and environmental conditions. The self-cleaning properties of gulls are such that long-term survival is not necessarily jeopardised and even in a breeding season, not all is lost in case of a spill.  相似文献   

Global-scale seismic interferometry: theory and numerical examples     

Elmer Ruigrok  Deyan Draganov  Kees Wapenaar 《Geophysical Prospecting》2008,56(3):395-417

Progress in the imaging of the mantle and core is partially limited by the sparse distribution of natural sources; the earthquake hypocenters are mainly along the active lithospheric plate boundaries. This problem can be approached with seismic interferometry. In recent years, there has been considerable progress in the development of seismic interferometric techniques. The term seismic interferometry refers to the principle of generating new seismic responses by cross‐correlating seismic observations at different receiver locations. The application of interferometric techniques on a global scale could create sources at locations where no earthquakes occur. In this way, yet unknown responses would become available for the application of travel‐time tomography and surface‐wave dispersion studies. The retrieval of a dense‐enough sampling of source gathers would largely benefit the application of reflection imaging. We derive new elastodynamic representation integrals for global‐scale seismic interferometry. The relations are different from other seismic interferometry relations for transient sources, in the sense that they are suited for a rotating closed system like the Earth. We use a correlation of an observed response with a response to which free‐surface multiple elimination has been applied to account for the closed system. Despite the fact that the rotation of the Earth breaks source‐receiver reciprocity, the seismic interferometry relations are shown to be valid. The Coriolis force is included without the need to evaluate an extra term. We synthesize global‐scale earthquake responses and use them to illustrate the acoustic versions of the new interferometric relations. When the sampling of real source locations is dense enough, then both the responses with and without free‐surface multiples are retrieved. When we do not take into account the responses from the sources in the direct neighborhood of the seismic interferometry‐constructed source location, the response with free‐surface multiples can still be retrieved. Even when only responses from sources at a certain range of epicentral distances are available, some events in the Green's function between two receiver locations can still be retrieved. The retrieved responses are not perfect, but the artefacts can largely be ascribed to numerical errors. The reconstruction of internal events – the response as if there was a source and a receiver on (major) contrasts within the model – could possibly be of use for imaging. With modelling it is possible to discover in which region of the correlation panel stationary phases occur that contribute to the retrieval of events. This knowledge opens up a new way of filtering out undesired events and of discovering whether specific events could be retrieved with a given source‐receiver configuration.  相似文献   

Minimal Detectable Biases of Cross-Correlated GPS Observations     

Kees De Jong 《GPS Solutions》2000,3(3):12-18

In this article, analytic expressions are given for the minimal detectable biases (MDBs) of dual-frequency cross-correlated global positioning system (GPS) single difference code and carrier observations. They are given for three different short baseline models. (Short here implies that orbital and atmospheric uncertainties are assumed absent.) A comparison is made with the expressions for the MDBs of non-cross-correlating receivers. Finally, in order to get a better understanding of them, MDBs are visualized as a function of the parameters on which they depend, such as the number ob tracked satellites and the number of observation epochs. ? 2000 John Wiley & Sons, Inc.  相似文献