Common-reflection-surface stack — a real data example     

Jürgen Mann  Rainer Jger  Thilo Müller  German Hcht  Peter Hubral 《Journal of Applied Geophysics》1999,42(3-4)

The simulation of a zero-offset (ZO) stack section from multi-coverage reflection data is a standard imaging method in seismic processing. It significantly reduces the amount of data and increases the signal-to-noise ratio due to constructive interference of correlated events. Conventional imaging methods, e.g., normal moveout (NMO)/dip moveout (DMO)/stack or pre-stack migration, require a sufficiently accurate macro-velocity model to yield appropriate results, whereas the recently introduced common-reflection-surface stack does not depend on a macro-velocity model. For two-dimensional seismic acquisition, its stacking operator depends on three wavefield attributes and approximates the kinematic multi-coverage reflection response of curved interfaces in laterally inhomogeneous media. The common-reflection-surface stack moveout formula defines a stacking surface for each particular sample in the ZO section to be simulated. The stacking surfaces that fit best to actual events in the multi-coverage data set are determined by means of coherency analysis. In this way, we obtain a coherency section and a section of each of the three wavefield attributes defining the stacking operator. These wavefield attributes characterize the curved interfaces and, thus, can be used for a subsequent inversion. In this paper, we focus on an application to a real land data set acquired over a salt dome. We propose three separate one-parametric search and coherency analyses to determine initial common-reflection-surface stack parameters. Optionally, a subsequent optimization algorithm can be performed to refine these initial parameters. The simulated ZO section obtained by the common-reflection-surface stack is compared to the result of a conventional NMO/DMO/stack processing sequence. We observe an increased signal-to-noise ratio and an improved continuity along the events for our proposed method — without loss of lateral resolution.  相似文献   

Book Review: Turbulence and Magnetic Fields in Astrophysics. By Edith Falgarone and Thierry Passot     

Rainer Arlt 《Astronomische Nachrichten》2004,325(9):762-762

  相似文献   

Dimensional analysis of two-phase flow including a rate-dependent capillary pressure–saturation relationship     

Sabine Manthey  S. Majid Hassanizadeh  Rainer Helmig  Rudolf Hilfer 《Advances in water resources》2008

The macroscopic modelling of two-phase flow processes in subsurface hydrosystems or industrial applications on the Darcy scale usually requires a constitutive relationship between capillary pressure and saturation, the P_c(S_w) relationship. Traditionally, it is assumed that a unique relation between P_c and S_w exists independently of the flow conditions as long as hysteretic effects can be neglected. Recently, this assumption has been questioned and alternative formulations have been suggested. For example, the extended P_c(S_w) relationship by Hassanizadeh and Gray [Hassanizadeh SM, Gray WG. Mechanics and thermodynamics of multiphase flow in porous media including interphase boundaries. Adv Water Resources 1990;13(4):169–86] proposes that the difference between the phase pressures to the equilibrium capillary pressure is a linear function of the rate of change of saturation, thereby introducing a constant of proportionality, the coefficient τ. It is desirable to identify cases where the extended relationship needs to be considered. Consequently, a dimensional analysis is performed on the basis of the two-phase balance equations. In addition to the well-known capillary and gravitational number, the dimensional analysis yields a new dimensionless number. The dynamic number Dy quantifies the ratio of dynamic capillary to viscous forces. Relating the dynamic to the capillary as well as the gravitational number gives the new numbers DyC and DyG, respectively. For given sets of fluid and porous medium parameters, the dimensionless numbers Dy and DyC are interpreted as functions of the characteristic length and flow velocity. The simulation of an imbibition process provides insight into the interpretation of the characteristic length scale. The most promising choice for this length scale seems to be the front width. We conclude that consideration of the extended P_c(S_w) relationship may be important for porous media with high permeability, small entry pressure and high coefficient τ when systems with a small characteristic length (e.g. steep front) and small characteristic time scale are under investigation.  相似文献   

Could surface roughness be a poor proxy for landslide age? Results from the Swabian Alb,Germany          下载免费PDF全文

Jason N. Goetz  Rainer Bell  Alexander Brenning 《地球表面变化过程与地形》2014,39(12):1697-1704

The potential of surface roughness to quantify geomorphological landforms and processes has been enhanced with the availability of high‐resolution digital terrain models (DTM). Recent studies that attempt to identify landslide features with surface roughness have suggested that this measure of topographic heterogeneity may also be applied to estimate the relative age of landslides. This is a provisional study that explores the potential of this relationship by assessing the ability of surface roughness to act as a proxy for relative landslide age. The surface roughness for a set of 12 dated landslides in the Swabian Alb that occurred between 1789 and 1985 was calculated from a 1 m² spatial resolution LiDAR DTM with three algorithms: root‐mean‐square‐height (RMSH), standard deviation of slope (SDS), and direction cosine eigenvalue ratios (DCE). Scale‐dependence was analysed by calculating surface roughness for a range of moving window sizes (3 × 3, 5 × 5, 9 × 9 and 15 × 15), and surface roughness for each landslide was summarized by the median and upper quartile. Only weak correlations (best Spearman's rho 0.58) were present between landslide age and surface roughness. This correlation becomes weaker with increasing moving window size. Given weak observed associations and discussed challenges pertaining to the complexities of landslide morphology change over time, we currently find that surface roughness alone may not be justifiable to act as a proxy for landslide age for our study region. Furthermore, we recommend future studies should focus on addressing possible natural and anthropogenic factors such as land use change that may alter surface roughness. These studies may focus on one of the three roughness measures used here as they are strongly correlated. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

The production of cosmogenic nuclides in stony meteoroids by galactic cosmic‐ray particles     

Ingo Leya  Hans‐Jürgen Lange  Sonja Neumann  Rainer Wieler  Rolf Michel 《Meteoritics & planetary science》2000,35(2):259-286

Abstract— We present a purely physical model for the calculation of depth‐ and size‐dependent production rates of cosmogenic nuclides by galactic cosmic‐ray (GCR) particles. besides the spectra of primary and secondary particles and the excitation functions of the underlying nuclear reactions, the model is based on only one free parameter—the integral number of gcr particles in the meteoroid orbits. We derived this value from analysis of radionuclide data in Knyahinya. We also show that the mean GCR proton spectrum in the meteoroid orbits has been constant over about the last 10 Ma. For the major target elements in stony meteoroids, we present depth‐ and size‐dependent production rates for ¹⁰Be, ¹⁴C, ²⁶Al, ³⁶Cl, and ⁵³Mn as well as for the rare gas isotopes ³He, ²⁰Ne, ²¹Ne, ²²Ne, ³⁶Ar, and ³⁸Ar. The new data differ from semi‐empirical estimates by up to a factor of 4 but agree within ～20% with results obtained by earlier parametric or physical approaches. The depth and size dependence of the shielding parameter ²²Ne/²¹Ne and the correlations ²⁶Al vs. ¹⁰Be, ²⁶Al vs. ⁵³Mn, ¹⁰Be/²¹Ne vs. ²²Ne/²¹Ne, and ³⁶Ar vs. ³⁶Cl for deciphering preatmospheric sizes, shielding depths, terrestrial residence times, and exposure histories are also discussed.  相似文献   

Evaluation of energy balance closure adjustment methods by independent evapotranspiration estimates from lysimeters and hydrological simulations          下载免费PDF全文

Matthias Mauder  Sandra Genzel  Jin Fu  Ralf Kiese  Mohsen Soltani  Rainer Steinbrecher  Matthias Zeeman  Tirtha Banerjee  Frederik De Roo  Harald Kunstmann 《水文研究》2018,32(1):39-50

Non‐closure of the surface energy balance is a frequently observed phenomenon of hydrometeorological field measurements, when using the eddy‐covariance method, which can be ascribed to an underestimation of the turbulent fluxes. Several approaches have been proposed in order to adjust the measured fluxes for this apparent systematic error. However, there are uncertainties about partitioning of the energy balance residual between the sensible and latent heat flux and whether such a correction should be applied on 30‐min data or longer time scales. The data for this study originate from two grassland sites in southern Germany, where measurements from weighable lysimeters are available as reference. The adjusted evapotranspiration rates are also compared with joint energy and water balance simulations using a physically based distributed hydrological model. We evaluate two adjustment methods: the first one preserves the Bowen ratio and the correction factor is determined on a daily basis. The second one attributes a smaller portion of the residual energy to the latent heat flux than to the sensible heat flux for closing the energy balance for every 30‐min flux integration interval. Both methods lead to an improved agreement of the eddy‐covariance based fluxes with the independent lysimeter estimates and the physically based model simulations. The first method results in a better comparability of evapotranspiration rates, and the second method leads to a smaller overall bias. These results are similar between both sites despite considerable differences in terrain complexity and grassland management. Moreover, we found that a daily adjustment factor leads to less scatter than a complete partitioning of the residual for every half‐hour time interval. The vertical temperature gradient in the surface layer and friction velocity were identified as important predictors for a potential future parameterisation of the energy balance residual.  相似文献   

Bottom-up and top-down control of seagrass overgrazing by the sea urchin Tripneustes gratilla     

Agustín Moreira-Saporiti  Dieuwke Hoeijmakers  Hauke Reuter  Flower E. Msuya  Katrin Gese  Mirta Teichberg 《Marine Ecology》2023,44(1):e12734

The lack of top-down control on Tripneustes gratilla, a sea urchin commonly known to graze on seagrass, and the bottom-up control of its feeding preference, led to the overgrazing of seagrass meadows of the species Thalassodendron ciliatum in Changuu Island (Zanzibar Archipelago). The impact of overgrazing on seagrasses was assessed by mapping the presence of grazed versus non-grazed seagrass patches in the study site, while the top-down control on T. gratilla was assessed by measuring the abundance of its fish predators. The feeding preference and distribution of T. gratilla were characterized by calculating the electivity indexes for each seagrass species and measuring sea urchin density, respectively. Approximately half of the patches of T. ciliatum were overgrazed, while predatory fishes of T. gratilla were absent from the site. The Vanderploeg and Scavia's Relativized Electivity Index indicated that T. gratilla had a feeding preference for T. ciliatum, which was also supported by higher urchin densities within T. ciliatum dominated patches. Bottom-up control of grazing activity was observed by quantifying and analyzing morphological, nutritional, and the chemical defense traits of the seagrass in relation to feeding preference and urchin density. Feeding was positively correlated to the seagrass tissue C:P ratio (ρ = 0.9), whereas urchin density showed no correlations. The bottom-up control of the feeding preference and agglomeration of T. gratilla in T. ciliatum meadows, together with the lack of evidence of substantial top-down control and the long recovery time of T. ciliatum led to the overgrazing of this species at this site. Overgrazing, therefore, was shown to be the result of multiple factors ranging from the traits of the seagrass and feeding preference of T. gratilla, to the abundance of predators in this area.  相似文献   

Galaxies and Star Clusters – From the Computer to the Real World     

Rainer Spurzem  Holger Baumgardt  Peter Berczik  Christian Boily  Stefan Deiters  Pavel Kroupa  Panos Patsis 《Astronomische Nachrichten》2005,326(7):589-605

G01 New evidence for a connection between massive black holes and ULX G02 Long‐Term Evolution of Massive Black Hole Binaries G03 NBODY Meets Stellar Population Synthesis G04 N‐body modelling of real globular star clusters G05 Fokker‐Planck rotating models of globular clusters with black hole G06 Observational Manifestation of chaos in spiral galaxies: quantitative analysis and qualitative explanation G07 GRAPE Clusters: Beyond the Million‐Body Problem G08 Orbital decay of star clusters and Massive Black Holes in cuspy galactic nuclei G09 An Edge‐on Disk Galaxy Catalog G10 Complexes of open clusters in the Solar neighborhood G11 Search for and investigation of new stellar clusters using the data from huge stellar catalogues G12 Computing 2D images of 3D galactic disk models G13 Outer Pseudoring in the Galaxy G14 Where are tidal‐dwarf galaxies? G15 Ultra compact dwarf galaxies in nearby clusters G16 Impact of an Accretion Disk on the Structure of a stellar cluster in active galactic nuclei G17 Order and Chaos in the edge‐on profiles of disk galaxies G18 On the stability of OB‐star configurations in the Orion Nebula cluster G19 Older stars captured in young star clusters by cloud collapse G20 General features of the population of open clusters within 1 kpc from the Sun G21 Unstable modes in thin stellar disks G22 From Newton to Einstein – Dynamics of N‐body systems G23 On the relation between the maximum stellar mass and the star cluster mass  相似文献   

Small satellites for global coverage: Potential and limits   总被引：2，自引：0，他引：2  

Rainer Sandau  Klaus Brieß  Marco D&#x;Errico 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(6):492-504

There is an increasing need for Earth Observation (EO) missions to meet the information requirements in connection with Global Change Studies. Small and cost-effective missions are powerful tools to flexibly react to information requirements with space-borne solutions. Small satellite missions can be conducted relatively quickly and inexpensively by using commercial off-the-shelf-technologies, or they can be enhanced by using advanced technologies. A new class of advanced small satellites, including autonomously operating “intelligent” satellites may be created, opening new fields of application. The increasing number of small satellites and their applications drive developments in the fields of small launchers, small ground station networks, cost-effective data distribution methods, and cost-effective management and quality assurance procedures. There are many advantages of small satellite missions, like more frequent mission opportunities, a faster return of data, larger variety of missions, more rapid expansion of the technical and/or scientific knowledge base, greater involvement of small industry, feasibility by universities and others.This paper deals with general trends in the field of small satellite missions for Earth observation. Special attention is given to the potential of spatial, spectral, and temporal resolution of small satellite based systems. Examples show small satellites offer also the unique possibility to install affordable constellations to provide good daily coverage of the globe and/or allow us to observe dynamic phenomena.The facts and examples given in this paper lead to the conclusion: Small satellites are already powerful tools for monitoring global, regional and local phenomena. In the future, their application spectrum will even broaden based on the ongoing development in many areas of technology and observation techniques.  相似文献   

Radiometric dating of the Middle Palaeolithic tool industry and associated fauna of Pin Hole Cave,Creswell Crags,England     

Roger M. Jacobi  Peter J. Rowe  Mabs A. Gilmour  Rainer Grün  Timothy C. Atkinson 《第四纪科学杂志》1998,13(1):29-42

Uranium-series dating of derived speleothem suggests that the sediments enclosing a Middle Palaeolithic stone artefact assemblage in Pin Hole Cave probably accumulated after about 64 ka, and ¹⁴C dates indicate a likely age of > 40 ka for the large mammal fauna associated with it. Electron spin resonance data from the fauna conform with these age constraints and are consistent with accumulation between 38 and 50 ka. This evidence supports the view that Britain was recolonised by hominids during Oxygen Isotope Stage 3. Stratigraphically higher stone tool industries demonstrate the local presence of both early Upper and late Upper Palaeolithic cultures. © 1998 John Wiley & Sons, Ltd.  相似文献