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  • Articles  (5)
  • Articles: DFG German National Licenses  (5)
  • Blackwell Publishers  (5)
  • 1995-1999  (5)
  • 1975-1979
  • Geosciences  (5)
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  • Articles  (5)
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  • Articles: DFG German National Licenses  (5)
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  • 1995-1999  (5)
  • 1975-1979
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  • 1
    Electronic Resource
    Electronic Resource
    Multiple prediction using the homeomorphic-imaging technique (1998)
    Oxford BSL : Blackwell Publishers
    Geophysical prospecting 46 (1998), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: A new method for predicting different kinds of multiples and peg-leg reflections in unstacked seismic data is discussed. The basis for this method is the fact that kinematic properties of multiples can be represented as a combination of kinematic properties of primary reflections. The prediction is made using a two-step process. In the first step, the values for the angle of emergence and radius of curvature of the wavefront for primary reflections from ‘multiple-generating’ interfaces are obtained. These parameters are estimated directly from unstacked data for every source point using the homeomorphic-imaging technique. The second step consists of prediction of multiples from primary reflections that satisfy a so-called ‘multiple condition’. This condition is the equality of the absolute values of the angles of emergence calculated from the first step. This method is effective even in complex media and information on the subsurface geology is not required. The parameters are estimated directly from the unstacked data and do not require any computational efforts such as in wavefield extrapolation of data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.1998.990331.x
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  • 2
    Electronic Resource
    Electronic Resource
    Seismic and ultrasonic velocities in permafrost (1998)
    Oxford BSL : Blackwell Publishers
    Geophysical prospecting 46 (1998), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: We calculate the compressional- and shear-wave velocities of permafrost as a function of unfrozen water content and temperature. Unlike previous theories based on simple slowness and/or moduli averaging or two-phase models, we use a Biot-type three-phase theory that considers the existence of two solids (solid and ice matrices) and a liquid (unfrozen water). The compressional velocity for unconsolidated sediments obtained with this theory is close to the velocity computed with Wood's model, since Biot's theory involves a Wood averaging of the moduli of the single constituents. Moreover, the model gives lower velocities than the well-known slowness averaging theory (Wyllie's equation). For consolidated Berea sandstone, the theory underestimates the value of the compressional velocity below 0°C. Computing the average bulk moduli by slowness averaging the ice and solid phases and Wood averaging the intermediate moduli with the liquid phase yields a fairly good fit of the experimental data. The proportion of unfrozen water and temperature are closely related. Fitting the wave velocity at a given temperature allows the prediction of the velocity at the whole range of temperatures, provided that the average pore radius and its standard deviation are known.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.1998.1000333.x
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    An experimental comparison of three direct methods of marine source signature estimation (1998)
    Oxford BSL : Blackwell Publishers
    Geophysical prospecting 46 (1998), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Three methods for estimation of the pressure wavefield generated by a marine airgun array are tested experimentally and compared. In the trial a variety of radiation angles and array configurations were used and some large synchronization errors were deliberately introduced. The source was equipped with near-field hydrophones and a subsource ministreamer. A tethered far-field hydrophone was used so that the three estimated far-field signatures could be compared with an independent measurement.The knowledge of the source signature is important for on-board source array QC, deconvolution, multiple attenuation, stratigraphic trap prediction, modelling and inversion, AVO analysis and reservoir monitoring.The methods perform very well and give estimates whose frequency-domain spectra match the measured spectra to within a few dB and within a few tens of degrees of phase over the tested bandwidth of 3.5–110 Hz. The time-domain error-energy is typically only a few per cent of the signal energy for radiation angles within about 30° of the vertical. The third method proved to be sensitive to an experimental shortcoming leading to overloading of the ministreamer and meaningful comparison was not possible for some test configurations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.1998.980334.x
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  • 4
    Electronic Resource
    Electronic Resource
    Joint estimation of AVO and kinematic parameters (1998)
    Oxford BSL : Blackwell Publishers
    Geophysical prospecting 46 (1998), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Conventional amplitude-versus-offset (AVO) analysis such as linear fitting of isotime samples after NMO correction does not give reliable results in the presence of interfering reflections or velocity errors. For this reason we propose a new method that is able to remove interference effects on the AVO of the target reflection and minimize the effects of residual moveout. The method is based on the minimization of the difference between observed data and a model that includes theoretical descriptions of the AVO and traveltimes. This minimization is carried out jointly with respect to AVO and kinematic parameters (velocities and traveltimes) and requires the a priori knowledge of the propagating wavelet. The kinematic parameters are given by the NMO equation extended to the fourth-order term and the AVO is described as a linear combination of a set of orthogonal functions. The AVO functions are derived from a statistical model of reflection amplitude in the presence of velocity error.Applications to synthetic and real data demonstrate the ability of the method to attenuate distortion effects on the AVO of the primary reflection by interfering coherent noise. The real data example pertains to a marine case where the primary event is contaminated by multiple reflections generated in the water layer and by another event, reflected from an interface deeper than the target, that merges with the examined reflections at the far-offsets. This causes a subtle tuning that distorts the AVO of the target. Our method attenuates the effects of the multiples and discriminates the ‘double event’ nature of the target reflection at the far-offsets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.1998.970332.x
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  • 5
    Electronic Resource
    Electronic Resource
    Optimum expression for computation of the gravity field of a polyhedral body with linearly increasing density (1998)
    Oxford BSL : Blackwell Publishers
    Geophysical prospecting 46 (1998), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The formula for the computation of the gravity field of a polyhedral body whose density is linearly dependent on some coordinate is derived and transformed into the optimum form for numerical calculation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.1998.960335.x
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