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  • 1
    Publication Date: 2019-11-04
    Description: Numerous geophysical techniques have successfully contributed to geotechnical engineering and environmental problems of the shallow subsurface. Geophysical surveys are used to: delineate geologic features, measure in-situ engineering properties, and detect hidden cultural features. Most technologies for the detection of shallow buried objects are electromagnetic methods which measure the contrast in ferrous content, electrical conductivity, or dielectric constant between the object and surrounding soil. Seismic technologies measure the contrast in mechanical properties of the subsurface, however, scaled down versions of conventional seismic methods are not suitable for the detection shallow buried objects. In this paper, we discuss the development of a method based on acoustic to seismic coupling for the detection of shallow buried object. Surface vibrations induced by an impinging acoustic wave from a loudspeaker is referred to as acoustic to seismic coupling. These vibrations can be remotely detected using a laser-Doppler vibrometer (LDV). If an object is present below the surface of the insonified patch, the transmitted wave is back scattered by the target towards the surface. For targets very close to the surface, the scattered field produces anomalous ground vibrational velocities that are indicative of the shape and size of the target.
    Description: JCR Journal
    Description: open
    Keywords: Acoustics ; seismic ; porous madia ; buried object ; 04. Solid Earth::04.02. Exploration geophysics::04.02.07. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 3616171 bytes
    Format: application/pdf
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 121 (1995), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Using the static form of a system of equations for seismic waves (de la Cruz & Spanos 1989), we show how various compressibilities can be calculated in a straightforward manner. The results obtained have many points of contact with those found in the literature. In particular, we verify all identities among drained compressibilities given in, e.g., Zimmerman (1991), thus providing an alternative route towards them. The undrained compressibility is described within the context of this work and its relation to the various drained compressibilities (Gassmann 1951) is verified. For greater experimental flexibility, we introduce a one-parameter family of compressibilities which includes the drained and the undrained compressibilities as members. The family of compressibilities is also used to obtain an expression for the pore-pressure build-up coefficient. In this work we also address the problem of macroscopic shearing. Experiments are proposed for the determination of the macroscopic shear modulus, leading to natural expressions for ‘Young's modulus’ and ‘Poisson's ratio’ for the porous medium under drained conditions. We also establish connections with Biot's (1956a) parameters.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 1995-05-01
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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  • 4
    Publication Date: 2013-09-12
    Description: [1]  Abundant short-period, small-scale gravity waves have been identified in the mesosphere and lower thermosphere over Halley, Antarctica, via ground-based airglow image data. Although many are observed as freely-propagating at the heights of the airglow layers, new results under modeled conditions reveal that a significant fraction of these waves may be subject to reflections at altitudes above and below. The waves may at times be trapped within broad thermal ducts, spanning from the tropopause or stratopause to the base of the thermosphere (~140 km), which may facilitate long-range propagation (~1000 s of km) under favorable wind conditions.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2014-04-15
    Description: We use a non-linear, fully-compressible, two-dimensional numerical model to study the effects of dissipation on gravity wave packet spectra in the thermosphere. Numerical simulations are performed to excite gravity wave packets using either a time-dependent vertical body forcing at the bottom boundary or a specified initial wave perturbation. Three simulation case studies are performed to excite (1) a steady-state monochromatic wave, (2) a spectrally broad wavepacket, and (3) a quasi monochromatic wave packet. In addition, we analyze (4) an initial condition simulation with an isothermal background. We find that, in cases where the wave is not continually forced, the dominant vertical wavelength decreases in time, predominantly due to a combination of refraction from the thermosphere and dissipation of the packets’ high frequency components as they quickly reach high altitude. In the continually-forced steady-state case, the dominant vertical wavelength remains constant once initial transients have passed. The vertical wavelength in all simulations increases with altitude above the dissipation altitude (the point at which dissipation effects are greater than the wave amplitude growth caused by decreasing background density) at any fixed time. However, a shift to smaller vertical wavelength values in time is clearly exhibited as high frequency, long vertical wavelength components reach high altitudes and dissipate first, to be replaced by slower waves of shorter vertical wavelength. Results suggest that the dispersion of a packet significantly determines its spectral evolution in the dissipative thermosphere.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2016-10-16
    Description: Joint inversion and time-lapse inversion techniques of geophysical data are often implemented in an attempt to improve imaging of complex subsurface structures and dynamic processes by minimizing negative effects of random and uncorrelated spatial and temporal noise in the data. We focus on the structural cross-gradient (SCG) approach (enforcing recovered models to exhibit similar spatial structures) in combination with time-lapse inversion constraints applied to surface-based electrical resistivity and seismic traveltime refraction data. The combination of both techniques is justified by the underlying petrophysical models. We investigate the benefits and trade-offs of SCG and time-lapse constraints. Using a synthetic case study, we show that a combined joint time-lapse inversion approach provides an overall improvement in final recovered models. Additionally, we introduce a new approach to reweighting SCG constraints based on an iteratively updated normalized ratio of model sensitivity distributions at each time-step. We refer to the new technique as the Automatic Joint Constraints (AJC) approach. The relevance of the new joint time-lapse inversion process is demonstrated on the synthetic example. Then, these approaches are applied to real time-lapse monitoring field data collected during a quarter-scale earthen embankment induced-piping failure test. The use of time-lapse joint inversion is justified by the fact that a change of porosity drives concomitant changes in seismic velocities (through its effect on the bulk and shear moduli) and resistivities (through its influence upon the formation factor). Combined with the definition of attributes (i.e. specific characteristics) of the evolving target associated with piping, our approach allows localizing the position of the preferential flow path associated with internal erosion. This is not the case using other approaches.
    Keywords: Marine Geosciences and Applied Geophysics
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 7
    Publication Date: 2019-08-01
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
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