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  • 2010-2014  (2)
  • 1980-1984  (3)
  • 1
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    On the retrieval of attenuation and site amplifications from ambient noise on linear arrays: further numerical simulations (2013)
    Oxford University Press
    Details
    Publication Date: 2013-05-09
    Description: While it is clear that ambient noise correlations contain information on seismic attenuation, retrieval of that information requires disentangling the influences of site amplification factors and anisotropic noise intensity. Recent work has argued that recognition that ambient noise intensity is governed by a radiative transfer equation will facilitate that retrieval. This sufficiently constrains the noise field to permit amplitudes of noise correlation waveforms to be fit to models of spatially varying attenuation, noise intensity and site amplification factors. Numerical simulations, for the case of a uniformly spaced linear array of receivers, homogeneous attenuation and wave speed and mild directionality to the noise field, were shown earlier to be consistent with the assertion. Here, the numerical simulations are extended to a broader class of systems. Accurate retrieval is demonstrated using a priori error estimates and weighted least-squares fitting. Attenuations and site factors are retrieved in systems with spatially varying attenuation, highly directional noise intensities, irregular line arrays and poor signal-to-noise ratios. Examination of a variety of systems illustrates some of the range of applicability and limits of the approach.
    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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  • 2
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    Energy Partitions among Elastic Waves for Dynamic Surface Loads in a Semi-Infinite Solid (2011)
    Seismological Society of America
    Details
    Publication Date: 2011-08-01
    Description: We examine the energy partitions among elastic waves due to dynamic normal and tangential surface loads in a semi-infinite elastic solid. While the results for a dynamic normal load on the surface of a half-space with Poisson ratio of 1/4 is a well-known result by Miller and Pursey (1955), the corresponding results for a dynamic tangential load are almost unknown. The partitions for the normal and tangential loads were computed independently by Weaver (1985) versus Poisson ratio (0〈 or =nu 〈 or =1/2), using diffuse-field concepts within the context of ultrasonic measurements. The connection with the surface load point was not explicit, which partially explains why these results did not reach the seismological and engineering literature. The characteristics of the elastic radiation of these two cases are quite different. For a normal load, about 2/3 of the energy leaves the loaded point as Rayleigh surface waves. On the other hand, the tangential load induces a similar amount in the form of body shear waves. It is established that the energies injected into the elastic half-space by concentrated normal and tangential harmonic surface loads are proportional to the imaginary part of the corresponding components of the Green's tensor when both source and receiver coincide. The relationship between the Green's function and average correlations of motions within a diffuse field is clearly established.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America
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  • 3
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    Sea-Ice and Snow-Cover Data Availability, Needs and Problems (1984)
    Cambridge University Press
    Details
    Publication Date: 1984-01-01
    Description: Various types of sea-ice and snow-cover data are required for operational purposes in real time, for engineering assessments of associated hazards and for regional to global-scale modeling of the climate system. Data on the primary characteristics of ice and snow (extent, depth or thickness, and ice concentration) are becoming available to meet many present types of modeling requirement but secondary properties such as snow-water content, ridging intensity, open-water fraction and ice drift are less readily available.Data for these major variables of snow and ice cover are considered with respect to problems encountered in obtaining and using digital information necessary for modern computer analyses. Such problems include the limitations of the basic observations (observational or sensor accuracy), the spatial and temporal resolution of different data sets, varying national practices of observing and reporting, and the problems of meshing data collected by different means and having spatial differences and temporal changes of observation time, site location, sensor system and resolution, etc. The relative reliability and climatic “information content” of some historical data sets are briefly examined and available digital data sets on modern global ice- and snow-cover conditions are described.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 4
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    Sea-Ice and Snow-Cover Data Availability, Needs and Problems (1984)
    Cambridge University Press
    Details
    Publication Date: 1984-01-01
    Description: Various types of sea-ice and snow-cover data are required for operational purposes in real time, for engineering assessments of associated hazards and for regional to global-scale modeling of the climate system. Data on the primary characteristics of ice and snow (extent, depth or thickness, and ice concentration) are becoming available to meet many present types of modeling requirement but secondary properties such as snow-water content, ridging intensity, open-water fraction and ice drift are less readily available. Data for these major variables of snow and ice cover are considered with respect to problems encountered in obtaining and using digital information necessary for modern computer analyses. Such problems include the limitations of the basic observations (observational or sensor accuracy), the spatial and temporal resolution of different data sets, varying national practices of observing and reporting, and the problems of meshing data collected by different means and having spatial differences and temporal changes of observation time, site location, sensor system and resolution, etc. The relative reliability and climatic “information content” of some historical data sets are briefly examined and available digital data sets on modern global ice- and snow-cover conditions are described.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 5
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    Pilot study and evaluation of a SMMR-derived sea ice data base (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Data derived from the Nimbus 7 scanning multichannel microwave radiometer (SMMR) are discussed and the types of problems users have with satellite data are documented. The development of software for assessing the SMMR data is mentioned. Two case studies were conducted to verify the SMMR-derived sea ice concentrations and multi-year ice fractions. The results of a survey of potential users of SMMR data are presented, along with SMMR-derived sea ice concentration and multiyear ice fraction maps. The interaction of the Arctic atmosphere with the ice was studied using the Nimbus 7 SMMR. In addition, the characteristics of ice in the Arctic ocean were determined from SMMR data.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: NASA-CR-175255 , NAS 1.26:175255
    Format: application/pdf
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