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  • COMMUNICATIONS AND RADAR  (2)
  • FLUID MECHANICS AND HEAT TRANSFER  (2)
  • 1
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    Near-nadir radar backscatter from a well-developed sea (1990)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Beschreibung: The Kirchhoff approximation for the case of well-developed seas is analyzed. In this peculiar case, the equilibrium range in the wave number spectrum corresponds to a cascade pattern in the surface geometry. Its high wave number cutoff is shown to be a major factor of the radar backscatter. This intrinsic scale is evaluated, and both the geometrical and the physical optics terms are related to major parameters of wind-wave dynamics. The range of validity of the Kirchhoff approximation and the relative importance of the diffraction correction are analyzed. Finally, the radar cross section sigma exp 0 of well-developed seas is compared with that of poorly developed seas. The great qualitative difference shown in the wind speed dependence of sigma exp 0 for these two regimes is pointed out as a source of a considerable error trend recently discovered in satellite altimeter wind measurements.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: Radio Science (ISSN 0048-6604); 25; 1211-121
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
  • 2
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    Statistical geometry of a small surface patch in a developed sea (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The fractal and marginal fractal regimes in surface geometry are studied. The basic notions of fractal geometry are applied to a small surface patch in a developed sea, corresponding to the equilibrium wave number spectrum. Topothesy, outer and inner boundaries of the fractal range, and a cascade pattern in surface geometry are discussed. Theoretical predictions of whitecap and foam coverage are presented. A fractal decomposition for a surface patch is developed based on the Karhunen-Loeve expansion. The resulting series formalizes the cascade process of constructing realization of a Gaussian random patch. The implications of the research for microwave remote sensing signatures are considered.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 94; 4998-501
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
  • 3
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    Multi-wave interaction theory for wind-generated surface gravity waves (1992)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-08-28
    Beschreibung: Consistently employing the assumption of localness of wave-wave interactions in the wavenumber space, the Kolmogorov treatment of the energy cascade is applied to the case of wind-generated surface gravity waves. The effective number v of resonantly interacting wave harmonics is not limited to four but is found as a solution of a coupled system of equations expressing: (i) the dependence of the spectrum shape on the degree of the wave nonlinearity, and (ii) the continuity of the wave action flux through the spectrum given a continuous positive input from wind. The latter is specified in a Miles-type fashion, and a simple scaling relationship based on the concept of the turnover time is derived in place of the kinetic equation. The mathematical problem is reduced to an ordinary differential equation of first order. The exponent in the 'power law' for the spectral density of the wave potential energy and the effective number of resonantly interacting wave harmonics are found as functions of the wave frequency and of external factors of wind-wave interaction. The solution is close to the Zakharov-Filonenko spectrum at low frequencies and low wind input while approaching the Phillips spectrum at high frequencies and sufficiently high wind.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: Journal of Fluid Mechanics (ISSN 0022-1120); p. 623-635.
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
  • 4
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    Fractal features of sea surface manifested in microwave remote sensing signatures (1988)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: The wave number spectrum of a well developed sea includes a broad range of wavenumbers (the equilibrium range) where the spectral density is governed by a power law, k exp p. In the approximation of a Gaussian surface, the exponent p is related to the Hausdorff dimension. For p less than 4 the Hausdorff dimension is greater than 2 and the surface is characterized by an increased number of steep and breaking wavelets and by an increased number of specular points at near vertical incidence. The former results in the so-called spike component in the total return at oblique incidence, whereas the latter leads to an increased backscatter at nadir and near-nadir angles. Theory for both cases is reviewed and implications for satellite scatterometer and altimeter measurements of surface winds are discussed.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: Wave Propagation and Scattering in Varied Media; Apr 06, 1988 - Apr 08, 1988; Orlando, FL; United States
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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    NASA TECHNICAL REPORTS
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