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  • 1
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    The case for aeolian control of meter-scale surface texture on Mars (1984)
    In:  CASI
    Details
    Publikationsdatum: 2006-04-06
    Beschreibung: The origin of Mars surface units and the extent of subsequent cratering play key roles in determining surface texture. At scale sizes of 0.1-10 meters, however, there is a growing body of evidence that wind is the dominant force. The direct and indirect evidence which implies that meter-scale surface texture on Mars is controlled by the wind is presented. Since radar is uniquely sensitive to structure on these scales, radio wave scattering data can provide insight on aeolian activity available from no other source.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: NASA. Washington Rept. of Planetary Geology Program, 1983; p 273-275
    Format: text
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  • 2
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    Voyager 2 radio science observations of the Uranian system Atmosphere, rings, and satellites (1986)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The results of preliminary analyses of radio occultation data obtained by Voyager 2 as it passed Uranus are described. The occultations took place between 2-7 deg S latitude and yielded atmospheric temperature profiles between pressure levels of 10-900 mbar, an altitude range of 100 km. The mole fractions of hydrogen and helium in the tropopause were estimated, in conjunction with IR data, to about 0.85 and 0.10-0.20, respectively. Radio signal intensity data indicated the presence of a cloud deck of CH4 ice at a pressure level of 1300 mbar and a temperature of 81 K, implying a CH4 mole fraction of 0.02 at very low altitudes. The ionosphere extended upward, in two levels, to more than 10,000 km altitude. The ring system was different than the one around Saturn and possessed cylindrical substructures. The radio data also permitted mass density estimates for the five major moons, i.e., about 1.40 gr/cu cm, a value which rules out cometary origins.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Science (ISSN 0036-8075); 233; 79-84
    Format: text
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  • 3
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    Scattering properties of Venus' surface (1992)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: Radar backscatter functions Sigma-(carat)(sub 0)(phi) for incidence angles between 0 less than or equal to phi less than or equal to 4-10 deg were derived from Magellan altimetry radar echoes. The procedure includes constrained solution of a system of simultaneous equations for which the echo-spectrum and echo time profile are inputs. A practical and workable set of constraints was applied; optimization and improved results are expected as the analysis matures. The scattering functions yield information on small-scale surface structures (tens of centimeters to tens of meters) but averaged over hundreds of sq km. RMS surface slopes derived from fits of analytic functions to the Sigma-(carat)(sub 0)(phi) results were converted to map form and show patterns similar to those reported using other techniques. While all three forms are found on Venus, fit residuals imply that an exponential scattering function matches data better than either the Hagfors or Gaussian form in most areas, although the Hagfors function may be a better descriptor at some sites. Limited study of image data indicates that average backscatter cross section, and possibly its slope, can be derived at oblique angles (17 deg less than or equal to phi less than or equal to 45 deg). Offsets of the echo peak in altimetry spectra are surprisingly common and are loosely correlated with Venus topography, but no cause for this phenomenon was identified.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Lunar and Planetary Inst., Papers Presented to the International Colloquium on Venus; p 128-129
    Format: application/pdf
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  • 4
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    Surface properties of Galilean satellites from bistatic radar experiments (1991)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: The icy moons of Jupiter were the first to show unusual radar backscatter behavior in Earth-based experiments. Studies of Europa, Ganymede, and Callisto revealed strong echoes and a reversed sense of circular polarization. No explanations were entirely satisfactory because of the difficult constraints imposed by the existing data. The (scalar) bidirectional coherence model predicts an opposition effect, or enhancement in the backscatter direction, resulting from coherent addition of backscatter from identical (but oppositely directed) ray paths. The mode decoupling model yields a similar, vector result in which the observed polarization properties of the backscattered wave can also be obtained. The possibilities were considered for conducting such experiments using the Galileo spacecraft. Both conventional oblique-forward bistatic experiments (to determine basic electrical and physical properties of the surface material on centimeter-meter scales) and near-backscatter experiments (to sample the enhanced backscatter lobe) were considered.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1990; p 317-319
    Format: application/pdf
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  • 5
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    Saturn's pole - geometric correction based on voyager UVS and radio occultations (1983)
    In:  Other Sources
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    Publikationsdatum: 2011-08-18
    Beschreibung: Measurements of of the opacity of Saturn's rings acquired during occultation experiments at radio (3.6 cm) and ultraviolet wavelengths were initially reduced to radial position rho using a standard pole vector. Common features in the two data sets from this reduction were offset by distances Delta rho(i). These offsets have been attributed to an error in the pole direction. Because the viewing geometries were quite different for the two experiments, the set of differences of Delta rho(i) provides a sensitive measure of corrections needed to refine the Saturn pole direction. The new standard pole vector in 1950.0 coordinates has right ascension alpha = 38.409 + or - 0.016 deg and declination delta = 83.324 + or - 0.002 deg.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Astronomical Journal (ISSN 0004-6256); 88; Oct. 198
    Format: text
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  • 6
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    Radar Imaging of the Icy Galilean Satellites During 1999 Opposition (2000)
    In:  Other Sources
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    Publikationsdatum: 2017-10-02
    Beschreibung: We report radar observations of Europa, Ganymede, and Callisto made during 1999 opposition using the Arecibo 12.6 cm and Goldstone 3.5 cm radar facilities.
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Materialart: Lunar and Planetary Science XXXI; LPI-Contrib-1000
    Format: text
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  • 7
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    Statistics of Aeolian Surface of Mars (1985)
    In:  CASI
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    Publikationsdatum: 2014-10-09
    Beschreibung: Aeolian control of large scale surface texture is apparent in orbiter images from selected regions of Mars -- the polar areas, equatorial canyons, and some craters. At other locations on Mars there is evidence suggesting aeolian control on meter scales within a context provided by larger landforms.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: NASA, Washington Repts. of Planetary Geol. and Geophys. Program, 1984; p 463
    Format: text
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  • 8
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    Mars Radar Catalog (1985)
    In:  CASI
    Details
    Publikationsdatum: 2014-10-09
    Beschreibung: Radar observations of Mars have been conducted since 1963 using four Earth based facilities. Wavelengths have ranged from about 3 to about 70 cm. Experiments have been conducted in ranging, spectral, and mixed modes. Results include topographic profiles, estimates of dielectric constant and meter scale surface roughness, and qualtitative determinations of centimeter scale structure.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: NASA, Washington Repts. of Planetary Geol. and Geophys. Program, 1984; p 461-462
    Format: text
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  • 9
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    Scattering by Venus' surface (1993)
    In:  Other Sources
    Details
    Publikationsdatum: 2019-01-25
    Beschreibung: During 1992, Magellan altimetry echoes were processed to yield scattering functions sigma(sub o)(phi) over near-nadir angles phi less than or equal to 10 deg from some 2000 Venus orbits. SAR image strips acquired simultaneously at oblique angles were also reduced to give scattering functions but over a few deg of incidence angle in the range 15 less than or equal to phi less than or equal to 45 deg. By sorting, the altimetry and SAR results can be combined to give composite scattering functions for much of Venus' surface. The data in hand should allow definition of such composite functions for 70-80 percent of Venus at resolutions of 20 km--approximately one million separate functions.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 3: N-Z; p 1311
    Format: text
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  • 10
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    Particle size distributions in Saturn's rings from Voyager 1 radio occultation (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Information on Saturn ring particle sizes obtained with the Voyager 1 ring occultation experiment is discussed. The theory underlying the determination of the particle size distribution is presented, including differential extinction and inversion of the scattered signal. Experimental observations and results for the observed spectra, differential cross sections, suprameter and sub- to suprameter size distributions are presented. The size and mass distributions both cut off sharply at about 4-5 m; the mass distribution peaks over the 3-4 m size range for four ring system features at 1.35, 1.51, 2.01, and 2.12 Saturn radii. A power-law type model is consistent with the data over a limited size range of 0.01 to 1 m. The fractional contribution of the suprameter particles to the microwave opacity for the four features appears to be about 1/3, 1/3, 2/3, and 1, respectively, and their cumulative surface mass per unit area are about 11, 16, 41, and 132 g/sq cm if the particles are solid water ice.
    Schlagwort(e): LUNAR AND PLANETARY EXPLORATION
    Materialart: (ISSN 0019-1035)
    Format: text
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