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  • 1
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    Profiling Saturn's rings by radio occultation (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The development of reconstruction algorithms that correct for diffraction effects in radio occultation measurements is described. The reciprocal Fresnel transform relationship between the complex amplitude of the observed coherent signal and the complex microwave transmittance of the rings is derived using the Huygens-Fresnel formulation of the diffraction problem. The effects of the finite data segment width, the uncertainties in the Fresnel scale, systematic phase errors in the kernel of the inverse transform, reference oscillator instabilities, and random noise measurements on the resolution of the reconstructed transmittance are analyzed. Examples of reconstructed opacity profiles for some regions of Saturn's rings derived by applying the reconstruction theory to Voyager 1 at Saturn data are presented.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 68; 120-166
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  • 2
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    Past and future of radio occultation studies of planetary atmospheres (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Measurements of radio waves that have propagated through planetary atmospheres have provided exploratory results on atmospheric constituents, structure, dynamics, and ionization for Venus, Mars, Titan, Jupiter, Saturn, and Uranus. Highlights of past results are reviewed in order to define and illustrate the potential of occultation and related radio studies in future planetary missions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research (ISSN 0273-1177); 7; 12, 1
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  • 3
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    Interannual variability of Mars South Polar cap (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Telescopic data on the twentieth century regressions of Mars' south polar cap were reexamined for evidence of interannual variability. Several regressions, particularly that of 1956, are found to differ significantly from the mean. The possibility of correlations with major dust storms is explored.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-180207 , NAS 1.26:180207
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  • 4
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    Persistent dust cloud activity on Mars near Echus Chasma in 1978 (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The Echus Chasma clouds of Mars, which are the first to be observed by spacecraft in the equatorial canyon region of the planet, extend the geographic and seasonal ranges in which dust stoms are known to occur. Viking camera observations of these clouds in red and violet filters are presently noted to imply their composition to be partly dust and partly condensate. Drainage winds, part of a diurnal wind system driven by thermal and elevation contrasts, are seen as a plausible interpretation of the observed phenomena.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 77; 35-58
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  • 5
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    Comment on 'Distribution of whistler mode bursts at Venus' by F.L. Scarf, K.F. Jordan, and C.T. Russell (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Consideration is given to the study of the 100-Hz electric field noise observed from the Pioneer Venus Orbiter (PVO) by Scarf et al. (1987). It is suggested that the study incorrectly interprets the results as evidence for lightning and volcanism at Venus. Statistical evidence is presented, suggesting that the distribution of the noise is essentially random, within the zone of occurrence of ion troughs, and decreases at the lowest PVO altitudes, closest to the neutral atmosphere. It is found that the topographic clustering reported by Scarf et al. is an artifact of the variable spatial distribution of troughs and associated noise.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 12087-12
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  • 6
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    Magnetic fields at Neptune (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The Voyager 2 magnetic field experiment discovered a complex and powerful magnetic field in Neptune, as well as an associated magnetosphere and magnetic tail. As the spacecraft exited the magnetosphere, the magnetic tail appeared to be monopolar. The auroral zones are probably located far from the rotation poles, and may possess complex geometry. The Neptune rings and all its known moons are imbedded deep within the magnetosphere (except for Nereid, which is outside when it lies sunward of the planet); the radiation belts have a complex structure due to the absorption of energetic particles by the moons and rings of Neptune, as well as losses associated with the significant changes in the diurnally varying magnetosphere configuration.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 246; 1473-147
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  • 7
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    Voyager radio occultation by Uranus' rings. I - Observational results (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The January 24, 1986 radio occultation of Voyager 2 by the Uranian rings yielded fine-resolution, 50- and 200-m optical depth profiles at a 3.6 cm wavelength for the nine pre-Voyager rings; these are found to be opaque, reaching optical depths as great as 6-8 in rings gamma and epsilon, which are the only two rings possessing extremely sharp inner and outer edges. Rings 6, 5, 4, and delta share a morphology characterized by a sharp outer-edge transition and a quasi-exponential inner edge one. In ring eta, this behavior is reversed, and ring beta exhibits both diffuse edges and the smallest of the observed opacities.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 78; 131-168
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  • 8
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    Subcentimeter-size particle distribution functions in planetary rings from Voyager radio and photopolarimeter occultation data (1987)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: Analysis of measurements of the scattered and direct components of Voyager 1 radio occultation signals at 3.5 and 13 cm wavelengths yield estimates of the distribution functions of supracentimeter-size particles and thickness of relatively broad regions in Saturn's rings. If mearurements of signal amplitude at a shorter wavelength are combined with the previously analyzed data, the shape of the distribution functions characterizing the smaller particles can be constrained. If size distributions of arbitrary form were considered, many solutions are found that are consistent with the three available observations of signal amplitude. The best-fit power law was calculated to the three observations at three wavelengths for several of the embedded Saturn ringlets. Mie scattering theory predicts that the measured phase of the radio occultation signal is highly sensitive to particles ranging from 0.1 to 1.0 wavelengths in size, thus additional constraints on the subcentimeter-size distribution functions for both the Saturn and Uranus rings can in principle be derived from radio phase measurements.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 55-56
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  • 9
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    An analysis of bending waves in Saturn's rings using Voyager radio occultation data (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Three oscillatory features in the Voyager 1 radio occultation map of Saturn's rings have been identified as the 5:3, 7:4, and 4:2 spiral bending waves excited by the satellite Mimas. The observations are presented and the wave properties are investigated. It is found that the Mimas 7:4 wave is consistent with the linear theory of bending waves, while the Mimas 5:3 wave may not be. A detailed analysis of the Mimas 4:2 bending wave was not possible due to the large optical depth in the region in which it propagates.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 68; 481-502
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  • 10
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    Martian north polar cap and circumpolar clouds - 1975-1980 telescopic observations (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Observational data on the late-winter/spring sublimation and recession of the north polar cap of Mars are analyzed statistically. Ground-based photographic data obtained by the International Planetary Patrol during the oppositions of 1975, 1978, and 1980 are compiled in tables and graphs, and Viking data from the 1977-1978 and 1980 recessions are included for comparison. The results indicate that the recession of the cap from its maximum extent (near 55 deg N) reaches a plateau during midspring. The end of this plateau is associated with (1) a sharp increase in circumpolar cloud cover (suggesting that the cap is the water source) and (2) a probable reversal of the northern-hemisphere meridional wind (as observed by Kahn, 1983).
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 71; 306-312
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