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  • Other Sources  (11)
  • 1980-1984  (11)
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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
    Publication Date: 2006-04-06
    Description: 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.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA. Washington Rept. of Planetary Geology Program, 1983; p 273-275
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  • 2
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    Saturn's pole - geometric correction based on voyager UVS and radio occultations (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: 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.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astronomical Journal (ISSN 0004-6256); 88; Oct. 198
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  • 3
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    Particle size distributions in Saturn's rings from Voyager 1 radio occultation (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: 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.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: (ISSN 0019-1035)
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  • 4
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    The microwave opacity of Saturn's rings at wavelengths of 3.6 and 13 cm from Voyager 1 radio occultation (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Information obtained about Saturn's rings through radio occultation observations with Voyager 1 is discussed. The experimental aspects are addressed, including the positional relationships and relative motions of the spacecraft, rings, and earth, the radio system, observables, microwave opacity, and diffraction. The data characteristics, reduction procedures, calibrations, and corrections are described, and results are presented for the opacity, complex extinction, and diffraction. Ring C is found to exhibit a gently undulating structure of normal opacity, except for several narrow imbedded ringlets. The normalized differential opacity indicates a substantial fraction of centimeter-size particles. In the Cassini division, the opacity appears to be nearly independent of wavelength. Ring A appears to be nearly homogeneous over much of its width, but with considerable thickening near its inner boundary with the Cassini division.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: (ISSN 0019-1035)
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  • 5
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    Radar measurement of heterogeneous small-scale surface texture on Mars Chryse (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Radar measurements from Chryse Planitia in 1978 confirm earlier estimates of 4-5 deg rms slope (on meter scales) over 45-50 deg W longitude. The new measurements also confirm a skewing of the measured spectra. This has now been interpreted as a combined result of large-scale surface tilt and a side effect of the decrease in small-scale roughness as the subradar point moves from the basin floor toward the west.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 85; Nov. 10
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  • 6
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    Viking bistatic radar experiment - Summary of first-order results emphasizing north polar data (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Initial results of bistatic radar observations of Mars made by the Viking Orbiter spacecraft are presented with particular emphasis on the previously unstudied polar regions. Bistatic radar scattering experiments were performed in near-equatorial regions by the Viking Orbiter 1, while other regions of the planet were observed by the polar-orbiting Orbiter 2, with scattered signals received by stations of the NASA Deep Space Network. In the equatorial region, the bistatic radar estimates of rms surface slope are found to be in qualitative agreement with results obtained using earth-based transmitter-receivers, showing a nearly 2:1 decrease in rms surface roughness between 20 and 22 deg N with no appreciable change in dielectric constant. Data in the north polar region reveal variations in surface roughness from 1 to 6 deg, with areas of smooth material generally located within rougher environs, surface roughness decreasing along Vastitas Borealis in the direction of the north pole, and north polar cap rms roughnesses on the order of 2.5-3.0 deg. Trends in radar reflectivity suggest a decreasing surface density with increasing latitude, consistent with a layer of seasonal CO2 or H2O snow increasing in depth as the pole is approached.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 46; June 198
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  • 7
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    Radar measurement of small-scale surface texture - Syrtis Major (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Available data on Syrtis Major is examined and compared in light of lunar experience in order to infer the small-scale structure and study the problem of origin and present state. The radar data are reviewed, introducing three previously unpublished sets of observations obtained during the 1978 Mars opposition. Syrtis Major is shown to be smooth and relatively homogeneous when sensed at centimeter wavelengths, root mean square surface slopes ranging from more than 1.5-2.0 deg in the east to less than 0.5 deg along the western margin at wavelength 12.6 cm. Radar reflectivity increases from about 5% to about 12% across Syrtis Major, being greatest near the western margin. A self-consistent model for the surface of Syrtis Major is arrived at which includes structure on all scales. It is shown that the moon is not a good radar analog for Syrtis Major.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 49; Feb. 198
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  • 8
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    Radar scattering laws for the lunar surface (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Bistatic radar observations of quasi-specular scatter from the lunar surface at 13 and 116 cm wavelengths have been expressed in terms of probability densities of the underlying surface slope distributions. These show best agreement with a Hagfors scattering function, although other forms having predominantly Gaussian or exponential characteristics also occur. Estimates of root mean square (rms) surface slope derived from these function range from 4 deg rms in maria to at least 8 deg rms in highlands. These are values appropriate to 25 m horizontal scales and represent averages over tens of square kilometers of surface area. The effective scattering roughness varies with wavelength, most strongly in maria, where its behavior is consistent with that expected from an immature, i.e., unsaturated cratered surface. There is very little variation in scattering roughness with wavelength in highlands area.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: IEEE Transactions on Antennas and Propagation; AP-30; May 1982
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  • 9
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    Viking bistatic radar experiment - Summary of results in near-equatorial regions (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Viking bistatic radar have been processed using Hagfors' scattering function to obtain estimates of rms surface roughness from ground tracks primarily in the equatorial region of Mars. Roughness varies from as little as 0.75 deg rms east of Solis and Sinai Plana to at least 8 deg on the western slope of Arsia Mons. Estimated roughness in cratered terrain is generally about 5 deg or less, implying the existence of smoothing processes on scales less than 100 m. There is good agreement between bistatic roughness estimates and earth-based results at ground track intersections near the equator in both cratered terrain and plains. Surface tilt probability density functions derived from these observations are usually more sharply peaked than the Hagfors function for similar values of rms surface roughness. Earlier results using the Gaussian model appear to have overestimated the surface roughness by 30-40 percent.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 10385-10
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  • 10
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    Saturn's rings - Voyager 1 radio occultation experiment results (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The Voyager 1 encounter with Saturn in 1980 included the first radio occultation measurements of the ring system. Opacity of and scattering by Saturn's rings were measured at 3.6- and 13-cm wavelengths using transmissions from the spacecraft to the earth. Detailed models of ring structure have been derived from these data at radial resolutions as small as 1 km, depending on the radio opacity of the region probed. Inverse power-law-type distributions of ring particle sizes with indices of about 3 and upper size cutoffs near 5 m are in good agreement with the data, but parameters vary throughout the rings. Occultation measurements have also provided information on ring dynamics and have led to a more precise definition of Saturn's pole vector.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); GE-22; 656-665
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