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  • 1990-1994  (10)
  • 1
    Publication Date: 1992-01-01
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
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  • 2
    Publication Date: 1992-02-07
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 3
    Publication Date: 2011-08-24
    Description: Radar studies of Mars have provided measurements of surface texture on scales of centimeters to hundreds of meters and measurements of surface material properties. Texture (rms surface tilts and estimates of small-scale roughness) may be inferred from dispersion and/or polarization of the radar echo; material properties (reflectivity of dielectric constant) are derived from echo strength. Mars is a diverse target; depending on location, rms surface tilts have been found to vary over the range 0.25 to 10 deg while reflectivity covers at least 3 to 13 percent. Plains units are the most variable, having both the smoothest and roughest surfaces, cratered terrain can be considered predictable and 'average' by comparison. Recent data identify scattering by small structures (perhaps rocks on or near the surface) as playing a more important role than previously recognized. Scattering by the residual ice cap near Mars' south pole is particularly unusual. The present state of radar surface studies is summarized.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: In: Mars (A93-27852 09-91); p. 652-685.
    Format: text
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  • 4
    Publication Date: 2011-08-24
    Description: Orbital debris objects with sizes of 6 mm and larger were detected when they passed through the main beam of the high-power, 12.6-cm wavelength radar at the Arecibo Observatory. The number of objects detected at altitudes below 1000 km in the size range of 6 mm to 2 cm agreed with orbital debris model predictions to better than a factor of two. Radar detections of larger orbital debris (10-cm diameter and above) were also compared with the objects in the U.S. Space Command catalog (the cataloged objects have UHF radar cross-sections larger than 0.01 sq m). This experiment demonstrated that the large, earth-based radar telescopes normally used for planetary studies can provide useful data about the near-earth orbital debris populations.
    Keywords: ASTRONAUTICS (GENERAL)
    Type: Geophysical Research Letters (ISSN 0094-8276); 19; 257-259
    Format: text
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  • 5
    Publication Date: 2013-08-31
    Description: The Magellan spacecraft was placed into orbit around Venus on 10 Aug. 1990 and started radar data acquisition on 15 Sep. 1990. Since then, Magellan has completed mapping over 2.75 rotations of the planet (as of mid-July 1992). Synthetic aperture radar (SAR), altimetry, and radiometry observations have covered 84 percent of the surface during the first mission cycle from mid-Sep. 1990 through mid-May 1991. Operations in the second mission cycle from mid-May 1991 through mid-Jan. 1992 emphasized filling the larger gaps (the south polar region and a superior conjunction) from that first cycle. Planned observations in the fourth mission cycle from mid-Sep. 1992 through mid-May 1993 will emphasize high-resolution gravity observations of the equatorial regions of Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Papers Presented to the International Colloquium on Venus; p 106-107
    Format: application/pdf
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  • 6
    Publication Date: 2013-08-31
    Description: Radar observations of Mars at Goldstone in 1990 were conducted by transmitting pure sinusoidal signals at 3.5-cm wavelengths and receiving the Doppler-spread echoes from Mars at Earth. Radar transmissions were circularly polarized and the echoes recorded in two senses: depolarized and polarized. Latitudes of the subradar points are between 3.5 deg and 11.1 deg S; longitude coverage is discontinuous. The observed depolarized and polarized echo total cross-sections and their ratios for two wavelengths were compared and discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1990; p 315-316
    Format: application/pdf
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  • 7
    Publication Date: 2014-09-04
    Description: Lunar pyroclastic deposits represent one of the primary anticipated sources of raw materials for future human settlements. These deposits are fine-grained volcanic debris layers produced by explosive volcanism contemporaneous with the early stage of mare infilling. There are several large regional pyroclastic units on the Moon (for example, the Aristarchus Plateau, Rima Bode, and Sulpicius Gallus formations), and numerous localized examples, which often occur as dark-halo deposits around endogenic craters (such as in the floor of Alphonsus Crater). Several regional pyroclastic deposits were studied with spectral reflectance techniques: the Aristarchus Plateau materials were found to be a relatively homogeneous blanket of iron-rich glasses. One such deposit was sampled at the Apollo 17 landing site, and was found to have ferrous oxide and titanium dioxide contents of 12 percent and 5 percent, respectively. While the areal extent of these deposits is relatively well defined from orbital photographs, their depths have been constrained only by a few studies of partially filled impact craters and by imaging radar data. A model for radar backscatter from mantled units applicable to both 70-cm and 12.6-cm wavelength radar data is presented. Depth estimates from such radar observations may be useful in planning future utilization of lunar pyroclastic deposits.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Joint Workshop on New Technologies for Lunar Resource Assessment; p 16-17
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  • 8
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    In:  CASI
    Publication Date: 2013-08-31
    Description: Researchers developed a radar-echo model for Mars based on 12.6 cm continuous wave radio transmissions backscattered from the planet. The model broadly matches the variations in depolarized and polarized total radar cross sections with longitude observed by Goldstone in 1986 along 7 degrees S. and yields echo spectra that are generally similiar to the observed spectra. Radar map units in the model include an extensive cratered uplands unit with weak depolarized echo cross sections, average thermal inertias, moderate normal refelectivities, and moderate rms slopes; the volcanic units of Tharsis, Elysium, and Amazonis regions with strong depolarized echo cross sections, low thermal inertia, low normal reflectivities, and large rms slopes; and the northern planes units with moderate to strong depolarized echo cross sections, moderate to very high thermal inertias, moderate to large normal reflectivities, and moderate rms slopes. The relevance of the model to the interpretation of radar echoes from Mars is discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Scientific Results of the NASA-Sponsored Study Project on Mars: Evolution of Volcanism, Tectonics, amd Volatiles; p 283-284
    Format: application/pdf
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  • 9
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    In:  Other Sources
    Publication Date: 2018-06-08
    Keywords: Communications and Radar
    Format: text
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  • 10
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    In:  Other Sources
    Publication Date: 2019-07-13
    Description: A radar-echo model for Mars based on 12.6 continuous-wave radio transmissions backscattered from the planet is developed. Mars' surface is divided into radar map units that are based on generalized geologic map units, and the radar map units are further subdivided using thermal inertias because the geologic units are insufficient to account for the quasi-specular echoes. The most important of the model's 118 radar-scattering units are characterized. Analyses of the observations and the model show that there are at least two populations of martian surfaces with distinct radar properties: the cratered uplands and northern low plains, and volcanoes and fields of lava flows. It is concluded that there are two dominant populations of surfaces that have distinct echo properties and that there is general agreement between the quasi-specular echo reflectivities of the present model and those of many other radar observations of Mars.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Science Conference; Mar 12, 1990 - Mar 16, 1990; Houston, TX; United States
    Format: text
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