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  • LUNAR AND PLANETARY EXPLORATION  (9)
  • INSTRUMENTATION AND PHOTOGRAPHY  (4)
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  • 1
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    Very-long-baseline interferometry techniques applied to problems of geodesy, geophysics, planetary science, astronomy, and general relativity. (1973)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: IEEE; vol. 61
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  • 2
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    Dynamics, winds, circulation and turbulence in the atmosphere of Venus (1977)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: With the possible exception of the lowest one or two scale heights, the dominant mode of circulation of Venus' atmosphere is a rapid, zonal, retrograde motion. Global albedo variations in the ultraviolet may reflect planetary scale waves propagating relative to the zonal winds. Other special phenomena such as cellular convection in the subsolar region and internal gravity waves generated in the interaction of the zonal circulation with the subsolar disturbance may also be revealed in ultraviolet imagery of the atmosphere. We discuss the contributions of experiments on the Orbiter and Entry Probes of Pioneer Venus toward unravelling the mystery of the planet's global circulation and the role played by waves, instabilities and convection therein
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Space Science Reviews; 20; June 197
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  • 3
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    Accuracy of relative positioning by interferometry with GPS Double-blind test results (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: MITES (Miniature Interferometer Terminals for Earth Surveying) observations conducted on December 17 and 29, 1980, are analyzed. It is noted that the time span of the observations used on each day was 78 minutes, during which five satellites were always above 20 deg elevation. The observations are analyzed to determine the intersite position vectors by means of the algorithm described by Couselman and Gourevitch (1981). The average of the MITES results from the two days is presented. The rms differences between the two determinations of the components of the three vectors, which were about 65, 92, and 124 m long, were 8 mm for the north, 3 mm for the east, and 6 mm for the vertical. It is concluded that, at least for short distances, relative positioning by interferometry with GPS can be done reliably with subcentimeter accuracy.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
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  • 4
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    Numerical model of the moon's rotation (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The differential equations for the Euler angles that define the moon's orientation with respect to an inertial coordinate frame have been integrated numerically. This numerical model of the moon's rotation, when used in conjunction with current lunar-orbit and earth-rotation models, fits lunar laser ranging observations over a five-year period within 28 cm (rms). The present model is also compared with the numerical model of Williams (1975) and Eckhardt's (1981) semianalytical model.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Moon and the Planets; 24; May 1981
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  • 5
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    Tidal dissipation in the moon (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Euler's equations of motion, modified to include elasticity and solid friction, were used to study the rotation of the moon. Two heuristic models for the anelasticity were considered: Q independent of frequency and Q inversely proportional to the frequency and Q inversely proportional to the frequency of the strain oscillation. Parameters in each model were estimated by weighted least squares from 9 years of lunar laser range observations. The root mean square of the postfit range residuals was 19 cm in each case. For a strain period of 1 month, the estimates of Q obtained with the two models were similar and surprisingly low: 23 + or - 6. The range of uncertaintly, + or - 6, represents our estimate of the true standard deviation of the estimate of Q, as affected by systematic errors; it is 3 times larger than the formal, statistical, standard error.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 86; Aug. 10
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  • 6
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    Zonal and meridional circulation of the lower atmosphere of Venus determined by radio interferometry (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The results of the Pioneer Venus differential long-baseline interferometry experiment are presented. The velocity component of the Pioneer probes as they fell to the surface of Venus was calculated from the Doppler shift of the received signal, and the other two orthogonal components were determined by long-baseline interferometry. The ambient wind velocity was about 1 m/s or less near the surface of the planet and about 100 m/s at an altitude of about 65 km at all four probe locations. Strata of high wind shear were found at altitudes of 15, 45, and 60 km. The wind velocity was always directed within a few degrees of due west except at a few km above the surface. The dominant motion of the lower atmosphere seems to be a retrograde zonal rotation, and eddies appear to account for most of the instantaneous meridional velocity. The data suggest that, within the clouds, a thermally driven mean meridional circulation is superimposed upon the much more rapid zonal rotation.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 85; Dec. 30
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  • 7
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    Venus winds are zonal and retrograde below the clouds (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Winds in the lower atmosphere of Venus, inferred from three-dimensional radio interferometric tracking of the descents of the Pioneer day and north probes, are predominantly easterly with speeds of about 1 M/sec near the surface, 50 at the bottom of the clouds, and more than 200 within the densest, middle cloud layer. Between about 25 and 55 km altitude the average flow was slanted equatorward, with superimposed wavelike motions and alternating layers of high and low shear
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 205; July 6
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  • 8
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    VLBI clock synchronization (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The potential accuracy of VLBI (very long baseline interferometry) for clock epoch and rate comparisons was demonstrated by results from long- and short-baseline experiments. It was found that atomic clocks at widely separated sites (several thousand kilometers apart) can be synchronized to within several nanoseconds from a few minutes of VLBI observations and to within one nanosecond from several hours of observations.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: IEEE; vol. 65
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  • 9
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    Structure and circulation of the Venus atmosphere (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The Pioneer Venus data relevant to the dynamics and thermodynamics of the atmosphere is summarized and interpreted. On the day side there is a thermosphere in which temperatures increase with height to an exospheric temperature of about 300 K. On the night side there is a cryosphere in which temperatures decrease with height to an exospheric temperature of about 100 K. The atmosphere is stratified stably from the highest altitudes down to about 28 km except for a layer in the clouds between about 50 and 55 km which is nearly adiabatic. Horizontal thermal contrasts are approximately 1 to 2% in the deep atmosphere and 100% in the upper atmosphere. The temperatures generally decrease with latitude at and below the clouds on constant pressure surfaces. Above the clouds there is a reversed zonally averaged latitudinal temperature gradient. The dominant circulation of the atmosphere above the lowest one or two scale heights is a zonal retrograde motion with 100 m/s winds at 60 km altitude. There is also a superrotation at altitudes of 150 km and above.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NAGW-47 , Journal of Geophysical Research; 85; Dec. 30
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  • 10
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    Study of lunar librations using differential very-long-baseline observations of ALSEPs (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Observations of signals from the ALSEP transmitters via differential very-long-baseline interferometry (VLBI) are being made to determine the relative selenocentric coordinates of the ALSEPs and the motion of the moon about its center of mass. By VLBI the relative positions of the ALSEPs can be determined with uncertainties less than 5 meters, and the orientation of the moon within 0.5 second of selenocentric arc.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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