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  • Other Sources  (9)
  • 1
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    Project Polaris: A Report (1980)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The project was proposed to meet the developing demands for higher resolution and accuracy polar motion and Earth rotation data to support modern geodynamic studies. The basis for the selection of radio interferometry, rather than lunar or artifical satellite laser ranging or Doppler satellite tracking, is described.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: NASA. Goddard Space Flight Center Radio Interferometry; p 455-460
    Format: application/pdf
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  • 2
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    NOS/NGS activities to support development of radio interferometric surveying techniques (1980)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: National Geodetic Survey activities towards the development of operational geodetic survey systems based on radio interferometry are reviewed. Information about the field procedures, data reduction and analysis, and the results obtained to date is presented.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: NASA. Goddard Space Flight Center Radio Interferometry; p 9-22
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  • 3
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    Comparison of earth rotation as inferred from radio interferometric, laser ranging and astrometric observations (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Results of measurements of the earth's rotation vector for a 400-day period from late September 1980 to December 1981, for which date from VLBI, satellite laser ranging (SLR), and lunar laser ranging (LLR) were available, are compared. The acquisition of the data and their evaluation are described. VLBI, SLR, and classical astrometric determinations of the X-parameter required to describe the location of the rotation pole on the earth's surface are shown, and VLBI, LLR, and classical astrometric determinations of the angle of rotation about this pole (UT1) are presented. The results indicate that VLBI and SLR, at their present stages of development, yield standard errors under 20 cm in the determinations of X, about twofold smaller than obtained from classical measurements, and that VLBI and LLR yield determination of UT1 with standard errors less than 40 cm, somewhat smaller than that of the corresponding determinations from classical observations. Methods for improving these types of intercomparisons are suggested.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 302; April 7
    Format: text
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  • 4
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    New test of the equivalence principle from lunar laser ranging (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: An analysis of six years of lunar-laser-ranging data gives a zero amplitude for the Nordtvedt term in the earth-moon distance yielding the Nordtvedt parameter eta = 0.00 plus or minus 0.03. Thus, earth's gravitational self-energy contributes equally, plus or minus 3%, to its inertial mass and passive gravitational mass. At the 70% confidence level this result is only consistent with the Brans-Dicke theory for omega greater than 29. We obtain the absolute value of beta - 1 less than about 0.02 to 0.05 for five-parameter parametrized post-Newtonian theories of gravitation with energy-momentum conservation.
    Keywords: ASTROPHYSICS
    Type: Physical Review Letters; 36; Mar. 15
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  • 5
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    Earth rotation measured by lunar laser ranging (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The estimated median accuracy of 194 single-day determinations of the earth's angular position in space is 0.7 millisecond (0.01 arc second). Comparison with classical astronomical results gives agreement to about the expected 2-millisecond uncertainty of the 5-day averages obtained by the Bureau International de l'Heure. Little evidence for very rapid variations in the earth's rotation is present in the data.
    Keywords: GEOPHYSICS
    Type: Science; 193; Sept. 10
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  • 6
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    Earth rotation information derived from MERIT and POLARIS VLBI observations (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Advanced methods involving observations of extraterrestrial objects, such as artificial satellites or quasars, may make it possible to monitor geometrical variations in survey networks of regional, continental, and global scale with a spatial resolution of a few centimeters and a temporal resolution of better than one day. However, in connection with a realization of this potential, it is necessary to account for variations in the orientation of the earth in space. The accuracy provided by the conventional approaches for determining the orientation of the earth is not sufficient in this case. However, an appropriate method could be based on the utilization of independent clock radio interferometry (commonly referred to as VLBI) observations of extragalactic radio sources. The project POLARIS (Polar-motion Analysis by Radio Interferometric Sampling) is concerned with an implementation of this method. The MERIT (Monitor Earth Rotation and Intercompare the Techniques of observation and analysis) observations represent an aid to project POLARIS. Attention is given to details regarding these programs and the results obtained thus far.
    Keywords: GEOPHYSICS
    Type: High-precision earth rotation and earth-moon dynamics: Lunar distances and related observations; May 22, 1981 - May 27, 1981; Alpes-Maritimes; France
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  • 7
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    Possible detection of the earth's free-core nutation (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The 5.5 years of VLBI observations primarily collected under project IRIS are used to search for evidence of the free-core nutation (FCN). The observations are consistent with an irregular excitation process, and a model which assumes a step excitation in the FCN amplitude to about 2.0 milliseconds of arc in late 1985 fits the data well. Theoretical analysis appears to rule out the strong Mexican earthquake of September 19, 1985, as a cause of the excitation.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 13; 949-952
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  • 8
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    University of Hawaii Lure Observatory (1973)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The University of Hawaii's Institute for Astronomy is currently constructing a lunar laser ranging observatory at the 3050-meter summit of Mt. Haleakala, Hawaii. The Nd YAG laser system to be employed provides three pulses per second, each pulse being approximately 200 picoseconds in duration. The energy contained in one pulse at 5320 A lies in the range from 250 to 350 millijoules. Details of observatory construction are provided together with transmitter design data and information concerning the lunastat, the feed telescope, the relative pointing system, the receiver, and the event timer system.
    Keywords: FACILITIES, RESEARCH, AND SUPPORT
    Type: Symposium on Earth''s Gravitational Field and Secular Variations in Position; Nov 26, 1973 - Nov 30, 1973; Sydney; Australia
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  • 9
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    Recent results of radio interferometric determinations of a transcontinental baseline, polar motion, and earth rotation (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Results are discussed for radio interferometric observations of extragalactic radio sources with antennas at Haystack Observatory in Massachusetts and the Owens Valley Radio Observatory in California (3900-km baseline) during 14 separate experiments distributed between September 1976 and May 1978. Simultaneous analysis of the data from several experiments yields estimates of changes in the x component of pole position and in earth's rotation (UT1). Comparison with the corresponding results obtained by the Bureau International de l'Heure (BIH) reveals systematic differences. In particular, the trends in the radio interferometric determinations of the changes in pole position are found to agree more closely with those from the International Polar Motion Service and from Doppler observations of satellites than with those from the BIH.
    Keywords: GEOPHYSICS
    Type: Time and the earth''s rotation; Eighty-second Symposium; May 08, 1978 - May 12, 1978; San Fernando; Spain
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