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  • 1
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    Measurement of horizontal motions in Alaska using very long baseline interferometry (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Results are presented on an analysis of VLBI measurements performed between 1984 and 1990 by means of a network of 53 sites in Alaska, the Yukon Territory, and the conterminous United States to determine the extent of horizontal motions in Alaska. Results are presented in two ways, one showing the evolution of individual baselines and the other yielding site velocities; both approaches use VLBI data from other permanent stations in order to define a global reference frame. It was found that VLBI sites within the Alaska-Aleutian subduction boundary zone (Yakataga, Kodiak, and Sand Point) had higher instantaneous velocities relative to eastern North America than the interior sites of Alaska. The results of Yakataga data modeling suggests that the observed motion is the result of elastic straining of the overriding plate due to a locked main thrust zone with a component of oblique slip.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 21991-22
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  • 2
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    Determination of relative site motions in the western United States using Mark III very long baseline interferometry (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Four years of very long baseline interferometry (VLBI) measurements involving fixed and mobile stations in the western U.S. are analyzed using weighted least squares. Baseline solution time series are used to estimate rates of change of the vector baseline between pairs of VLBI stations. Horizontal vector motions are determined for 18 sites with respect to a site in the Mojave desert. Six sites west of and two sites just to the east of the San Andreas fault show northwestward motion closely parallel to the San Andreas fault. Their motions range from 18 to 43 mm/yr and are significant at confidence levels greater than 99 percent. Motions in California relative to interior North American plate sites are used to estimate an integrated contribution from Basin and Range spreading to the total relative Pacific plate motion as 9-10 mm/yr. A maximum relative velocity of 50-51 mm/yr is found between the interior North American sites and the western California sites, in close agreement with the NUVEL-1 plate motion model.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 12741-12
    Format: text
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  • 3
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    Geodetic measurement of deformation in the Loma Prieta, California earthquake with very long baseline interferometry (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: VLBI measurements were conducted immediately after the Loma Prieta earthquake and compared with VLBI gathered at Monterey, San Francisco, and Point Reyes since 1983 to obtain preearthquake deformation rates with respect to a North American reference frame. The estimated displacements at Monterey and San Francisco are consistent with the static displacements predicted on the basis of a coseismic slip model in which slip on the southern segment is shallower than slip on the northern segment of the fault rupture. Cartesian positions are presented at epoch 1990.0 of a set of VLBI fiducial stations and the three mobile sites in the earthquake's vicinity.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1215-121
    Format: text
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  • 4
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    Radio interferometric detection of a traveling ionospheric disturbance excited by the explosion of Mount St. Helens (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A large-amplitude traveling ionospheric disturbance (TID) was detected over Owens Valley, California, on May 18, 1980, by a highly sensitive very long baseline interferometry (VLBI) radio astronomy experiment. This TID is interpreted as the response of the ionosphere to a gravity wave excited in the neutral atmosphere by the explosion of Mount St. Helens that took place at 1532 UT on that day. A model, invoking the point-excitation of internal gravity waves in an isothermal atmosphere, which fits observations of the TID at several other stations, leads to identification of the features observed in the VLBI data. Small-amplitude higher-frequency changes in the ionosphere were detected for several hours after the passage of the large-amplitude Mount St. Helens TID, but it is not clear whether these were excited by the passage of the gravity wave or were background fluctuations.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 87; Aug. 1
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  • 5
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    Comparison of VLBI and SLR geocentric site coordinates (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Results are reported from a systematic comparison of the geocentric coordinates determined for 18 pairs of VLBI and satellite laser ranging (SLR) sites. The data and results are presented in tables and briefly characterized. The rms differences in the X, Y, and Z coordinates are found, after a 7-parameter frame adjustment, to be 15, 22, and 22 mm, respectively. The potential usefulness of a combined VLBI-SLR reference frame for spacecraft tracking and similar applications is indicated.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 18; 231-234
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  • 6
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    Application of very long baseline interferometry to Astrometry and Geodesy: effects of frequency standard instability on accuracy (1974)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The accuracy of geodetic and astrometric information obtained from very long baseline interferometry (VLBI) observations is dependent upon the stability of the frequency standard, or clock, used at each site of VLBI array. The sensitivities of two hydrogen maser frequency standards of different design to pressure, temperature, and magnetic field variations were measured; and, for one of the standards, sensitivity was found to be severe enough to degrade the information content of VLBI measurements. However, the effect on the geometric and astrometric information of such clock instabilities, with time scales of hours or greater, can be sharply reduced through the use of differencing techniques.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Its Proc. of the Sixth Ann. Precise Time and Time Interval (PTTI) Planning Meeting; p 349-359
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  • 7
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    Mark 3 system overview (1980)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Mark 3 very long baseline interferometry (VLBI) system, comprising a complete end to end VLBI system optimized for both high accuracy geodesy and radio astronomy, is described. The data flow, the data base handler system, and the field station component and configurations are briefly discussed. The use of mobile and transportable stations allows measurements to be taken from a large number of sites with relatively few sets of equipment. Fixed stations form a long term reference network for tying together the measurements with the mobile and transportable stations.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Radio Interferometry; p 285-290
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  • 8
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    Polar motion and UT1: Comparison of VLBI, lunar laser, satellite laser, satellite Doppler, and conventional astrometric determinations (1980)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Very long baseline interferometry observations made with a 3900 km baseline interferometer (Haystack Observatory in Massachusetts to Owens Valley Observation in California) were used to estimate changes in the X-component of the position of the Earth's pole and in UT1. These estimates are compared with corresponding ones from lunar laser ranging, satellite laser ranging, satellite Doppler, and stellar observations.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Radio Interferometry; p 33-44
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  • 9
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    Automation of the Mark 3 field system (1980)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The software and hardware components which will enable hands off operation are described. The operation of the field system begins with the scheduling of observations. An interactive program, SKED, provides displays of mutual visibility, automatic calculation of telescope slewing times, and the ability to list and edit the schedule. The output of SKED is a schedule file containing commands in the Standard Notation for Astronomy Procedures (SNAP) language which the field system uses for controlling events during the experiment. The most important features of SNAP include sophisticated time sequencing of events, automatic logging of all commands and responses, and the ability to define often used sequences of commands as procedures. A control program, BOSS, running in an HP 1000 minicomputer, reads the SNAP commands from a schedule file and interprets them in terms of commands and requests to devices. Interactive command input is possible through the operator's display terminal. Communication with all of the Mark 3 electronics modules is done via a small general purpose interface board (a microprocessor based ASCII transceiver) which has been installed in each module. Additional devices are controlled and monitored using the IEEE 488 General Purpose Interface Bus.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Radio Interferometry; p 291-295
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  • 10
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    Precision geodesy using the Mark-III very-long-baseline interferometer system (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Very-long-baseline interferometry (VLBI) has been used to make precise measurements of the vector separation between widely separated antennas. The system for acquiring and processing VLBI data known as Mark-III is described. Tests of the system show it to have millimeter-level accuracy on short baselines; measurements of baselines longer than a few hundred kilometers suggest that accuracy is limited by the uncertainty in the calibration of tropospheric path delay to the level of a few centimeters. VLBI experiments conducted between 1976 and 1983 have demonstrated the stability of the North American plate by showing that there is no change in the distance between eastern California and Massachusetts at the level of a few millimeters per year or greater. Experiments made from 1980 to 1984 indicate that the distance from Massachusetts to Sweden is increasing by 1.7 + or - 1 cm/year where the quoted standard deviation includes the estimated effects of systematic errors.
    Keywords: GEOPHYSICS
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); GE-23; 438-449
    Format: text
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