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  • 1
    ISSN: 1432-1394
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract We have used Very Long Baseline Interferometry (VLBI) data to compute the site coordinates and constant velocity components for 29 fixed antenna sites and 25 mobile sites. The three singularities which occur in the adjustment with respect to the rotation of the system have been resolved by a constraint holding the net rotation of seven fixed antennas, distributed on the stable portions of four of the geologic plates, to the net rotation for these sites as defined by the NNR-NUVEL1 no net rotation model. In order to achieve a minimally constrained adjustment of this type we have found it necessary to use a new adjustment procedure in which we solve for the coordinates of each site at the weighted mean epoch of all the observations involving that site. Using the results of the above solution we have computed the departure for each site from the NNR-NUVEL1 rigid plate model. These departures show that the transition zone in western North America from the region of rigidity to the plate boundary is at least 400 km wide, in general agreement with Ward (1988,1990).
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1394
    Keywords: Key words. MINQUE ; Block-diagonal bordered systems ; VLBI
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. A sparse matrix method is developed for computing variance factors for block-diagonal, bordered systems of equations using MINQUE (Minimum Norm Quadratic Unbiased Estimation). This method greatly reduces the computational effort required to apply MINQUE, thus making it practical to compute variance factors for some very large systems of equations. The computer implementation of the method is described and applied to the computation of variance factors for a combination of 1609 VLBI (Very Long Baseline Interferometry) observing sessions. The purpose of this test was to compute a variance factor for each of the data sets and, perhaps, to obtain more realistic variance estimates to replace those in common use for the analysis of VLBI data. It was found that the method is satisfactory for use with such large problems, and the test served to verify that the variances in current use in VLBI data adjustments are adequate.
    Type of Medium: Electronic Resource
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