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  • 1
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    An a priori model for the reduction of nutation observations: KSV(1994.3) nutation series (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: We discuss the formulation of a new nutation series to be used in the reduction of modern space geodetic data. The motivation for developing such a series is to develop a nutation series that has smaller short period errors than the IAU 1980 nutation series and to provide a series that can be used with techniques such as the Global Positioning System (GPS) that have sensitivity to nutations but can directly separate the effects of nutations from errors in the dynamical force models that effect the satellite orbits. A modern nutation series should allow the errors in the force models for GPS to be better understood. The series is constructed by convolving the Kinoshita and Souchay rigid Earth nutation series with an Earth response function whose parameters are partly based on geophysical models of the Earth and partly estimated from a long series (1979-1993) of very long baseline interferometry (VLBI) estimates of nutation angles. Secular rates of change of the nutation angles to represent corrections to the precession constant and a secular change of the obliquity of the ecliptic are included in the theory. Time dependent amplitudes of the Free Core Nutation (FCN) that is most likely excited by variations in atmospheric pressure are included when the geophysical parameters are estimated. The complex components of the prograde annual nutation are estimated simultaneously with the geophysical parameters because of the large contribution to the nutation from the S(sub 1) atmospheric tide. The weighted root mean square (WRMS) scatter of the nutation angle estimates about this new model are 0.32 mas and the largest correction to the series when the amplitudes of the ten largest nutations are estimated is 0.18 +/- 0.03 mas for the in phase component of the prograde 18. 6 year nutation.
    Keywords: ASTRONOMY
    Type: NASA-CR-200040 , NAS 1.26:200040 , NIPS-96-07292
    Format: application/pdf
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  • 2
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    Methods of correction for the 'wet' atmosphere in estimating baseline lengths from VLBI (1988)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The error in VLBI estimates of baseline length caused by unmodelled variations in the propagation path through the atmosphere is greater for longer baselines. Series of estimates of baseline lengths obtained using different methods to correct for the propagation delay caused by atmospheric water vapor are presented and discussed. The main methods are use of data from: a water-vapor radiometer (WVR) and Kalman-filtering of the VLBI data themselves to estimate the propagation delay. Since the longest timespan of WVR data associated with geodetic VLBI experiments was obtained at the Onsala Space Observatory in Sweden, results are presented for the following three baselines: (1) Onsala-Wettzell, FRG (920 km), (2) Onsala-Haystack/Westford, MA (5600 km), and (3) Onsala-Owens Valley (7914 km).
    Keywords: ASTRONOMY
    Type: IAU Symposium on the Impace of VLBI on Astrophysics and Geophysics; May 10, 1987 - May 15, 1987; Cambridge, MA; United States
    Format: text
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  • 3
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    Radio-source positions from VLBI (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Positions of 85 compact extragalactic radio sources and the Galactic object Beta Persei (Algol) have been determined in the J2000.0 coordinate system for analysis of VLBI observations made with the bandwidth-synthesis technique. Twenty-four of these sources were observed with the Mark I VLBI system in 37 sessions distributed between April 1972 and May 1978, and 82 of the sources were observed with the Mark III system in 85 sessions distributed between August 1979 and December 1982. Each session spanned at least 24 hr. Standard errors for the estimated positions on the sky of the about 10 sources frequently observed with the Mark I system are about 1 mas, except for the declinations of nearly equatorial sources, where these errors approach 5 mas. Corresponding uncertainties for the about 20 sources frequently observed with the Mark III system are 0.3 and 2 mas, respectively.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 92; 1020-102
    Format: text
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