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Direct estimation of nutation coefficients from VLBI data

Published online by Cambridge University Press:  03 August 2017

W. E. Himwich
Affiliation:
Interferometrics Inc., 8150 Leesburg Pike, Suite 1400, Vienna, VA 22180
E. J. Harder
Affiliation:
Interferometrics Inc., 8150 Leesburg Pike, Suite 1400, Vienna, VA 22180

Abstract

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Previous analyses of nutation angle errors from Mark III VLBI data have been made by estimating offset corrections to the instantaneous nutation angles from single-day observing sessions. Adjustments to the coefficients of the nutation model were then estimated from the time series of offset corrections. In this paper we estimate the corrections to the nutation series coefficients directly from the multi-year ensemble of data. The resulting corrections have smaller uncertainties than corrections estimated from the daily offsets because the direct solution has many fewer degrees of freedom. We have forced the corrections to occur at the periods of the dominant terms of the IAU 1980 nutation series instead of allowing the pole orientation to vary freely on each day. Results from daily offset adjustment and direct nutation series adjustment from nearly seven years of data agree at the level of the combined one-sigma uncertainties, 0.1 milliarcseconds. The amplitude of the free core nutation was also estimated from the daily offset data; no significant amplitude was observed.

Type
V. Precession & Nutation
Copyright
Copyright © Reidel 1988 

References

Gwinn, C. R., Herring, T. A., and Shapiro, I. I., ‘Geodesy by Radio Interferometry: Studies of the Forced Nutation of the Earth, 2. Interpretation’, J. Geophys. Res. 91, 47454754, 1986.Google Scholar
Herring, T. A., Gwinn, C. R., and Shapiro, I. I., ‘Geodesy by Radio Interferometry: Studies of the Forced Nutation of the Earth, 1. Data Analysis’, J. Geophys. Res. 91, 47554765, 1986.Google Scholar