AN A PRIORI MODEL FOR THE REDUCTION OF NUTATION OBSERVATIONS: A'SVi 994.3 NUTATION SERIES

r • Abst.ra.ct! We discuss the formulation of a new nutation series to be used 'in the reduction of modern space geodetic data. The motivation for devel: oping such a series is to develop a nutation series that has smaller short . period errors than the IAU 1980 nutat ion series and to provide a series that can be used wi th techniques such as the Global Positioning System (GPS) eo • that have sensitivity to nutations but can directly separate the effects of o M ' nutations from errors in the dynamical force models that effect the satellite ^ to ,$• orbits. A modern nuta t ion series should allow the errors in the force models ^ *o <? . f o r GPS to be bet ter understood. The series is constructed by convolving 2 £ § the Kinoshi ta and Souchay rigid Earth nuta t ion series wi th an Earth response funct ion whose parameters are par t ly based on geophysical models ^ 't of the Earth and partly estimated from a long series (1979-1993) of very x. long baseline interferometry (VLBI) estimates of nutation angles. Secular 2 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 5i 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 0.17 ± 0.03 mas for the in phase component of the prograde 18.6 year nutation.