Brian J. Luzum

Prediction of earth orientation

SummaryThe method for predicting x, y, and UT1-UTC as conceived and implemented by the Subbureau for Rapid Service and Prediction of the International Earth Rotation Service (IERS) is shown. For polar motion, the method is an extrapolation of an annual ellipse and Chandler circle. The method for UT1-UTC involves a simple differencing technique.

Observations of luni-solar and free core nutation

An analysis of the differences between observed nutation angles and the 1980 IAU Nutation Theory shows the existence of currently unmodeled effects. An empirical set of corrections to the 1980 IAU Nutation Theory is presented and compared with current geophysical models. A retrograde periodic variation (period ≃ 418 days), which may be related to the theoretical free core nutation, is seen

Combination of precise observations of the orientation of the Earth

SummaryThe procedure for computing Earth orientation parameters (EOPs) implemented by the Subbureau for Rapid Service and Prediction of the International Earth Rotational Service (IERS) is described. This scheme involves the use of weighted cubic splines and provides smoothing of observations consistent with the agreement between contributed data sets.

Using GPS to Determine Earth Orientation

Analyses of the orbits of the satellites of the Global Positioning System (GPS) by participants in the International GPS Service (IGS) (Mueller and Beutler, 1992) provide daily observations of high-accuracy polar motion. These data are used routinely by the International Earth Rotation Service (IERS) (see, for example, IERS Annual Report for 1993). The GPS data have also been analyzed by some centers to produce estimates of UT1-UTC. Currently, the UT1-UTC data are not used because of large systematic errors, but this situation is expected to change in the near future due to the results of ongoing research.

Accuracy of High-Frequency Observations of Earth Orientation

An area of increasing interest in the study of the Earth’s rotation is the nature of variations with characteristic periods less than a few days. Analyses of the orbits of the satellites of the Global Positioning System (GPS) by participants in the International GPS Service (IGS) (Mueller and Beutler, 1992) have provided daily observations of high-accuracy polar motion described by the pole coordinates x along the Greenwich meridian and y along the meridian of ninety degrees west. These data can be very useful in the study of high-frequency polar motion provided that the errors associated with them are properly understood and their accuracy can be evaluated. The purpose of this paper is to provide a preliminary assessment of these observations in an effort to establish the observational accuracy of the data.