Dennis D. McCarthy

Considerations concerning the non-rigid Earth nutation theory.

This paper presents the reflections of the Working Group of which the tasks were to examine the non-rigid Earth nutation theory. To this aim, six different levels have been identified: Level 1 concerns the input model (giving profiles of the Earths density and theological properties) for the calculation of the Earths transfer function of Level 2; Level 2 concerns the integration inside the Earth in order to obtain the Earths transfer function for the nutations at different frequencies; Level 3 concerns the rigid Earth nutations; Level 4 examines the convolution (products in the frequency domain) between the Earths nutation transfer function obtained in Level 2, and the rigid Earth nutation (obtained in Level 3). This is for an Earth without ocean and atmosphere; Level 5 concerns the effects of the atmosphere and the oceans on the precession, obliquity rate, and nutations; Level 6 concerns the comparison with the VLBI observations, of the theoretical results obtained in Level 4, corrected for the effects obtained in Level 5.Each level is discussed at the state of the art of the developments.

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.

Latitude and longitude

The latitude of a location specifies the angle between an imaginary line directed generally toward …

Secular Motions of Extragalactic Radio-Sources and the Stability of the Radio Reference Frame

The best current approximation to an inertial reference frame is provided by Very Long Baseline Interferometry (VLBI) observations of extragalactic radio sources with red shifts (z) up to 3.8. The stability of the resulting reference frame directly depends on the amount of any secular changes in the observed source positions.

Proposed terminology in fundamental astronomy based on IAU 2000 resolutions

We present the proposals of the IAU Division I Working Group on Nomenclature for Fundamental Astronomy (NFA) that was formed at the IAU XXV General Assembly in 2003.

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.

Geodetic reference systems

2. STAR CATALOGS: OBSERVATIONS monitoring programs star catalogs and accuracies aberration and corrections parrallax and corrections proper and apparent star motions precession, nutation and polar motion 8. SUPERNETWORKS & DATUMS conventional terrestrial system world geodetic reference systems global geophysical networks global height systems national geodetic datums active control systems