A new method to improve the prediction of the celestial pole offsets

Santiago Belda,Robert Heinkelmann,Harald Schuh,José M Ferrándiz

doi:10.1038/s41598-018-32082-1

Abstract

Knowledge of the Earth’s changing rotation is fundamental to positioning objects in space and on the planet. Nowadays, the Earth’s orientation in space is expressed by five Earth Orientation Parameters (EOP). Many applications in astronomy, geosciences, and space missions require accurate EOP predictions. Operational predictions are released daily by the Rapid Service/Prediction Centre of the International Earth Rotation and Reference Systems Service (IERS). The prediction procedures and performances differ for the three EOP classes: polar motion, rotation angle (UT1-UTC), and the two celestial pole offsets (CPO), dX and dY. The IERS Annual Report 2016 shows Rapid Service CPO predictions errors with respect to IERS 08 C04 observations in 2016 ranging from 120 to 140 μas in 40 days for dX, and 100–160 μas for dY. We test a new method for the CPO prediction based on the recent availability of sophisticated empirical models for the Free Core Nutation, a main component of the CPO variations. We found it allows predicting both CPO with error estimates for the period 2000–2016 lower than the 2016 Rapid Service products, reaching about 85 μas after 40 days and near 90 μas after a year. These results would represent a 35–40% improvement.

Highlights

The Earth’s orientation in space can be expressed through three independent angles
The wrms of the celestial pole offsets (CPO) series can be significantly reduced by subtracting an accurate Free Core Nutation (FCN) model, and it is conceivable that the variance of the CPO predictions may be reduced using a suitable FCN prediction
We investigated the CPO prediction procedure built on adopting the FCN model B1648 to predict the contributions to CPO attributable to the FCN

Summary

Introduction

The Earth’s orientation in space can be expressed through three independent angles (e.g. the Euler angles). The Earth Orientation Centre (EOC) of the International Earth Rotation and Reference Systems Service (IERS) obtains and releases a solution with daily EOP values, named C04, which comprise the terrestrial pole coordinates (xp, yp), the difference UT1-UTC, and the Celestial Pole Offsets (CPO), together with their respective formal errors. Those figures indicate the level of agreement between the solutions computed by the IVS and its main AC; the EOP series of the IERS Rapid Service/Prediction Centre (RS/PC) are not very different from a former uncertainty estimation of about 80–90 μas in average[17]. Those figures seem to be lowering slowly in the last years. Optimally specific methods would be used depending on the EOP groups: ERP and CPO

Methods

Results

Conclusion